Univox Square Wave fuzz

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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LucifersTrip
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Post by LucifersTrip »

In searching here, I didn't get any hits for "Univox Square Wave" and only one mention of it for "Univox SquareWave" (did I miss something?), so:


...finally got around to building this one.

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The first thing I did was try a bunch of different JFETs. The classic J201 won out. All others gave me a more gated, broken sound.

There were 2 problems. It was way below unity and the fuzz was still mildly gated with too much pick percussion (clickiness) evident. It turned out to much easier fixes than expected. I built two versions:

#1
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Volume problem:
To increase volume, I slowly increased the vol pot. Even at 1M, it was still below unity. So, I added diodes in parallel. Finally it was above unity, but now the distortion (really a tone control...closer to 0K the more bassy) didn't give me a good sweep. So, I simply increased the 27K cutoff to 100K and subbed a 1M distortion pot instead of the 250K. Beautiful! That gave me a nice sweep from just barely too bassy to a nice thin fuzz.

Mild Gating Problem:
Anytime I see an odd small value from an emitter, bass or collector to a rail, I always suspect it to be very sensitive, and it was...I slowly increased from 0K and hit a perfect spot around 2.6-2.8K. The mild gating and pick percussion were gone, resulting in a killer smooth fuzz with super long sustain. It was nearly perfect, but a bit too harsh on the highs. A simple tweaking of the 680 gave me a sweet spot right around 1.8-2.2K. If you raise it much higher, you'll wind up with less power...and around 4-5K will start to gate again. Further, I increased the 2M to 3M, which gave a bit more richness to the higher strings. I tried up to 7M...still good (thicker on the high strings) but I didn't want to take a chance it would change the tone too much.

Here's the final with voltages...It's a pretty loud (will feedback at full) fuzz with a good sweep from fat to thin and killer sustain. It really doesn't sound exactly like many of the other fuzzes. The only thing it slightly reminded me of was a Carlsbro Suzz (v2):

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#2 (cheapout version)
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Volume problem:

Well, there's no cheaper way to increase the volume than remove the diodes...and in this circuit, the diodes don't do nearly as much as others...just a bit more fizz.

I removed the diodes, but realized that if I left one in place it gave more richness to the high strings and killed a little harshness. With the increase in volume, came an increase in bass & boomy-ness. After trying numerous values, I decreased the vol pot to 20K which solved the problem. Like in version 1, I lost a good distortion sweep, so I increased the cutoff to 100K and the pot to 500K. In this case 1M thinned it out too much.

Though I could've probably tweaked the 3.9K and 680, I didn't since there was absolutely no gating or pick percussion with the diodes removed. Also, I built this version first, so I didn't think about doing that, since it was unnecessary.

Image

have a blast

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