Loading ...
Sorry, an error occurred while loading the content.

Re: [micbuilders] Re: Polarization Voltage

Expand Messages
  • bblack
    I know some people that claim that they can hear a difference in absolute polarity. I can t, and I think the vast majority of people cannot, but again, I do
    Message 1 of 19 , Mar 7, 2013
    • 0 Attachment
      I know some people that claim that they can hear a
      difference in absolute polarity. I can't, and I think the
      vast majority of people cannot, but again, I do know some
      who claim to be able to tell if the polarity is inverted,
      even in a single microphone recording. YMMV.
      Of course, in a multi-mic setup, (especially a stereo array)
      if one mic is polarity reversed with respect to the others,
      it will cause cancellations.

      Bryan


      > Sound should not change. Mostly it's been positive in
      > phantom-powered mics because phantom power is positive
      > voltage.
      >
      > There may well be something different with respect to dust
      > , though. I remember something about Neumann changing to a
      > 0v diaphragm with polarized backplate, because otherwise
      > dust tended to be attracted to the diaphragm.
      >
      > -Scott
      >
      > > Thanks for the help. I'm not sure I was totally clear.
      > > Let's say you have a single diaphragm omni condenser
      > > polarized at +60V (backplate is 0V, diaphragm is +60).
      > > Then you change the polarizing voltage to -60V. Will
      > the mic performance be exactly the same as before, except
      > > that the polarity of the output is inverted, or will
      > > there be some other difference, such as noise floor,
      > frequency response, etc? >
      > > -Chris
      > >
      > > --- In micbuilders@yahoogroups.com, David Pickett
      > <dmp@...> wrote: >>
      > >> As I think you may realize, it affects the polarity of
      > the electrical >> signal. -60v on the rear for figure of
      > eight, produces a negative >> lobe, whereas +60v on the
      > front produces a positive lobe, which is >> what you want
      > for a fig 8 pattern. Omni is produced from +60 or -60 >>
      > on BOTH sides. Of course, the following amplifier may
      > well invert >> the signal, so it is wise always to do an
      > actual comparison of a new >> microphone with one which
      > has the standard polarity and make a change >> inside if
      > the polarity of the one you built is opposite to the
      > standard. >>
      > >> Hope this helps.
      > >>
      > >> David
      > >>
      > >> At 15:38 06-03-13, ctown000 wrote:
      > >> >I'm curious whether it makes any difference whether
      > positive or >> >negative polarization voltage is used on
      > a condenser? Does it change >> >the frequency response
      > or anything? >> >
      > >> >I would assume it does NOT because a standard
      > multi-pattern condenser >> >uses negative polarization
      > (e.g., -60V) on the rear capsule to do >> >figure-8. And
      > for the figure-8 patterns I've looked at the >>
      > >cancellation of the omni portion seems quite good, which
      > wouldn't >> >happen so much if the frequency response was
      > shifted. >> >
      > >> >But I'm sure some people here know the real answer,
      > so I'll stop >> >speculating. Thoughts?
      > >> >
      > >> >
      > >> >-Chris
    • Jerry Lee Marcel
      My experience tells me that polarity can be heard only when some element in the chain has asymetric behaviour, and as a result, the sound is objectively (i.e.
      Message 2 of 19 , Mar 8, 2013
      • 0 Attachment
        My experience tells me that polarity can be heard only when some element
        in the chain has asymetric behaviour, and as a result, the sound is
        objectively (i.e. measurably) changed. Most electronic equipment doesn't
        suffer from asymetric behaviour, unless purposedly so (AM broadcast
        limiters are an example), but transducers, in particular loudspeakers
        exhibit a noticeable dose of asymetry. My first exposure to this
        phenomenon was in the 1980's, in a sudio with a pair of JBL 4331's.
        After having changed their amp, they complained about the lack of bass,
        which they demonstrated by playing a typical disco-era kick drum.
        My spontaneous move was to check the polarity for an inversion, but it
        was not the case.
        Some microphones may also, to a lesser extent. But reversing the
        polarization voltage does not change the mechanical response of a
        diaphragm, so it cannot be an intrinsic cause of response alteration.
        It may however make asymetry heard in the following stages of the
        reproduction chain.


        Le 07/03/2013 19:32, bblack a écrit :
        >
        > I know some people that claim that they can hear a
        > difference in absolute polarity. I can't, and I think the
        > vast majority of people cannot, but again, I do know some
        > who claim to be able to tell if the polarity is inverted,
        > even in a single microphone recording. YMMV.
        > Of course, in a multi-mic setup, (especially a stereo array)
        > if one mic is polarity reversed with respect to the others,
        > it will cause cancellations.
        >
        > Bryan
        >
        > > Sound should not change. Mostly it's been positive in
        > > phantom-powered mics because phantom power is positive
        > > voltage.
        > >
        > > There may well be something different with respect to dust
        > > , though. I remember something about Neumann changing to a
        > > 0v diaphragm with polarized backplate, because otherwise
        > > dust tended to be attracted to the diaphragm.
        > >
        > > -Scott
        > >
        > > > Thanks for the help. I'm not sure I was totally clear.
        > > > Let's say you have a single diaphragm omni condenser
        > > > polarized at +60V (backplate is 0V, diaphragm is +60).
        > > > Then you change the polarizing voltage to -60V. Will
        > > the mic performance be exactly the same as before, except
        > > > that the polarity of the output is inverted, or will
        > > > there be some other difference, such as noise floor,
        > > frequency response, etc? >
        > > > -Chris
        > > >
        > > > --- In micbuilders@yahoogroups.com
        > <mailto:micbuilders%40yahoogroups.com>, David Pickett
        > > <dmp@...> wrote: >>
        > > >> As I think you may realize, it affects the polarity of
        > > the electrical >> signal. -60v on the rear for figure of
        > > eight, produces a negative >> lobe, whereas +60v on the
        > > front produces a positive lobe, which is >> what you want
        > > for a fig 8 pattern. Omni is produced from +60 or -60 >>
        > > on BOTH sides. Of course, the following amplifier may
        > > well invert >> the signal, so it is wise always to do an
        > > actual comparison of a new >> microphone with one which
        > > has the standard polarity and make a change >> inside if
        > > the polarity of the one you built is opposite to the
        > > standard. >>
        > > >> Hope this helps.
        > > >>
        > > >> David
        > > >>
        > > >> At 15:38 06-03-13, ctown000 wrote:
        > > >> >I'm curious whether it makes any difference whether
        > > positive or >> >negative polarization voltage is used on
        > > a condenser? Does it change >> >the frequency response
        > > or anything? >> >
        > > >> >I would assume it does NOT because a standard
        > > multi-pattern condenser >> >uses negative polarization
        > > (e.g., -60V) on the rear capsule to do >> >figure-8. And
        > > for the figure-8 patterns I've looked at the >>
        > > >cancellation of the omni portion seems quite good, which
        > > wouldn't >> >happen so much if the frequency response was
        > > shifted. >> >
        > > >> >But I'm sure some people here know the real answer,
        > > so I'll stop >> >speculating. Thoughts?
        > > >> >
        > > >> >
        > > >> >-Chris
        >
        >



        [Non-text portions of this message have been removed]
      • ctown000
        Thanks guys. Maybe a more relevant question is how does the absolute polarization voltage affect the response of a condenser? My rudimentary understanding is
        Message 3 of 19 , Mar 8, 2013
        • 0 Attachment
          Thanks guys. Maybe a more relevant question is how does the absolute polarization voltage affect the response of a condenser? My rudimentary understanding is that larger polarization voltages pull the diaphragm more towards the back plate, which I guess to some degree increases the tension on the diaphragm. I think this means that if the voltage is high enough the sensitivity of the mic will go down. Are there any other effects, such as changes in frequency response, as the voltage is varied?

          -Chris

          --- In micbuilders@yahoogroups.com, Jerry Lee Marcel <jerryleemarcel@...> wrote:
          >
          > My experience tells me that polarity can be heard only when some element
          > in the chain has asymetric behaviour, and as a result, the sound is
          > objectively (i.e. measurably) changed. Most electronic equipment doesn't
          > suffer from asymetric behaviour, unless purposedly so (AM broadcast
          > limiters are an example), but transducers, in particular loudspeakers
          > exhibit a noticeable dose of asymetry. My first exposure to this
          > phenomenon was in the 1980's, in a sudio with a pair of JBL 4331's.
          > After having changed their amp, they complained about the lack of bass,
          > which they demonstrated by playing a typical disco-era kick drum.
          > My spontaneous move was to check the polarity for an inversion, but it
          > was not the case.
          > Some microphones may also, to a lesser extent. But reversing the
          > polarization voltage does not change the mechanical response of a
          > diaphragm, so it cannot be an intrinsic cause of response alteration.
          > It may however make asymetry heard in the following stages of the
          > reproduction chain.
          >
          >
          > Le 07/03/2013 19:32, bblack a écrit :
          > >
          > > I know some people that claim that they can hear a
          > > difference in absolute polarity. I can't, and I think the
          > > vast majority of people cannot, but again, I do know some
          > > who claim to be able to tell if the polarity is inverted,
          > > even in a single microphone recording. YMMV.
          > > Of course, in a multi-mic setup, (especially a stereo array)
          > > if one mic is polarity reversed with respect to the others,
          > > it will cause cancellations.
          > >
          > > Bryan
          > >
          > > > Sound should not change. Mostly it's been positive in
          > > > phantom-powered mics because phantom power is positive
          > > > voltage.
          > > >
          > > > There may well be something different with respect to dust
          > > > , though. I remember something about Neumann changing to a
          > > > 0v diaphragm with polarized backplate, because otherwise
          > > > dust tended to be attracted to the diaphragm.
          > > >
          > > > -Scott
          > > >
          > > > > Thanks for the help. I'm not sure I was totally clear.
          > > > > Let's say you have a single diaphragm omni condenser
          > > > > polarized at +60V (backplate is 0V, diaphragm is +60).
          > > > > Then you change the polarizing voltage to -60V. Will
          > > > the mic performance be exactly the same as before, except
          > > > > that the polarity of the output is inverted, or will
          > > > > there be some other difference, such as noise floor,
          > > > frequency response, etc? >
          > > > > -Chris
          > > > >
          > > > > --- In micbuilders@yahoogroups.com
          > > <mailto:micbuilders%40yahoogroups.com>, David Pickett
          > > > <dmp@> wrote: >>
          > > > >> As I think you may realize, it affects the polarity of
          > > > the electrical >> signal. -60v on the rear for figure of
          > > > eight, produces a negative >> lobe, whereas +60v on the
          > > > front produces a positive lobe, which is >> what you want
          > > > for a fig 8 pattern. Omni is produced from +60 or -60 >>
          > > > on BOTH sides. Of course, the following amplifier may
          > > > well invert >> the signal, so it is wise always to do an
          > > > actual comparison of a new >> microphone with one which
          > > > has the standard polarity and make a change >> inside if
          > > > the polarity of the one you built is opposite to the
          > > > standard. >>
          > > > >> Hope this helps.
          > > > >>
          > > > >> David
          > > > >>
          > > > >> At 15:38 06-03-13, ctown000 wrote:
          > > > >> >I'm curious whether it makes any difference whether
          > > > positive or >> >negative polarization voltage is used on
          > > > a condenser? Does it change >> >the frequency response
          > > > or anything? >> >
          > > > >> >I would assume it does NOT because a standard
          > > > multi-pattern condenser >> >uses negative polarization
          > > > (e.g., -60V) on the rear capsule to do >> >figure-8. And
          > > > for the figure-8 patterns I've looked at the >>
          > > > >cancellation of the omni portion seems quite good, which
          > > > wouldn't >> >happen so much if the frequency response was
          > > > shifted. >> >
          > > > >> >But I'm sure some people here know the real answer,
          > > > so I'll stop >> >speculating. Thoughts?
          > > > >> >
          > > > >> >
          > > > >> >-Chris
          > >
          > >
          >
          >
          >
          > [Non-text portions of this message have been removed]
          >
        • David Pickett
          ... Yes. IF it is very high, but by then it will not work very well. Everything else being equal, an increase in polarizing voltage is supposed to increase
          Message 4 of 19 , Mar 8, 2013
          • 0 Attachment
            At 13:59 08-03-13, ctown000 wrote:
            > Maybe a more relevant question is how does the absolute
            >polarization voltage affect the response of a condenser? My
            >rudimentary understanding is that larger polarization voltages pull
            >the diaphragm more towards the back plate, which I guess to some
            >degree increases the tension on the diaphragm. I think this means
            >that if the voltage is high enough the sensitivity of the mic will go
            >down.

            Yes. IF it is very high, but by then it will not work very well.

            Everything else being equal, an increase in polarizing voltage is
            supposed to increase the sensitivity:

            The output of a capacitor mic, dV is given by -dC * V/C,

            Where dC is the change in capacitance due to the signal
            V is the polarizing voltage
            C is the static capacitance of the capsule.

            But, unless we are talking about small changes of polarizing voltage,
            such that the diaphragm is not materially attracted more towards the
            backplate, everything is probably not equal. In other words,
            changing the polarizing voltage can change other parameters that
            affect sensitivity.

            I should expect that, if the tension is increased on the diaphragm
            because the diaphragm has been attracted to the backplate by a higher
            than designed voltage, there would be two effects:

            1. Increased tension would increase the resonant frequency of the capsule.

            2. a) The effect of increased tension would likely restrict the
            movement of the capsule, so dC would go down due to this, but the
            change in dC might in any case be greater as the membrane is nearer
            to the backplate.

            b) The static capacitance would have gone up due to the reduced
            distance between the membrane and the backplate, though whether this
            would compensate for the increase in voltage and result in a zero sum
            result would depend on the actual case.

            So, apart from the effect on resonant frequency, I find the answer
            imponderable.

            However, it must be said that the larger danger of too high a
            polarizing voltage is to actually cause the membrane to touch the
            backplate. This is definitely not a good idea, and can result in
            permanent damage.

            David
          • ctown000
            I m trying to get my head around some of the basics of condenser circuits, and in the standard Schoeps schematic it looks the backplate is at +60V.
            Message 5 of 19 , Mar 12, 2013
            • 0 Attachment
              I'm trying to get my head around some of the basics of condenser circuits, and in the "standard" Schoeps schematic it looks the backplate is at +60V.

              http://www.twin-x.com/groupdiy/albums/userpics/Schoeps.gif

              In the MXL 990 schematic, which looks mostly like a copy of the Schoeps circuit, the backplate is a grounded and the diaphragm is at B+ (60V?).
              http://www.gearslutz.com/board/attachments/geekslutz-forum/301810d1342987154-mxl-990-resistor-replacement-how-far-off-schema-sp-1-mxl990.gif

              It seems like the more common style is for the backplate to be grounded, as is done in the MXL example. Is there any particular reason for using one approach over the other?

              Thanks,
              Chris


              --- In micbuilders@yahoogroups.com, David Pickett <dmp@...> wrote:
              >
              > At 13:59 08-03-13, ctown000 wrote:
              > > Maybe a more relevant question is how does the absolute
              > >polarization voltage affect the response of a condenser? My
              > >rudimentary understanding is that larger polarization voltages pull
              > >the diaphragm more towards the back plate, which I guess to some
              > >degree increases the tension on the diaphragm. I think this means
              > >that if the voltage is high enough the sensitivity of the mic will go
              > >down.
              >
              > Yes. IF it is very high, but by then it will not work very well.
              >
              > Everything else being equal, an increase in polarizing voltage is
              > supposed to increase the sensitivity:
              >
              > The output of a capacitor mic, dV is given by -dC * V/C,
              >
              > Where dC is the change in capacitance due to the signal
              > V is the polarizing voltage
              > C is the static capacitance of the capsule.
              >
              > But, unless we are talking about small changes of polarizing voltage,
              > such that the diaphragm is not materially attracted more towards the
              > backplate, everything is probably not equal. In other words,
              > changing the polarizing voltage can change other parameters that
              > affect sensitivity.
              >
              > I should expect that, if the tension is increased on the diaphragm
              > because the diaphragm has been attracted to the backplate by a higher
              > than designed voltage, there would be two effects:
              >
              > 1. Increased tension would increase the resonant frequency of the capsule.
              >
              > 2. a) The effect of increased tension would likely restrict the
              > movement of the capsule, so dC would go down due to this, but the
              > change in dC might in any case be greater as the membrane is nearer
              > to the backplate.
              >
              > b) The static capacitance would have gone up due to the reduced
              > distance between the membrane and the backplate, though whether this
              > would compensate for the increase in voltage and result in a zero sum
              > result would depend on the actual case.
              >
              > So, apart from the effect on resonant frequency, I find the answer
              > imponderable.
              >
              > However, it must be said that the larger danger of too high a
              > polarizing voltage is to actually cause the membrane to touch the
              > backplate. This is definitely not a good idea, and can result in
              > permanent damage.
              >
              > David
              >
            • mcglynn_matt
              ... I believe the 990 polarizes the capsule at ~42V, not 60V. You can change the diode at D3 to alter the polarization voltage. (We do this in our mod kits,
              Message 6 of 19 , Mar 12, 2013
              • 0 Attachment
                --- In micbuilders@yahoogroups.com, "ctown000" <ctown000@...> wrote:

                > In the MXL 990 schematic, which looks mostly like a copy of the Schoeps circuit, the backplate is a grounded and the diaphragm is at B+ (60V?).

                I believe the 990 polarizes the capsule at ~42V, not 60V. You can change the diode at D3 to alter the polarization voltage. (We do this in our mod kits, e.g. http://microphone-parts.com/mod-kits/mxl-990-upgrades/ )

                --
                matt.
              • Jerry Lee Marcel
                When the diaphragm is polarized, it attracts particles of dust, which accumulates. Moisture bindsto the accumulated dust, resulting in partial short-circuit
                Message 7 of 19 , Mar 12, 2013
                • 0 Attachment
                  When the diaphragm is polarized, it attracts particles of dust, which
                  accumulates. Moisture bindsto the accumulated dust, resulting in partial
                  short-circuit and spurious noise.
                  When the backplate is polarized, the accumulation of dust is localized
                  to a tiny area, which can be easily insulated.


                  Le 12/03/2013 08:37, ctown000 a écrit :
                  >
                  > I'm trying to get my head around some of the basics of condenser
                  > circuits, and in the "standard" Schoeps schematic it looks the
                  > backplate is at +60V.
                  >
                  > http://www.twin-x.com/groupdiy/albums/userpics/Schoeps.gif
                  >
                  > In the MXL 990 schematic, which looks mostly like a copy of the
                  > Schoeps circuit, the backplate is a grounded and the diaphragm is at
                  > B+ (60V?).
                  > http://www.gearslutz.com/board/attachments/geekslutz-forum/301810d1342987154-mxl-990-resistor-replacement-how-far-off-schema-sp-1-mxl990.gif
                  >
                  > It seems like the more common style is for the backplate to be
                  > grounded, as is done in the MXL example. Is there any particular
                  > reason for using one approach over the other?
                  >
                  > Thanks,
                  > Chris
                  >
                  > --- In micbuilders@yahoogroups.com
                  > <mailto:micbuilders%40yahoogroups.com>, David Pickett <dmp@...> wrote:
                  > >
                  > > At 13:59 08-03-13, ctown000 wrote:
                  > > > Maybe a more relevant question is how does the absolute
                  > > >polarization voltage affect the response of a condenser? My
                  > > >rudimentary understanding is that larger polarization voltages pull
                  > > >the diaphragm more towards the back plate, which I guess to some
                  > > >degree increases the tension on the diaphragm. I think this means
                  > > >that if the voltage is high enough the sensitivity of the mic will go
                  > > >down.
                  > >
                  > > Yes. IF it is very high, but by then it will not work very well.
                  > >
                  > > Everything else being equal, an increase in polarizing voltage is
                  > > supposed to increase the sensitivity:
                  > >
                  > > The output of a capacitor mic, dV is given by -dC * V/C,
                  > >
                  > > Where dC is the change in capacitance due to the signal
                  > > V is the polarizing voltage
                  > > C is the static capacitance of the capsule.
                  > >
                  > > But, unless we are talking about small changes of polarizing voltage,
                  > > such that the diaphragm is not materially attracted more towards the
                  > > backplate, everything is probably not equal. In other words,
                  > > changing the polarizing voltage can change other parameters that
                  > > affect sensitivity.
                  > >
                  > > I should expect that, if the tension is increased on the diaphragm
                  > > because the diaphragm has been attracted to the backplate by a higher
                  > > than designed voltage, there would be two effects:
                  > >
                  > > 1. Increased tension would increase the resonant frequency of the
                  > capsule.
                  > >
                  > > 2. a) The effect of increased tension would likely restrict the
                  > > movement of the capsule, so dC would go down due to this, but the
                  > > change in dC might in any case be greater as the membrane is nearer
                  > > to the backplate.
                  > >
                  > > b) The static capacitance would have gone up due to the reduced
                  > > distance between the membrane and the backplate, though whether this
                  > > would compensate for the increase in voltage and result in a zero sum
                  > > result would depend on the actual case.
                  > >
                  > > So, apart from the effect on resonant frequency, I find the answer
                  > > imponderable.
                  > >
                  > > However, it must be said that the larger danger of too high a
                  > > polarizing voltage is to actually cause the membrane to touch the
                  > > backplate. This is definitely not a good idea, and can result in
                  > > permanent damage.
                  > >
                  > > David
                  > >
                  >
                  >



                  [Non-text portions of this message have been removed]
                • ctown000
                  Thanks, interesting. But it seems that most circuits I ve looked at put a positive voltage on the diaphragm and ground the backplate, so therefore would
                  Message 8 of 19 , Mar 12, 2013
                  • 0 Attachment
                    Thanks, interesting. But it seems that most circuits I've looked at put a positive voltage on the diaphragm and ground the backplate, so therefore would attract more dust. I wonder why that is the typical approach, if this problem can occur? I presume there must be some additional benefits that potentially outweigh the downsides.

                    -Chris

                    --- In micbuilders@yahoogroups.com, Jerry Lee Marcel <jerryleemarcel@...> wrote:
                    >
                    > When the diaphragm is polarized, it attracts particles of dust, which
                    > accumulates. Moisture bindsto the accumulated dust, resulting in partial
                    > short-circuit and spurious noise.
                    > When the backplate is polarized, the accumulation of dust is localized
                    > to a tiny area, which can be easily insulated.
                    >
                    >
                    > Le 12/03/2013 08:37, ctown000 a écrit :
                    > >
                    > > I'm trying to get my head around some of the basics of condenser
                    > > circuits, and in the "standard" Schoeps schematic it looks the
                    > > backplate is at +60V.
                    > >
                    > > http://www.twin-x.com/groupdiy/albums/userpics/Schoeps.gif
                    > >
                    > > In the MXL 990 schematic, which looks mostly like a copy of the
                    > > Schoeps circuit, the backplate is a grounded and the diaphragm is at
                    > > B+ (60V?).
                    > > http://www.gearslutz.com/board/attachments/geekslutz-forum/301810d1342987154-mxl-990-resistor-replacement-how-far-off-schema-sp-1-mxl990.gif
                    > >
                    > > It seems like the more common style is for the backplate to be
                    > > grounded, as is done in the MXL example. Is there any particular
                    > > reason for using one approach over the other?
                    > >
                    > > Thanks,
                    > > Chris
                    > >
                    > > --- In micbuilders@yahoogroups.com
                    > > <mailto:micbuilders%40yahoogroups.com>, David Pickett <dmp@> wrote:
                    > > >
                    > > > At 13:59 08-03-13, ctown000 wrote:
                    > > > > Maybe a more relevant question is how does the absolute
                    > > > >polarization voltage affect the response of a condenser? My
                    > > > >rudimentary understanding is that larger polarization voltages pull
                    > > > >the diaphragm more towards the back plate, which I guess to some
                    > > > >degree increases the tension on the diaphragm. I think this means
                    > > > >that if the voltage is high enough the sensitivity of the mic will go
                    > > > >down.
                    > > >
                    > > > Yes. IF it is very high, but by then it will not work very well.
                    > > >
                    > > > Everything else being equal, an increase in polarizing voltage is
                    > > > supposed to increase the sensitivity:
                    > > >
                    > > > The output of a capacitor mic, dV is given by -dC * V/C,
                    > > >
                    > > > Where dC is the change in capacitance due to the signal
                    > > > V is the polarizing voltage
                    > > > C is the static capacitance of the capsule.
                    > > >
                    > > > But, unless we are talking about small changes of polarizing voltage,
                    > > > such that the diaphragm is not materially attracted more towards the
                    > > > backplate, everything is probably not equal. In other words,
                    > > > changing the polarizing voltage can change other parameters that
                    > > > affect sensitivity.
                    > > >
                    > > > I should expect that, if the tension is increased on the diaphragm
                    > > > because the diaphragm has been attracted to the backplate by a higher
                    > > > than designed voltage, there would be two effects:
                    > > >
                    > > > 1. Increased tension would increase the resonant frequency of the
                    > > capsule.
                    > > >
                    > > > 2. a) The effect of increased tension would likely restrict the
                    > > > movement of the capsule, so dC would go down due to this, but the
                    > > > change in dC might in any case be greater as the membrane is nearer
                    > > > to the backplate.
                    > > >
                    > > > b) The static capacitance would have gone up due to the reduced
                    > > > distance between the membrane and the backplate, though whether this
                    > > > would compensate for the increase in voltage and result in a zero sum
                    > > > result would depend on the actual case.
                    > > >
                    > > > So, apart from the effect on resonant frequency, I find the answer
                    > > > imponderable.
                    > > >
                    > > > However, it must be said that the larger danger of too high a
                    > > > polarizing voltage is to actually cause the membrane to touch the
                    > > > backplate. This is definitely not a good idea, and can result in
                    > > > permanent damage.
                    > > >
                    > > > David
                    > > >
                    > >
                    > >
                    >
                    >
                    >
                    > [Non-text portions of this message have been removed]
                    >
                  • Jerry Lee Marcel
                    Apparently the only reason is that it s easier to manufacture. This is particularly true for multi-pattern mics, that require isolated backplates (4-wire ).
                    Message 9 of 19 , Mar 12, 2013
                    • 0 Attachment
                      Apparently the only reason is that it's easier to manufacture.
                      This is particularly true for multi-pattern mics, that require isolated
                      backplates (4-wire

                      ).
                      Le 12/03/2013 18:27, ctown000 a écrit :
                      >
                      > Thanks, interesting. But it seems that most circuits I've looked at
                      > put a positive voltage on the diaphragm and ground the backplate, so
                      > therefore would attract more dust. I wonder why that is the typical
                      > approach, if this problem can occur? I presume there must be some
                      > additional benefits that potentially outweigh the downsides.
                      >
                      > -Chris
                      >
                      > --- In micbuilders@yahoogroups.com
                      > <mailto:micbuilders%40yahoogroups.com>, Jerry Lee Marcel
                      > <jerryleemarcel@...> wrote:
                      > >
                      > > When the diaphragm is polarized, it attracts particles of dust, which
                      > > accumulates. Moisture bindsto the accumulated dust, resulting in
                      > partial
                      > > short-circuit and spurious noise.
                      > > When the backplate is polarized, the accumulation of dust is localized
                      > > to a tiny area, which can be easily insulated.
                      > >
                      > >
                      > > Le 12/03/2013 08:37, ctown000 a écrit :
                      > > >
                      > > > I'm trying to get my head around some of the basics of condenser
                      > > > circuits, and in the "standard" Schoeps schematic it looks the
                      > > > backplate is at +60V.
                      > > >
                      > > > http://www.twin-x.com/groupdiy/albums/userpics/Schoeps.gif
                      > > >
                      > > > In the MXL 990 schematic, which looks mostly like a copy of the
                      > > > Schoeps circuit, the backplate is a grounded and the diaphragm is at
                      > > > B+ (60V?).
                      > > >
                      > http://www.gearslutz.com/board/attachments/geekslutz-forum/301810d1342987154-mxl-990-resistor-replacement-how-far-off-schema-sp-1-mxl990.gif
                      > > >
                      > > > It seems like the more common style is for the backplate to be
                      > > > grounded, as is done in the MXL example. Is there any particular
                      > > > reason for using one approach over the other?
                      > > >
                      > > > Thanks,
                      > > > Chris
                      > > >
                      > > > --- In micbuilders@yahoogroups.com
                      > <mailto:micbuilders%40yahoogroups.com>
                      > > > <mailto:micbuilders%40yahoogroups.com>, David Pickett <dmp@> wrote:
                      > > > >
                      > > > > At 13:59 08-03-13, ctown000 wrote:
                      > > > > > Maybe a more relevant question is how does the absolute
                      > > > > >polarization voltage affect the response of a condenser? My
                      > > > > >rudimentary understanding is that larger polarization voltages pull
                      > > > > >the diaphragm more towards the back plate, which I guess to some
                      > > > > >degree increases the tension on the diaphragm. I think this means
                      > > > > >that if the voltage is high enough the sensitivity of the mic
                      > will go
                      > > > > >down.
                      > > > >
                      > > > > Yes. IF it is very high, but by then it will not work very well.
                      > > > >
                      > > > > Everything else being equal, an increase in polarizing voltage is
                      > > > > supposed to increase the sensitivity:
                      > > > >
                      > > > > The output of a capacitor mic, dV is given by -dC * V/C,
                      > > > >
                      > > > > Where dC is the change in capacitance due to the signal
                      > > > > V is the polarizing voltage
                      > > > > C is the static capacitance of the capsule.
                      > > > >
                      > > > > But, unless we are talking about small changes of polarizing
                      > voltage,
                      > > > > such that the diaphragm is not materially attracted more towards the
                      > > > > backplate, everything is probably not equal. In other words,
                      > > > > changing the polarizing voltage can change other parameters that
                      > > > > affect sensitivity.
                      > > > >
                      > > > > I should expect that, if the tension is increased on the diaphragm
                      > > > > because the diaphragm has been attracted to the backplate by a
                      > higher
                      > > > > than designed voltage, there would be two effects:
                      > > > >
                      > > > > 1. Increased tension would increase the resonant frequency of the
                      > > > capsule.
                      > > > >
                      > > > > 2. a) The effect of increased tension would likely restrict the
                      > > > > movement of the capsule, so dC would go down due to this, but the
                      > > > > change in dC might in any case be greater as the membrane is nearer
                      > > > > to the backplate.
                      > > > >
                      > > > > b) The static capacitance would have gone up due to the reduced
                      > > > > distance between the membrane and the backplate, though whether this
                      > > > > would compensate for the increase in voltage and result in a
                      > zero sum
                      > > > > result would depend on the actual case.
                      > > > >
                      > > > > So, apart from the effect on resonant frequency, I find the answer
                      > > > > imponderable.
                      > > > >
                      > > > > However, it must be said that the larger danger of too high a
                      > > > > polarizing voltage is to actually cause the membrane to touch the
                      > > > > backplate. This is definitely not a good idea, and can result in
                      > > > > permanent damage.
                      > > > >
                      > > > > David
                      > > > >
                      > > >
                      > > >
                      > >
                      > >
                      > >
                      > > [Non-text portions of this message have been removed]
                      > >
                      >
                      >



                      [Non-text portions of this message have been removed]
                    • archieaa1
                      Sometimes conventions become conventions simply because no one thought to do it otherwise. Archie
                      Message 10 of 19 , Mar 12, 2013
                      • 0 Attachment
                        Sometimes conventions become conventions simply because no one thought to do it otherwise.

                        Archie



                        --- In micbuilders@yahoogroups.com, "ctown000" <ctown000@...> wrote:
                        >
                        > Thanks, interesting. But it seems that most circuits I've looked at put a positive voltage on the diaphragm and ground the backplate, so therefore would attract more dust. I wonder why that is the typical approach, if this problem can occur? I presume there must be some additional benefits that potentially outweigh the downsides.
                        >
                        > -Chris
                        >
                        > --- In micbuilders@yahoogroups.com, Jerry Lee Marcel <jerryleemarcel@> wrote:
                        > >
                        > > When the diaphragm is polarized, it attracts particles of dust, which
                        > > accumulates. Moisture bindsto the accumulated dust, resulting in partial
                        > > short-circuit and spurious noise.
                        > > When the backplate is polarized, the accumulation of dust is localized
                        > > to a tiny area, which can be easily insulated.
                        > >
                        > >
                        > > Le 12/03/2013 08:37, ctown000 a �crit :
                        > > >
                        > > > I'm trying to get my head around some of the basics of condenser
                        > > > circuits, and in the "standard" Schoeps schematic it looks the
                        > > > backplate is at +60V.
                        > > >
                        > > > http://www.twin-x.com/groupdiy/albums/userpics/Schoeps.gif
                        > > >
                        > > > In the MXL 990 schematic, which looks mostly like a copy of the
                        > > > Schoeps circuit, the backplate is a grounded and the diaphragm is at
                        > > > B+ (60V?).
                        > > > http://www.gearslutz.com/board/attachments/geekslutz-forum/301810d1342987154-mxl-990-resistor-replacement-how-far-off-schema-sp-1-mxl990.gif
                        > > >
                        > > > It seems like the more common style is for the backplate to be
                        > > > grounded, as is done in the MXL example. Is there any particular
                        > > > reason for using one approach over the other?
                        > > >
                        > > > Thanks,
                        > > > Chris
                        > > >
                        > > > --- In micbuilders@yahoogroups.com
                        > > > <mailto:micbuilders%40yahoogroups.com>, David Pickett <dmp@> wrote:
                        > > > >
                        > > > > At 13:59 08-03-13, ctown000 wrote:
                        > > > > > Maybe a more relevant question is how does the absolute
                        > > > > >polarization voltage affect the response of a condenser? My
                        > > > > >rudimentary understanding is that larger polarization voltages pull
                        > > > > >the diaphragm more towards the back plate, which I guess to some
                        > > > > >degree increases the tension on the diaphragm. I think this means
                        > > > > >that if the voltage is high enough the sensitivity of the mic will go
                        > > > > >down.
                        > > > >
                        > > > > Yes. IF it is very high, but by then it will not work very well.
                        > > > >
                        > > > > Everything else being equal, an increase in polarizing voltage is
                        > > > > supposed to increase the sensitivity:
                        > > > >
                        > > > > The output of a capacitor mic, dV is given by -dC * V/C,
                        > > > >
                        > > > > Where dC is the change in capacitance due to the signal
                        > > > > V is the polarizing voltage
                        > > > > C is the static capacitance of the capsule.
                        > > > >
                        > > > > But, unless we are talking about small changes of polarizing voltage,
                        > > > > such that the diaphragm is not materially attracted more towards the
                        > > > > backplate, everything is probably not equal. In other words,
                        > > > > changing the polarizing voltage can change other parameters that
                        > > > > affect sensitivity.
                        > > > >
                        > > > > I should expect that, if the tension is increased on the diaphragm
                        > > > > because the diaphragm has been attracted to the backplate by a higher
                        > > > > than designed voltage, there would be two effects:
                        > > > >
                        > > > > 1. Increased tension would increase the resonant frequency of the
                        > > > capsule.
                        > > > >
                        > > > > 2. a) The effect of increased tension would likely restrict the
                        > > > > movement of the capsule, so dC would go down due to this, but the
                        > > > > change in dC might in any case be greater as the membrane is nearer
                        > > > > to the backplate.
                        > > > >
                        > > > > b) The static capacitance would have gone up due to the reduced
                        > > > > distance between the membrane and the backplate, though whether this
                        > > > > would compensate for the increase in voltage and result in a zero sum
                        > > > > result would depend on the actual case.
                        > > > >
                        > > > > So, apart from the effect on resonant frequency, I find the answer
                        > > > > imponderable.
                        > > > >
                        > > > > However, it must be said that the larger danger of too high a
                        > > > > polarizing voltage is to actually cause the membrane to touch the
                        > > > > backplate. This is definitely not a good idea, and can result in
                        > > > > permanent damage.
                        > > > >
                        > > > > David
                        > > > >
                        > > >
                        > > >
                        > >
                        > >
                        > >
                        > > [Non-text portions of this message have been removed]
                        > >
                        >
                      • LESLIE WATTS
                        There are reasons to use a hot diaphragm ...i.e. connected to polarization. It gets rid of the typical coupling capacitor from backplate to gate...thus
                        Message 11 of 19 , Mar 13, 2013
                        • 0 Attachment
                          There are reasons to use a "hot diaphragm"...i.e. connected to polarization.

                          It gets rid of the typical coupling capacitor from backplate to gate...thus allowing polarization voltage changes (for attenuation and other things) without presenting large voltage spikes to the fet.

                          We prefer it to shunt capacitance as attenuators, as they cause distortion and usually audible switching noise.

                          As far as dust...

                          Grounded conductors attract dust as well by charge image
                          formation. This is how electrostatic powder painting systems work...the object to be painted is usually grounded.

                          Dust particles can be positive or negatively charged, uncharged, or have a dipole moment. If one looks at the triboelectric series it can be seen that much dust is positively charged...particularly textile fiber components.
                          Some minerals and aerosols can be negatively charged.
                          Induced dipoles can happen if the particles are slightly conductive or if non conductive opposite charge particles
                          clump together.

                          So even though much dust is repelled from a positively charged diaphragm, we used a fairly fine guard mesh also charged to polarization voltage in front of the diaphragm.
                          This offers protection and is part of the acoustic resistance
                          system.

                          Les
                          L M Watts Technology

                          ----- Original Message -----
                          From: archieaa1
                          To: micbuilders@yahoogroups.com
                          Sent: Tuesday, March 12, 2013 3:29 PM
                          Subject: [micbuilders] Re: Polarization Voltage - Schoeps Circuit



                          Sometimes conventions become conventions simply because no one thought to do it otherwise.

                          Archie

                          --- In micbuilders@yahoogroups.com, "ctown000" <ctown000@...> wrote:
                          >
                          > Thanks, interesting. But it seems that most circuits I've looked at put a positive voltage on the diaphragm and ground the backplate, so therefore would attract more dust. I wonder why that is the typical approach, if this problem can occur? I presume there must be some additional benefits that potentially outweigh the downsides.
                          >
                          > -Chris
                          >



                          [Non-text portions of this message have been removed]
                        • Jerry Lee Marcel
                          typical coupling capacitor from backplate to gate I don t get it. It seems to me getting rid of the coupling cap just involves connecting the bias voltage to
                          Message 12 of 19 , Mar 13, 2013
                          • 0 Attachment
                            "typical coupling capacitor from backplate to gate"
                            I don't get it. It seems to me getting rid of the coupling cap just
                            involves connecting the bias voltage to one of the electrodes, whether
                            it's the backplate or the diaphragm, and connecting the other directly
                            to the gate (with a "gate-leak" resistor).
                            In that respect, and for practicality, I would think that connecting the
                            bias voltage to an isolated backplate and the diaphragm to the FET would
                            be the best, in particular considering the parasitic capacitance of the
                            backplate is generally larger than the diaphragm's.

                            I note with interest your comment on "much dust is positively charged".

                            Do you think it's the main reason why "(quote Chris) most circuits I've
                            looked at put a positive voltage on the diaphragm and ground the
                            backplate ", or a more practical reason?
                            It's so much easier to have the backplate grounded and a 500pF ceramic
                            cap cost almost nothing...manufacturing costs.

                            Regarding your "fairly fine guard mesh also charged to polarization
                            voltage in front of the diaphragm", have you deemed necessary to make
                            them removable so they can be cleaned? I think in the end the mesh will
                            gather some dust and may clog...or is it a fantasy?

                            Le 13/03/2013 11:15, LESLIE WATTS a écrit :
                            >
                            > There are reasons to use a "hot diaphragm"...i.e. connected to
                            > polarization.
                            >
                            > It gets rid of the typical coupling capacitor from backplate to
                            > gate...thus allowing polarization voltage changes (for attenuation and
                            > other things) without presenting large voltage spikes to the fet.
                            >
                            > We prefer it to shunt capacitance as attenuators, as they cause
                            > distortion and usually audible switching noise.
                            >
                            > As far as dust...
                            >
                            > Grounded conductors attract dust as well by charge image
                            > formation. This is how electrostatic powder painting systems
                            > work...the object to be painted is usually grounded.
                            >
                            > Dust particles can be positive or negatively charged, uncharged, or
                            > have a dipole moment. If one looks at the triboelectric series it can
                            > be seen that much dust is positively charged...particularly textile
                            > fiber components.
                            > Some minerals and aerosols can be negatively charged.
                            > Induced dipoles can happen if the particles are slightly conductive or
                            > if non conductive opposite charge particles
                            > clump together.
                            >
                            > So even though much dust is repelled from a positively charged
                            > diaphragm, we used a fairly fine guard mesh also charged to
                            > polarization voltage in front of the diaphragm.
                            > This offers protection and is part of the acoustic resistance
                            > system.
                            >
                            > Les
                            > L M Watts Technology
                            >
                            > ----- Original Message -----
                            > From: archieaa1
                            > To: micbuilders@yahoogroups.com <mailto:micbuilders%40yahoogroups.com>
                            > Sent: Tuesday, March 12, 2013 3:29 PM
                            > Subject: [micbuilders] Re: Polarization Voltage - Schoeps Circuit
                            >
                            > Sometimes conventions become conventions simply because no one thought
                            > to do it otherwise.
                            >
                            > Archie
                            >
                            > --- In micbuilders@yahoogroups.com
                            > <mailto:micbuilders%40yahoogroups.com>, "ctown000" <ctown000@...> wrote:
                            > >
                            > > Thanks, interesting. But it seems that most circuits I've looked at
                            > put a positive voltage on the diaphragm and ground the backplate, so
                            > therefore would attract more dust. I wonder why that is the typical
                            > approach, if this problem can occur? I presume there must be some
                            > additional benefits that potentially outweigh the downsides.
                            > >
                            > > -Chris
                            > >
                            >
                            > [Non-text portions of this message have been removed]
                            >
                            >



                            [Non-text portions of this message have been removed]
                          • LESLIE WATTS
                            See jim s zapnspark files for a description of the two connection alternatives. For me it s not about the cost of a 1 nF coupling cap. It s about using shunt
                            Message 13 of 19 , Mar 13, 2013
                            • 0 Attachment
                              See jim's zapnspark files for a description of the two connection alternatives.

                              For me it's not about the cost of a 1 nF coupling cap.

                              It's about using shunt capacitors as capsule attenuating devices. They cause the capsule to become much more nonlinear, and often cause large thumps when switched in.
                              I decided I didn't want to use that method after a customer
                              switched in attenuation on one of my prototypes in a live PA situation and nearly blew out his PA speakers.

                              Attempts to keep the attenuation caps charged up compromise noise.

                              So after a discussion with Richard I looked at reduced polarization voltage attenuation. Some analysis will show that very large negative voltages will appear on the gate with a grounded diaphragm/coupling cap system if polarization voltage is suddenly reduced.

                              This doesn't happen so much with hot diaphragm/ no coupling cap configuration.

                              So My microphones attenuate by dropping polarization from
                              60 volts to 20 and are completely silent. Variable polarization voltage can be easily done also if desired.

                              We do have to factor in that changing plarization voltage:
                              1) changes diaphragm tension
                              2) changes squeeze film damping
                              3) changes max SPL

                              as well as sensitivity.

                              In the past I had looked at typical dust composition. It varies widely with location, but the typical household textile fiber
                              seems to be mostly positive. I think my cat is positively charged too! He hates the sparks when I pet him. But in some locations there can be a lot of negatively charged particles. It depends on the composition.

                              The guard screen can be removed for cleaning.

                              To put this in perspective...we're talking 60 volts here. On dry winter days you can easily have 5-10 kV between your body and the floor. And textile product fibers can have high potentials since they are removed by friction (like petting my cat) and drift away from the original source...dropping the capacitance to it. Q/C goes way up.

                              But we don't want any diaphragm contamination, and I was not willing to accept loud pops and significant harmonic distortion caused by shunt cap type attenuators.

                              In the end hot diaphragm cost more...we have to electrically isolate the capsule...an inconvenience in pencil mics.

                              Les
                              L M Watts Technology

                              ----- Original Message -----
                              From: Jerry Lee Marcel
                              To: micbuilders@yahoogroups.com
                              Cc: LESLIE WATTS
                              Sent: Wednesday, March 13, 2013 6:43 AM
                              Subject: Re: [micbuilders] Re: Polarization Voltage - Schoeps Circuit



                              "typical coupling capacitor from backplate to gate"
                              I don't get it. It seems to me getting rid of the coupling cap just
                              involves connecting the bias voltage to one of the electrodes, whether
                              it's the backplate or the diaphragm, and connecting the other directly
                              to the gate (with a "gate-leak" resistor).
                              In that respect, and for practicality, I would think that connecting the
                              bias voltage to an isolated backplate and the diaphragm to the FET would
                              be the best, in particular considering the parasitic capacitance of the
                              backplate is generally larger than the diaphragm's.

                              I note with interest your comment on "much dust is positively charged".

                              Do you think it's the main reason why "(quote Chris) most circuits I've
                              looked at put a positive voltage on the diaphragm and ground the
                              backplate ", or a more practical reason?
                              It's so much easier to have the backplate grounded and a 500pF ceramic
                              cap cost almost nothing...manufacturing costs.

                              Regarding your "fairly fine guard mesh also charged to polarization
                              voltage in front of the diaphragm", have you deemed necessary to make
                              them removable so they can be cleaned? I think in the end the mesh will
                              gather some dust and may clog...or is it a fantasy?

                              Le 13/03/2013 11:15, LESLIE WATTS a écrit :
                              >
                              > There are reasons to use a "hot diaphragm"...i.e. connected to
                              > polarization.
                              >
                              > It gets rid of the typical coupling capacitor from backplate to
                              > gate...thus allowing polarization voltage changes (for attenuation and
                              > other things) without presenting large voltage spikes to the fet.
                              >
                              > We prefer it to shunt capacitance as attenuators, as they cause
                              > distortion and usually audible switching noise.
                              >
                              > As far as dust...
                              >
                              > Grounded conductors attract dust as well by charge image
                              > formation. This is how electrostatic powder painting systems
                              > work...the object to be painted is usually grounded.
                              >
                              > Dust particles can be positive or negatively charged, uncharged, or
                              > have a dipole moment. If one looks at the triboelectric series it can
                              > be seen that much dust is positively charged...particularly textile
                              > fiber components.
                              > Some minerals and aerosols can be negatively charged.
                              > Induced dipoles can happen if the particles are slightly conductive or
                              > if non conductive opposite charge particles
                              > clump together.
                              >
                              > So even though much dust is repelled from a positively charged
                              > diaphragm, we used a fairly fine guard mesh also charged to
                              > polarization voltage in front of the diaphragm.
                              > This offers protection and is part of the acoustic resistance
                              > system.
                              >
                              > Les
                              > L M Watts Technology
                              >
                              > ----- Original Message -----
                              > From: archieaa1
                              > To: micbuilders@yahoogroups.com <mailto:micbuilders%40yahoogroups.com>
                              > Sent: Tuesday, March 12, 2013 3:29 PM
                              > Subject: [micbuilders] Re: Polarization Voltage - Schoeps Circuit
                              >
                              > Sometimes conventions become conventions simply because no one thought
                              > to do it otherwise.
                              >
                              > Archie
                              >
                              > --- In micbuilders@yahoogroups.com
                              > <mailto:micbuilders%40yahoogroups.com>, "ctown000" <ctown000@...> wrote:
                              > >
                              > > Thanks, interesting. But it seems that most circuits I've looked at
                              > put a positive voltage on the diaphragm and ground the backplate, so
                              > therefore would attract more dust. I wonder why that is the typical
                              > approach, if this problem can occur? I presume there must be some
                              > additional benefits that potentially outweigh the downsides.
                              > >
                              > > -Chris
                              > >
                              >
                              > [Non-text portions of this message have been removed]
                              >
                              >

                              [Non-text portions of this message have been removed]





                              [Non-text portions of this message have been removed]
                            • Jerry Lee Marcel
                              I think I haven t made myself clear. I don t question the relevance of avoiding the coupling cap (I was just mentioning that it is a cost-saving choice). You
                              Message 14 of 19 , Mar 13, 2013
                              • 0 Attachment
                                I think I haven't made myself clear.
                                I don't question the relevance of avoiding the coupling cap (I was just
                                mentioning that it is a cost-saving choice).
                                You said previously: "> There are reasons to use a "hot
                                diaphragm"...i.e. connected to polarization.
                                >
                                > It gets rid of the typical coupling capacitor from backplate to gate..."
                                But having the backplate "hot" also gets rid of the coupling cap.

                                I don't either question the fact that reducing sensitivity with a shunt
                                cap is not satisfactory in terms of distortion (for the same reason that
                                charge amplifiers are not satisfactory either). The added switching
                                problem is definitely a good reason to avoid them shunt caps.

                                Le 13/03/2013 12:57, LESLIE WATTS a écrit :
                                >
                                > See jim's zapnspark files for a description of the two connection
                                > alternatives.
                                >
                                > For me it's not about the cost of a 1 nF coupling cap.
                                >
                                > It's about using shunt capacitors as capsule attenuating devices. They
                                > cause the capsule to become much more nonlinear, and often cause large
                                > thumps when switched in.
                                > I decided I didn't want to use that method after a customer
                                > switched in attenuation on one of my prototypes in a live PA situation
                                > and nearly blew out his PA speakers.
                                >
                                > Attempts to keep the attenuation caps charged up compromise noise.
                                >
                                > So after a discussion with Richard I looked at reduced polarization
                                > voltage attenuation. Some analysis will show that very large negative
                                > voltages will appear on the gate with a grounded diaphragm/coupling
                                > cap system if polarization voltage is suddenly reduced.
                                >
                                > This doesn't happen so much with hot diaphragm/ no coupling cap
                                > configuration.
                                >
                                > So My microphones attenuate by dropping polarization from
                                > 60 volts to 20 and are completely silent. Variable polarization
                                > voltage can be easily done also if desired.
                                >
                                > We do have to factor in that changing plarization voltage:
                                > 1) changes diaphragm tension
                                > 2) changes squeeze film damping
                                > 3) changes max SPL
                                >
                                > as well as sensitivity.
                                >
                                > In the past I had looked at typical dust composition. It varies widely
                                > with location, but the typical household textile fiber
                                > seems to be mostly positive. I think my cat is positively charged too!
                                > He hates the sparks when I pet him. But in some locations there can be
                                > a lot of negatively charged particles. It depends on the composition.
                                >
                                > The guard screen can be removed for cleaning.
                                >
                                > To put this in perspective...we're talking 60 volts here. On dry
                                > winter days you can easily have 5-10 kV between your body and the
                                > floor. And textile product fibers can have high potentials since they
                                > are removed by friction (like petting my cat) and drift away from the
                                > original source...dropping the capacitance to it. Q/C goes way up.
                                >
                                > But we don't want any diaphragm contamination, and I was not willing
                                > to accept loud pops and significant harmonic distortion caused by
                                > shunt cap type attenuators.
                                >
                                > In the end hot diaphragm cost more...we have to electrically isolate
                                > the capsule...an inconvenience in pencil mics.
                                >
                                > Les
                                > L M Watts Technology
                                >
                                > ----- Original Message -----
                                > From: Jerry Lee Marcel
                                > To: micbuilders@yahoogroups.com <mailto:micbuilders%40yahoogroups.com>
                                > Cc: LESLIE WATTS
                                > Sent: Wednesday, March 13, 2013 6:43 AM
                                > Subject: Re: [micbuilders] Re: Polarization Voltage - Schoeps Circuit
                                >
                                > "typical coupling capacitor from backplate to gate"
                                > I don't get it. It seems to me getting rid of the coupling cap just
                                > involves connecting the bias voltage to one of the electrodes, whether
                                > it's the backplate or the diaphragm, and connecting the other directly
                                > to the gate (with a "gate-leak" resistor).
                                > In that respect, and for practicality, I would think that connecting the
                                > bias voltage to an isolated backplate and the diaphragm to the FET would
                                > be the best, in particular considering the parasitic capacitance of the
                                > backplate is generally larger than the diaphragm's.
                                >
                                > I note with interest your comment on "much dust is positively charged".
                                >
                                > Do you think it's the main reason why "(quote Chris) most circuits I've
                                > looked at put a positive voltage on the diaphragm and ground the
                                > backplate ", or a more practical reason?
                                > It's so much easier to have the backplate grounded and a 500pF ceramic
                                > cap cost almost nothing...manufacturing costs.
                                >
                                > Regarding your "fairly fine guard mesh also charged to polarization
                                > voltage in front of the diaphragm", have you deemed necessary to make
                                > them removable so they can be cleaned? I think in the end the mesh will
                                > gather some dust and may clog...or is it a fantasy?
                                >
                                > Le 13/03/2013 11:15, LESLIE WATTS a écrit :
                                > >
                                > > There are reasons to use a "hot diaphragm"...i.e. connected to
                                > > polarization.
                                > >
                                > > It gets rid of the typical coupling capacitor from backplate to
                                > > gate...thus allowing polarization voltage changes (for attenuation and
                                > > other things) without presenting large voltage spikes to the fet.
                                > >
                                > > We prefer it to shunt capacitance as attenuators, as they cause
                                > > distortion and usually audible switching noise.
                                > >
                                > > As far as dust...
                                > >
                                > > Grounded conductors attract dust as well by charge image
                                > > formation. This is how electrostatic powder painting systems
                                > > work...the object to be painted is usually grounded.
                                > >
                                > > Dust particles can be positive or negatively charged, uncharged, or
                                > > have a dipole moment. If one looks at the triboelectric series it can
                                > > be seen that much dust is positively charged...particularly textile
                                > > fiber components.
                                > > Some minerals and aerosols can be negatively charged.
                                > > Induced dipoles can happen if the particles are slightly conductive or
                                > > if non conductive opposite charge particles
                                > > clump together.
                                > >
                                > > So even though much dust is repelled from a positively charged
                                > > diaphragm, we used a fairly fine guard mesh also charged to
                                > > polarization voltage in front of the diaphragm.
                                > > This offers protection and is part of the acoustic resistance
                                > > system.
                                > >
                                > > Les
                                > > L M Watts Technology
                                > >
                                > > ----- Original Message -----
                                > > From: archieaa1
                                > > To: micbuilders@yahoogroups.com
                                > <mailto:micbuilders%40yahoogroups.com>
                                > <mailto:micbuilders%40yahoogroups.com>
                                > > Sent: Tuesday, March 12, 2013 3:29 PM
                                > > Subject: [micbuilders] Re: Polarization Voltage - Schoeps Circuit
                                > >
                                > > Sometimes conventions become conventions simply because no one thought
                                > > to do it otherwise.
                                > >
                                > > Archie
                                > >
                                > > --- In micbuilders@yahoogroups.com
                                > <mailto:micbuilders%40yahoogroups.com>
                                > > <mailto:micbuilders%40yahoogroups.com>, "ctown000" <ctown000@...> wrote:
                                > > >
                                > > > Thanks, interesting. But it seems that most circuits I've looked at
                                > > put a positive voltage on the diaphragm and ground the backplate, so
                                > > therefore would attract more dust. I wonder why that is the typical
                                > > approach, if this problem can occur? I presume there must be some
                                > > additional benefits that potentially outweigh the downsides.
                                > > >
                                > > > -Chris
                                > > >
                                > >
                                > > [Non-text portions of this message have been removed]
                                > >
                                > >
                                >
                                > [Non-text portions of this message have been removed]
                                >
                                > [Non-text portions of this message have been removed]
                                >
                                >



                                [Non-text portions of this message have been removed]
                              Your message has been successfully submitted and would be delivered to recipients shortly.