Zonk Machine Woes...

[eightsevenzero]

I'm a glutton for punishment and decided to try my hand at building a zonk. I for the life of me get it Q2 and Q3 bias correctly which I know can be a bit common. If I was to sub resistors for trimmers to try and determine what values I need to use, which resistors control biasing? The fuzz control also being a bias is throwing me in this circuit. Thanks!

[Rob Strand]

I'm assuming you are building the Zonk 1 with germaniums.  The circuit which is similar to a Tone bender Mk1.

Try to get Q2 biased first.

There's a circuit on the web which shows 3k3 across the fuzz control.   I believe that should be 33k, which is shown on some schematics.  Make sure you have 33k.

Just to be clear.   Measure voltages from ground (battery +) to the indicated point.   If your -ve meter probe is on ground you should get negative voltage measurements.  Make sure it's negative.  When I mention voltages I'm ignoring the sign.

The Fuzz control sets the bias for Q2.   What range of collector voltages are you getting on Q2 when the Fuzz control is adjusted from one extreme to the next?

You want the collector voltage on Q2 to cover at least 5V to 8V.   A bit outside those ranges at the extremes of the Fuzz control is fine.

If your Q2 collector voltage is too low, try increasing the value of the resistor between the base of Q2 and the supply (battery -).
Alternative if the voltages are too high try reducing the resistor.

[eightsevenzero]

Thanks for the tips, today I dove into this a bit more and found some higher leak transistors that seem to help though I'm still struggling to get it fine-tuned (these are all -v):

Q1- C: 9.47v/ B: .89v / E: .87v
Q2 Full Fuzz pot- C: 3.75v B: 170.5mv E: 0
Q2 Min Fuzz pot- C: 9.35v B: 44.7mv E: 0
Q3- C: 8.5v B: 62mv E: 0

My main question is how do I adjust Q2 to get the pot to NOT go above 7.5V at the minimum resistance?

Also, if I understand correctly I should adjust the base to ground resistor of Q3 to get the collector voltage to around 7v right?

[Rob Strand]

My main question is how do I adjust Q2 to get the pot to NOT go above 7.5V at the minimum resistance?

I'd let it go to at least 8V.  In your case where the battery voltage is high (9.47V)  you might even let it go to 8.5V.   Basically within 1V of the supply rail.  The Q2 collector voltage on some units go within 0.5V of the supply rail.     The thing is if you allow the Q2 collector voltage to go higher you can always throttle it back with the Fuzz pot.   If you cut it short you can adjust the Fuzz pot to make it go higher.    At the end of the day the best place is to go as high as it sounds good to you.

If you want to precisely set the Q2 collector voltage when the Fuzz pot is on minimum resistance then you are best tweaking the 2k2 resistor between the base of Q2 and the Fuzz pot.

Also, if I understand correctly I should adjust the base to ground resistor of Q3 to get the collector voltage to around 7v right?

Yes, that will do it.    Typical values for Q3 collector voltage are in the zone 0.5V to 2V from the supply rail so for your 9.47V battery that's about  7.5V to  9.0V.   Again you might want to play around voltage to get the sound you like.


FWIW, the Q1 emitter voltage should be at least 1.3V  (typically somewhere around 1.3V to 2V and upto as high as 3V).

[eightsevenzero]

As hard as I try I can't get the Q1 emitter above 1v by adjusting the base to ground resistor. Really aggravating, I suspect it has to be more leakage or something.

[Rob Strand]

As hard as I try I can't get the Q1 emitter above 1v by adjusting the base to ground resistor. Really aggravating, I suspect it has to be more leakage or something.

If the transistor doesn't have enough leakage or is low gain it might not be possible.   At some point the base resistor is so large it's not making much improvement.  You can always add a large value resistor from the base of Q1 to the supply.   That provides the base current to pull the emitter voltage up.   If you go that route, perhaps leave the base to ground resistor at the stock value.

[eightsevenzero]

Thanks so much for chiming in! I'll give it a shot!