(512)ae Inamorata Fuzz

[mmolteratx]

Was planning on offering up a few circuits I've been screwing with for a while for sale, but with grad school applications fucking with my free time for the next few months, that could be a ways off. So I've decided to offer them up here in the mean time for DIY'ers, and may be down for selling PCBs if there's enough interest.

First up is my take on the Big Muff, which has been a constant on my bench for forever. My fuzzy little mistress, if you will. A few things always bugged me a bit, like the low input impedance, that it was a bit of a one trick pony, the noise at higher gain settings, etc. Screwed around with a bunch of different mods for a long time, and wound up with the Cornish buffer up front and a bog standard BJT buffer at the output, the Blackout Effectors/Earthbound focus/density control at the input, Orman's mid boost and then constantly tweaking layouts and high frequency filtering to lower the noise floor. End result was fairly nice, but the circuit was huge and the focus/density control range is pretty garbage if I'm honest.

I moved on to mictester's 21st Century Big Muff (with the gain control in the feedback loop of the first stage instead of a voltage divider following) in an attempt to simplify, but for some reason the fact the volume wouldn't go completely off always bugged me. So I swapped his output stage for an inverting stage, and added a Timmy bass control to control the low end up front and get some more overdrive-ish tones, and the range blew that of the focus/density control out of the water. I loaned that build out to a buddy, who used it for recording, but he didn't like that it would invert phase when he kicked it on during recording. I didn't really care though and left it as is for a good while since input impedance and gain in an inverting stage was an issue I didn't feel like tackling.

Then, one day, I was thumbing through Walt Jung's "Audio IC Op-Amp Applications" (thanks to Bjorn Juhl for the rec), and saw a high input impedance inverting stage, and decided to try it, with the shelving filter added on of course. It worked pretty god damn well. Though revisiting the circuit, I realized that the range of the "body" control was shit with the gain turned down low, and reverted to using a 100kA pot after the input stage for a gain control, and arrived at the circuit attached. Range of tones is pretty great, and I haven't really heard anything bad about it yet. Low end can get pretty tight with the body control, and the gain can get pretty crazy. Blues, classic rock, stoner, hair metal, doom, thrash, etc. are all in there to some degree. Not the most dynamic circuit, seeing as how the clipping is pretty much bog standard Big Muff, but lots of fun.

In between all this, I dicked around with a gate control (which can still be seen on the revision of the PCB used in my last build), but it never worked as well as I'd have liked, so I removed it.

Circuit is verified, and here's a pic of one of my builds, which also has a switchable buffer on the bypass daughter board. Pretty bog standard bootstrapped voltage follower and buffered Vref, and not terribly interesting, though I guess I could post that if anyone cares.

[tschrama]

That 470K input resistor is gonna give you lots of noise/hiss. Why don't you just use a non-inverting stage?

[mmolteratx]

That 470K input resistor is gonna give you lots of noise/hiss. Why don't you just use a non-inverting stage?

For the first part, we're talking sqrt(4*k*T*R), which gives ~88nV for a spectral power density. Even integrating across the audio bandwidth doesn't give you significant noise. After building it, I can confirm that it's got lower noise at the same levels of gain as a bog standard Muff.

As for the latter, as I said above, it was for a friend who was using a low gain setting as a gain boost during recording and didn't like the phase reversal. So I changed it at his request, and kinda stuck with it. I can throw up a version with a non-inverting stage later. Sounds the same really.

[grrrunge]

That's a great looking build! Kudos Matt!
Funny thing with the timmy/zendrive-alike bass cut on the first op-amp stage. I've been playing around with the exact same thing for ages
How does it sound?

[mmolteratx]

That's a great looking build! Kudos Matt!
Funny thing with the timmy/zendrive-alike bass cut on the first op-amp stage. I've been playing around with the exact same thing for ages
How does it sound?

Yea, I use it up front in pretty much every OD/distortion/fuzz I build. Super useful for setting the voicing of the circuit on the fly. Mostly I play doom and prog metal, so being able to take a circuit from super tight to super loose is really useful for me.

All I've got is a lousy sound clip I recorded drunk the night I built the first proto on that board. It goes from super loose, sludgy fuzz tones with the body control maxed to pretty tight and defined distortion tones with it at min, with various tones in between. Gets some tones reminiscent of the Cornish G-2 I had at lower gain settings with the mids knob turned up a bit. Higher gain 80s tones are in there too. It's pretty versatile, and response from guys I've let play it has been pretty good. Currently have a prototype traveling around the country so guys I talk with another forum can screw around with it.

[tschrama]

That 470K input resistor is gonna give you lots of noise/hiss. Why don't you just use a non-inverting stage?

For the first part, we're talking sqrt(4*k*T*R), which gives ~88nV for a spectral power density. Even integrating across the audio bandwidth doesn't give you significant noise. After building it, I can confirm that it's got lower noise at the same levels of gain as a bog standard Muff.

As for the latter, as I said above, it was for a friend who was using a low gain setting as a gain boost during recording and didn't like the phase reversal. So I changed it at his request, and kinda stuck with it. I can throw up a version with a non-inverting stage later. Sounds the same really.

Even that TL072 with about 20nV/sqrtHz is adds significant noise to the inherent noise of the pickups dc R (about 10nV/sqrtHZ). Let alone a 470k with, thank you for the math, 88nV/sqrtHZ. It's gonna be noisy as hell and hiss like crazy. And it's easily remedied by using an non-inverting stage without series resistance. Your design is needlessly decreasing signal-to-noise with about 9 times, that almost 20dB...

Happy hissing.....

[grrrunge]

All I've got is a lousy sound clip I recorded drunk the night I built the first proto on that board.

Awesome! Care to share?

[mmolteratx]

That 470K input resistor is gonna give you lots of noise/hiss. Why don't you just use a non-inverting stage?

For the first part, we're talking sqrt(4*k*T*R), which gives ~88nV for a spectral power density. Even integrating across the audio bandwidth doesn't give you significant noise. After building it, I can confirm that it's got lower noise at the same levels of gain as a bog standard Muff.

As for the latter, as I said above, it was for a friend who was using a low gain setting as a gain boost during recording and didn't like the phase reversal. So I changed it at his request, and kinda stuck with it. I can throw up a version with a non-inverting stage later. Sounds the same really.

Even that TL072 with about 20nV/sqrtHz is adds significant noise to the inherent noise of the pickups dc R (about 10nV/sqrtHZ). Let alone a 470k with, thank you for the math, 88nV/sqrtHZ. It's gonna be noisy as hell and hiss like crazy. And it's easily remedied by using an non-inverting stage without series resistance. Your design is needlessly decreasing signal-to-noise with about 9 times, that almost 20dB...

Happy hissing.....

Doh you're right. Should have done the calculations before saying anything. Last time I had to calculate noise was a lab junior year and I (foolishly) extrapolated the results without checking to see if they're still valid. Like I said, I'll upload a non inverting version in a bit.

I still say that despite the noise difference on paper, the inverting design isn't that much noisier in practice and is still quite a bit less hissy than any of the straight Big Muff clones I have around at the same gain levels.

[tschrama]

...

I still say that despite the noise difference on paper, the inverting design isn't that much noisier in practice and is still quite a bit less hissy than any of the straight Big Muff clones I have around at the same gain levels.

That's interesting ! ... the actual sound is far more important than some calculated numbers .. BTW, your PCB and build look stunning! Good work

[mmolteratx]

...

I still say that despite the noise difference on paper, the inverting design isn't that much noisier in practice and is still quite a bit less hissy than any of the straight Big Muff clones I have around at the same gain levels.

That's interesting ! ... the actual sound is far more important than some calculated numbers .. BTW, your PCB and build look stunning! Good work

Yea, it's weird. Taking the whole stage into account, it should be quite a bit noisier. Maybe there's just too much background noise at my place to make an accurate assessment, but even shunting the input to ground gives similar results. I've got to build up one of each and try them somewhere else. I'm right in the middle of most of the major telecom companies and interference is pretty crazy here.

And thanks. Board design is my favorite. No calculations to screw up.

[mmolteratx]

And non inverting as promised. This one has a tad bit more range in the focus control, but it's not a huge difference. Just used 68n for C3 because I didn't have an 82n on hand and I never changed it. Just in case my testing was flawed, I recommend this for your own build, unless you really need the inverting first stage. I'll update this once the inverting input is tested in better conditions to see if it fares as well as it does in my apartment.

[grrrunge]

And non inverting as promised. This one has a tad bit more range in the focus control, but it's not a huge difference. Just used 68n for C3 because I didn't have an 82n on hand and I never changed it. Just in case my testing was flawed, I recommend this for your own build, unless you really need the inverting first stage. I'll update this once the inverting input is tested in better conditions to see if it fares as well as it does in my apartment.

How about a non-inverting output stage as well? That way the phase reversal isn't an issue anymore

[tschrama]

neh... plenty of phase flipping pedals around.... I think it's time for a sound clip

[mmolteratx]

Here's the drunk one I mentioned earlier. Recorded through a DSLR mic, so sound quality is shit, but you sort of get an idea. I guess I forgot I was supposed to be showing off the range for about the first minute, so whatever. Skip to around 2:00 for lower(ish) gain tones. Wound up lowering the gain after I built this version, which was supposed to have about as much gain at max as a Musket and wound up being a bit useless for anything but heavier tones.

[grrrunge]

Nice tight low end! Sounds great

[tschrama]

Here's the drunk one I mentioned earlier. Recorded through a DSLR mic, so sound quality is shit, but you sort of get an idea. I guess I forgot I was supposed to be showing off the range for about the first minute, so whatever. Skip to around 2:00 for lower(ish) gain tones. Wound up lowering the gain after I built this version, which was supposed to have about as much gain at max as a Musket and wound up being a bit useless for anything but heavier tones.

+1 Very nice, tight low end, sounds cool to me .

[mmolteratx]

Okay, so I decided to redo this with active tone controls in place of the BMP tone stack. So I'm posting the old PCB design on OSHPark for those interested. Final schematic for this version is attached. This is the non inverting input version, and is ready to build.

https://oshpark.com/shared_projects/gHmBBL3c