LM311 comparator fuzz

7/7/2014

EDIT 2014-08-28
I added a PCB layout. I wasn't going to do a PCB layout for this one, but I needed the practice. :) So the pdf contains two different layouts if anyone would want to build it. I also moved the VERO layout to the bottom of the post.

Here is something that is mostly just proof of concept. I was playing around with Craig Anderton's Comparator Fuzz, but I wanted to try a dedicated comparator IC insted of an op amp. It's probably tried and tested before, but I could not find anything on a LM311 based fuzz, only this thread that doesn't say alot. Anyway, this is what I came up with. It works well and sounds good. I need to think of a better name for it though.. :)

At 0:46 I lower the guitar output for a very short decay on the notes. It's a very gated fuzz (all comparator fuzzes are). A good idea would be to put a booster in front with a volume pot to control the sustain and make it more friendly to low output pickups.

lm311_fuzz_pcb.pdf
File Size:	95 kb
File Type:	pdf

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lm311_fuzz.gif
File Size:	16 kb
File Type:	gif

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27 Comments

anders

10/1/2014 03:19:07 am

Any progress with this one? Built it and it's sounds awesome as is. A separate lpd1 booster in front of the circuit and a big muff tonecontrol after would be my tweaks. Once again, thanks for a great site. Cheers.

Fredrik Lyxzén link

10/4/2014 06:28:43 am

I'm glad you like it! Your tweaks sounds like good addons :) I have not had time to play with it again since I'm been working on a original phaser lately that but I have an idea for a follow up that will use a dual comparator chip (LM393).

10/14/2014 12:37:08 am

Added the BMP tone control and boxed it up today. Didn't added a boost as it's works quite well with hot humbuckers. The tone stack adds a whole new dimension to this circuit, Sound like a cross of a Moog high gain fuzz and a square wave Op Amp Muff. Me like!

10/14/2014 07:39:29 am

Awesome! I would love to see a picture of your finished build.:)

10/15/2014 04:15:45 am

Will do! :-) When I get a fully functional cell phone. I have some more lm311's, will build another one with some more addons :-). I'm really looking forward for the lm393 version and the phaser as well. Cheers A

Trehbz

10/16/2016 02:10:00 pm

made this but sounds more like a wimpy fuzz/boost. Any reason why?

10/27/2016 05:53:02 am

Hi Trehbz,
It's hard to say without more info. Try another LM311 chip, check the component values with a multimeter and check for tiny solder bridges. Also try to reflow the solder.
Best regards
/ Fredrik

tim

2/1/2017 05:57:41 pm

THANKYOU. Finally!! someone built this.sounds very synthy on single notes. i like.

2/4/2017 03:29:52 pm

Hi Tim. I'm glad you like it. :)
Cheers / Fredrik

mercury8 link

1/22/2019 06:18:31 pm

really like those leadtones from 40-45 sec . what does thesennsitivity control do on the original ca ultra fuzz?? and can it be added to this circuit?

2/6/2019 05:42:22 am

The Ultra fuzz sensitivity control adjusts the threshold level for the comparator stage (the part that turns the signal into a square wave)

4/15/2019 06:50:24 pm

I keep coming back to this thing as it sounds so cool on single note lines.thanks for the reply. im trying to decide whether I should add the bandxall eq or a ca supertone control to the end. love the new wave. ive been waiting for someone to design a utility super awesome lfo cv box like this forever. also love the multiwave. will buy a couple multiwaves soon

4/17/2019 04:28:22 am

I'm glad you like it! Thanks for the nice comment. :)

Eduardo link

5/26/2020 02:52:51 pm

Hey!

I'm planning to build this for my violin, so I usually need a boost before. If adding a BMP tonestack after everything, would be good to add with another boost, to compensate any volume loss? or just the bost before?

5/27/2020 03:30:46 am

Hello

It has a very loud output, so I don't think that it's necessary to add a boost after the tonestack. :)

Eduardo

5/27/2020 04:11:15 pm

Nice! Will breadboard everything as soon the pieces arrives and give it a try.
Any news on that lm393 version? Haha

6/30/2020 10:51:54 am

hey Fredrik!

Built this one yesterday and it sounds killer, the type of fuzz that I like. I was wondering, is there any way to add a "gain" knob, so it can control the saturation? Or the nature of the LM is this always on full?

Thanks <3

Fredrik Lyxzen link

7/2/2020 11:56:03 am

Hi Eduardo,

There's no way to add a gain knob to this design i'm afraid. The comparator only has two output states (low or high) so the output will always be a square wave. Since it has no negative feedback like an op amp amplifier, it's not possible to modify the gain.

Cheers / Fredrik

7/10/2020 06:43:28 am

Hi again Fredrik, sorry to bother you!

I built the vero version, but got no sound. Noticed that the Vero has a 1M resistor that the pcb doesn't. Is that right? Anyway, thanks for the help (:

7/20/2020 04:12:02 am

Yes, the vero has a 1M pulldown input resistor, which isn't really needed, but it can help reduce bypass switch popping.

Make sure you didn't miss the double link next to pin 1 of the comparator chip.

7/20/2020 04:58:18 am

Hey man!

My problem in the end was a faulty socket. One of the legs was broken and I didn't saw, until I took it out. Now is up and running, in all of his glory (:

Thanks so much for the design and the insights!

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2/25/2023 11:52:01 pm

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3/15/2023 12:58:06 am

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man from tucson

4/5/2025 10:51:15 am

Whats this compared to your RayGun Youth? is there a ray gun youth schematic somewhere?

4/8/2025 09:14:10 am

This is just a simple comparator/square wave fuzz while the Raygun Youth uses a Phase Locked Loop chip aswell. You can find the Raygun Youth pedal schematic in the build document on the "build docs" page.

LM311 comparator fuzz

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