The Week on the Breadboard: EQD Hoof - Boneyard Mod

Chuck D. Bones

Circuit Wizard
I'm feeling a bit nostalgic on this one, my first PedalPCB project from August 2018. I've had a love/hate relationship with the Big Muff for many, many moons. For all it's potential, I've struggled to get one to sound the way I like. Smarter people might say "maybe you're building the wrong pedal." I was intrigued by EQD's use of Germanium transistors and LEDs in the clipping stages. Fast forward 5 1/2 years and I thought I'd revisit the design, this time on a breadboard.

Here's my original build:
HooF.jpg

And here's the breadboard...
Knobs (L-R): LEVEL - TONE - SHIFT - FAT sw - FUZZ
Fooh v3.1 breadboard 02.jpg

I found that the best transistors for the clipping stages (Q2 & Q3) are low-HFE Germanium. I have two MP38 installed; their HFE measures around 50-55. The leakage was low enough that I did not need to tweak the bias. DC voltages are noted on the schematic. This is a medium-gain pedal. With these transistors, the distortion is never harsh. I tried a couple of 2N1308s and it was way too nasty. I tweaked a few component values in the tone stack. The TONE and SHIFT knobs are now usable over their entire range. The biggest improvement was adding the FAT switch up front. As you know, the BMP is bottom-heavy. Probably ok with a Strat, but too muddy for my liking with Humbuckers. The FAT switch clears that right up. C1A can be tweaked to taste. Be careful about fiddling R1A. I had 10K in there and it allowed C1A to resonate with the pickup's inductance yielding a stuck-wah honk. The other thing I did, and it's completely optional, was move the LEVEL control before the last stage. Just for fun, I replaced Q4 with a JFET. In the original circuit, Q4 had enough gain to saturate on the peaks when TONE was dimed. With the LEVEL control ahead of the last stage, we can better control the signal level. We can get plenty of output at all TONE settings without saturating the last stage. As a bonus, we get a lower output impedance.
FooH v3.1.png

BTW, if you notice your American friends acting crabby or distracted today, it's because it's Tax Day. I used to live near LAX and for fun I would drive down to the Postal Annex around 11:30PM on 4/15 to watch people line up to mail their tax forms at the last minute. I even witnessed one poor guy filling out his forms on the sidewalk under a street lamp.
 
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Sweet. Does R1A affect the EQ? Seems like it would just add some gain, and you could still have the fat sw just by switching C1.

I also don’t find the BM to be my favorite, so maybe your take would hit the spot.
 
Yes, you could just leave R1A out and the the FAT switch would work fine. R1A is there to provide a little gain boost in TIGHT mode and it is also part of the EQ between the input jack & Q1. C1A attenuates a good portion of the bass & midrange, so I wanted to make up for some of the loss by boosting the gain a few dB.

All component values are negotiable. Since C1, C1A, R1 & R1A all work together to control the EQ going into Q1, if you change one, you may well end up changing some of the others. You may find that you can dial-in the perfect EQ just by selecting a smaller value for C1, in which case you won't need the FAT switch, C1A or R1A. I wanted to accommodate a range of pickups, which is why I included a FAT switch.
 
Noice! I do have some MP38 Germs (and a god bunch of MP38A, not to be confused) I will stick the fork into that one me thinks. Are here god alternatives to the 2SK30A jfet that I might have in my stash, aka things like J111/112/113?
 
Here's the latest version. I used a MOSFET booster for the last stage and retuned the tone stack a little. This schematic is drawn for modding the Hoof board. If you're designing a new board, I'd make the SHIFT pot (VR3) A50K, wire it backwards (CW increases resistance) and label it MIDS. R18 can go on either side of VR3, whatever makes the layout neater.

FooH v3.3.png
 
I have not played the original EQD Hoof, but I really don't need to, because this things rocks!
Very versatile, great sounding, I dig both the lower Fuzz settings as well as Fuzz cranked, great range in Tone and Mids, super versatile.
In the lower Fuzz settings it has a smooth fat singing quality, almost 'dumble-lesque' dare I say.
Thanks again for magician @Chuck D. Bones for all those great circuits and tweaks!

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