Andy's Simple Fuzztone !

[frank_p]

The sounclips sound great, even in my little laptop speakers, wow.
Now, I got to put some heaphones...
Delicate and subtile...

[DougH]

Also look in the art of electronics about how the gain changes with input level.

I read that in AoE too, Gus. For a general amplifier design, that's a bad thing because you want predictable behavior. But I'm thinking for a circuit like this that could be a good thing. It might add some nice dynamics.

[FiercelyFuzzy]

Hi All

I breadboarded this using a 3904 & 2906 combo & also just got a huge volume boost 

FF

[cheezit]

Okay, I re-did my breadboarding to verify my layout and found a couple of things.
- I swapped in and out 2n3904, 2n4401, pn2369a for the first stage, and 2n2907, 2n3906 for the second stage.  The varying hfe values made a HUGE difference in the resulting sound.  I had two pn2369a's, and they sounded quite different. 
- I tried various values for the input and output caps.  Just like a Fuzz Face, the charm here is in the low mids, and using a small value will not get you a brighter sound.  It'll just give you a boxy middy sound.
- I tried an extra stage with a J201 (10k on the drain, 12k on the source, with a 1uf cap from the emitter of the PNP stage).  Nothing too exciting here, just smoothed everything out.
- at one point I ran my signal through my pedalboard, and when my TS5 (non-true-bypass) was in the chain the gain jumped dramatically. But it wasn't really an improvement in the overall sound.  So just like an FF, this circuit is very sensitive to input impedance and buffering.
- different guitars gave quite different results---more so than most circuits.  Again, the input is highly sensitive and somewhat picky.

At no point did I get anything like the clips, even when using the same transistors Andy used, but with the highest HFE value transistors I got a nice fuzz grind, and with lower ones I got boost but very little fuzz.   At all times the volume boost was very large and my 1M output pot was turned down most of the way. 

Then, after looking at the Bazz Fuss schem, I tried a red LED from base to collector on the NPN stage.   This gave a nice, synthy saturated sound that might actually be a keeper!  But it's still not the same as the original clips.  The LED works better with some transistor combinations than others---for some it just led to gating and fizz.  In this mode I don't think the second stage is doing a whole lot.

I'm coming to the conclusion that this is a pretty finicky circuit and doesn't behave consistently if anything is varied.

[Gus]

The answers are in AOE
Hints
transistor input R and hfe, emitter resistance, Ie
bias string resistance and transistor input resistance

Calculate gains at different ratios of collector to power supply voltage with a grounded E circuit like this.

The output transistor is a EF so as long as the hfe is high enough it should not load down the collector  lowering its gain.  Collector R is the C resistor and the input load of the EF

Circuit looks like it "wants" high hfe transistors to me to get fuzz.

[cheezit]

I dug out my venerable copy of AOE, which is not as well-worn as it probably should be.  Anyhow---

Looks to me like the first stage is a grounded-emitter, which AOE says has all sorts of nonlinearities, including temperature sensitivity.  But the peak-compression is obviously interesting.  And the ASF biases the base, which the Fuzz Face doesn't.

The second stage is an emitter follower.  I think it is just buffering and possibly adding gain but not a great deal of fuzz.  Not sure on that one, I clearly need to give this chapter a thorough reading.

From your post, it sounds like varying the first-stage collector resistor might do something interesting.  I'll go down to the cave and give it a shot...

[Rodgre]

I built it up the other day with 3904 and 3906 trannies and added 1N4001 clipping diodes at the output and it has a very nice and squishy Bosstone vibe, as was suggested by Andy. I like this one a lot!

Roger

[Valoosj]

Damn, this does sound good indeed. I just have one question: how could you add a gain knob? Preferably to make it even harder 

[DougH]

The second stage is an emitter follower. 

It's a gain stage.

[John Lyons]

For a fuzz control just turn down your guitar's volume control
or wire in a volume pot (voltage divider) before the circuit.

john

[SISKO]

The second stage is an emitter follower. 

It's a gain stage.

As i see it, its an emitter follower because the signal its taken from the emitter and colletor is tied to negative. Being a pnp tranny, that the way it should be hooked for an emitter folower. But i can be mistaken 

[arawn]

ok Here is my take on this! Yes it is perfboard I like perfboard! I added a saturation control and diodes at the tail end of the circuit especially since it sounds like it is very loud and powerful regardless of any other results. I am hoping someone could model this in spice and see how it looks in simulation (I would do this myself but I am ignorant and lacking)

Thanks guy's

[earthtonesaudio]

The second stage is an emitter follower. 

It's a gain stage.

As i see it, its an emitter follower because the signal its taken from the emitter and colletor is tied to negative. Being a pnp tranny, that the way it should be hooked for an emitter folower. But i can be mistaken 

Yes, the second stage is an emitter follower.  But it has a high input impedance which doesn't load down the first stage as much as some effect or amp inputs would.  Therefore you get more gain in some cases, and more repeatability in all cases.  And emitter followers do provide current gain, so you're both right.

[Kultur Vultur]

Running this into LTspice definately shows fuzz, but the output swings between 0 and 8V with a 250mV input, so no kidding people were complaining about it being extremely loud. Various load resistances did not help...

Unfortunately I haven't learned enough in class to figure out how to lower the overall gain here. Maybe someone with more knowledge can help?

[Kultur Vultur]

I replaced the output cap with the AMZ Presence Control and used a 1M volume pot and from the simulation it seems to be better. There's still a boatload of gain available, but it's not as extreme as the near 40dB LTspice predicted!

The whole simplicity thing is kind of thrown out the window here, but this will definately hit the breadboard next time I'm home.


This isn't the solution I hoped for (every year I wish I knew more and more...), but we'll see how it goes.

[Dragonfly]

try putting a small resistor to ground from Q1's emitter

also, raise the value of the 1k ( a large value - 100k - 220k - might make it more of a clean-ish booster though)

[Kultur Vultur]

I actually never thought to increase the 1K resistor. Thanks!

At 100K the output is still just as square as it was with 1K (tells you something about the first gain stage), and the output is still swinging between 0 and 4V with the volume knob at noon(which is definately an improvement!). Maybe I'll look at this again tomorrow. Thanks again!

[Gus]

OK a lab

calculate the input R for hfe 100, 200, 500, 1000 of the first stage do this at 1/2 power supply.

Next built a fet input opamp buffer stage gain of one use the other half of the dual(if you used a tl072 etc) to buffer the Vref

install resistors that are close to the calculated input R for the input resistor of the buffer.  Look at the in to out with a guitar plugged in with a scope OR compare input to output with a switch to an amp and speakers.  Note how the input loading changes things.

This is a little different than the input node of a FF type circuit.

[DougH]

The second stage is an emitter follower. 

It's a gain stage.

As i see it, its an emitter follower because the signal its taken from the emitter and colletor is tied to negative. Being a pnp tranny, that the way it should be hooked for an emitter folower. But i can be mistaken 

A yeah, it's pnp... My eyes are failing me...

So the overall topology is similar to a sam ash fuzz then.

[Gus]

If you like the first gain stage of this but want more gain look close at a BeeBaa.  a small highjack of the thread
http://www.diystompboxes.com/pedals/mbb.GIF

I built something like that without the tone section.  I think people will like this and maybe people will understand some of the design.  With the gain available layout is important

maybe take parts of that and buffer the in and out of Andy's Simple Fuzztone.