Anderton Comparator Fuzz

[soulsonic]

Hello everyone,
I finally dug up the book with this one in it. It's an old comparator-based fuzz designed by Craig Anderton. It was originally published in Popular Electronics, July 1972 in an article entitled, "Build the Optimum Fuzz Adapter". I've seen people ask about square wave circuits around here a few times, so I figure folks might enjoy this - it's as square wave as you can get!

http://www.aronnelson.com/gallery/main.php/v/soulsonic-fx/AndertonComparatorFuzz.gif.html
I built one of these in high school and it was probably the second thing I ever built. It gets a big buzzy square wave sound that reminds me of the sort of tones you hear on Siamese Dream. One thing to note is the fact that the negative terminal of the battery does not connect to ground, so you wouldn't be able to do the usual input jack shorting trick to switch it on and off. I suppose you could have a switch mounted to one of the pots to switch the power or something like that. Maybe you could have the power switched on the third pole of a 3PDT bypass switch, but I'm not sure if that would make a power-up pop when switching. There's alot of room for more ideas here!
I believe this could be considered an early version of what later became the "Ultra Fuzz" project from Electronic Projects for Musicians, which is also a comparator circuit.
Sorry, I don't have a layout for this; when I built it I wired it point-to-point with terminal strips... seriously! I did a crummy job of building it too, but it still worked!

[R.G.]

I always liked that one too. The 741 might not be the best opamp to do that with these days, as there are quieter ones, and also opamps that have a cleaner entry/exit from overload. The opamp is always in overload, either banged against the top power supply or the bottom.

The only thing I didn't like about it is that there's a DC transient at the start of every note. The resting state of the op amp between notes is always either full-positive or full-negative, so the output cap is charged to the full power supply one way or the other. When the note comes along, the DC level on the output changes to half the DC supply, and so the output after the output cap has a transient to be passed along.

I think if I were working with that today, I'd do a side chain which provided a "note present" gate signal that starts the note off a bit softly. That would open the note with a low gain to the DC transient and soften the "snap" a bit.

The other thing that would be interesting is to use a real comparator like the LM339 or one of its eight-pin variants as the comparator. This might produce lower noise.

[Dragonfly]

Thanks Soulsonic - I probably won't have time to breadboard it anytime soon, but I'll definitely save it for future reference. I appreciate the redraw and posting ....

[ollie]

Siamese Dream?



Actually need to build me one of these!

[Mark Hammer]

The only thing I didn't like about it is that there's a DC transient at the start of every note. The resting state of the op amp between notes is always either full-positive or full-negative, so the output cap is charged to the full power supply one way or the other. When the note comes along, the DC level on the output changes to half the DC supply, and so the output after the output cap has a transient to be passed along.

Q:  Did the EPFM Ultra-Fuzz - another comparator based square-wave generator - manage to get past those hurdles?

[CodeMonk]

I just finished building this one tonight.
It kicks ass, big time.
Out of the 4 fuzzes I have built (Jordan Bosstone, Mosrite Fuzzrite, Dallas Arbiter, and this one), its my favorite one by a long shot.
I'm gonna call it "ZipTone". I didn't have an enclosure, so I gutted a power adapter for a Zip drive and stuffed it all in there.

RG, would a LM339 be a direct swap for the 741?
Mine is actually a UA741CP (Radio Shack is all I have locally, and even that is 30 miles away).

Thanks

[caspercody]

I made one of these last night, using a veroboard layout. And I get no sound out of it. I tried a audio probe up to pin 2, i get sound. But nothing out of pin 6. I have 9 volts positive and negative to the IC, with the ground connections connected separately and not to  connected to the negative of the battery.

[reddesert]

It's a simple inverting comparator circuit. The 100K and 100nf pairs drawn above the opamp are just setting a reference voltage to ground, midway between -4.5V and +4.5V supplies. The Attack pot sets the level of the input signal at which something happens, and the op-amp is running open-loop trying to slam the output against the + or - supply rail depending on the value of the input. You may have a layout problem or some kind of DC offset such that the DC level of pin 2 is different from ground, so that even though audio is present on pin 2, the comparator never switches states.

[diffeq]

It's a simple inverting comparator circuit. The 100K and 100nf pairs drawn above the opamp are just setting a reference voltage to ground, midway between -4.5V and +4.5V supplies. The Attack pot sets the level of the input signal at which something happens, and the op-amp is running open-loop trying to slam the output against the + or - supply rail depending on the value of the input. You may have a layout problem or some kind of DC offset such that the DC level of pin 2 is different from ground, so that even though audio is present on pin 2, the comparator never switches states.

This is mostly likely, and pin 7 is on the same vero track as pin 2, offsetting it high above reference point. Maybe checking DC on pin 2 in unconnected state can give any valuable info?

[caspercody]

Here is the layout I am using. I can get voltage readings later.

[caspercody]

Never mind, it works.

I was testing it with my headphone amp, and it did not work. Plugged it into my Marshall and it works. Plus used a different guitar. But both have passive humbuckers.

Thanks
Rob

[caspercody]

So, I tried the pedal again and it did not work. Then I plugged it in just by itself, and only powering this one pedal and it worked.

I cannot plug this pedal into the same daisy chain of power cords I have coming from my 1Spot. When i place it in my pedal board I need to use a separate power supply, then it works.

Not sure if this helps anyone, but thought I would share my experience.

Thanks
Rob

[thermionix]

One thing to note is the fact that the negative terminal of the battery does not connect to ground

This is why you can't daisy chain the power with other (neg. ground) devices.

[Aph]

One thing to note is the fact that the negative terminal of the battery does not connect to ground

This is why you can't daisy chain the power with other (neg. ground) devices.

Or, you could add this to the circuit:

[caspercody]

I added that power supply to the circuit, and still can not use a daisy chain power cord. Works with its own power cord.

[Aph]

And you're sure the adapter power coming in is ONLY connected to ground and to the point marked +9v?
In other words, just like a normal guitar effects pedal.

[caspercody]

Yes.

I connected the +9 volts power to the Fuzz circuit and pin 8 of the LT1054.

I connected the -9 volts power to the ground on the LT1054 ground connection.

The ground on the Fuzz circuit does not connect to any -9 volt power, or ground connection on the LT1054.

I did forget the 1K resistor on the LT1054 board.

[Aph]

Ground is ground is ground.




ALL grounds connect together.
If you make it like this schematic, it WILL work.

[Kipper4]

Whats the point of R3, R2. Why not just connect pin 3 (to Ground (Ironically pin 3 (lt1054) too)?

[Aph]

Whats the point of R3, R2. Why not just connect pin 3 (to Ground (Ironically pin 3 (lt1054) too)?

Not real sure. You'll have to ask Craig Anderton. I've taken out C1, C2, R2, and R3 and it makes no difference... at least in the circuit I posted.
I'm not sure what you meant about the two pin 3's. They ARE, of course, connected to ground. I do not know why the original schematic was drawn showing the two capacitor/resistor pairs connected to pin 3. It's just one way of showing that they are connected to ground.