Univox Superfuzz and its pots

[tjdracz]

Hi there! I've built Univox Superfuzz some time ago as my third fully working circuit (after Big Muff and Fuzzrite which are both amazing). I've been mainly playing around with Fuzzrite I've boxed but decided to fire up Superfuzz for some over the top sounds. But before I box it in, I've got a question about the controls, especially the Expander pot. I understand it's a gain control but it doesn't seem to be doing much. I mean it's working, you can hear subtle difference as the pot turns and the signal cuts out at the CCW position as it should but it's not really big change from everything cranked up to 11 and 12'o clock position and so on. Searched around this forum and the Internet and it seems that other people reported the same problem (feature?) and Superfuzzees in the video demos I've seen on youtube also behave in that way. YET, I've also seen messages from people that insist the Expander should be doing much...
So... what's the consensus? I love the sound of the effect, it fuzzes alright, the tone scoops up with the switch, all seems fine. Just wanted to check whether I made a small mistake somewhere that affects the Expander.
BTW, it was built from IvIark's vero layout: http://tagboardeffects.blogspot.co.uk/2012/01/univox-super-fuzz.html Trannys are 2N2222a's and both pots are Alpha's B50K's

[cortezthekiller]

From my experiences with the superfuzz circuit the stock linear pots bunch up most of the gain/volume at the beginning of the rotation.
Perhaps use audio 50K pots, they would even out the perceived changes.

[tjdracz]

From my experiences with the superfuzz circuit the stock linear pots bunch up most of the gain/volume at the beginning of the rotation.
Perhaps use audio 50K pots, they would even out the perceived changes.

Thought so. Should have A50K from my ill-fated Percolator build. Will wire it up tomorrow and see how it goes.
Anyone else care to comment about their experience with the circuit?

[muehring]

Did you try the A50K pot yet?  I'm building one of these now using the sabrotone layout.

[Mark Hammer]

Some of the sound comes from everything that is before the diode pair, but as long as the "Expander" pot is up even a little bit, you end up pushing those diodes into clipping, and that tends to homogenize the sound, such that 11:00 isn't much different from 1:00 or 3:00.

The good news is that the unit will still yield interesting fuzz tones without those clipping diodes.  They won't be as intense, but they will be loud and are most definitely fuzz.

I sold off one a while back that had a 3-position toggle for germanium diodes, silicon diodes, and no diodes.  Other sorts of diode configurations are certainly feasible and musically valid.

[muehring]

Thanks for the info!  I did see some super-fuzz builds with diode switches.  The power starve pot seems like a good addition too to dial in the octave. Blondegraeme has a youtube video using it.
I noticed the vero layouts don't include a trimmer on the board like the originals.  Anyone know why that is omitted?

[Mark Hammer]

It varied from issue to issue.  If the other components are well-matched, thr trimmer isn't needed.  On the other hand, using the trimmer can sidestep the need to match the components.  But, while not essential, it's handy for getting a more noticeable octave-up.

[tjdracz]

Did you try the A50K pot yet?  I'm building one of these now using the sabrotone layout.

I did and I wholeheartedly recommend using log pot there. Now it's actually doing something and you can dial in more tones. Some subtler ones too and that over the top fuzz is there for you at the end of the pot turn. Do it! Also, out of curiosity, what transistors are you using? I tried 2N3904 but settled on these metalcans 2N2222A. Much smoother and nicer sound overall.

It varied from issue to issue.  If the other components are well-matched, thr trimmer isn't needed.  On the other hand, using the trimmer can sidestep the need to match the components.  But, while not essential, it's handy for getting a more noticeable octave-up.

I am also interested in this trimmer pot, Mark. As I understand from the schematic, it is placed between the two 22K resistors from the bases of Q4 and Q5 and when  it is omitted, they just go straight to the ground. So just to double check, is wiring it like shown below correct? Sorry for the shoddy paint edit. Basically I just moved the 22K ends from the ground rail to free rail below, insert a trimmer legs 1 and 3 on this rail with the cut inbetween so it does not short and leg 2 goes to the ground. Hope that's correct.

[tjdracz]

Actually... do I need trimmer at all? I mean I understand that matching components refers to Q4 and Q5 here and 22K and 100K transistors connected to base of each, right? I am pretty sure that mine Q4 and Q5 were pretty much the same hfe (216 or so +/- 1 difference) and all transistors are metal 1% ones so...

I checked voltages and they're exactly the same on both Q4 and Q5. Actually there was a miniscule solder bridge that I had to clear and now it's way better.
But comparing to Superfuzz voltages posted elsewhere (http://www.diystompboxes.com/smfforum/index.php?topic=64068.0) I notice two major differences.

My voltages:
Q1
5.36
0.69
0.14

Q2
9.03
5.36
4.79

Q3
6.06
3.26
2.93

Q4&Q5
3.26
1.58
1.03

Q6
3.66
1.14
0.54
All C,B,E top to bottom, naturally.

Now Q6's got nowhere near as high collector voltage as one specified above. Any tips here? Transistor with another hfe? Some resistor swapping? Am I missing the secret mojo?

The other thing that's concerning me is Q3 and quite a low difference between B and E there <0.5V. Should I be worried? Panicking even? 

[muehring]

Good to know about the expander pot, thanks!  I'll try the A50K there.  I have mine all wired up now except for that pot because I ran out of log and lin 50k pots.  I have both coming in the mail.  I used 2n2222 metal can transistors too.  From other build reports I read it seemed like those were the favorites.  I'll let you know how it goes once the expander is wired up.

[tjdracz]

Good to know about the expander pot, thanks!  I'll try the A50K there.  I have mine all wired up now except for that pot because I ran out of log and lin 50k pots.  I have both coming in the mail.  I used 2n2222 metal can transistors too.  From other build reports I read it seemed like those were the favorites.  I'll let you know how it goes once the expander is wired up.

It is definitely worth it. It made my Superfuzz go from kind of one-trick-pony to an actually usable and cool little pedal capable of achieving really a lot with some pots fiddling + equalizer + guitar volume & tone. Possibilities are limitless! Might just try to tweak the base to ground resistor from Q6 and see how it changes the tone. Good luck with your build!

[tjdracz]

Good to know about the expander pot, thanks!  I'll try the A50K there.  I have mine all wired up now except for that pot because I ran out of log and lin 50k pots.  I have both coming in the mail.  I used 2n2222 metal can transistors too.  From other build reports I read it seemed like those were the favorites.  I'll let you know how it goes once the expander is wired up.

Mate. Tweak the voltages. You should do it. No, you MUST do it. I replaced the Q6 15K bias transistor with 12K (11.90 to be precise) to get more voltage and WOW! Just WOW! Now it's something like:
Q6:
C      B     E
5.56 0.93 0.34

Don't get me wrong, it was pretty great effect before but now it is THE one. Scooped mids tone is now tighter, with more clarity and the other tone's got more meat and balls. I strongly recommend this little modification (unless you use some low hfe ~40 for Q4 but with metal cans 2n2222a, you probably got them all around 200-220). Now to the enclosure it goes! Might actually wire the tone switch as a footswitch instead of a toggle one to be able to change them on the fly for some crushing unexpected mayhem sounds.

[muehring]

Thanks for the suggestion.  I'll compare my voltages to yours and see where I'm at.  I'm hoping my parts order arrives tomorrow.  Post some pics of yours when you get it boxed up if you can.

[muehring]

So, I finished wiring this up over the weekend and have been messing with it the past couple of days.  I'm not sure it's working quite right.  It sounds like a superfuzz, but I feel the gain is a little weak for a fuzz and there's not much sustain with it.  When sustaining the notes seem to die out like with a dead battery.  My voltage readings look like they're in the right ranges.
Q1
5.5
0.61
0.07

Q2
9.48
5.55
4.93

Q3
7.47
2.70
2.05

Q4&Q5
5.54
1.36
0.77

Q6
5.70
1.00
0.39
All C,B,E top to bottom

Any thoughts?  How's the sustain on yours?

[tjdracz]

So, I finished wiring this up over the weekend and have been messing with it the past couple of days.  I'm not sure it's working quite right.  It sounds like a superfuzz, but I feel the gain is a little weak for a fuzz and there's not much sustain with it.  When sustaining the notes seem to die out like with a dead battery.  My voltage readings look like they're in the right ranges.
Q1
5.5
0.61
0.07

Q2
9.48
5.55
4.93

Q3
7.47
2.70
2.05

Q4&Q5
5.54
1.36
0.77

Q6
5.70
1.00
0.39
All C,B,E top to bottom

Any thoughts?  How's the sustain on yours?

Sustain seems fine on mine. I can make some demo sound of mine so you can compare it to yours. Also there is definitely a volume drop compared to when bypassed if thats what you mean. Also Q3,Q4 and Q5 collector voltages seem to be bit high on yours but I've got no idea on proper transistor biasing here so I guess you should wait for some of the forum gurus to chime in

[muehring]

Yeah, they do seem a tad high.  Thanks for pointing that out.  I'll start troubleshooting there.

[tjdracz]

Here's how mine sounds. Excuse sloppy playing and sound quality, it was amp miced using some microphone that came with my ancient reel to reel. All recorder with my Strat using middle+bridge position. Expander and balance on full, playing roughly the same thing using both tone control positions. As you can hear, there is plenty of sustain there. Then you can hear how turning expander knob up and down affects the sound, then there is the same thing with balance and at the end, I'm trying to show how does the guitar volume control work with the Superfuzz. Mind you it's not boxed and no wires are screened yet so its probably picking up a fair ammount of unwanted noise.

http://audiour.com/2sl0klmp