[sdiy] Jupiter-8 'selected' op-amp replacement

[Tony Kalomiris]

At 11:48 AM 10/17/2005, Harry Bissell Jr wrote:


>I'd wonder if you're looking in the wrong place...
>Have you checked the S/H outputs for the VCO CVs ?
>This is a usual spot on most synths for problems
>common
>to several VCOs

Success !

The problem was on interface board that supplies the 16 VCO's KCV's .

At first I found the demux  IC26 common to all my problem voices 5,6, 
and 8, so I \
pulled it out and put in a, *cough*, socket , but the feedback nature 
of the glide circuit
made it difficult to diagnose.

To make a long story short it was the sample and hold J-FET op-amps 
,TL082, that were generating
a 60hz 0.5 V P-P sawtooth wave to modulate the keyboard cv's. Ok I 
probably shouldn't do it but I'm
tempted to leave the sockets in there (the good low profile machined 
types- Augat) and glue gun the IC
for good measure. but seeing this is a crucial circuit . . . I have a 
feeling I'll be replacing some more very soon.

I had a bit of a scare cause the next chip to check was the quad 
integrator (IR3109)in the
voltage controlled glide circuit ,and that's a special Roland chip !

Thanks for your help Harry,

Tony

oh btw I will require to select these for low offest (colour dot) . . 
. hmm I wonder if I can sub TL072's





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