Univox Superfuzz diode options

[mordechai]

I'd like to learn more about diode options in the Superfuzz -- I've heard it with Ge and Si, but I am curious about asymmetrical arrangements of either, or even using LEDs.  I've looked for threads about this butI have a feeling this particular topic is buried somewhere that I missed.  So, any comments or suggestions about this?

[R.G.]

Comments or suggestions?

Sure.

Try it and let us know what you think. 

[mordechai]

Will do.

In the interim, I was going through an old thread:  http://www.diystompboxes.com/smfforum/index.php?topic=78980.0

Toward the bottom of the thread is a comment from Mark (Hammer) which reads as follows:

"The diode pair closest to the output side is not really necessary, or can even be altered.  I have a Si/Ge/nothing switch in mine.  As well, the midscoop filter can be reduced in effect by inserting a small resistance between the 1uf cap and ground.  A 5k pot or even a 2k pot will serve to retain more mids, and a "throatier" sound."

Was this a typo, and did he mean the .1uF cap going to ground toward the front end of the circuit?

[mordechai]

Oh, wait...I see what he was talking about -- the cap going to ground that sits on the rail between the 22k and 10k resistors.

This brings me to a different question, though: would changing the value of these resistors (higher than 22k on one end, lower than 10k on the other) yield a wider tonal rift between the non-scooped and scooped tones?  Or would this have an adverse effect on noise, volume, or otherwise?

[slacker]

If you keep the total value to about 32k but make one resistor smaller and one bigger then it moves the frequency where the scoop happens. Some people like the 10 and 22k swapped.

[Mark Hammer]

1) Yes, it is the 0.1uf cap to ground (100nf).

2) A 4k7, 10kpot, 15k arrangement would probably by useful for moving around the "scoop".  With that first resistor = 4k7, the treble rolloff begins around 340hz.  With the wiper moved over so that there is 14k7 of resistance on one side of the cap, and 15k on the other, that treble rolloff moves down to 108hz.  Given the rolloff is pretty shallow, you'll have lots of lower mids if you wish.

3) It is an octave fuzz.  That means you are (or at least should be) FAR more concerned about the balancing of complementary versions of the signal during octave production than you are about any additional clipping diodes.  Besides, if what arrives at the clipping diodes is already distorted, how much difference do you think symmetrical vs asymmetrical diodes you will be able to hear?  What you'll hear is a difference in level, and probably not that much more.

[LucifersTrip]

I did a lot of experimenting with that one...but not with the diodes.  There's a bunch of threads & experimenting mentioning diodes & the scoop/octave, but surprisingly very little (at least that I could find on a quick search) regarding the gains and voltages of the transistors, especially Q6.

I found that the gains and voltages of Q6 make a big difference to the sound.  Note that if you use a 200 hfe or 50 hfe and set the collector voltages the same for each, the tone will be different. It's not just the hfe's that matter.

Solidhex was cool enough to post voltages from a killer sounding original:
http://www.diystompboxes.com/smfforum/index.php?topic=64068.0

C B E
Q1 6.01 .66 .117
Q2 8.88 6.01 5.41
Q3 6.23 3.27 2.72
Q4 3.1 1.7 1.11
Q5 3.1 1.67 1.11
Q6 5.75 .98 .361

I got so close to those voltages with no adjusting with transistors in the 100 - 150 hfe range (which is prob what the original had). Q6 was the only one that was off and I had to adjust.

I tried about 20 different transistors in Q6 in the 125 - 700 range and the highest collector voltage I got was 4.6v. A 2N5088 with around 600+ gave me around 3.5v and a 2SC1815 with 125 gave me the 4.7v. So, I dropped an old Heathkit transistor in there with a gian of 55 and hit the mark almost right on the money, 5.8v. Big difference...it's less sharp, with a little less pronounced octave, but smoother, richer and seemingly fuzzier. The 5088 was the worst...much more harsh and not as smooth.

This is really an easy fuzz to get to sound good since I was able to adjust the collector voltage all the way from 2.1v up to 7.2v and still get a killer fuzz throughout with no gating or poor decay. The big difference is the tone. Down at 2.1v it's fatter and richer and 7.2v thinner.

[mordechai]

2) A 4k7, 10kpot, 15k arrangement would probably by useful for moving around the "scoop".  With that first resistor = 4k7, the treble rolloff begins around 340hz.  With the wiper moved over so that there is 14k7 of resistance on one side of the cap, and 15k on the other, that treble rolloff moves down to 108hz.  Given the rolloff is pretty shallow, you'll have lots of lower mids if you wish.

Mark, that is an interesting idea.  I wonder, though, if a similar audible tone shift could be had by incorporating the cap blend pot similar to Joe's Easy Face.  Here's a tentative schematic describing what I have in mind, a pot that shifts the signal to one cap or another to control the degree of midscooped tone:

http://s1130.photobucket.com/albums/m533/mordechaibenzev/?action=view&current=SuperfuzzMidscoopcontrol.jpg

Would this be effective too?

[mordechai]

I wonder if THIS might do both what Mr. Hammer suggested (re: a pot between a 4.7K and a 15K for the midscoop control) and what I suggested (re: a cap blend pot):

http://s1130.photobucket.com/albums/m533/mordechaibenzev/?action=view&current=SuperfuzzMidscoopANDtonecontrol.jpg

Sort of a tone control within a tone control.  What do you think?