GGG ITS8 Weak Output

[Bill_N]

Well, after sorting through basic stupid problems such as insulating a metal DC jack using a rubber grommet, and building General Guitar Gadgets' Tube Screamer clone without the clipping diode switch, I have ran into a problem with weak output. I have checked and rechecked all of my offboard wiring along with electrolytic cap, diode, and transistor orientation, and am scratching my head trying to figure out what to do to solve this problem. Anyways, here's the info.

Source of schematic: http://generalguitargadgets.com/pdf/ggg_its8_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
Source of PCB Layout: http://generalguitargadgets.com/pdf/ggg_its8_lo_no_clipper_sw.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

Voltages:

IC1:
1: 5.2v
2: 5.4v
3: 5.12v
4: 0v
5: 5.2v
6: 5.2v
7: 5.2v
8: 10.5v

Q1:
B: 2.95v
C: 10.5v
E: 3.35v

Q2:
B: 3v
C: 10.5v
E: 3.46v

[arawn]

emitter voltages look high and your base should be a diode drop higher like .5-.7 that's the first thing i see.

[Bill_N]

Judging from the layout, could it mean that the transistor I used is in backwards, causing the low volume problem?

[ugly_guitar_guy]

Did you use the germanium diodes from the mod kit? I tried it and it was VERY quiet, so I went back to the 1N4148's and it was full volume like it was supposed to be.

[Bill_N]

I used the 1n914 diodes in the feedback loop of the opamp as it is in the schematic. I have 50+ of the 1n4148s laying around so I will try that. That does make sense though, seeing as general guitar gadgets warned about the volume changes. The diode type probably has something to do with it. I will try the diode lift mod (removing diodes) from loop and see where that gets me before putting in the 1n4148s.

[Bill_N]

Edit: I did the diode lift modification and I still have the same problem. 

[arawn]

Check your transistor pinouts, I am thinking the output buffer maybe out of whack somehow and killing your signal
actually both buffers seem to be out of whack  so i would start there

[Bill_N]

These are the transistors I am using for this. I just noticed that the schematic calls for a pair of 2N4401s. I will check around the transistors for any bridges or bad joints. http://www.onsemi.com/pub_link/Collateral/2N3903-D.PDF

[Bill_N]

Could the transistor voltages be incorrect because of a bad bias voltage? Or would that not matter seeing as they provide no gain.

[arawn]

afraid i am now in over my head

[stringsthings]

Could the transistor voltages be incorrect because of a bad bias voltage? Or would that not matter seeing as they provide no gain.

1) yes ... 2) it depends on how "bad" the bias voltage was

however, in this case:

Q1:
B: 2.95v
C: 10.5v
E: 3.35v

Q2:
B: 3v
C: 10.5v
E: 3.46v

.. the voltages that you measured at the bases of the transistors are less than the voltages that you measured at the emitters ... that's probably not going to give you the results that you want ... for this particular part of the circuit to function, you want to see the voltage at the base be higher than the voltage at the emitter ... ( for example:  on Q1, Vb = 3.55 and Ve = 3.05 )  ... the same idea applies for Q2 ....

[Bill_N]

Well, fast forward a bit later and my ITS8 is working and functional! I made a huge error in ordering the film capacitors from mouser as 10mm spacing, thus making everything not have that good of a connection. I replaced all of the film caps with WIMA box film caps and now this pedal screams! Thank you for all of the help everyone!