Still having problems with Thor

[ranchak]

I'm still having trouble with my Thor build.

Battery  7.89v

      Q1       Q2        Q3         Q4
D    6.4       4.5       3.865     7.89
G    .619     .290      .645      4.51
S    0         0           0           3.62

Pin 1     .136v
Pin 2     3.945v
Pin 3     3.912v
Pin 4     0v
Pin 5     .136v
Pin 6     3.944v
Pin 7     7.89v
Pin 8     0

My build is a PCB from the ROG website, the only substitution that I made is I replaced C3 and C4 with 220pf capacitor. I originally had 470pf and thought maybe I had a problem with them. I have tripled checked my semiconductors for orientation and to make sure the correct ones are in place. The electolytics are oriented properly. I get signal through C2 and it is barely audible at the source of Q2. Any thoughts?

[MartyMart]

It doesn't look a million miles off, though with Battery @ 7.89v Q1 drain should be more like 5.3v and
Q2 more like 3.7v for 1/2 supply , 4.5 and 6.4 only applies to a 9v battery !
If there's no audio after Q2 , I would say that's the problem so check for solder blobs
cold solder .... blah blah all the usual suspects and everything after Q2 .....
You CAN'T have it "right" as it's not working ....... right ??

MM.

[southtown]

get a new battery

[stm]

The battery voltage should not be the culprit of your build not working, however it may certainly impair the sound quality as the headroom of the opamp is reduced, thus it is advisable to try with a fresher battery anyways (>8.6V).

One thing that calls my attention is that you mention the signal at Q2 "SOURCE" is barely audible, which is OK, since Q2 "DRAIN" is the point where the signal is actualy amplified.  Please verify that Q2-source resistor is actualy 1k and that Q2-drain trimpot is set for at least 5k or so. Also, please make sure it is actually Q2-drain where you are taking the signal for the next stage and that you actually have some signal just there.  Another problem might be around the wiring of the GAIN pot, or with the GAIN pot itself.  I've heard before about builds that didn't work because of a faulty pot.

If the above doesn't help you might consider using an audio probe to check the travel of the signal so as to find where it stops.

Good luck.