A successful Zonk experiment report

[MarkALeuchter]

I've spent the last week carefully tuning a Zonk I'm making for a player going on tour this summer. It's not a pure Zonk -- I made some changes to the input cap, the output cap, a trimmer on Q3 instead of the 15K, and some minor changes to the volume pot.  But otherwise, it's a pretty straightforward Zonk and as many have noted, the transistor choices made all the difference. 

I auditioned a few different sets involving some of the types and specs I've used in various Mk I builds, and I found two combos that sounded excellent but in different ways. 

For a "bigger" and thicker tone that still had some really rich and open harmonic character, I used a 2SB54 with about 190 Hfe and 250uA leakage for Q1, a CV7355 at about 115 Hfe and 06uA for Q2, and an AC125 at 120 Hfe and 300uA in Q3.

For a slightly more gated (with a tiny bit of octave), psychedelic tone that still has plenty of weight, the measurements changed.  Q1 was an OC75 at 85 Hfe and 350uA; a 2N1378 at 126 Hfe and 04uA at Q2, and Q3 was a Matsush*ta 2SB176 at 93 Hfe and 190uA leakage.  This was my favorite of the two (though the setup noted above still sounded fabulous), and just to check, I replaced the OC75 with an OC71 with very similar gain and leakage, and the tone was virtually identical.  Same with Q3...I replaced the 2SB176 with an AC125 with the same specs, and the sound was also nearly identical, requiring only the tiniest of adjustments on the Q3 trimmer.

I used a 470K on the base of Q2 for both setups.  This worked very well and allowed for a very usable range of sounds along the sweep of the fuzz control.
 
I should note that though the two setups had some differences in the gains of Q1 and Q3, both were about equally aggressive.  The character of the aggression was a bit different; as I said, the first set up felt a touch thicker, maybe "chewier" for lack of a better word. But the second setup still had plenty of depth and richness, and didn't feel any less present or powerful.

I hope this report is helpful to anybody building up this circuit. I'd be curious to hear back from anybody who is tinkering with this the circuit and has something else or different to report from their own testing.

[karsten_h]

curious to see your schematic and voltages?