[sdiy] ARP axxe popping revisited

[Bob Weigel]

I pulled this thing up again today.  If anyone has the schematics handy 
and you want to review this fairly simple to describe situation I'd 
appreciate it.  An extra brain would be nice..mine is worn out :-).  To 
review,

1) Signal/noise ration seems pretty bleak and I'm not sure how much 
these things have.  I noted  that part of it was related to wiring near 
the transformer.  However...I came back later and it had no correlation 
and the noise level was a lot lower but still kind of hissy.  Which was 
kind of odd..

2) There is a horrendous popping during envelope transitions.. 

Tonight I looked over the circuitry and found a transistor lead in the 
gating circuitry that had cracked the trace going to Z5...but repairing 
that there was no difference.  But I found that the pop is definitely 
sourcing from the ADSR.  I can see the pop...something like a few tenth 
of a volt 150usec wide triangle that preceeds the envelope's movement, 
on test point 4 and 5.  It was difficult to see on the input of Z7 
though,  but using the listening device, it sounds the same on the input 
pin 3 as on the output of Z7 the last op amp in the adsr.

The signal gets much weaker if you move across either 1K resistor 
connected to that point.  Both resistors measure 1.03K.  The capacitor 
is well within esr spec and the ground is good.  What...in the 
world....   I've replaced the op amp twice now.  I've had so many crazy 
problems like this.... I can't see the pop at all on the power supply 
rails btw.    Any thoughts? -Bob