Super-fuzz signal gating issue

[nate77]

I've recently built a superfuzz on vero and it's is awesome but when the signal drops off it gates the signal. It is almost really col because all intended signal passes (when I'm playing actively) but the signal completely stops shortly after. The sustain is adequate but I cant get any feedback even placing my LP directly in front of my 100 watt Marshall half stack. Is this normal?

[R.G.]

No.

It has a slight biasing problem. See "Debugging: what to do when it doesn't work".

[nate77]

Thanks R.G.  It seems I have to re-read that section every month or so for something new I come across. Is that just a result of one of the trannies closing earlier than it should?

[GibsonGM]

Yes.  You need to take some measurements, do a little modding.

Some people use a pot to bias, so they can adjust the gating and get some of that 60s vintage vibe )

I do fuzzes with a pot while breadboarding, then measure the value on the pot and replace with a fixed resistor when building the permanent version.

If you post a link to the schematic we can tell you which resistor to adjust.

[cortezthekiller]

+1 for gibsonGM

If the version you built has a trimpot for adjusting the balance of the octave, that can be adjusted to add or removing the gating effect. Otherwise, if there is not a trimpot, the two transistors in the octave-generating section you used could be closely matched and be gating the signal while producing a more prominent octave. Hope this helps.

[Canucker]

which diodes did you use? If they are silicone your superfuzz could sound as gross as mine did before I got my hands on some germanium...silicone worked but didn't make it a pedal you'd want to hear to much of.

[nate77]

This is a link to the schematic http://media.photobucket.com/user/denmarc0/media/equipment/effects%20pedals/UnivoxSuperFuzzsch.gif.html?filters%5Bterm%5D=univox&filters%5Bprimary%5D=videos&filters%5Bsecondary%5D=images&sort=1&o=115

There is no trimpot in the layout I worked from. A link to a layout is
http://3.bp.blogspot.com/-gLy8HWE7qQs/TyBDc5__vMI/AAAAAAAAAcg/HiPt_bZl5-w/s1600/Univox+Super-Fuzz.png

To be honest, I almost dug the gating, because it made the pedal so quiet, but it is too much. I wish I was smart enough to adjust this for the gating at a lesser point, so it would be super quiet when I wasn't playing, but I think I may be tackling a g-string decimator soon......... 
Thanks for the help guys. Guitar mike, you've helped me a dozen times, thanks dude.

[GibsonGM]

No prob, Nate, everyone here wants to help everyone else, since nobody can know it all and anyway, it's challenging!!

What you need to do, man, is first - are the diodes germanium or silicon?  Are they the 1N34's called for, do you know?  Did you buy a kit, or use stuff you had around? What transistors, do you know?

2) you have to label the transistors on the scematic (Q1 and so on), match that to the ones on the board, and provide voltages for each of their pins (emitter, base, collector, just use E B C).      Do this with power on but no input signal.    At minumum, do this in order left to right for the ones on the layout (indicate whether you used layout or schematic when measuring).


3) alternative: have someone strum your axe making that gating sound, and use an audio probe to listen to the base and collector of each transistor.  There might be one place you find that the gate starts, pin-pointing which one has a bias issue.   Ex, you might be ok for the first 2 transistors and then find it starting on the third, something like that.   

That's a more complex fuzz than usual, so I can't say "measure this or that on Q2".    We have to dig inside to find the off values.

[nate77]

I used 1n34s for diodes. 2n2222 trannies, I built it on vero from the layout I linked a couple posts ago and I sourced all the parts myself. My friend is borrowing this pedal for a gig this weekend so it'll be a few days before I can measure or probe this thing unfortunately. I'll get this bad boy back ASAP and get some measurements and probe it (2 approaches is better than 1?). Thanks again mike, an yeah, this seems to be an unusually complicated fuzz. Thanks man

[GibsonGM]

I hear ya, they do this sometimes.    PinkJimiPhoton is a fuzz-master - I do them once in a while, not the greatest fan but know how they work.  I like Dist+ gain+diodes distortions.   Anyway, tho, I think an audio probe at bases + collectors could tell you something, plus be good experience for debugging! 

[Canucker]

Did you get those diodes from Tayda? If so then thats it right there. People have repeatedly complained on here about the 1N34 diodes from there saying that they aren't actually germanium....I don't know specific data I just know the specific specs on them but I tried those in a few projects and they did not do what they were suppose to....then I ordered some from SmallBear and it improved the projects I put them in dramatically (Superfuzz and Green Ringer).....did I mention DRAMATICALLY!!!!???!!! Not much else to complain about with tayda but those diodes for sure. 

[nate77]

I did get them from Tayda. I've notice that the j201s and the Ge diodes I've gotten from them are all over the place when I measure them. Personally, I love Tayda because they are super cheap and have great shipping rates, but there is no doubt that some of their stuff is sub-par. There are only 2 diodes in this circuit, would a pair of shitty diodes cause gating like this, though?

[Canucker]

thats funny cus the J201s I got from them weren't even J201's....they were a slightly more expensive item (that I didn't want) put in a package labled J201's....but I only ordered four of them and my order was over two hundred parts so I didn't bother contacting them about it... They are great for shipping and they are fast which are two big factors for me up here in Canada...I've ordered from them 4 times and from SmallBear once which says a lot I guess.

2 incorrect diodes could totally to it...its part of the circuit so its going to play a part in how it sounds. The best part of all of this is you got sound out if your superfuzz and I haven't heard you complain about volume issues or things cutting in and out...so really its a matter of swapping some parts and figuring out which ones....its a pain in the butt when you build a project and you get no sound out of it...I've done that more times then I care to admit!

[GibsonGM]

You could go to Runoff Groove and built the little jig under the Fetzer Valve link to test and label your J201's....worth doing, you can sort them by Vp and Idss for later projects, no more guessing...

[nate77]

I've been kicking around the idea of putting together a Fetzer for a while, so it's definitely time to get this thing done. Having to measure my trannies every time I need a specific range sucks. I'd love to be able to measure them all and sort by value range. How would faulty diodes cause gating? Like my Canadian freind said, it works as it should, no volume issues, etc. and it sounds great but the gating takes away much of the fun of a fuzz. And like you Mike, I'm not a huge fuzz guy, I tend to be obsessed with overdrives and dirty boosts, things like that. I figured that since I've got a few dozen ODs and such that I would see what's up with some classic fuzz circuits. And yeah, it is a better problem than having a pedal that passes no signal, which has also happened to me many times (including this one the first time I fired it up!).

[Canucker]

I'm not an expert on any of this stuff...I barely rank as a novice  I just know how drastically different the results have been for me when using different diodes on projects.....swap them out for silicone and see how different the results are.
My fave dirty boost is the Zvex SHO....I have yet to try out any that I like half as much as that one.

[nate77]

Ge diodes are much smoother than Si, that's for sure. I love the SHO and all of its incarnations. I whipped up a naga viper, which is loosely based off of a classic treble booster but you can alter the range it boosts. It is different but equally as great as a SHO. Give it a shot if you haven't tried it

[GibsonGM]

Well, you can probably fix the gating, Nate.  I've made fuzzes and had them 'stay on' much longer than what you might expect from hearing a 'typical' fuzz.   It's just about tweaking the bias values.  Since the 2 trannies work together (in your case here, more than that!), you have to get a balance.   Some guys really dig these, and spend endless time tweaking.  I'm more into the 'tried and true', don't like those little surprises!

Different diodes can cause gating because Si 'turns on' at about .5v, and Ge at about .3.   You can already see how it takes a larger signal to turn the Si on, and it will also turn OFF sooner.   Its 'ON envelope' (made up term) is therefore not as big as Ge.    If a circuit wants Ge and you put in Si, expect this kind of issue.