Frequency comp on CA3140: how to?

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rjd2
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Frequency comp on CA3140: how to?

Post by rjd2 » Tue Apr 20, 2010 4:02 am

hi folks, so ive got a Yamaha CS-5 i've almost fully restored here. one last thing:

there is a buffer IC (IC 3) that was shot in the portamento section, causing the keyboard output voltage to not pass. it was listed as a"TA7505". i couldnt find it, so the closest i could get was a pinout equivalent, a CA3140. it passes keyboard voltage from input to output, but there is a bad side effect that im hoping to fix:

with portamento at 0, keyboard scales and works 100%. the closer to 10 portamento gets, there is an "offset" that kicks in, dropping the pitch(as well as adding portamento). the datasheet for the CA3140 says it is externally compensated; i tried both a 30pf and 100nf cap across pins 1 and 8, and it didnt change the behavior.

datasheet for the 3140 here:
http://mouser.com/ProductDetail/CA3140M ... gI8w%3d%3d

any ideas? thanks, rj

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