wish i could help. i tried to do some very minute EG calibrations by ear once on my 80. wasnt working. (luckily got it close enough to be not noticable). best of luck!
--- On Tue, 2/1/11, David Rogoff <david@...> wrote:
From: David Rogoff <david@...>
Subject: [yamahacs80] Need help calibrating envelope generators on CS80!
To: yamahacs80@yahoogroups.com
Date: Tuesday, February 1, 2011, 12:06 AM
Hi all.
I've been working on a CS80 for a bit now and finally have it all
functioning to some degree. I'm going through the full
tuning/calibration procedure now
(http://therogoffs.com/cs80/CS80%20Adjustment%20Procedures%20and%20updates.PDF)
and am having difficulty with the envelope times. I've never tried this
before. On all units I've worked on, I've only needed to do the power
supply and the usual M-card tuning.
However, this beast had some of its M-cards replaced from a very giving
CS-60 and the EG times, filter cutoffs, and levels are really whacked
out from board to board. So, I'm trying to do the VCF Attack time on
page 9 and VCA Attack time on page 15. I came up with a nice trigger
source: they specify a 3Hz square wave of +/-10v. I found that tapping
the output of the Sub-Oscillator square wave before its output resistor
divider makes a great trigger. I just ran this, through a 1K resistor,
to one input of my 'scope and then to the TR input of the M-card. I
trigger on this channel and then connect the specified EG testpoint to
the other input of the 'scope.
This sort-of works, at least for the calibration of the short (4ms)
time. Triggering and observing signals this slow on an old, analog
oscilloscope is a real pain. Again, I got it somewhat stable for the
4ms measurement. However, for the 125ms measurement, I don't have a
prayer. With the low repeat rate and long time measurement, the display
is too erratic to get any useful measurements. At work I have access to
nice digital HP/Agilent 'scopes that can do this in their sleep, but I
don't really want to bring the CS80 to work! What did Yamaha intend to
be used for this measurement back in 1976? I guess an old analog
storage 'scope would have worked, but those were pretty rare.
Anyway, I'd appreciate any tips from folks who have (successfully) tried
this!
By the way, since I've had to pull the M-cards out to do the full
calibration, for tuning I've been able to grab the sine wave right off
the wave shape converter chip at pad CP1. I run this into one input of
my 'scope and my iPhone, running Cleartune (in pitch-pipe mode with sine
wave) into the other 'scope input and set it to X-Y mode. Beautiful
Lissajous patterns that make it a snap to tune! Of course, since the
cards are out, the temperature isn't quite right and I'll have to do a
final tweak when it's all put back together. For that I'll use the
excellent iStrobesoft strobe tuner app from Peterson. It's $10, but well
worth it, especially since a hardware strobe tuner from Peterson start
at $100 and go up to $800!
Thanks again,
David
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