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Re: [Altair Computer Club] Sol-20 ACI question

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  • corey986
    I pretty much knew it would depend on the circuit, and the ripple is on the regulated side so it would feed into everything. I guess I was just wondering if
    Message 1 of 3 , Jun 26, 2013
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      I pretty much knew it would depend on the circuit, and the ripple is on the regulated side so it would "feed" into everything. I guess I was just wondering if anyone had experience with this on the Sol-20 cassette adapter circuit as I could easily see it being a problem but would really have to look the circuit over to see how tollerant it should be, I'm guessing not, but I might as well ask.

      Cheers,
      Corey

      --- In altaircomputerclub@yahoogroups.com, Bob Grieb <bobgrieb@...> wrote:
      >
      > Corey,
      >
      >     Different circuits can tolerate different amounts of supply noise.  If the supplies are
      > only being used to power op amps, then a lot of ripple would be OK.  (Op amps have
      > a spec called "power supply rejection ratio" which measures their ability to reject noise
      > on the supplies.  They are pretty good at it) The amount of expected ripple
      > can be calculated based on the frequency (120 Hz, usually) the current, and the supply
      > capacitance.  Also, if there are regulators between the voltage with the ripple and the
      > circuit you are interested in, then it's really not an issue unless the voltage drops way down,
      > which could mean a bad filter cap (or something drawing a lot of current).
      >
      >     How much ripple are you seeing?  On a 15V supply, I would expect less than 0.25V
      > pk-pk, but that's just a rough guess.  In many cases, more would be OK.  Something I
      > was working on recently had about 2V of ripple on a 10V supply.  It was only used to
      > feed a 5V regulator, so that was not a problem.  The 5V regulator needed about 7V minimum
      > to hold its output up, and that was met.
      >
      >     But some circuits may use a voltage divider with one end tied to one of the supply rails
      > to level shift a signal.  In that case, supply noise can couple directly into the signals in the circuit
      > and would be a much bigger issue.  So it depends on the circuit.
      >
      >     Bob
      >
      >
      >
      >
      > ________________________________
      > From: corey986 <no_reply@yahoogroups.com>
      > To: altaircomputerclub@yahoogroups.com
      > Sent: Wednesday, June 26, 2013 6:55 PM
      > Subject: [Altair Computer Club] Sol-20 ACI question
      >
      >
      >
      >  
      > So I got to work today with my oscilliscope on the MARCH museum's Sol-20 cassette interface.
      >
      > I replaced the PLL and was able to set calibrate the adjustment as per the sol manual.
      > Next I replaced the UART as it was bad.
      >
      > I can now get a XEQ command to read the name of the file off my iPod, but it has a load error. I checked all the other chips in the input part of the circuit.
      >
      > What I am suspecting is ripple on the supply. I put the big caps on my scope and the power was pretty "fuzzy". BTW: on my personal sol that works the powe across the caps is smooth with just a little cycling around the expected voltage.
      >
      > So could my suspicion be correct? The noise on the supply from the caps is causing a cassette interface read error.
      >
      > Just want to understand if that is a viable place to look next. I'm making progress in that I get the program name and the error instead of "nothing"
      >
      > Thanks,
      > Corey
      >
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