ToneBender Howling Like a Pig

[Wagster]

I built a TB MKII using the board and layout from GGG.I got the transistors from SmallBear.It was sounding awesome and all of a sudden it started howling.When I turn the gain down it drops the pitch.Below 3:00 the noise goes away but the pedal still sounds weird.I've checked the transistors and they seem fine.Any ideas on what it could be?

Thanks,
Billy

[mac]

Check the filter cap across the power supply.

mac

[R.G.]

Is it set up with PNP transistors and negative ground?

[Dragonfly]

Is it set up with PNP transistors and negative ground?

You should make that your "signature", R.G. 

It might save you from having to ask all the time !

[R.G.]

I should, but putting it in a signature is placing it where it will certainly be ignored. 

[Wagster]

Check the filter cap across the power supply.

mac

I found that the solder broke free from the board on the power supply cap.I fixed it but it's still howling.Hmmmmmmmm

[Wagster]

Is it set up with PNP transistors and negative ground?

No it's PNP positive ground.

[petemoore]

Any ideas on what it could be?
  Yes, it is a Tonebender which doesn't function correctly and needs debugged.
  See the debugging thread, or at least post battery and circuit point voltages [from Gnd. across supply, then to each transistor pin].
   
When I turn the gain down it drops the pitch.
  = Oscillating
  Below 3:00 the noise goes away
  pitch and oscillation are gain dependant
  If
  but the pedal still sounds weird
  Q2 and Q3 of Tonebender is a Fuzz Face [so all fuzz face related debugging info applies]
  Q1 of tonebender is the extra gain stage tacked on the FF's front end.

[Dragonfly]

I should, but putting it in a signature is placing it where it will certainly be ignored. 

[Wagster]

I'm such a newbie 

I'll I took some reading and here's what I got

Voltage at the circuit board end of the black battery lead = 9.62

Here's the Schematic   http://www.generalguitargadgets.com/diagrams/tonebender_m2p_sc_pp.gif

Q1)
C= 7.05
B= 0.09
E = 0.00

Q2)
C= 0.40
B= 0.11
E=0.00

Q3)
C= 0.45
B= 0.40
E= 5.30

[Wagster]

Do the readings look okay?

[petemoore]

  DId you socket the transistors?
  Find the Tonebender 'ballpark voltages at ROG, Homewrecker or GGG [I forget where I see those], or use just the FF to debug the FF portion of the TB..
  and start with Q1, treat it like the booster stage it is.
    Q1)
C= 7.05 Collector is near top rail, what does it's bias resistor measure? 
B= 0.09 Base needs to be >1 diode drop above emitter, check any resistors *connected to it
E = 0.00 Seems 'near 'nuf' to ground being at exactly ground potential.
  *When measuring these resistors, choose 'distant point' [farthest probe point] to also test as many connections as possible at the same time
Q2)
C= 0.40  {Low, apply DMM to measure bias resistor,
B= 0.11  [Should be higher, probably comes up when collector does,
E=0.00  = Gnd.

Q3)
C= 0.45   {Measure bias resistor,
B= 0.40   [nothing but Q2 collector on this one 
E= 5.30  {Oh my, much higher than collector, which is wierd, collector should be the one connected nearest the voltage farthest from ground...I suspect typo, mis-pinout or...hmm...check everything including resistance to ground here, 100k to Q2base etc. something funny going on here.

[Dragonfly]

Use the search function, keywords : Tonebender voltages

[mac]

Q1: if the transistor is leaky then collector voltage goes down. If leakage is very small, like a Si, then you need to add an extra resistor of about 1M from C to B.
I'd like Vc1=8.0v or so.

mac

[Wagster]

I really appreciate the help guys.I ordered another board from GGG.I'm going to debug this one first.I have a lot to learn and this place is full of valuable info.I'll use the search function next time 

Thanks,
Billy

[mac]

If you plan to build more pedals I suggest you to buy a breadboard. It will save you a lot of trouble.

mac