This Week on the Breadboard: The Dark Esbat

Am I right in suggesting that this circuit (both the originals and Chuck's modded version) have at their core a Blue Breaker (Bluesbreaker) topology? If so, I'm wondering if your modded version is getting close to EHX's new "Spruce Goose"? EHX's Spruce Goose marketing copy seems to suggest it's a Bluesbreaker tweak with a Bandaxall...

Looks like it won't be too long before we know for sure!
 
I was playing around with boosts and the mofeta, and ran the dark esbat into it. Sounded pretty Iommically legit! Boosts in general really made the Mofeta jump to life. It--or my build of it-- is pretty muffly on its own. I even got high-gain metal sounds out of the dimed Colorsound boost-mofeta combo.
 
did you consider replacing the 3x series 4148s with LEDs? the keeley rotten apple (pedalPCB sour grape) did that, being an adaptation of the op amp big muff (pedalpcb dream fuzz). the LEDs would have about the same Vf but maybe a different curve and tone.
 
I had not thought about it until now. The diode current is less than 200μA, so it's hard to gauge the LED's Vf from the datasheets. LED leakage and capacitance vary quite a bit so you might end up selecting LEDs or at least qualifying lots. 1N4148s are very consistent. Try it and let us know how it goes.
 
FWIW, I didn't experiment with different clipping diodes in Chuck's modified Dark Esbat, but I did socket the clipping diodes in my Ember Boost build. (The Ember Boost/TCE Spark Booster is essentially the same circuit as the stock Dark Esbat/BCC TI Boost.) I experimented with LEDs, fewer 1n4148s, mosfets-as-diodes, asymmetric arrangements, etc. That was quite a while ago, so I don't remember the details. I do recall that I preferred the stock arrangement. But there was some noticeable difference in tone and feel with different clippers, and I'd wager others would have a different preference.

One thing I did not try, but think is worth trying, is a pair of 1n4848s (instead of a triplet), but also adding a resistor (say 6k8) in series with the clippers, like the Blue Breaker and all the derivatives, e.g. King of Tone, do. This Dark Esbat shares some topology similarities with the Bluesbreaker family.

I still have spare PCBs for Chuck's modified circuit (see post #28 above), I'm happy to drop one in the mail for anyone that wants one. You could socket the clipping diodes and easily experiment with different arrangements.
 
Chuck D. Bones said:
The 1st stage in the TCE Spark Boost & BCC TI Boost is a 32KHz 2nd-order low-pass filter. My philosophy is "why use 10 parts when 2 will do?" so I ditched the 1st stage. R2 & C2 provide all the input filtering we need. We also don't need a Vref buffer, so that's another opamp gone. TCE uses the OPA2134. That's a very good FET-input dual opamp. BCC uses the MC33178, which is a good BJT dual opamp. I went with the good ol' TL072. Any of them will work in this circuit.
Click to expand...

@Chuck D. Bones - the way the first opamp stage of the stock Dark Esbat/Spark Boost is wired: as you said, it's a filter. But does it also act as a "boostrap"? I.e., a way to increase the input impedance?
 
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