Another fOXX Tone Machine build

[lethargytartare]

Been on a tear lately, so returned to this.  I got a populated board in a trade several years ago, and it kinda worked.  Then I reboxed it and it still kinda worked -- seems ok, but just can't get over unity, basically.  The schematic was basically the same as JD Sleep's, so I used that for comparison purposes and found two errors:  tone and sustain pot caps were reversed; and the final chain of components going to the volume pot were on the wrong side of Q4 (they were on the ground side not the V side).  But fixing all that didn't fix the output volume.

So last night I was checking voltages and discovered that the trannies used (BC550C) all have EBC pinouts and the schematic and layout were clearly designed for CBE -- so the trannies were all getting current on their emitters, not collectors.  But that aside, the voltages all looked pretty good (more on that below).

I found a discussion where someone mentioned that npns can be reversed and will work, but the overall output might be reduced -- I was hopeful that that was going to be the silver bullet.  So last night I pulled all the trannies and put in sockets, and flipped them all...and everything sounds the same, and the output level is unchanged. 

There are three component differences between this build and the more common schematics out there, that I don't think are significant:  R1 1M instead of 4M7 (but I think that's a pulldown, and shouldn't be an issue), C10 of .0033 instead of .003 and C11 of .047 instead of .05 (I think these are part of the tone control, and are such small variances, I can't imagine they're culpable).

SO my plan for tonight is to try different trannies:  I have BC109s and 2N5089s that I've read others have used.  So with everything socketed, that's plan G or H or whatever I'm on.

Here are my voltages.  One that I wonder about is Q3.  In the other builds I've seen, the collector voltage was higher than mine (relative to all of the readings, that is), and for Q2, most builds had a wider gap between the collector and base than mine.  I'll see if that pattern holds with new components in there:

Q       C         B        E
Q1   2.09     .72    .149
Q2   7.59   3.47   1.495 << C-B difference was bigger in other builds
Q3   6.77    .812    .235 << C was bigger in other builds
Q4   7.51    .816    .247

I'll add info as I go.

[PRR]

> Q       C         B        E
> Q2   7.59   3.47   1.495

That's clearly dubious or wrong. B-E voltage of a happy transistor will always be near 0.6V. Maybe 0.5 or 0.7, but NOT 2 Volts.

It is so difficult to force a transistor B-E above 0.7V that I would suspect a dead (burned up) transistor.

If 2N5089 is correct polarity and workable pin-out, I'd bet it is "same as" '550 for most pedal purposes. (The fat '550 will be better for motor-control or low-low-Z mike preamp, but that's not what you got.) I have a feeling that the '109 "is" the original '5089 except marketed in England, so should also work.

[lethargytartare]

No progress.  And my readings are a bit more odd now...and yet overall the pedal works the same    Probably just going to shelve it for a while now that I've heard the noise ensemble...I'll put in the BC109s and get those readings before I pack it away.

GGG:
Q     C       B     E
Q1  2.2    0.73  0.16
Q2  7.5    2.2    1.6
Q3 7.28   0.78  0.21
Q4  7.63  0.84  0.26

Mine with socketed 2N5089s:
Q     C       B     E
Q1  3.27 0.60  .068
Q2  6.25  3.26 2.67
Q3  7.38  0.68  .142
Q4  7.87  0.65  .134

[PRR]

Re-re-check that pinout. You said it was wrong once, now you have changed transistors and I sure can't remember which pin is where.

The numbers suggest the transistors have very low gain, but we know '5089 is very high gain.

> mentioned that npns can be reversed and will work

Yes; but at very low current gain. Performance is better the "right" way.

You "can" drive the car to the store backward. But it's really made to go better the other way.

[lethargytartare]

Yeah, one more time, and I'm going to zero in on the pins and the board...ya know, I have had the assumption in mind that they are all consistent -- but maybe he got one of them "right" and the rest were reversed.  I'll retrace the board against the schematic again, too.