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Unicord / Univox Super Fuzz - modifications

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Unicord / Univox Super Fuzz - modifications

Postby maz » December 22nd, 2019, 2:34 pm

Hi people,

It's been a long time since I didn't post but here I am with a great circuit, the legendary Univox Super Fuzz :D

Recently I built that fuzz on vero board and was so amazed with the result, from the very first notes I heard it was like, I HAVE BEEN LOOKING FOR THIS SOUND FOR ALL MY LIFE !! So I thought about sharing my experience with you.

It all began after hearing a sound clip on youtube



ref: https://www.youtube.com/watch?v=4DUiUObY5SQ

Ohhhh man the sound of that crazy octave fuzzy godness !! :shock: It was a must for me, I had to built this pedal as soon as possible !

Since I was very excited to hear this baby, I looked on the internet to find an already made nice vero board, which I quickly found -> http://tagboardeffects.blogspot.com/201 ... -fuzz.html

As I was lookng at this vero layout, trying to figure out the schematic in my head, the first thing I had in my mind was this circuit, even if it looks more complicated than a traditional fuzz, remains quite easy to built, and I probably have all the parts to give a try, so I did..

..Then after only an hour, here it is. I must say that I'm very happy with the sound, I really love the normal setting side, I mean the one bypassing the mid scoop filter, so I let this side 'as is'. On the other hand, the mid scoop setting is nice but maybe a little limited, so I thought about some modifications.

I first tried to add a B10K potentiometer between that 0.1 uF capacitor (mid scoop filter) and the ground.. it was much better but I wasn't totally satisfied, then I went on replacing the switch with another B10K pot, didn't like the result at all, makes too little change from one side to the other and I'm not sure it keeps the original settings, so after some more googling I finally found my way, the best solution is to wire a smaller-value capapacitor in parallel with the 0.1 uF (I end up using a .022 uf), both caps are then connected at one end to the junction of the 10k and 22k resistors. At the other end, each cap are connected to an outside lug of a B10K pot, then the wiper of the pot goes to ground. Rotating the pot in one direction or the other makes the series resistance for one cap higher and the other lower, this yields two different flavours of mid-scoop and variable midlift. Thanks to Mr. Mark Hammer for this great mod, that's the way to go :great:

Also while playing on the mid scoop side, especially at some sound settings (using my new mid control pot) 8-) I found the bass frequencies being too much, so I thought about a switchable bass cut (high pass) filter and found that by using a 0.033 uF capacitor in serie with the signal I can reduce that excess of bass exactly where I want it to be, you can experiment with other capacitor values like 0.01 0.022 or 0.047 uF, again that will be only effective on the mid scoop side, all the mods won't affect the other side.

Image

Univox / Unicord complete schematic with modifications

Transistors gain / voltages :

V+ = 9.03 - ( 8.86 because of the schottky diode voltage drop )
---------------- hFE ------- C ---------- B --------- E
Q1 : 2N3903 - 119 ----- 5.82 ----- 0.716 ----- 0.106
Q2 : 2N4123 - 95 ------ 8.86 ------ 5.82 ------ 5.17
Q3 : 2N3904 - 150 ----- 5.98 ------ 3.5 ------- 2.88
Q4 : 2N3903 - 123 ------ 2.4 ------ 1.8 ------- 1.17
Q5 : 2N3903 - 123 ------ 2.4 ------ 1.8 ------- 1.17
Q6 : 2N4123 - 73 ------- 4.77 ----- 1.06 ----- 0.417

Note : All voltages have been taken with the trimpot centered (in the middle position).

Diodes:
Germanium (unknown taken from a crap pcb), was about 0.262 V

Note about the B10K trim pot, which is there to (un)balance Q4 and Q5, but also to adjust how much octave effect will be blend in the sound : I first tried to adjust this sucker with the scope, as shown in this video -> https://www.youtube.com/watch?v=uH5Tt30BaBQ , but I wasn't satisfied with the sound coming from the perfectly balanced waves, then I went on adjusting it by ear, spent a lot of time only on this trimpot, then I finally found the best way, I realized that I have to listen carefully by using headphones, if you pay attention at some point you can hear a kind of high octave blending in the sound, yeah the sweet spot is right there. On the scope one wave is slightly unbalanced from the other, on my circuit it is just slightly back from the center on the trimpot. Also it is more convenient to inject some signal (sine wave), that way this high octave I'm talking about can be catched much more easily.

UPDATE - Jan 6th 2020 :

Even if I like pedals with as little noise as possible, I'm not a big fan of gated fuzzes so I just wanna report the final trimpot adjustment I did on the Univox Super Fuzz.

Below is the circuit on its final test :

Image

The transistors :

Image

I really prefer the sound with the trimpot adjusted that way, I would say between 1 and 2 o'clock, now it's much more 'open' with a 'very little' gate effect, the sustain is far much better, to my ears it sounds closer to the original right now, I would be curious to check some of them on the scope, maybe unbalanced's better, I played for about an hour with the trimpot adjusted that way, I'm so much amazed with the growl the fuzz is able to scream, I'm freaking in love with it! :love:

The only bad is that the circuit has more noise that way (while not playing), but it's not yet inside an enclosure so I think it will be good.

Image

Unknown germanium diodes :

Image

I'll be back soon with some sound samples

That's it !! It's a great fuzz, with those 2 little mofifications now I love both sides of the switch, I can barely say which one I prefer. To me, this is a keeper for sure !! :D

Happy mods all !!
All together, bigger we can be!
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maz
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