I have a '60's Univox Superfuzz unit with some issues.  First the unit had a 10k resistor where a 10u cap should be.  That was between the diodes and the resistor divider for the unscooped tone.   That resulted in the full volume to the unit with the fuzz active being noticable lower than the bypassed volume.

This lead me to the question of which way should the polarity of the caps on either side of the diodes be.  I figure the cap between the diodes and the octive transistors should have it's positive side towards the transistors.  I have seen this oriented the other way around in some schematics.

Second, is the other cap even necessary?  After the first cap the signal is AC.  Ultimately at the far end of this section of the signal path there is another cap with it's positive end facing the base of teh last transistor.  So all DC is already blocked on this section of the signal path.  As I see it that second cap the one between the diodes and the mid notch circiut could just as well be replaced with a jumper.  Just out of curiosity which orientation would be best for that cap?

On to some of the other issues.  I ended up replacing all the electrolytics.   The pedal now has a noticeably tighter more focused tone that is also less organic.  Has any one else experienced a change of tone after recapping a superfuzz?

Lastly, are replace NOS film caps available anywhere for these units.  The 1n cap in the mid notch circuit broke one of it's leads off right at it's base.  I replaced it with a 1n cap I had on hand, although the treble now sounds quite brittle.

Quote from: FredB on September 05, 2011, 09:25:56 PM
I have a '60's Univox Superfuzz unit with some issues.  First the unit had a 10k resistor where a 10u cap should be.  That was between the diodes and the resistor divider for the unscooped tone.   That resulted in the full volume to the unit with the fuzz active being noticable lower than the bypassed volume.

This lead me to the question of which way should the polarity of the caps on either side of the diodes be.  I figure the cap between the diodes and the octive transistors should have it's positive side towards the transistors.  I have seen this oriented the other way around in some schematics.

A good follow-up question is "should be, according to whom?" The general answer is that all electros should have a DC voltage across them so that the combined AC + DC instantaneous voltage never reverses the capacitor. The incoming cap has its + side tied to the collectors of the rectifier transistors, so that's OK.  The outgoing cap has one end tied to the diodes, which alternate above and below ground no more  than about +/- 0.3V, and its other side tied to ground through resistors. It's reverse biased about half the time, but by so little that it probably doesn't do much. That leads to your second question:

QuoteSecond, is the other cap even necessary?  After the first cap the signal is AC.  Ultimately at the far end of this section of the signal path there is another cap with it's positive end facing the base of teh last transistor.  So all DC is already blocked on this section of the signal path.  As I see it that second cap the one between the diodes and the mid notch circiut could just as well be replaced with a jumper.  Just out of curiosity which orientation would be best for that cap?

There isn't one. It ought to be a jumper, a low value resistor, or an NP cap.

QuoteI ended up replacing all the electrolytics.   The pedal now has a noticeably tighter more focused tone that is also less organic.  Has any one else experienced a change of tone after recapping a superfuzz?

Let me address this another way. As electros age, they develop leakage and higher Equivalent Series Resistance, which acts like a real resistor in series with the cap, but one you can't get at to change other than by replacing the cap or adding to it with an external resistor. So if the pedal from - 1968? 1970? - had original caps, they're way past their "use by" date. Some or all of them to varying degrees were leaking and had high ESR. Could the change in bias conditions and added resistance change the sound? Yep. Absolutely.

It change the sound back in the direction of how it sounded when it was first manufactured. I (sadly) suspect that you didn't replace them one at a time, labeling caps with positions and doing listening tests for how the sound changed with which cap. So we're left with something of a conundrum about how the sound changed with respect to what aging defect, and which cap(s) is responsible for most of it.

QuoteLastly, are replace NOS film caps available anywhere for these units.  The 1n cap in the mid notch circuit broke one of it's leads off right at it's base.  I replaced it with a 1n cap I had on hand, although the treble now sounds quite brittle.

Maybe somewhere. The problem is that you don't know that any old NOS cap, even one from the same batch, would restore the tone. The tolerance of those caps was big; 20% was not uncommon for "jellybean" film caps back then. So it may be that dinking with other modern caps in the next few sizes up/down from the nominal that was lost may restore the sound.

Um, if that was really what changed the sound and not the electros.

I'm not trying to be a nay-sayer; it's just that the reality is more complex than you may have considered.

Hey R.G.,

Yes, sadly I neglected to replace the caps one by one.  That will be a good thing for next time.

The change in tone from the electros and the film caps are two separate things.  The electros have a an over all general effect upon the tone:  Tighter more focused.  I did consider that's what the pedal sounded like originally.  The electos that were in it were a mixed bunch, some shinei, some wako, some marked only with an s, and some marked only with voltage and capacity.  All were gray except for one blue one that was physically larger than the rest.

The film cap broke a little while after I had replaced the other caps.  Curiosity got the best of me, and I replaced the 10k resistor between the diodes and the mid-notch circuit.  After that I noticed the unit sounded very muddy.   Zero treble.  That one film cap I had noticed was already on the verge of breaking.  I guess the extra tweaking was just too much for it.

The cap I replaced it with was a pull from an old TV.  It might be ceramic.  It's small and squarish with a J152 mark.  I guess it's 1n5 actually.  I'll order a few proper polyester caps and try them out.

Another interesting thing about this unit is that it has very little octave sound in it.  While I had the board loose I put in on my scope and saw that the two octave transistors must be a little out of proper bias.   I'm considering ordering a trim pot for it.  I read about the Wattson version of this pedal and they also changed the lower bias resistors when they put the trimmer back in the circuit.

Before replacing the caps I had to replace the pots and switch.  The battery snap had been cut.  Apparently some one had tried to wire it up to a AC adapter.  So I replaced the battery snap too.

For your viewing pleasure, here a couple of pics.  As you can see, I already have the jumper installed.  





The old knobs failed to fit on the new pots, so the knobs are new too.  Which is good, because  the silver cap had fallen off of one of the old knobs.

I remember that well. I traced out an identical unity in 1970. It took me about five years after that to understand it, though, and my first clone board for it didn't work. I did my first PCB etch try on a sharpie-marker board that I tried to etch in an aluminum cake pan. Bad mistake. I learned how much more FeCl wants aluminum than copper. Second try turned up a board that never worked. But I kept after it.

I did a version of the superfuzz circuit PCB that DID work in the early 90s, and posted the schemo to the internet. It's still there in the many copies of Leper's archive.

The exact value of the lower bias resistors with/without a trimmer is not super critical. The trimmer in the SF circuit has been hashed over many times in this forum. Search should turn up a lot of entries.

I had never heard of Wattson, but then there are hundreds of new effect companies that come out every month, so I'm not surprised that I wouldn't have.

If you can pick out which cap the 1.5n was, or where it is in the schemo, I may be able to offer some advice.  A ceramic cap might account for the tonal issues, not least because ceramic tolerances are typically bigger than film.

I think I still have the instructions and layout for the board that worked. I'll go look it up.

In this schematic the cap I replaced with the 1n5 cap is circled: 





Any help with the layout would be appreciated.  I've been working on a perf-board layout.  For this: 




My version is fairly close to the original with just a few values things changed, the diode clipping softened, and emitter follower buffers added before and after the classic circuit.

Now I got that one sounding about as good to be fun to play through.  Sound clip:    http://www.mediafire.com/?5w7p99ncvp5m7k0

I'm just hoping I can find someone who would like the original one.

OK, got it. The reason the broken off cap makes things muddy is that the circuit section it is in is a mid-scoop fixed tone control. The cap is what lets all the treble side through, so only the bass comes through with it gone. The value can be adjusted to taste. Film caps work well there, and they don't need to be mystical magic mojo caps. The first transistor and the resistors that touch it are important for low noise. Making those metal film and replacing the first transistor with new low noise type may alleviate some of the hiss I remember.

The hiss is acceptable as it is.  There was more before I replaced the electros.  I kind of liked it.  It gave the pedal a smokey fuzz tone.

Today I installed a 10k trimmer I had on hand.  It was another pull from an old TV or something.   I hooked the thing back up to my signal generator and scope and quickly tweaked to octave engine perfection.

The tone in general sounds a lot better now, with the treble noticeably less brittle.  I have film caps on order as well as a non polar to try.  I might as well cover all the bases while I still have the real deal to play with.

You probable remember what the thing sounds like new.  I was out of diapers by at the time it was made, and might even have been tall enough to look over the counter to see the "Transistor" radio the use to fill our kitchen with that strange noise called music...