Help Please! - Univox Super Fuzz Clone Not Working :(

[krjohnson29]

Hi! I'm new here. I've built ~10 pedals before, always based on a kit or purchased PCB. This is the first one where I've tried to trace out the layout on perfboard. I used this method that I found on youtube:
https://youtu.be/_ypW45Y8VSs

The layout I used was from the effects layouts blog:
http://effectslayouts.blogspot.com/2015/07/univox-super-fuzz.html

I think all the parts I used were exactly as called for on the layout. Because I was tracing it out with wire, some of the traces are not *identical* with the layout on the backside (to make the traces easier), but they should be functionally the same. Also, the electrolytic caps I bought appear to have been larger than what the layout author anticipated (maybe because I bought ones rated for 100V?), and so some were a bit tough to squeeze in, as you can see in the images. Also you'll see that a few of the resistors have their paint damaged. This happened when I was soldering them in because I started soldering on a painted desk surface and when the resistor heated up it must have bonded with the paint somehow. After I noticed what was happening I switched to a better surface, but I measured the resistors and they still seem to be good.

The problem is that it seems the output is WAY too high. Barely turning the knob up seems to nearly blow up my little amp. Definitely fuzzy (as expected), but I'm not sure it sounds exactly correct either.

The readings I'm getting on the transistors are very similar to what I found in another post on this forum, with the exception of Q6C, which was about 2V lower than expected. I checked all the resistors around Q6, and they seem to all ohm out just fine. I checked the 9V rail on the board with the power supply plugged in and it was indeed just under 9V.

I'm not really sure where to go from here... can anyone point me in the right direction? Thank you so much! I'm trying to build this pedal for my dad for father's day, so hoping I can get this figured out and fixed before then.

The transistor voltage measurements I got with my power supply plugged in were:
        C         B         E
Q1  5.32     0.70     0.13
Q2  8.90     5.31     4.72
Q3  5.93     3.51     2.95
Q4  3.16     1.62     1.04
Q5  3.18     1.62     1.04
Q6  3.42     1.14     0.54

I compared to:
https://www.diystompboxes.com/smfforum/index.php?topic=64068.0

Also, please ignore the A500K pot in one of the pictures, it is not hooked up to this board (or anything, actually, at the moment). It's in the picture because I am boxing this board with another effect.

[willienillie]

Schematics are easier to follow that layouts.  A lower-than-expected voltage reading could be meter loading.  A linear taper volume pot will come on very fast, switch to audio (log) taper if it's a problem.

[slashandburn]

Mines was built using that exact same layout, albeit the pcb version rather than the perfboard, so the layout isn't the problem.

>>   The problem is that it seems the output is WAY too high

This circuit seems to like lower gain transistors, 2n5088 might be a bit too hot. I started off with some 2N3904 in mines that measured around 300-350 hfe. Which was great and perfectly usable but ended up swapping in some even lower gain 2N2222 (I think around 200hfe) which seemed to tame it somewhat more.

Also iirc I'm sure I remember reading somewhere that it helps to try to match Q4 and Q5.

[digi2t]

I'm really not impressed with that layout. But, I digress...

Are the lug 1's of the expander and/or balance pots connected to ground (check continuity)? When you say you measured the resistors, did you measure them in place, or removed from the board?

Don't worry about Q6C voltage too much. That fact that it's low is because of the very high gain transistors that you are using. You're in the wheelhouse. Gains for typical Superfuzz transistors tend to be in the 150 to 175 range, and not the 300 to 600 range that the 5088's tend to inhabit. You might want to try 2N2222's in here, it'll sound more open (less compressed) than the 2N5088's.

Upping the voltage on Q6C will only make it louder. The numbers published by Solidhex, he may have had a unit with an especially low gain Q6, hence the high C voltage. I've measured 2SC828's of that era, and they are no where near the typical gains found in 5088's. They tend to range between 125 and 180. You can always tweak this voltage by using a different value resistor in place of the 15K to ground on Q8B. I tend to prefer a 25K trimmer here, and then tune it by ear. I usually end up around the 4 to 5v range.

I see that you have silicon diodes in the clipping section. Wrong. The norm here is germanium. The much lower vF of the germaniums will clip the signal significantly more than silicon, so output will be lower. Silicon diodes will indeed make this quite LOUD! Also, silicon diodes just don't impart the same clipping characteristic where the tone is concerned and will make it sound very harsh, especially when you throw 5088's into the mix. I don't know why 1N4148's were spec'd here. That's just not correct. If you want to mod the germanium clip for more roar, then a 1K or 2K resistor from the diodes to ground may be added.

As slash points out, matching Q4/Q5 pair helps with the octave output. The later units with the 10K balancing trimmer help tune the octave further.

[krjohnson29]

Thanks for your help!

To answer your questions:
1) Lug 1 of both pots read 0 ohms resistance to ground
2) I measured the resistance in place. I've added an image of the layout with a black box around the ones I measured. There is an orange box around the resistor going from Q6B to 9V, that one measured only 35k instead of the spec of 100k. I figured this must be an effect of the transistor, though, because the rings were the same as all of the 100k resistors and there should have been no 35k resistors in my order. All other resistors in the black box measured nearly exactly the spec'd value.



I will get some different transistors on order and try those out. I'll also see if I can find some germanium diodes. Thanks!

[slashandburn]

What digi2t said^^.   Maybe my memory is playing tricks on me but it may well have been his posts on the other forum I was reading when I built mines.

In my own experience measuring components in-circuit will give you some weird results. If the resistor colour codes indicate its 100k and your is measuring 35k in circuit id assume the resistor is fine and doing its job.

Someone smarter than me might be able to give you a more scientific answer that mathematically explains why you're reading 35k instead of 100k.

Also, welcome!

[willienillie]

Gains for typical Superfuzz transistors tend to be in the 150 to 175 range, and not the 300 to 600 range that the 5088's tend to inhabit...I've measured 2SC828's of that era, and they are no where near the typical gains found in 5088's. They tend to range between 125 and 180.

How low is too low, you reckon?  I've never messed with the Super Fuzz circuit, but I like it in demos I've heard.  I have a number of Matsushita 2SC828s left over from my Univibe build, but all P bucket instead of Q, gains ranging from about 60 to 122.  Yes I know it would be better to hit the right gains than use a particular part number, but mojo is mojo.  Also, seems Univox used different transistors at different times, but the schematic I have shows a mix of 2SC828 and 2SC539, not sure why.

Edit: Also, does anybody know which bucket the '539s were?  I'd assume same as Univibe, but I was never able to determine that.