Problems with an piggyback fuzz using an IC and Induction's Javelina schematic

[Chris S]

I built a piggyback fuzz face using Induction's Javelina schematic.

Instead of using four 2n3904's I used one MPQ3904.

I did this for no other reason than the joy of trying to get a Germanium sound from an IC.

It sounds good but...
1. There is a whine when I turn the fuzz all the way up. Would boxing this completely cure this? (its currently in a cardboard box)? Will increasing the cap between base and collector on Q2 help this? Any wires that i should avoid having too close together? Anything else I should try?

2. The fuzz and drops off sharply when a single note rings, kind of like a noise gate. I'm not sure what to tinker with. I have played with the bias but the problem is there from 0 to 5k. This is the main problem as I can live with the fuzz at 90%

3. What should I do with pins 4 and 11 on the IC?

Also any other advice on why this idea was always doomed welcomed!

Thanks!

[chuckd666]

1. A whine sounds more like something from a badly filtered power supply rather than something with those two 100pf caps. They're there for high end roll off.

2. Sounds like something to do with bias... I can't help you cause I'm dumb.

3. They're not connected to anything but each other, so I suppose you could use it as a jumper if needed.

[robthequiet]

Noise and such are typically better when the pedal is boxed, depending on what the cause is. What kind of voltages are you getting on your collectors?

Datasheet says pins 4 & 11 are n/c.

[Chris S]

Thanks Chuck and Rob. Fixed all the problems... A faulty 5k bias pot. All fixed and one working IC fuzz that gets me closer to Hendrix tones than anything else I've owned / built.

[chuckd666]

Well done!

[pinkjimiphoton]

I built a piggyback fuzz face using Induction's Javelina schematic.

Instead of using four 2n3904's I used one MPQ3904.

I did this for no other reason than the joy of trying to get a Germanium sound from an IC.

It sounds good but...
1. There is a whine when I turn the fuzz all the way up. Would boxing this completely cure this? (its currently in a cardboard box)? Will increasing the cap between base and collector on Q2 help this? Any wires that i should avoid having too close together? Anything else I should try?

2. The fuzz and drops off sharply when a single note rings, kind of like a noise gate. I'm not sure what to tinker with. I have played with the bias but the problem is there from 0 to 5k. This is the main problem as I can live with the fuzz at 90%

3. What should I do with pins 4 and 11 on the IC?

Also any other advice on why this idea was always doomed welcomed!

Thanks!

this is cool as hell. i did something barely like that a few years back fudging up err... working up the suzy q overdriver. if memory serves (hazy) i had a ge and a mosfet piggybacked. i think it was a ..... shoot. i forget... vpn2222 or something like that? with the right combo of a germanium and the mosfet you can really get a stupidly tube like kinda sound.

i think i may try this one out, it looks really cool!!
rock on man

[Chris S]

this is cool as hell.

Thanks Jimi! High praise from a legend. Would love to see you morph this into one of your awesome creations. I changed the output cap to 47nF and the small caps between bases and collectors to 47pf. Otherwise it's all the same. The resistors between the emitors let you control the HFE values (I'm sure you knew that). Apart from the fun of getting the germanium sound from an IC I think i read somewhere that ICs tend to have more consistent values than transistors so hopefully it'll mean that one schematic will work for everyone rather than playing for hours with various resistor values.

[287m]

errr, OOT

can we use that MPQ to build something like Big Muff Family?
just think because that MPQ have 4 NPN. hahaha

[Chris S]

In theory yes you can, although I dont think 2n3904s are preferred transistors for muffs.

[duck_arse]

if it has more than three transistors, chances are digi2t has done it with an array. and veroboard. see here, search for others:

http://www.diystompboxes.com/smfforum/index.php?topic=106531.0

[287m]

woohooo
thanks Chris and Stephen, so just search for MPQ**** high hfe then?

[pinkjimiphoton]

this is cool as hell.

Thanks Jimi! High praise from a legend. Would love to see you morph this into one of your awesome creations. I changed the output cap to 47nF and the small caps between bases and collectors to 47pf. Otherwise it's all the same. The resistors between the emitors let you control the HFE values (I'm sure you knew that). Apart from the fun of getting the germanium sound from an IC I think i read somewhere that ICs tend to have more consistent values than transistors so hopefully it'll mean that one schematic will work for everyone rather than playing for hours with various resistor values.

i'm just a dude bro, no legend here, believe me!! i look forward to getting down to my bench again soon... had a stroke last new years and a brutal gigging schedule so it's been a long long time since i built anything really. mostly just guitars these days more than fx or amps.
but thanks for the kind words. i believe this project is worth playing with, it looks wicked wicked cool!

[pinkjimiphoton]

In theory yes you can, although I dont think 2n3904s are preferred transistors for muffs.

they sound great in big muffs. some will sound better than others. i've built big muffs out of all kindsa weird stuff. jfets, mosfets, germanium, silicon, you name it. even a quad opamp at one point. the only one i kept has completely mismatched transistors, there's a 3904 in there, some npn ge, i think a 5088 and a vn2222 mosfet even. it's pretty hip. i would suggest just slapping in some sockets and paying no attention whatsoever to anyone else and just put stuff in until it sounds good to you.

3904's can make a real nice fuzz despite being bog standard ubiquitous parts.
so i'd say... hell yeah

[induction]

Hi Chris. I'm glad you got some use out of the schematic. I have a few questions, if you don't mind my curiosity:

1. Did you measure the hfe of the transistors in the array? If so, what were they?
2. Did you experiment with the combined hfe of the piggybacked transistors?
3. Did you end up using the same piggyback resistors that I used, or did you change them?
4. What hfe's did you end up with?
5. Did you fine tune the bias pot to your preferred range? Do you find the external bias control to be useful?

[Chris S]

Hi Induction,

1. No - I don't have a multimeter that measures HFE I've looked at building a circuit that does that (I think I saw that somewhere once) but thought I'd just build it to see if it works before fine tuning.
2. No. Just went with pairing the transistors which made the layout simplest.
3. Used your piggy back values (82k & 220k) and liked the sound enough to keep them for now, but I have socketed them. I'm also a fuzz novice so I'm not entirely how a too high or too low HFE transistor in either Q1 or Q2
4. See 1. Sorry.
5. The bias pot didn't seem to make a huge change, which made me wonder if I'd wired it up wrong. Didn't get that Miss biased fuzz sound. But there was a point that sounded smoother than others.

The only major change I made was lowering the output cap to 47nF. I found it cleans up nicely with my childs child size strat (no bleed cap) but not so nicely with my guitars both which have treble bleed caps in them.

Sorry that's a lot of writing and very little useful information for you. Thanks for sharing the original schematic! If I do measure the hfes i'll post here.