Univox Super Fuzz Modded

[FredB]

Here is the story of a Super Fuzz I modded:

Univox Super Fuzz Episode 2 - YouTube

And some miscellaneous sound clips:

Univox Super Fuzz Episode 2 Misc Clips - YouTube

I have a question for those who have some to do with these pedals, that is which diodes sound the most organic? This last pedal had OA90 diodes that were marked as such and sounded less organic than I would like. The first pedal I recapped had unmarked diodes that actually sounded pretty darn good. I have tried 1N34A diodes and they sound OK, although they still sounded a bit light and fizzy.

[Mark Hammer]

These units distort with or without diodes. I recently sold one I had made with a switch that selected silicon, germanium, or no diodes. The no-diode setting was much louder, as you can imagine, but still had lots of distortion, just less buzz.

The forward voltage of the diodes selected determines the clipping threshold, but also the maximum output volume. Since the diodes"clamp" the maximum output level, lowering the threshold will appear to impose more consistent signal level and compression. LEDs will yield less additional clipping but higher output level than silicon, and silicon less clipping and more output than germanium, and Schottky falls below germanium. You can dicker with combiations of diodes since their forward voltages are additive. E.g., two germanium diodes with forward voltages of 273mv and 327mv, in series, yield a forward voltage of 600mv.

I have no idea what you mean by "organic". Kind of an under-specified term.

[FredB]

The original unmarked diodes in the one unit sounded more tube like in distortion, less like symmetrical diode clipping. Perhaps the forward voltage in the pair was off a bit, so the clipping ended up being asymmetrical.

Organic, its hard to describe, it's kind of like going from silicon to germanium, where the clipping is softened, sounding less harsh and even. In this case the difference was between two types of germaniums. I have some more germaniums on order so I can compare them too.

Adding in some serial resistance to the diodes also made the unit a little louder. I noticed the input section is somewhat like a Fuzz Face, and that it was well into clipping at only a 300mv input signal. Rebiasing there also changed the character of the pedals tone.

I've tried Schotty diodes in my bread boarded Super Fuzz, they sound harsh. The germaniums just have a smoother sounding clipping I suppose with more noise in the midrange frequencies that make the clipping sound a bit richer then silicon diodes. Attempting to soften silicon or Schotty diodes with some serial resistance fails to really change the very even sounding clipping. So, I suppose organic means more fuzzy rather than buzzing clipping.

These units distort with or without diodes. I recently sold one I had made with a switch that selected silicon, germanium, or no diodes. The no-diode setting was much louder, as you can imagine, but still had lots of distortion, just less buzz.

The forward voltage of the diodes selected determines the clipping threshold, but also the maximum output volume. Since the diodes"clamp" the maximum output level, lowering the threshold will appear to impose more consistent signal level and compression. LEDs will yield less additional clipping but higher output level than silicon, and silicon less clipping and more output than germanium, and Schottky falls below germanium. You can dicker with combiations of diodes since their forward voltages are additive. E.g., two germanium diodes with forward voltages of 273mv and 327mv, in series, yield a forward voltage of 600mv.

I have no idea what you mean by "organic". Kind of an under-specified term.

[Mark Hammer]

Gotta say, I'm not a big advocate of different diodes having a different character. Yes, they have different "knees" when it come to conducting, but those knees occur at the sorts of frequencies well above those which interest us as guitar players. That a given diode could switch at 500khz but not nearly fast enough at 800khz or 1mhz is pretty much moot for me.

AFAIC, audible differences between diodes stem almost entirely from the shift in forward voltage and the impact that has on both what proportion of the guitar signal ends up being maximally clipped (because it isn't all above clipping threshold), and what sorts of levels can be produced to push subsequent stages (including the amp itself). The symmetrical/asymmetrical thing only matters up to a point. Beyond that all you really have is hard-clipped positive and negative half-cycles with different amplitude levels, and below a certain point, you don't have ANY asymmetry.

[FredB]

I'm thinking the shape of the VI curve might have some effect on the tone of the clipping. An angular VI curve I presume would sound more harsh and unpleasant than a gently curved one.

[Mark Hammer]

Those curves do not occur at all frequencies from what I understand, and are essentially non-existant for guitar signals.

It's a bit like slew rate in op-amps. It matters, sort of, if you have a very busy audio signal that needs to be responded to quickly and have more than a little bit of gain applied to it. But for guitar, nothing over 1v/usec ihas any audible consequence, and even that is probably pushing it.

This is a perennial problem with people applying stuff that makes perfect sense in the realm of high-end audio reproduction, but has no impact whatsoever when it comes to the guitar context.

Changing diode type WILL make things sound different, and that's a reason to play with them...just not for the reasons that people think.

[s500]

Hello I'm new here and have a question for you guys. I'm not meaning to hyjack your thread by no means. I do not have the amount of knowledge with these superfuzz pedals as you guys apparently do. I was wondering if maybe you can shed some insight on a problem I'm having with an early model, I believe it's a U-1093 Grey Box. When the tone switch is on the number 2 position, it appears to work exactally as it should, but when switched to the number 1 it does not sound like it use to. The fuzz is very weak and hollow sounding. It use to sound real deep and thick. It does not have that Octave ring modulation it use to have either. Do either of you have an idea what is wrong and what do you suggest the best way is to correct this.

[FredB]

I would check to see if any of the leads for the components have broken, especially the the green caps. If one of the wires on those caps in the mid scoop circuit breaks it can cause just what you are describing.

It could also be something else, which would be hard to pin down without going through the circuit with a signal generator and scope to see where the problem is.

[s500]

I did find that the wire on the tone switch for that circuit broke when I pulled the switch out to clean. It wasn't soldered on very well. I resoldered it but the problem is still there. I will pull the board and inspect the underside for anything that might be visible. Maybe I'll get lucky and it will be something simple. Thanks for the tips I'll keep you posted.

[Mark Hammer]

It's an old pedal. Switches can go wonky with the passage of time and extended use, from loosening and poor contact, or from tarnish of the contacts. The best test of that is to desolder the wire on the side of the switch that is presenting the problem, and simply connect it directly to the output (common) lug of the switch. If you get your sound back, then obviously the problem is the switch. If you don't get it back, then the problem may lie elsewhere in the tone circuit (e.g., cracked trace on the board)

[dumbassbob]

even a little Deoxit on the jacks and some contact cleaner doesn't hurt.I live at the beach and need to do it to everything in my studio...

[s500]

It's an old pedal. Switches can go wonky with the passage of time and extended use, from loosening and poor contact, or from tarnish of the contacts. The best test of that is to desolder the wire on the side of the switch that is presenting the problem, and simply connect it directly to the output (common) lug of the switch. If you get your sound back, then obviously the problem is the switch. If you don't get it back, then the problem may lie elsewhere in the tone circuit (e.g., cracked trace on the board)

That's not a bad idea. I've already re-soldered the wire that is on the side which is presenting the problem back on to the switch. When I removed the switch it just fell off with minimal movement. Don't know if it was like that from the factory or if someone had done work on it but it was only holding on by a strand of wire. I could probably test your theory by using a short jumper wire to the common lug without touching a soldering iron. This pedal is old and is in like new condition and supposedly has had very little use which is very obvious by it's appearance. I've cleaned the switch, pots, and jacks with Deoxit twice so they are probably as clean as there going to get and they all feel nice and tight, they don't have that sloppy worn out feel.

[FredB]

There's little underneath to go bad. If the pedal is in good condition otherwise, I would expect the problem is in one of the wires, leads, or moving parts such as the switch, or pots.

With the last pedal I worked on I found out there are actually three different board versions for the '68 model. Any chance you could post a pic?

[s500]

There's little underneath to go bad. If the pedal is in good condition otherwise, I would expect the problem is in one of the wires, leads, or moving parts such as the switch, or pots.

With the last pedal I worked on I found out there are actually three different board versions for the '68 model. Any chance you could post a pic?

I've read that before but I have no idea which one mine is. If I was to guess I'd say it's probably a later one. I think the early ones had the brown caps were as mine has the green ones. But I'm only guessing.

One other question, is it safe to use a 9V DC power supply with these old pedals. I've read that they actually supply higher voltage than a 9V battery even though there called a 9V power transformer.

Actually I just checked the 9V battery that I was using which was new and the multimeter is reading 8.70V. I got a fresh 9V and it's around 9.5V. I also checked the 9V DC power Transformer supply and it's 9.5V so I guess I answered my own question.

The other thing I noticed is that the Balance pot starts out on 10 fully to the left and as I turn clockwise it increases to a maximum of 18 then starts descending to 0 by the time its all the way to the right. This is with the ohm meter set on 200K. When the pot is turned to the right side of 18 it appears to have a heck of a lot more volume. When turned to the left of 18 has less volume. It increases and decreases in smooth even increments. Is this pot operating the way it's suppose to for this pedal.

I did pull the board and can see nothing out of the normal. Soldering looks good and no loose wires. I even did a continuity test or all the wires and it was all good. Tested the Switch with a multimeter and jumper wire and it's working like it should.

[FredB]

It looks like you have the same board that was in the one I just worked on. It's the middle board as far as I can tell. There were three, the first had cutouts for a trimpot and some came with a trimpot and some came with jumpers, the second like the one you have is just like the first except without the cutouts for the trimpot, the third, is without cutouts for the trimpot and all the wires attach to one side of the board.

Looking at the schematic it appears you could measure the expander in circuit because it's DC isolated from both transistors to which it's connected. It's probable a 100K pot, although it might be a 50K. The main thing with the pots is if they sound scratchy when you turn them. That would indicate that they are worn.

The switch if the first unit I worked on was so badly worn I had to giggle it quite a bit in order to get it to make contact, and the pots were very scratchy. So, I replaced them all.

Oh, by the way, does the switch on the input jack actually cut the battery off, or has it been wired closed all the time. It appears in your photo that both leads of the battery snap are connected to the expander pot. So I'm guessing that the switch in the input jack is a normally closed one, that is useless for cutting off the batter when the plug is pulled out. The one I just worked on was like that. I wonder how many they made that way, hundreds, thousands???

Oh yes, and the green caps were the older ones.