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mca sp1 mod help

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  • xhavepatiencex
    I am looking to do my first mic modding project, I would like to work on the sp1 I got the files posted by zapnspark which are great, I am curious what other
    Message 1 of 17 , Oct 1, 2008
      I am looking to do my first mic modding project, I would like to work
      on the sp1 I got the files posted by zapnspark which are great, I am
      curious what other people are doing, are you replacing the caps? If so
      are you replacing all of them? or just the Electrolytics? is anyone
      replaces the resistors as well? Sorry if these are somewhat novice
      questions, but I am a novice. Or if anywhere someone has posted
      exactly what they are replacing and with what, that would be very
      awesome.
    • Jim G.
      ... work ... so ... I can t speak about the usefulness of some of the other China mic mods that are floating around on the internet. For specific information
      Message 2 of 17 , Oct 1, 2008
        --- In micbuilders@yahoogroups.com, "xhavepatiencex"
        <xhavepatiencex@...> wrote:
        >
        > I am looking to do my first mic modding project, I would like to
        work
        > on the sp1 I got the files posted by zapnspark which are great, I am
        > curious what other people are doing, are you replacing the caps? If
        so
        > are you replacing all of them? or just the Electrolytics? is anyone
        > replaces the resistors as well? Sorry if these are somewhat novice
        > questions, but I am a novice. Or if anywhere someone has posted
        > exactly what they are replacing and with what, that would be very
        > awesome.
        >

        I can't speak about the usefulness of some of the other China mic
        mods that are floating around on the internet.

        For specific information on exactly what I have replaced/changed in
        the MCA SP-1 microphones, look in the Files, Zapnspark folder for:

        GenMCAMic.txt
        GenChinaMic.pdf vs MCA SP-1 board designation

        For reference, see the GenChinaMic.pdf and GenChinaMod.pdf schematics.

        Cheers.

        Jim G.
        ZAPNSPARK
      • xhavepatiencex
        ... Awesome, thank you a bunch I did not see that file while I was diggin around before I posted. I will check it out! David
        Message 3 of 17 , Oct 1, 2008
          --- In micbuilders@yahoogroups.com, "Jim G." <zapnspark@...> wrote:
          >
          > --- In micbuilders@yahoogroups.com, "xhavepatiencex"
          > <xhavepatiencex@> wrote:
          > >
          > > I am looking to do my first mic modding project, I would like to
          > work
          > > on the sp1 I got the files posted by zapnspark which are great, I am
          > > curious what other people are doing, are you replacing the caps? If
          > so
          > > are you replacing all of them? or just the Electrolytics? is anyone
          > > replaces the resistors as well? Sorry if these are somewhat novice
          > > questions, but I am a novice. Or if anywhere someone has posted
          > > exactly what they are replacing and with what, that would be very
          > > awesome.
          > >
          >
          > I can't speak about the usefulness of some of the other China mic
          > mods that are floating around on the internet.
          >
          > For specific information on exactly what I have replaced/changed in
          > the MCA SP-1 microphones, look in the Files, Zapnspark folder for:
          >
          > GenMCAMic.txt
          > GenChinaMic.pdf vs MCA SP-1 board designation
          >
          > For reference, see the GenChinaMic.pdf and GenChinaMod.pdf schematics.
          >
          > Cheers.
          >
          > Jim G.
          > ZAPNSPARK
          >


          Awesome, thank you a bunch I did not see that file while I was diggin
          around before I posted. I will check it out!

          David
        • handprintsoncavewalls
          xhavepatiencex, The most basic mod is removing: R8-(1 gigohm) [SAVE for another project] & C13-(1 nF ceramic). Start there, no soldering skills required
          Message 4 of 17 , Oct 1, 2008
            xhavepatiencex,

            The most basic mod is removing:

            R8-(1 gigohm) [SAVE for another project] & C13-(1 nF ceramic).

            Start there, no soldering skills required (soldering
            recommended). Make a before and after recording. Take pictures. Take
            lots of notes.

            After that a scope is required to grade/match transistors. Stay
            within Zap's recommendations at least at first. He really knows his
            stuff. After Zap's mods the payoff drops quickly.


            ~Micro
          • xhavepatiencex
            ... I am scopeless, Is there anyway around that while swapping out the transistors. Do all of them need to be biased?
            Message 5 of 17 , Oct 2, 2008
              --- In micbuilders@yahoogroups.com, "handprintsoncavewalls"
              <handprintsoncavewalls@...> wrote:
              >
              > xhavepatiencex,
              >
              > The most basic mod is removing:
              >
              > R8-(1 gigohm) [SAVE for another project] & C13-(1 nF ceramic).
              >
              > Start there, no soldering skills required (soldering
              > recommended). Make a before and after recording. Take pictures. Take
              > lots of notes.
              >
              > After that a scope is required to grade/match transistors. Stay
              > within Zap's recommendations at least at first. He really knows his
              > stuff. After Zap's mods the payoff drops quickly.
              >
              >
              > ~Micro
              >


              I am scopeless, Is there anyway around that while swapping out the
              transistors. Do all of them need to be biased?
            • Jim G.
              ... Take ... Stay ... his ... The problem is that JFETs have a very wide range in parameters, even when they are of the same type and from the same batch. Here
              Message 6 of 17 , Oct 2, 2008
                --- In micbuilders@yahoogroups.com, "xhavepatiencex"
                <xhavepatiencex@...> wrote:
                >
                > --- In micbuilders@yahoogroups.com, "handprintsoncavewalls"
                > <handprintsoncavewalls@> wrote:
                > >
                > > xhavepatiencex,
                > >
                > > The most basic mod is removing:
                > >
                > > R8-(1 gigohm) [SAVE for another project] & C13-(1 nF ceramic).
                > >
                > > Start there, no soldering skills required (soldering
                > > recommended). Make a before and after recording. Take pictures.
                Take
                > > lots of notes.
                > >
                > > After that a scope is required to grade/match transistors.
                Stay
                > > within Zap's recommendations at least at first. He really knows
                his
                > > stuff. After Zap's mods the payoff drops quickly.
                > >
                > >
                > > ~Micro
                > >
                >
                >
                > I am scopeless, Is there anyway around that while swapping out the
                > transistors. Do all of them need to be biased?
                >

                The problem is that JFETs have a very wide range in parameters, even
                when they are of the same type and from the same batch.

                Here are some alternatives:

                * Leave the 2SK170 and the 2 biasing resistors as is.

                * Use the J305 JFET and the biasing resistors can be 330k and 680k
                as shown in:
                GenChinaMod.pdf
                This puts you in the ballpark for proper biasing but may not be ideal.

                * Make the biasing test fixture (BiasingFETScopeMethod.pdf) . Use the
                J305 JFET. No signal input. +12 volt supply. Adjust the pot to get ~
                +9.2 volts from Drain to ground and ~ +2.8 volts from Source to
                ground. Remove the pot and measure the resistances as shown.
                Once again, that's ballpark biasing and may not be the best.

                I hope this helps.

                Cheers

                Jim G.
                ZAPNSPARK
              • handprintsoncavewalls
                What does a Scope cost? Where can they be purchased? Anybody?
                Message 7 of 17 , Oct 3, 2008
                  What does a Scope cost? Where can they be purchased?

                  Anybody?





                  --- In micbuilders@yahoogroups.com, "Jim G." <zapnspark@...> wrote:
                  >
                  > --- In micbuilders@yahoogroups.com, "xhavepatiencex"
                  > <xhavepatiencex@> wrote:
                  > >
                  > > --- In micbuilders@yahoogroups.com, "handprintsoncavewalls"
                  > > <handprintsoncavewalls@> wrote:
                  > > >
                  > > > xhavepatiencex,
                  > > >
                  > > > The most basic mod is removing:
                  > > >
                  > > > R8-(1 gigohm) [SAVE for another project] & C13-(1 nF ceramic).
                  > > >
                  > > > Start there, no soldering skills required (soldering
                  > > > recommended). Make a before and after recording. Take pictures.
                  > Take
                  > > > lots of notes.
                  > > >
                  > > > After that a scope is required to grade/match transistors.
                  > Stay
                  > > > within Zap's recommendations at least at first. He really knows
                  > his
                  > > > stuff. After Zap's mods the payoff drops quickly.
                  > > >
                  > > >
                  > > > ~Micro
                  > > >
                  > >
                  > >
                  > > I am scopeless, Is there anyway around that while swapping out the
                  > > transistors. Do all of them need to be biased?
                  > >
                  >
                  > The problem is that JFETs have a very wide range in parameters, even
                  > when they are of the same type and from the same batch.
                  >
                  > Here are some alternatives:
                  >
                  > * Leave the 2SK170 and the 2 biasing resistors as is.
                  >
                  > * Use the J305 JFET and the biasing resistors can be 330k and 680k
                  > as shown in:
                  > GenChinaMod.pdf
                  > This puts you in the ballpark for proper biasing but may not be ideal.
                  >
                  > * Make the biasing test fixture (BiasingFETScopeMethod.pdf) . Use the
                  > J305 JFET. No signal input. +12 volt supply. Adjust the pot to get ~
                  > +9.2 volts from Drain to ground and ~ +2.8 volts from Source to
                  > ground. Remove the pot and measure the resistances as shown.
                  > Once again, that's ballpark biasing and may not be the best.
                  >
                  > I hope this helps.
                  >
                  > Cheers
                  >
                  > Jim G.
                  > ZAPNSPARK
                  >
                • picnet2
                  Jim, Could the circuit be modified for lower voltage operation and the scope substituted with a pc sound card running a scope application to visualise the
                  Message 8 of 17 , Oct 4, 2008
                    Jim,
                    Could the circuit be modified for lower voltage operation and the scope substituted
                    with a pc sound card running a scope application to visualise the waveform, with the
                    output from the same card acting as the signal generator? - I know baudline would be
                    capable of such configuration, as most likely some windows based sound card scope's
                    would do the same ?

                    Alternatively to the original question:-

                    Scopes, depends if you buy a boat anchor (old relic from 1980/1990 that cost the earth
                    during that time, but are now sold off fairly cheap due to lack of calibration or lack of any
                    more parts to service them. (e.g ex government) - I have an old HP54501A which apparently was used to monitor the space shuttles booster tanks at some point (not "the"
                    actual scope, but same model...)

                    Also consider something inbetween - pc based devices also exisit e.g bitscope or
                    usbinstruments, or a decent TEK bench scope. Ive used all of thost, the TEK being the
                    best simply due to its bandwidth, but thats not everything, e.g the usbinstruments device
                    is 12 bit at 500khz. A decent pc sound card is a good option provided theres adequate
                    buffering first...

                    Most probes are also relative to the scope ground unless operating from a battery scope /
                    - thus you may also require a differential probe... (which is recommended as part of the t&
                    m gear...)

                    -Mike.


                    --- In micbuilders@yahoogroups.com, "Jim G." <zapnspark@...> wrote:
                    >
                    > --- In micbuilders@yahoogroups.com, "xhavepatiencex"
                    > <xhavepatiencex@> wrote:
                    > >
                    > > --- In micbuilders@yahoogroups.com, "handprintsoncavewalls"
                    > > <handprintsoncavewalls@> wrote:
                    > > >
                    > > > xhavepatiencex,
                    > > >
                    > > > The most basic mod is removing:
                    > > >
                    > > > R8-(1 gigohm) [SAVE for another project] & C13-(1 nF ceramic).
                    > > >
                    > > > Start there, no soldering skills required (soldering
                    > > > recommended). Make a before and after recording. Take pictures.
                    > Take
                    > > > lots of notes.
                    > > >
                    > > > After that a scope is required to grade/match transistors.
                    > Stay
                    > > > within Zap's recommendations at least at first. He really knows
                    > his
                    > > > stuff. After Zap's mods the payoff drops quickly.
                    > > >
                    > > >
                    > > > ~Micro
                    > > >
                    > >
                    > >
                    > > I am scopeless, Is there anyway around that while swapping out the
                    > > transistors. Do all of them need to be biased?
                    > >
                    >
                    > The problem is that JFETs have a very wide range in parameters, even
                    > when they are of the same type and from the same batch.
                    >
                    > Here are some alternatives:
                    >
                    > * Leave the 2SK170 and the 2 biasing resistors as is.
                    >
                    > * Use the J305 JFET and the biasing resistors can be 330k and 680k
                    > as shown in:
                    > GenChinaMod.pdf
                    > This puts you in the ballpark for proper biasing but may not be ideal.
                    >
                    > * Make the biasing test fixture (BiasingFETScopeMethod.pdf) . Use the
                    > J305 JFET. No signal input. +12 volt supply. Adjust the pot to get ~
                    > +9.2 volts from Drain to ground and ~ +2.8 volts from Source to
                    > ground. Remove the pot and measure the resistances as shown.
                    > Once again, that's ballpark biasing and may not be the best.
                    >
                    > I hope this helps.
                    >
                    > Cheers
                    >
                    > Jim G.
                    > ZAPNSPARK
                    >
                  • Jim G.
                    ... Mike, Very good suggestion. Using a PC soundcard and making an external stunt box for audio testing has been on my to-do list forever. I have played with
                    Message 9 of 17 , Oct 4, 2008
                      --- In micbuilders@yahoogroups.com, "picnet2" <picnet@...> wrote:
                      >
                      > Jim,
                      > Could the circuit be modified for lower voltage operation and
                      > the scope substituted with a pc sound card running a
                      > scope application to visualise the waveform, with the
                      > output from the same card acting as the signal generator?
                      > - I know baudline would be capable of such configuration,
                      > as most likely some windows based sound card scope's would
                      > do the same ?

                      Mike,

                      Very good suggestion. Using a PC soundcard and making an external
                      stunt box for audio testing has been on my to-do list forever.
                      I have played with freebie PC based software waveform and scope
                      applications in the past. They worked OK for some audio testing.
                      My knowledge about what is available now is very out of date.
                      Perhaps someone else can chime in here and suggest some freebie or
                      low cost scope/generator software. That seems like just the thing for
                      money challenged DIYers (like myself)

                      Sorry Mike, I don't quite follow the lower voltage operation question.
                      I chose 12 volts because that's the voltage that I measured in a
                      typical China Schoeps-like circuit at the JFET phase splitter.

                      Cheers

                      Jim G.
                      ZAPNSPARK

                      PS
                      This is completely off topic. I have been cleaning up some of my
                      files and I just noticed that Yahoo has increased the Micbuilders
                      Photos storage space to 100 Gigabytes. That's not a typo.

                      >
                      > Alternatively to the original question:-
                      >
                      > Scopes, depends if you buy a boat anchor (old relic from 1980/1990
                      that cost the earth
                      > during that time, but are now sold off fairly cheap due to lack of
                      calibration or lack of any
                      > more parts to service them. (e.g ex government) - I have an old
                      HP54501A which apparently was used to monitor the space shuttles
                      booster tanks at some point (not "the"
                      > actual scope, but same model...)
                      >
                      > Also consider something inbetween - pc based devices also exisit
                      e.g bitscope or
                      > usbinstruments, or a decent TEK bench scope. Ive used all of
                      thost, the TEK being the
                      > best simply due to its bandwidth, but thats not everything, e.g the
                      usbinstruments device
                      > is 12 bit at 500khz. A decent pc sound card is a good option
                      provided theres adequate
                      > buffering first...
                      >
                      > Most probes are also relative to the scope ground unless operating
                      from a battery scope /
                      > - thus you may also require a differential probe... (which is
                      recommended as part of the t&
                      > m gear...)
                      >
                      > -Mike.
                      >
                    • Scott Helmke
                      No need to change the circuit voltages - just build a homebrew 10x probe like the real scopes use. That s all of two resistors in series, say 100K between
                      Message 10 of 17 , Oct 4, 2008
                        No need to change the circuit voltages - just build a homebrew "10x
                        probe" like the real scopes use. That's all of two resistors in series,
                        say 100K between signal source and audio input on the PC, and a 10K
                        resistor from there to ground to create voltage divider. That would
                        knock the voltage as seen by the "scope" down to 10% of the original value.

                        It's probably not a big deal to go into an audio input anyway - just use
                        a mixer, mic pads, whatever to knock the signal down. Might have to
                        create some reference voltages for matching, but that shouldn't be very
                        hard.

                        -Scott

                        Jim G. wrote:
                        > --- In micbuilders@yahoogroups.com, "picnet2" <picnet@...> wrote:
                        >> Jim,
                        >> Could the circuit be modified for lower voltage operation and
                        >> the scope substituted with a pc sound card running a
                        >> scope application to visualise the waveform, with the
                        >> output from the same card acting as the signal generator?
                        >> - I know baudline would be capable of such configuration,
                        >> as most likely some windows based sound card scope's would
                        >> do the same ?
                        >
                        > Mike,
                        >
                        > Very good suggestion. Using a PC soundcard and making an external
                        > stunt box for audio testing has been on my to-do list forever.
                        > I have played with freebie PC based software waveform and scope
                        > applications in the past. They worked OK for some audio testing.
                        > My knowledge about what is available now is very out of date.
                        > Perhaps someone else can chime in here and suggest some freebie or
                        > low cost scope/generator software. That seems like just the thing for
                        > money challenged DIYers (like myself)
                        >
                        > Sorry Mike, I don't quite follow the lower voltage operation question.
                        > I chose 12 volts because that's the voltage that I measured in a
                        > typical China Schoeps-like circuit at the JFET phase splitter.
                        >
                        > Cheers
                        >
                        > Jim G.
                        > ZAPNSPARK
                        >

                        --
                        ---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
                        And you'll visualize not taking any chances
                        But meet them halfway with love, peace, and persuasion
                        And expect them to rise to the occasion
                        (from "Glad Tidings", by Van Morrison)
                      • psi2006@yahoo.com.ar
                        Hi everyone, Same as Jim also have pending to wire my SoundBlaster for basic wave measurement. There is a nice freeware at:
                        Message 11 of 17 , Oct 5, 2008
                          Hi everyone,

                          Same as Jim also have pending to wire my SoundBlaster for
                          basic wave measurement.

                          There is a nice freeware at:

                          http://www.mitedu.freeserve.co.uk/Prac/winscope.htm

                          Not much time ago I saw as shareware within winscope.com but this domain is not longer related.

                          Just to remember that this sound measuremente doesn't go beyond 20kHz so limited mainly to be used within the Acustics field

                          Just a safety reminder, test the above on an SB16 original (it's enough) or on a cheapo compatible soundcard not on your SuperUltraPlus DSP enabled audiocard.

                          :)


                          Best wishes.

                          Nestor

                          _________________


                          Re: mca sp1 mod help

                          Posted by: "Jim G." zapnspark@... zapnspark
                          Sat Oct 4, 2008 1:33 pm (PDT)
                          --- In micbuilders@ yahoogroups. com, "picnet2" <picnet@...> wrote:
                          >
                          > Jim,
                          > Could the circuit be modified for lower voltage operation and
                          > the scope substituted with a pc sound card running a
                          > scope application to visualise the waveform, with the
                          > output from the same card acting as the signal generator?
                          > - I know baudline would be capable of such configuration,
                          > as most likely some windows based sound card scope's would
                          > do the same ?

                          Mike,

                          Very good suggestion. Using a PC soundcard and making an external
                          stunt box for audio testing has been on my to-do list forever.
                          I have played with freebie PC based software waveform and scope
                          applications in the past. They worked OK for some audio testing.
                          My knowledge about what is available now is very out of date.
                          Perhaps someone else can chime in here and suggest some freebie or
                          low cost scope/generator software. That seems like just the thing for
                          money challenged DIYers (like myself)

                          Sorry Mike, I don't quite follow the lower voltage operation question.
                          I chose 12 volts because that's the voltage that I measured in a
                          typical China Schoeps-like circuit at the JFET phase splitter.

                          Cheers

                          Jim G.
                          ZAPNSPARK


                          Yahoo! Cocina
                          Recetas prácticas y comida saludable
                          http://ar.mujer.yahoo.com/cocina/
                        • srrvnnt
                          O. K. Here is the link for a free Winscope http://www.mitedu.freeserve.co.uk/Downloads/scope.zip Now, is a homemade probe necessary to measure an MCA SP-1? If
                          Message 12 of 17 , Oct 6, 2008
                            O. K. Here is the link for a free Winscope
                            http://www.mitedu.freeserve.co.uk/Downloads/scope.zip
                            Now, is a homemade probe necessary to measure an MCA SP-1? If so what
                            are the specs? Where in Zaps schem. are the measurements taken? What
                            values are we looking for? Sorry still a novice at this.

                            J. R.










                            --- In micbuilders@yahoogroups.com, "psi2006@..." <psi2006@...> wrote:
                            >
                            > Hi everyone,
                            >
                            > Same as Jim also have pending to wire my SoundBlaster for
                            > basic wave measurement.
                            >
                            > There is a nice freeware at:
                            >
                            > http://www.mitedu.freeserve.co.uk/Prac/winscope.htm
                            >
                            > Not much time ago I saw as shareware within winscope.com but this
                            domain is not longer related.
                            >
                            > Just to remember that this sound measuremente doesn't go beyond
                            20kHz so limited mainly to be used within the Acustics field
                            >
                            > Just a safety reminder, test the above on an SB16 original (it's
                            enough) or on a cheapo compatible soundcard not on your SuperUltraPlus
                            DSP enabled audiocard.
                            >
                            > :)
                            >
                            >
                            > Best wishes.
                            >
                            > Nestor
                            >
                            > _________________
                            >
                            >
                            > Re: mca sp1 mod help
                            >
                            > Posted by: "Jim G." zapnspark@... zapnspark
                            > Sat Oct 4, 2008 1:33 pm (PDT)
                            > --- In micbuilders@ yahoogroups. com, "picnet2" <picnet@> wrote:
                            > >
                            > > Jim,
                            > > Could the circuit be modified for lower voltage operation and
                            > > the scope substituted with a pc sound card running a
                            > > scope application to visualise the waveform, with the
                            > > output from the same card acting as the signal generator?
                            > > - I know baudline would be capable of such configuration,
                            > > as most likely some windows based sound card scope's would
                            > > do the same ?
                            >
                            > Mike,
                            >
                            > Very good suggestion. Using a PC soundcard and making an external
                            > stunt box for audio testing has been on my to-do list forever.
                            > I have played with freebie PC based software waveform and scope
                            > applications in the past. They worked OK for some audio testing.
                            > My knowledge about what is available now is very out of date.
                            > Perhaps someone else can chime in here and suggest some freebie or
                            > low cost scope/generator software. That seems like just the
                            thing for
                            > money challenged DIYers (like myself)
                            >
                            > Sorry Mike, I don't quite follow the lower voltage operation
                            question.
                            > I chose 12 volts because that's the voltage that I measured in a
                            > typical China Schoeps-like circuit at the JFET phase splitter.
                            >
                            > Cheers
                            >
                            > Jim G.
                            > ZAPNSPARK
                            >
                            >
                            > Yahoo! Cocina
                            > Recetas prácticas y comida saludable
                            > http://ar.mujer.yahoo.com/cocina/
                            >
                          • Jim G.
                            If you have a Scope and signal generator, use the test fixture and procedure shown in: BiasingFETScopeMethod.pdf Signal gen. and scope to select microphone
                            Message 13 of 17 , Oct 6, 2008
                              If you have a Scope and signal generator, use the test fixture and
                              procedure shown in:

                              BiasingFETScopeMethod.pdf
                              Signal gen. and scope to select microphone JFET bias resistors

                              If you don't have a scope and signal generator, the alternatives are
                              listed in message # 10068

                              * Leave the 2SK170 and the 2 biasing resistors as is.

                              * Use the J305 JFET and the biasing resistors can be 330k and 680k
                              as shown in:

                              GenChinaMod.pdf

                              This puts you in the ballpark for proper biasing but may not be ideal.

                              * Make the biasing test fixture (BiasingFETScopeMethod.pdf) . Use the
                              J305 JFET. No signal input. +12 VDC volt supply. Adjust the pot to get ~
                              +9.2 volts DC from Drain to ground and ~ +2.8 volts DC from Source to
                              ground. Remove the pot and measure the resistances as shown.
                              Once again, that's ballpark biasing and may not be the best.

                              I'm still investigating scope software and the hardware required.

                              Cheers

                              Jim G.
                              ZAPNSPARK


                              --- In micbuilders@yahoogroups.com, "srrvnnt" <srrvnnt@...> wrote:
                              >
                              > O. K. Here is the link for a free Winscope
                              > http://www.mitedu.freeserve.co.uk/Downloads/scope.zip
                              > Now, is a homemade probe necessary to measure an MCA SP-1? If so what
                              > are the specs? Where in Zaps schem. are the measurements taken? What
                              > values are we looking for? Sorry still a novice at this.
                              >
                              > J. R.
                              >
                            • Stan Noel
                              Where does one find: BiasingFETScopeMethod.pdf? thanks. ... [Non-text portions of this message have been removed]
                              Message 14 of 17 , Oct 6, 2008
                                Where does one find: BiasingFETScopeMethod.pdf?
                                thanks.


                                At 08:34 AM 10/6/2008, you wrote:

                                >If you have a Scope and signal generator, use the test fixture and
                                >procedure shown in:
                                >
                                >BiasingFETScopeMethod.pdf
                                >Signal gen. and scope to select microphone JFET bias resistors
                                >
                                >If you don't have a scope and signal generator, the alternatives are
                                >listed in message # 10068
                                >
                                >* Leave the 2SK170 and the 2 biasing resistors as is.
                                >
                                >* Use the J305 JFET and the biasing resistors can be 330k and 680k
                                >as shown in:
                                >
                                >GenChinaMod.pdf
                                >
                                >This puts you in the ballpark for proper biasing but may not be ideal.
                                >
                                >* Make the biasing test fixture (BiasingFETScopeMethod.pdf) . Use the
                                >J305 JFET. No signal input. +12 VDC volt supply. Adjust the pot to get ~
                                >+9.2 volts DC from Drain to ground and ~ +2.8 volts DC from Source to
                                >ground. Remove the pot and measure the resistances as shown.
                                >Once again, that's ballpark biasing and may not be the best.
                                >
                                >I'm still investigating scope software and the hardware required.
                                >
                                >Cheers
                                >
                                >Jim G.
                                >ZAPNSPARK
                                >
                                >--- In
                                ><mailto:micbuilders%40yahoogroups.com>micbuilders@yahoogroups.com,
                                >"srrvnnt" <srrvnnt@...> wrote:
                                > >
                                > > O. K. Here is the link for a free Winscope
                                > >
                                > <http://www.mitedu.freeserve.co.uk/Downloads/scope.zip>http://www.mitedu.freeserve.co.uk/Downloads/scope.zip
                                > > Now, is a homemade probe necessary to measure an MCA SP-1? If so what
                                > > are the specs? Where in Zaps schem. are the measurements taken? What
                                > > values are we looking for? Sorry still a novice at this.
                                > >
                                > > J. R.
                                > >
                                >
                                >


                                [Non-text portions of this message have been removed]
                              • dugless_p
                                Hi all: I m brand new here and am intrigued by the partial mod to the SP1 involving the removal of one cap and one resistor. (The rest of the mods are
                                Message 15 of 17 , Oct 9, 2008
                                  Hi all:

                                  I'm brand new here and am intrigued by the "partial mod" to the SP1
                                  involving the removal of one cap and one resistor. (The rest of the
                                  mods are beyond my current ability.)

                                  I'm wondering if anyone has done just the partial mod and what kind of
                                  results were achieved.

                                  Cheers,
                                  Doug
                                • handprintsoncavewalls
                                  dugless, Post Op the mic should have less noise overall, but not as big of a difference as the part swapping. Do the removal carefully and if you don t like
                                  Message 16 of 17 , Oct 9, 2008
                                    dugless,

                                    Post Op the mic should have less noise overall, but not as big of a
                                    difference as the part swapping.

                                    Do the removal carefully and if you don't like the change in timbre
                                    put 'em back. No big deal.

                                    In general the less parts in the signal chain the more pure the tone,
                                    especially if the parts are only so-so.

                                    The primary difference between higher-end and lower-end mics are the
                                    parts (electrical components) that form the whole.

                                    ~Micro


                                    --- In micbuilders@yahoogroups.com, "dugless_p" <dugless_p@...> wrote:
                                    >
                                    > Hi all:
                                    >
                                    > I'm brand new here and am intrigued by the "partial mod" to the SP1
                                    > involving the removal of one cap and one resistor. (The rest of the
                                    > mods are beyond my current ability.)
                                    >
                                    > I'm wondering if anyone has done just the partial mod and what kind of
                                    > results were achieved.
                                    >
                                    > Cheers,
                                    > Doug
                                    >
                                  • dugless_p
                                    Micro: Thanks for the response. That s exactly the kind of info I was hoping to get.
                                    Message 17 of 17 , Oct 10, 2008
                                      Micro:

                                      Thanks for the response. That's exactly the kind of info I was hoping
                                      to get.
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