Yamaha CS80

Matching the waveforms to a previously calibrated board is what I wanted to do.  I tried it and it does work, being  also easy to do. And removing the top panel is a brilliant idea. The difficulty, IMHO, is finding the point where to measure 125 ms  at 3V! 
I have an old Tektronix 2225, very basic but solid as a rock, but can't buy a new one (as a hobbyist it's enough...).
Honestly, I did not catch the 5b). Could you please explain more in detail please?

Thanks!

Fernando 




Il giorno 09/mag/2011, alle ore 19.44, David Rogoff ha scritto:

> >
> > 
> >
> >
> > ----------------------------------------------------------
> >
> > Fernando Zarone <mailto:fernandozarone@...>
> > May 9, 2011 2:57 AM
> >
> >
> > Hi all,
> > after the long trip through overhauling my CS 80, I got to the point 
> > of VCF/ VCA calibrations.
> > David, I appreciated your idea of connecting wires to the trigger 
> > points so much! Now, I am using a square wave from my aux outs of the 
> > 921 oscillator (Moog modular 55) and it works fine.
> > I am facing the same problem as you did, David: no problem for the 
> > short Attack time, but setting the 3V at AF the slope of the scope 
> > visualization becomes almost horizontal, so the end point is very 
> > tricky to be detented and matching the time measurement to specs is 
> > not easy.
> > How did you solve the problem? I think that, once having one M-board 
> > calibrated, it should be an (annoying) game, superimposing the other 
> > boards' waveforms to it. But what for the first board ??? Yamaha 
> > suggested to use "one good M-board for comparison", but I found the 
> > short calibrations (8V at AF) longer than required (about 25 ms): 
> > probably they used to be calibrated by ear, so I guess no one board is 
> > reliable as to factory specs.
> > I think that the topic is paramount.
> >
> >
> > ----------------------------------------------------------
> 
> Here's what I did.
> 1) removed top panel so I could get to back of M-cards without removing 
> them from (raised) card cage
> 2) unsoldered all TRG wires to M cards and soldered in little wire loops 
> I could easily attach clip leads to
> 3) connected all TRG inputs to Sub Osc square wave (tapped off op-amp, 
> before resistor attenuator
> 4) calibrated first (M-11) card with 'scope. Took many passes back and 
> forth between 4ms and 125ms settings. 125ms very hard to see with 
> analog 'scope. I used falling edge of Sub Osc as trigger (negative 
> voltage = note on)
> 5) calibrated other M cards by displaying them at same time as M-11 on 
> screen and getting waveforms to match.
> 5b) for channel II boards, used 2nd voltmeter to measure difference in 
> attack voltage between Channel I and Channel II and made sure it was 0 
> volts by tweaking panel slider.
> 



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