Noob-with-breadboard stuff (fuzz)

[thermionix]

So for some time I've been wondering about something in relation to early fuzz circuits.  Seems to me the simplest idea to get distortion is to cascade one gain stage into another.  Think basically LPB-1, gain pot, LPB-1, volume pot, out.  Yet I haven't seen that, and I'm not sure why.  Not saying that nobody did it, just that I haven't seen it so far.  Fuzz Face for example has direct coupling, feedback loop, gain adjusted at Q2e...more complicated concepts than what I'm talking about, though the parts count is obviously minimal.  Maybe the use of feedback helps yield more consistent results from various transistors?  I don't know.

Another purpose of my experimenting today was to see if I could do anything useful with a couple low-hFE AC128s I have, other than a darlington pair.  Can I get useful gain and volume with these just by messing around with resistor values?  Well, turns out I can.  I used no formulas, read no voltages, just plugged parts in until I got sounds I liked.  Added clipping diodes before the volume pot and it sounds pretty damn good.  Not saying "best fuzz ever" but something quite useable for sure.

Here's what I have so far:



Not a finished product by any means, but it only took minutes to come up with this arrangement, and it holds its own with many other fuzz circuits out there.  So surely there is a similar circuit in use somewhere, it's so simple and intuitive.  Seems like the first thing people would have tried when coming up with the first fuzz effects.

FWIW, I initially had a 1M from Q1b to ground, but I liked the sound better after I pulled it.

[thermionix]

So I breadboarded this with my little $5 solid state amp in my workroom.  Just now I took it upstairs to my real amp.  Not surprisingly it sounds better.  Fairly dark, but smooth.  Then I kicked my wah on in front (has FoxRox clone output buffer).  Holy smokes!  Sounds awesome!  Absolutely kills my FF and my BMP with the wah in front.

So what is this a variation of?  Gotta be something.  Might have to box it up as is, but maybe with selectable or variable input cap.

[PRR]

Mosrite Fuzzrite is similar, more feature. Yours depends on leakage, the MFR has base resistors. And it also has a fader to select stage 1, stage 2, or a mix, which makes a mess which may be useful.

http://www.diystompboxes.com/smfforum/index.php?topic=69800.0

[thermionix]

a fader to select stage 1, stage 2, or a mix

The "tone" pot:



I'm guessing it really acts more like a "fuzz" control?  Seems like it would be cleaner adjusted toward Q1, dirtier toward Q2.

[duck_arse]

is it not possible that manufacturers shied away from the vagaries of leakage bias? there are a number of circuits similar layout to yours, but with different bias arrangements and/or an extra buffering Q in front. as for the mosrite, the fuzz/tone pot has inverse signal at each end, so there is a load of complex cancellation effects found along the pot travel.

[thermionix]

is it not possible that manufacturers shied away from the vagaries of leakage bias?

Sure thing.  I was expecting to bias the bases when I started on the breadboard, but I followed my ears and wound up here.  Still I meant the concept overall, slamming one simple gain stage into another for distorion.

as for the mosrite, the fuzz/tone pot has inverse signal at each end, so there is a load of complex cancellation effects found along the pot travel.

Oh yeah, duh, each gain stage inverts the signal.  Is there a point on the tone pot where the signal gets really weak?  Seems like an odd idea.

[PRR]

> Seems like an odd idea.

Yes. So is leak-bias. Run with it.

[Aph]

Knightkit fuzz (1969):

[Ben Lyman]

The Zvex Box of Rock looks a little bit like 4 Zvex SHO's in a row.. not sure if that's a similar idea to what you are referring
http://3.bp.blogspot.com/-kq989pNrtME/TxQ5v0UVl8I/AAAAAAAAAkQ/tQV0VA6M2QQ/s1600/zvex_boxofrock_schematics.jpg

[thermionix]

Knightkit fuzz (1969):

Yeah very similar!

[duck_arse]

Is there a point on the tone pot where the signal gets really weak?  Seems like an odd idea.

I built one to the fffworks schem, w/ B250k for the fuzz/mix [and some added switches], and it's all killer, no filler. no dead/dull/weak/dim spots. my favourite sounding fuzz built so far.

[thermionix]

I've thought about it, after hearing some clips on youtube.  Seems like a cool fuzz.  Any particular transistor specs that work best in the fuzzrite?

[duck_arse]

I'd say no, but I'm sure others would say yes. mine has a pair of 2SBsomethings, I didn't even mark the gains on my drawing, both between 60 and 120 128 and 140 hFE's.

[edit :] antonis nagged me.

[antonis]

[and some added switches]

<NOT ENOUGH DATA>     

[duck_arse]

switch one selects R1, 10M or 470k. switch two selects C5 2n2 or 47nF. Q1 is 2SB324 hFE 128/330uA leak. Q2 is 2SB175, hFE 140/250uA. [via the Keen method, but I'm not 110% on those leaks.]

[thermionix]

Well, this is happening.  Smaller input cap cleared up the mud, and this is a very usable Ge fuzz.  Kinda plain vanilla, but nice.  Ordered some 16mm pots and a SPDT on-off-on from The Bear last night.  Switch will parallel input caps for tonal options, still need to experiment on the BB to settle on which values, but I have time.  Months ago I built a DOD 250 clone that has been collecting dust since the new wore off, so I'm gonna yank that board and build this in that enclosure.  Cheap.  I'll keep the 250 board and pots together, in case I want one again in the future.  This will be my first "original circuit" build, if anything this simple can be called an original circuit.  At least it isn't a clone of anything, I'll put it that way.