6 knob compressor help - no compression

[Stefan]

Thanks for helping me troubleshoot my latest project.

the 5 knob compressor LM13700 version w/optional tone control













I'm only getting clean signal with the pedal powered on.  Output controls the volume, but there's no compression, clip, attack, or tone effect.  As more blend is added (clockwise on the pot), the audio signal diminishes and eventually goes away completely.

I suspect there's an issue where the signal splits, but for the life of me I haven't been able to find it.  It's been days of going over schematics, checking solders, testing and retesting, and still nothing.  I'm hoping someone sees something I'm missing.

Things I've done so far:

1. Started completely over.  This is my second attempt at this pedal and it's giving me the same issue.  Nothing was reused from the previous build.

2. Checked and rechecked all the cuts before building.  Made sure there was no continuity between points there shouldn't be.

3. Each resistor and capacitor was checked on a DMM before soldering to the board.  All resistors are within 1%, all capacitors within 5%

4. My initial thought was that I had a bridge to ground, so I spent time soldering, resoldering, and ensuring there were no bridges.  That's why the back looks a little messy.  I've visually inspected each rail with a loupe and see no bridges.  I've also tested adjacent rails for continuity.

6. Changed out the TL072 three times to make sure the IC wasn't bad.  Did the same with the LM13700.

7. Swapped every transistor.

8. Read every debugging thread on the 4 and 5 knob compressors that preceded this version.  Still stuck.

Voltages follow:

               TL072                          LM13700                                       C         B         E
     4.42   1 -- 8  8.85              1.26    1 -- 16  0                     Q1      6.98     2.22    1.86
     4.68   2 -- 7  4.41              0.731  2 -- 15  0                     Q2      6.71     2.68    2.15
     4.39   3 -- 6  4.42              4.49    3 -- 14  0                     Q3      8.68      0          0
          0   4 -- 5  4.39              4.5     4 -- 13  0                     Q4      8.68      0          0
                                             2.68   5 -- 12  0.748               Q5      8.86      8.68    8.27
                                                 0    6 -- 11  8.85                
                                             4.2     7 -- 10  0                                       2N5088
                                             0.657  8 -- 9   0.665

Last, here are the results of my audio probe.  Green is audio, black is no audio.  Red is audio with blend off (full CCW) but no audio with blend on (full CW).



Any help would be warmly welcome.