zonk machine question

[bonehead1972]

hey guys
i just built one, i tried a lot of transistors and finally got some nice sound out of it. bias voltages are ok, no ugly noises on the decay
its gated in a nice way, with a hint of octave up when i back the guitar vol pot a little....
what bothers me is on a certain combination on the guitar volume pot and the "fuzz''/ bias pot it produces a kind of octave down sound which is actually very pleasant
my question is whether this is normal. i havent heard of a zonk pedal doing this

i would appreciate your answers...cheers!

[glops]

I have no idea if that is common and haven't read of any such instances in all of my forum research on the zonk/mk1. Really just stopping by to say that I finally built one of these a few months ago and really love it. I breadboarded the circuit and then test probably 50 transistors until I found the perfect combination. I ended up installing a rotary switch for 3 different input caps, one being the stock zonk and then 2 higher values to get closer to the MK1 and then fatter. The zonk setting is my favorite for sure, the value for MK1 sounds good too and the fat E string gives a nice blown horn type of sound but definitely don't hear any octave down which I imagine on yours must send incredible. I was able to get this circuit sounding pretty decent with several transistor combos but there were only like 2 combos that really stood out and sounded completely ripping. My unit sounds the best with the volume unlike most fuzzes I have built. Very interesting circuit.

[bonehead1972]

Thanks for your answer man!
I made a forum research on the zonk/mk1 as well and found nothing about this

[antonis]

R.G. dealt with Zonk analysis and tuning..

http://www.geofex.com/Article_Folders/zonkmach/zonkbst.pdf

[amptramp]

Your octave down may be only within a range of input frequencies and it may have to do with the output stage bias.  Imagine C3 pulls hard negative to turn Q3 on.  The emitter-base junction of Q3 acts as a diode and delivers current back to C3.  It is now biased towards cutoff and the next alternation of the audio may not be able to overcome the bias.  After the charge on C3 leaks off, the next alternation of the signal will again drive the Q3 output stage normally.  This would give the effect of amplifying every other pulse at the input - in other words, a signal one octave down.

If you tune one of these for a good sound at one temperature, this may not hold for any other temperature due to the temperature variation of the leakage current doubling for every 10° C temperature rise.  One trick that used to be seen on transistor radios was to have a reverse-biased diode from base to emitter so when the transistor leakage increased, the diode leakage would also increase and absorb the increase in bias current.  Then you could tune for the correct sound over a wider temperature range.  If you come in from the cold for a gig or you have an afternoon gig outdoors in blazing heat, this could make the situation a bit better.

[bonehead1972]

Thanks  for your input Antonis! Always very helpful!
I have read this and followed his tuning instructions.i like the result...just wondering how this sub octave showed up (with certain positions of  the pots I can actually  dial it out via fuzz(bias) pot. Hot weather...low battery... I don't know:) cheers!

[antonis]

just wondering how this sub octave showed up (with certain positions of  the pots I can actually  dial it out via fuzz(bias) pot.

Ron exhibited a very good and comprehensive interpretation just above..

[bonehead1972]

Amptramp, thank you for your answer!

[bonehead1972]

hi,
2 days later managed to get back to the zonk ..

after a few seconds of playing i realize that Mr Amptramp got it dead on.. the octave is within a certain range of frequencies.
i will try a diode on Q3 B-E . i have plenty of AA113  and D9E germaniums.. i hope they would do the job.
should this diode go with the negative side to emitter for an PNP transistor?

thank you for your help guys!

[antonis]

i will try a diode on Q3 B-E . i have plenty of AA113  and D9E germaniums.. i hope they would do the job.
should this diode go with the negative side to emitter for an PNP transistor?

Negative side should face to the opposite direction of Emitter symbol arrow..
(like an antiparallel pair..)

[amptramp]

You can test the diodes you intend to use.  Just check that the reverse leakage of the diode is roughly the same as the collector-to-base leakage of the transistor at the same temperature and bias conditions and the temperature sensitivity should track.  Where a stage depends on leakage current for biasing, you may have to change the bias if you use a leakage diode.

[antonis]

Or simply use a same type/batch with Q3 BJT, wired as diode (B-E shorted)..

[bonehead1972]

Thanks for your help guys!