ZONK MACHINE: Component Values Table

Not a huge amount of variation on Zonks in terms of component values, and at one stage this was all on the MKI table, but I decided to split the two.  

ZONK MACHINE SCHEMATIC

ZONK MACHINE COMPONENT VALUES

Link to table

BUILD NOTES

In my experience the Zonk can be a little easier to make than the MKI in terms of transistor selection, and just getting a sound out of it - but it's still not one to rush into without a good stock of transistors to test.  It's still a difficult circuit to get sounding good.  You can end up with a thin nasty sounding beast that sounds nothing like the demos. 

Transistors

Q1 needs leakage to work.   Q2 doesn't need leakage to work, but it uses an OC75, which are usually quite leaky compared to other transistors.   Q3 should also need leakage to work, but it has an OC44 here, which are generally quite low in terms of leakage - this is partly where the gated sound comes from.

Dave Main of D*A*M fame was kind enough to share some voltages and transistor hfe on a schematic, which is as follows.

Q1     Texas Instruments AO2650      hfe 30

Q2     Mullard OC75                          hfe 156

Q3     Mullard OC44                          hfe 69

Voltage on Q2 collector

-5.1v on full fuzz

-9.6v at zero

Most batteries start life at 9.5v so I have no idea what kind of freak battery Dave had plugged in to get -9.6 volts.  Anyways, it will be a high voltage in any case, a range of -5 to -7v would be pretty normal.

And here's another set of quite different readings from an original Zonk, care of acidfuzz on freestompboxes.   Great to see some leakage measurements as well. 

Q1    Texas Instruments AO2650        Hfe   180   leakage    0.12mA
Q2    Mullard OC75                            Hfe   78     leakage   0.29mA
Q3    OC44                                          Hfe   58     leakage   0

and here's a demo, of what might be the very same pedal, as the video is provided by acidfuzz.  

Input capacitor

The 1nf input capacitor is really the standout component value on a Zonk - this is really what sets it apart from the MKI Tone Bender.   In the video demo above, the Zonk sounds quite fat - it's not easy getting this tone.   I've found that a higher hfe Q1 helps.

If your Zonk is sounding a bit thin and nasty, it's not the end of the world if you increase the size of the input cap until you get it to a place that you're happy with.  Try a 3n3.   There's a lot of builders out there that offer this circuit with a MKI switch, which basically swaps or adds another input cap to increase the value to something like a MKI (10nf).

The sizzle

The what now?  Zonks sometimes have an annoying sizzle on the decay, some people say it sounds like bacon cooking, and you don't really want that.  Some sizzle is not unusual on the decay of a MKI style circuit, but the Zonk can have way too much at times.

If you can't fix sizzle with transistor swaps, add a low value cap directly on the input of the circuit.  You want something big enough to reduce the sizzle down to manageable levels, but not so big that it changes the tone too much, although this can sound kind of cool, it's a bit like a cocked wah sound if you go too big.  A 1nf cap often does the trick without affecting the sound..

 

ZONK RESOURCES;

• Fuzzboxes.org for a bit of Zonk History

• Tagboard layout 

• Hybrid - vero layout

• Vero layout with input cap switch

ZONK HYBRID READING

Great thread on FSB can be found here

Voltages supplied by Acid Fuzz (very kind of him to share)

Trimmer set to about 152k.  Here are the voltages at ~70°F with a 9V battery:

1/2 "FUZZ" Full "FUZZ"

Q1:  

        C -8.98V   -8.95V

        B -.707V   -.715V

        E -.656V   -.676V

Q2:    

        C -7.16V   -3.632V

        B -.643V   -.672V

        E -0.1mV  -0.1mV

Q3: 

        C -7.99V   -7.51V

        B -51.7mV  -51mV

        E -0.1mV  -0.1mV