univox superfuzz Q5/Q6?

[hellwood]

i built one of these and i must say, it has to be one of my top two favorite pedals on earth. anyway, i measured a pile of trannys yesterday for an unrelated build and the results were so disturbing i pulled Q5 and Q6 out of the USF to see how well matched they were. at the time, i  figured since i was using a trim pot, i can compensate for any variance between them. i almost had a heart attack when Q5 read 641Hfe??! and Q6 read 79Hfe. so, my questions are...

1)since i am using a trim pot to balance Q5/6, would this even matter?
2)could this be interesting because when i pan hard right or left i get a bigger range of sounds?
3)im blowing it big time and should match them right away?

[Solidhex]

How does it sound? I was pretty damn happy with mine. I matched my 5088's before putting them in. They were all around 600. I did the Q5 Q6 thing with a pot on the outside but regret it now since I can't really here much of a difference wherever the knob is set. The only thing that seems to happen is that when its set anywhere other than around 12 o'clock I get a bunch of hiss. Maybe using different transistor gains would offer more variety. I've got my tranny's socketed so I'll give it a try.

--Brad

[Sir H C]

The matching of the hfe of the devices sets the amplitude that they are being driven to be "similar" (since the impedances seen from the phase splitter will look about the same if the Hfes are the same), the trim resistor is more to set both transistors to the same bias current which is independent of the Hfe of the transistor.

[hellwood]

How does it sound? I was pretty damn happy with mine. I matched my 5088's before putting them in. They were all around 600. I did the Q5 Q6 thing with a pot on the outside but regret it now since I can't really here much of a difference wherever the knob is set. The only thing that seems to happen is that when its set anywhere other than around 12 o'clock I get a bunch of hiss. Maybe using different transistor gains would offer more variety. I've got my tranny's socketed so I'll give it a try.

--Brad

i gotta tell you...this pedal F***in smokes!!!!!! the bias pot seems to be very effective and offers quite a variety i must say! around 2 o'clock all of the rich octave harmonics begin to stir up the dead beneath my house. its a really inspiring adventure every time i step on it! i guess im just greedy, tryin to cheat even more out of it.

The matching of the hfe of the devices sets the amplitude that they are being driven to be "similar" (since the impedances seen from the phase splitter will look about the same if the Hfes are the same), the trim resistor is more to set both transistors to the same bias current which is independent of the Hfe of the transistor.

...so would you guess or calculate that im screwing myself out of even more wicked tone?

[Solidhex]

Yo

  Yeah I threw a bunch of different transistors in the Q6 position and didn't really notice much of a change in the way the knob works. I used a 10k since it was what I had laying around. Either way the pedal sounds great. I used the Ustomp layout if I didn't mention that before.

--Brad

[hellwood]

Yo

  Yeah I threw a bunch of different transistors in the Q6 position and didn't really notice much of a change in the way the knob works. I used a 10k since it was what I had laying around. Either way the pedal sounds great. I used the Ustomp layout if I didn't mention that before.

--Brad

i used the unicord schematics from 4-6-68 and it calls for a 10k-b trim pot. maybe the linear taper is more noticeable? so when you changed Q6, how did it affect the pedal? did you notice any loss of octave activity w/ Q5/6 unbiased?

[Sir H C]

Does Q6 come off the emitter or the collector of the phase splitter?

[hellwood]

Does Q6 come off the emitter or the collector of the phase splitter?

here is the schematic i followed:
http://filters.muziq.be/files/schematics/unicord_superfuzz.gif

[Sir H C]

If you call Q5 the one on the left, and Q6 the one on the right, Q6 is much more immune to low beta devices.  If you put one on the other side, you will affect the level.

[Solidhex]

I used a linear taper 10k... Hopefully there's something I can do to make the effect of the bias knob more present. I didn't really notice much of a change using the different transistors. I should try it through some more amps.

--Brad