ToneBender MKII Debug/Tuning - Oscillation

[woolley]

Hi all
I've perfed up a ToneBender MKII. Problem is it oscillates at around a Low E tone.
I don't know a hell of a lot about this sort of stuff, but I guess its a mis-biased transistor or two, or three.
So, here is some data i've got for your de-bugging/tuning needs.
Anything else you need to know? Any help appreciated. And sorry the tables don't line up.

Data from runoffgroove on a SmallBear Matched Set
http://www.runoffgroove.com/tbmk2.html
 
   hfe|Q1:68 |Q2:86 |   Q3:120|
   ---|---------|-------|---------|
    C |8.67    |.560   | 5.07    |      
    B |82mV  |.121   |   .563    |
    E |0         |0       |   .441    |
   -------------------------------
========================================
My Matched Set from SmallBear
***9v Battery: 7.8v (if that makes a difference)
PNP Positive Ground

   hfe|Q1:75 |Q2:96 |   Q3:121|
   ---|--------|--------|---------|
    C |7.57    |.529   | 4.60    |      
    B |90mV  |.112   |   .528    |
    E |0         |0       |   .385    |
   -------------------------------

Thanks, and please help me

[bwanasonic]

I don't know a hell of a lot about this stuff either, but my hunch is your numbers look pretty good and the problem might be lead dress or layout type issues. Also, what grounding scheme did you use? That type of oscillation was a problem when I attempted a PNP/ Neg. ground Fuzz Face. From what little I know the oscillation you describe doesn't sound like a symptom of misbiased transistors.

Kerry M

[woolley]

it's (+) Ground, if that's what you meant. the perf layout is pretty much the same as the TB schem that SmallBear provides. By lead dress, do you mean i should be using shielded wire at specific points? It sorta sounds like the 4ms Atoner.
thanks

[Thomas P.]

Do you have good qualitiy cap between V+ and V-?
Also you can install a diode in parallel with the cap.

[petemoore]

They have the pin V's of tonebenders at RUnoff Groove,,, but I don't remem seeing Q2 emitter sitting at ground [I would go look there for ballpark voltage readings to compare to].

[Thomas P.]

They have the pin V's of tonebenders at RUnoff Groove,,, but I don't remem seeing Q2 emitter sitting at ground [I would go look there for ballpark voltage readings to compare to].

Looking at the schematic I think it's right haveing Q2's emitter at GND.

[Jason M.]

Do you have a fresh battery to try?
7.8V is a little low.

Perhaps the increased impedance from your dying battery is contributing to the oscillation.

J.

[woolley]

No fresh batteries at this stage. I tried it with a 9v reg. power supply rather than the battery and there was no oscillation, no fuzz either. With the battery, as soon as it's plugged in, the pitch of the oscillation lowers from maybe low A slowly to the low E. You can still hear some fuzzed guitar through it, but not with the PS, it's just clean, but the tone and vol knobs work.

[woolley]

ok, here is what has happened.
i've used the PS for the ToneBender, and put a Ro/Dy Comp infront. the Comp has no power (not pluged in coz it's Neg ground) and is 'on' rather than Bypassed (it's TrueBypass).
Now the ToneBender works!
I tried it with the 7v battery in the TB and the PS in the Comp and it didn't make a sound.

Is this an impedence thing? Are all ToneBenders like this?