Troubleshooting: Forest Green Compressor

[DK1]

Recently have been working on a compressor build, and it is becoming frustrating to troubleshoot due to the nature of "compression" being difficult to hear. Using an audio probe to track the signal is basically worthless.

So, what I have is a pedal that sort of works, but doesn't appear to be doing what I think it should. The volume knob works as expected if the "sustain" is switched on, but is vastly less responsive if that switch is off. Tone knob appears to do nothing. Compression knob appears to do nothing. It does "work" in that I currently have a weird boost pedal that exhibits different levels of gain when I flip the compressor/sustain switch.

I've checked the wiring for appropriate connection and continuity. Twice. I've checked the location of all components, the values of every resistor, verified all the cuts and  links,  and scraped my vero channels to handle any possible bridges. Checked the led, and it's modulating with signal. I've checked the ldr for continuity, since it's socketed currently. Tried three different vactrols (nsl32sr2, nsl32sr3, and a hand rolled red led/norps12[didn't realize how big that stupid thing was before ordering]). Only variation from the verified build would be the ldr, but I think these are within the tolerance for this build.

I've reach the point where my ego is ready to concede I need outside help. :-/

If anyone has any thoughts, I'd appreciate it.

Vero layout: http://tagboardeffects.blogspot.com/2012/03/mad-professor-forest-green-compressor.html
Schematic: http://1.bp.blogspot.com/-lFaW7baQFHY/TxgL2Kh3zLI/AAAAAAAAAoA/iH0mVjiMO84/s1600/FGCC.png


Voltages, labeled as in the vero layout.

[ ] V+ 9.1v
[ ] D1(1n4001), a 9.1v, c8.45v
[ ] D2(1n914), a0v,c? Varies 4-15mv
[ ] D3(1n914) , a0v, c0v
[ ] D4(led), a4.99v, c3.432v
[ ] IC(ne5534ap), 1: 6.37v, 2:varies, 3: 3.4v, 4: 0v, 5: 3.08v, 6: 3.74v, 7: 8.45v, 8: 6.39v
[ ] Q1(2sk170): D8. 18v, G3.54v, S4.45v
[ ] Q2(bc550c: C3.97v, B1.59v, E1.04v
[ ] Q3(bc550c): C3.43v, B25mv, E0.1mv
[ ] Q4(bc550c): C3.43v, B0v, E0v
[ ] Q5(bc560c): C7.57V, B7.61V, E8.18v
[ ] Reg(78l05): I8.45v, G0v, O5.01v

[duck_arse]

Q2 and Q3 are identical for DC in this app. why yours have differing volts? and, the Q4 base should be ~1V6, but isn't.

[DK1]

The vero is labeled differently than  the schematic. So, my Q3 & Q4 are the Q2 & Q3 in the schem.  Not sure why I've got 25mv on the Q3 base, but that's what it checks at. Q4 in the schem is my Q2, which does indeed have a base voltage at 1.6v.

Thank you for taking a look.

[duck_arse]

what voltage do you have at Vb? next step would be to post photos of your build, both sides, and off board parts.

[DK1]

what voltage do you have at Vb? next step would be to post photos of your build, both sides, and off board parts.

Thanks again. Vb is 4.19v.

Photos are the best I could get with my phone. If I need better I can break out a dslr, but that'll take a bit more doing.

Wiring (messy, I know)
http://m.imgur.com/PAgMtD1

Board front
http://m.imgur.com/tSxrXKh

Board rear (mirrored so that it lines up with top layout)
http://m.imgur.com/2TpD9Va

[duck_arse]

hmm, I'll have to have a look at those overnight, I'll get back to you.

a few minor things - did you reverse the image of the underside? the pot-lug rivet-holes are NOT for us to use as wiring points, it will only cause tears. are you sure of your vactrols led orientation? does an ordinary led inserted instead glow dimly, and brighten with signal?

can you remove the IC and the transistors (leave the regulator in), and measure the voltages at the empty socket pins?

[DK1]

hmm, I'll have to have a look at those overnight, I'll get back to you.

a few minor things - did you reverse the image of the underside? the pot-lug rivet-holes are NOT for us to use as wiring points, it will only cause tears. are you sure of your vactrols led orientation? does an ordinary led inserted instead glow dimly, and brighten with signal?

can you remove the IC and the transistors (leave the regulator in), and measure the voltages at the empty socket pins?

I did mirror the bottom side, so that it should overlay directly to the top view of the board.

I did not know that about the pot rivets. I've used them to save space in small enclosures and reduce hassle with jumping lugs. I will definitely keep that in mind in the future.

I'm pretty confident of the vactrol orientation. If you look closely in the wiring shot, you can just make out the dot marker facing the "bottom" of the board. Per the spec sheet, that's the cathode. I have checked with a regular led, and it softens/brightens with signal.

I'll check empty voltages this evening after work.

Thank you!

[DK1]

Empty voltages:

[ ] V+ 9.1v
[ ] D1(1n4001), 9.1v, 8.5v
[ ] D2(1n914), 0v, 24mv
[ ] D3(1n914) , 0v, 27mv
[ ] D4(led), a5v, c0v
[ ] IC(ne5534ap), 1: 55mv?, 2:0.49v, 3: 3.85v, 4: 0v, 5: 70mv, 6: varies v, 7: 8.5v, 8: 0v
[ ] Q1(2sk170): D8.63v, G3.62, S0v
[ ] Q2(bc550c: C7.07v, B2.25v, E0v
[ ] Q3(bc550c): C0v, B7mv, E0v
[ ] Q4(bc550c): C0v, B8mv, E0v
[ ] Q5(bc560c): C0V, B0V, E8.63v
[ ] Reg(78l05): I8.45v, G0v, O5.01v

[duck_arse]

pin 6 - see it is connected to pin 2 via LDR//comp pot//2k4? please measure the resistance between those pins with the comp pot at min and max. that pin6 voltage shouldn't vary with no IC fitted.

I couldn't see any build errors, and if you've seen the light light, it would seem to work to some extent.

[DK1]

pin 6 - see it is connected to pin 2 via LDR//comp pot//2k4? please measure the resistance between those pins with the comp pot at min and max. that pin6 voltage shouldn't vary with no IC fitted.

I couldn't see any build errors, and if you've seen the light light, it would seem to work to some extent.

I get 2.4k min and 446k max.

[duck_arse]

well, that's not the problem then. I'm at a loss.  put the junk back in, have another listen, try and describe the symptoms better/different, maybe someone who knows compressors will stop by and lend a hand.

[DK1]

well, that's not the problem then. I'm at a loss.  put the junk back in, have another listen, try and describe the symptoms better/different, maybe someone who knows compressors will stop by and lend a hand.

Man, I appreciate the help. I think I'm going to shelve this one for a while. Maybe come back later with more motivation on it. I think I need a break from this one.

Thank you again.