Why aren't there more one transistor fuzzes out there?

[jm22]

Full disclosure, I am very new to pedals, and I'm trying to discover some of the fundamental principles of fuzz circuits. I was curious, so I googled one transistor fuzz. There were a few results, but I was unable to find information of the kind I was looking for.

My questions are, why are one transistor fuzzes so uncommon? What is the main limiting factor in a one transistor fuzz that might explain why they're not more common?

[antonis]

One transistor can only be an awfully overdriven distortion effect, if pushed to its limits - which ideally are 20 times power supply voltage..
Even with NFB applied, it's still a single stage amp so the term "overall feedback" is of no meaning..

[toneman]

put several transistor clipping circuits in PARALLEL and run their individual outputs into a resistor mixer. 1 tranny for final output. Could have a preamp tranny 2.

kinda like the PAIA QuadraFuzz....but NO opamps!!

[R.G.]

One transistor fuzzes often don't have enough gain for modern tastes. So one-transistor setups tend to get distortion by biasing  near saturation or cutoff, a different kind of nonlinearity.

[idy]

Do "electra" style count, one transistor and diode clipping?

[Bunkey]

One transistor fuzzes often don't have enough gain for modern tastes. So one-transistor setups tend to get distortion by biasing  near saturation or cutoff, a different kind of nonlinearity.

This.

The sound depends of course on how you're actually clipping the signal - whether its transistor clipping or diode clipping.

The fuzz effect relies on square waves to sound fuzzy. A single transistor can't amplify the signal enough to generate a nice square wave, so typically the input signal is boosted by a first transistor stage and that larger wave gets fed into a second transistor stage, making the resulting clipped wave much more square. ie. Fuzz Face

From my limited experience designing circuits, mis-biasing a single transistor to achieve the same thing just doesn't sound very musical - It destroys a lot of the guitar's tone and natural harmonics and turns it into a monotonous noise. You can also end up in a situation where you build something that sounds ok on a guitar with high output pickups played loudly, then you roll the volume back or plug in something with low output single coils and the thing just sounds pants or doesn't work at all; which obviously isn't acceptible for a commercial pedal that has to work with all sorts of guitars.

Diode clipping can give better results on a single transistor because the transistor can be biased properly to retain the guitar's tone but it'll only lightly clip the signal (clipping a 4.5v peak to 0.7v as a common example) and the volume from the pedal will be limited to the diode used - a lower forward voltage diode like a 0.3v Ge or 0.15v schottky will clip squarer as it cuts more off the peaks but it will also be quieter as the output is limited to that forward voltage - again a bit compromised for a commercial pedal if it'll barely put out unity gain (and schottky's don't sound great as clippers either imo).

It can be done but there are easier ways to build a fuzz that actually sounds like a fuzz.

[PRR]

A single BJT needs 20mV signal to sound bent, 200mV signal to "fuzz".

Most guitar amps are more sensitive than that. A "Fuzz" should stay fuzzy down well below 20mV.

Also a single BJT tends to have a low input impedance, which loads-down the guitar, making signal weaker.

What is the problem with two transistors? Cost? Or complexity?

[jm22]

Thank you for the very helpful replies. They're helping me gain some understanding of the fuzz circuit.

What is the problem with two transistors? Cost? Or complexity?

Being so new to circuit design, i need to understand the most general principles of the most basic fuzz pedals. I merely wondered why one transistor fuzzes were so uncommon. I wanted to know what exactly it is that makes them less viable than two or three transistor fuzzes.

The responses have given me the insight I was looking for, but I have two new questions. Are three transistor fuzzes essentially the same as two transistor fuzzes, except there's an extra gain stage of the third transistor, meaning that one does not need as much gain for any one of them?

And is it possible to make a fuzz using diodes instead of transistors? Or is there some fundamental difference between diode and transistor clipping?

[Rob Strand]

The responses have given me the insight I was looking for, but I have two new questions. Are three transistor fuzzes essentially the same as two transistor fuzzes, except there's an extra gain stage of the third transistor, meaning that one does not need as much gain for any one of them?

You should look at the evolution of fuzzes in the 60's upto the early 70s.

Maestros (many versions) , Tone Benders (many versions), Fuzz Face, Jordan Boss Tone (a few version), Big Muff.  A few others like the Mosrite Fuzzrite,  Burns Buzzaround.   You will see many repeated circuit ideas throughout.

The Maestro 1a starts out with three transistors.  That's a two transistor fuzz and a buffer.

Some followed the maestro pattern.  Some tried to get more gain from two transistors using different circuits, like the fuzz face.  Then as time went on it ended up with three transistors all providing gain.  Perhaps ending with the Big Muff with four transistors.    There's a kind of a progression of more gain over time.

[amptramp]

You can look at a transistor amplifier in terms of transfer function - the output you get for every input.

For a single transistor amplifier, this is asymmetrical because if you are going into an NPN device, voltages going up can give you a large growth of the waveform in the positive input / negative output direction whereas transistors in a fuzz are usually biased close to cutoff so the signal going more negative doesn't do anything - it just cuts off and leaves the collector of the transistor close to the rail.  This gives you a transition from a sine wave input to one with a lot of range on the negative output but little variation on the positive output.  If you had two common-emitter stages cascaded, you could have something closer to symmetrical clipping which is what a lot of fuzzes do.

Symmetrical clipping gives largely odd harmonics whereas asymmetrical clipping gives mainly even harmonics.  Both are used depending on what you want the output to sound like.  Odd harmonics sound more like a clarinet whereas even harmonics sound more "warm" or "mellow".

[soggybag]

This discussion is making this make more sense to me.

http://guitar-fx-layouts.42897.x6.nabble.com/file/n6967/DBA_FuzzWar.gif

Totally the opposite of a single transistor fuzz.

[Bunkey]

If you take the 4 transistor Big Muff that Rob mentioned; it has an input booster, a first clipping stage, second clipping stage, then the last stage is a second booster to recover the volume lost from the preceding passive tone control. Therefore two of the 4 stages clip the signal whereas the other two just amplify it. Cascading stages like this is as much about shaping the waveform to make it sound the way it does as it is to make it bigger - the resulting waveform from the Big Muff actually looks like a square with a peaky flick at the beginning.

In terms of the ability to use less gainy transistor's, a 2-stage fuzz face has transistors in the region of 100x gain (the hfe), whereas a single transistor fuzz like the bazz fuss people seem to have a better time with hfe's of 500+, so there is merit there to using lower gain transistors in multiple stages but there's no reason you couldn't use high gain either, it all comes back to how you want to shape the tone.

Check out a site called electrosmash - the guy has posted analyses of a few common pedals which I found really insightful.

At the end of the day there are only a few ways to actually configure an amplifier stage, mostly variations of stabilising the bias, and they're all similar in principle whether its a BJT, FET or even a valve. Different pedals use variations and combinations of these different techniques for different flavours but the ingredients are all the same.