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Old 3rd Dec 2021, 7:51 am   #47
Mooly
Octode
 
Join Date: May 2011
Location: Lancashire, UK.
Posts: 1,349
Default Re: Quad 34 preamp volume knob clicks

Devil is in the detail here...

C89 affects only the CD input when that input is selected. -0.41 millivolts is getting down to acceptable levels and within what the 'input voltage offset' of a TL072 or OPA2134 might be.

Earlier we had:

Quote:
as above with cd selected, I get -4.5mv/-3.7mv on IC27 op.
which is to high.

Work with one input at a time and if needs be isolate everything on that line until you find what it pulling the line down.

You can use braid to unsolder pins 9 and 10 of IC22 (so they are free floating) and that will isolate them from that run of print.

This is for an OPA2134, the TL072 will be in the same ballpark.
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