tone bender MKIII problem

[alange5]

I posted in diystompboxes, but the thread hit a dead end.  Maybe someone here can help.


I recently built a MKIII Tone Bender.


Schematic:



Layout:





My voltages:
Q1 & Q2: C  -3.8v                B -1.52v                E -1.49v
Q3:         C -3.2v                B -.06v                E 0v




The problem:  When I turn my guitar's volume knob down even a tiny bit, the fuzz gets extremely muddy.  All the high end is lost, and my tone knob does nothing.  At full volume, it sounds excellent.  I'm using a tele with 50's wiring through a Princeton Reverb.  I don't have this problem with any other pedal.

Interestingly, when the pedal has a buffer in front of it (in my case, a TU-2), it sounds perfect.  I can clean it up with my volume knob, and the tone knob works as it should.  All the high end is retained through the full sweep of the guitar's volume knob.

What is the buffer doing to clean it up so well?  Why is it so muddy when the buffer is removed?

Any insight is much appreciated.

[HotBluePlates]

Disclaimer: I know nothing about stompboxes, or troubleshooting them.  That said, I'll try to help. 

My voltages:
Q1 & Q2: C  -3.8v                B -1.52v                E -1.49v
Q3:         C -3.2v                B -.06v                E 0v

Is it odd that Q1 & Q2 have the same base and emitter voltages?  Q2's base should be the same voltage as Q1's emitter (since there's a direct connection), and the two transistors are biased differently.  Q1 has the 10kΩ emitter resistor and two resistors setting its base voltage, but Q2 uses a different emitter resistor and its base is pinned to Q1 emitter.  I don't know what's typical for this circuit, but I'd have guessed Q1 and Q2 would have different emitter voltages (if only to bias Q2 on).

Disclaimer: I know nothing about stompboxes, or troubleshooting them.  That said, I'll try to help. 

Interestingly, when the pedal has a buffer in front of it (in my case, a TU-2), it sounds perfect.  I can clean it up with my volume knob, and the tone knob works as it should.  All the high end is retained through the full sweep of the guitar's volume knob.

What is the buffer doing to clean it up so well?  ...

Is it normal for a MkIII Tonebender to work well with a buffer in front?  Did you use Germanium transistors?  I ask because I thought the conventional wisdom was a buffer in front of Germanium makes them sound harshly bright...

Got a clear photo of your board?

I wonder if Q2 has the correct orientation of emitter & base (different than Q1).  If Q1 & Q2 had their emitters connected, and Q2's base attached to the 3.3kΩ & 10µF, that could cause some weirdness...

[super&plexi]

3 of the same transistors but each one has a different pinout?  did you have to twist the legs around, and it looks like positive ground am I mistaken?

[jojokeo]

alange5,
Just seeing this. Where are you at on this? What transistors did you use as HBP said? I'm assuming you followed the instructions and used germaniums. These "can" be inherently dark depending on exactly which types and models used but when combined interestingly enough they will sometimes lose this behavior. Voltage and biasing also will make a differences. Lastly, their true gain values again will make sometimes big differences and all the things mentioned goes into a "soup" where the outcome is not always predictable unless you use the same ingredients and follow the same recipe so to speak.
 
One big concern and question mark: you are plugging a "normally powered pedal" aka the tu-3 tuner into a circuit designed with pnp transistors that is supposed to function with the power supply configured opposite to this. These should not be used together as never the twain (sharing the same common ground as their grounds are different) shall meet - unless you are also using a separate isolation and voltage converter chip. Meaning that the tuner uses positive 9v and ground is at 0 volts potential. The Tonebender III (and other pnp pedals of this type) "ground" is actually at a lower potential than true ground and the transistors and e-lytic caps are wired oppositely and are at -9 volts. So this circuit's ground is at a negative voltage while the tu-3 is to be at 0 volts - they cannot share the same ground power supply or guitar chords.