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Project: Corvus (Op-Amp Big Muff)
Variant: The "Modified" Tone Control

Build description

RESISTORS: All 1% metal film. Carefully rechecking the values helped ‘coz a lot of those have out of range values. I’ll be using Yageo brand resistors from now on.

CAPACITORS: All Panasonic solid polymers and/or low ESR mini electros & premium quality film & stacked metallized caps.

DIODES: six (6) 1N914

I opted for the “Modified” tone control.

OpAmps: I conducted experiments with several OpAmp combinations & finally settled for an RC4558P for IC1 and NE5532 for IC3. This is the best OpAmp combination for me.

OTHER OpAmp combo tests I tried:
• 4558 on IC1 + 741 on IC3 = lacks headroom. I had to turn the volume knob all the way up to try to match my guitar’s clean volume.

• two (2) NE5532 = the overall sound lacked the punch

• two (2) 4558s = similar to just using one 4558. Just a little louder.

Just FYI. I use a P-touch 2730, Mac & Win compatible tape printer for the labels, 3M vinyl car wraps for color & aesthetics & ribbon cables for the pot connections. Last but not the least, Small Bear’s light plate!

TESTING EQUIPMENTS: Marshall JVM 205H head / Marshall 1960A cab / IBANEZ S5470Q guitar. Jackson Japan-made Warrior guitar with genuine SD Invader humbuckers. Only Corvus Fuzz is connected.

TEST RESULTS: With the Tone Bypass switch in the OFF position, the sound is unmistakably 100% Mosrite Fuzzrite, the fuzz pedal that the late Iron Butterfly guitar player Eric Brann used in the IAGDV and Ball albums. Amazingly, the Corvus sounds more Iron ButterFuzz-like compared to all the Mosrite fuzz clones I have. And of course, the overall sound & tone quality of the Corvus Fuzz mimics the signature guitar sound of the Smashing Pumpkins dead-on. With the switch in the “Modified” position, I have no doubt that this redesigned fuzz could very well rival other pedals in its kind when used into the hard rock & metal genre ‘coz it takes on another distortion character as soon as the toggle switch is engaged in the Modified position where the tone control is at your mercy.

Thanks to Kevin & the AION techies for a better (if not the best) re-design of the BMP OpAmp version.

How many BMP variants have you cloned? Try the Corvus Fuzz & enjoy the journey from psychedelia to metalmania. Tell us about it, please. Thanks.

Modifications or part substitutions

AION stock tone control mod

Dirk Funk

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Project: Corvus (Op-Amp Big Muff)
Variant: Modified (Jumpered) and TL072 in IC3.

Build description

My first build, and luckily no real issues. I think it sounds great! In general, I stuck to the “Where to Buy What” guide under Resources, but I will share some extra details that may help others in selecting components.

RESISTORS: 1/4W Xicon metal film.

CAPACITORS: EPCOS box film and Nichicon electrolytic. I used the parts list for the L5 Preamp as a reference for part numbers, then selected the values needed for the Corvus. Kemet MLCC for C6.

POTS: I used the “new version” Alpha pots from SBE, not realizing that the footprint is slightly different. Since there is no 2mm extension on the terminals, I had to bend them out at an angle, then bend the tips so that they lined up with the holes in the PCB. No big deal. You can see how I bent them in the pre-PCB enclosure photo. Ignore the footswitch orientation in that photo, I accidentally rotated it 90 degrees.

OP AMPS: RC4558P in IC1 and TL072 in IC3. I also tried a 741 in IC2, and really couldn’t hear a difference, but I stuck with the TL072. It should be noted that I never really had a golden ear for tone. Also, I mixed up the IC placement on the first try, not realizing that IC3 is directly above IC1. Figured it out pretty quick, but for about 2 minutes I was bummed.

FOOTSWITCH: The recommended red 3PDT was out of stock at PPP, so I bought the “industrial” blue-green switch.

ENCLOSURE: I rolled the dice with a random powder coat 1590B from PPP. Not sure how best to describe the color, its a silver powder coat with a slightly yellow tint. I’m really pleased with it.

WIRING: The wiring was the trickiest part of the build. Next build, I’m going to solder most of the wires to the PCB from the back side, or maybe insert the wire through the back and solder from the front. My point is, its a little awkward to solder the wire from the same side that the wire is inserted. It also leaves more bare wire than I would like. Next time I’m also going to buy the footswitch PCB just to save time, plus its cheap and looks more professional.

Modifications or part substitutions

C9: I didn’t have a 120n capacitor for C9, so I measured all of my 100n’s and used the highest value, 107n. Just in case, I socketed C9, although it sounds fine as-is.

Modified circuit: As recommended, I socketed the jumpers for “Normal” and “Modified”. I left it jumpered to the modified circuit.