DEMO EHX Op-Amp Big Muff With Aion/JHS Mods (Vero)

[Ginsly]

Build Rating

5.00 star(s)

I have no no horse in the Big Muff 2 race, but if nothing else it reminded me that I've always wanted to try an IC-based Big Muff. I intend on picking up Robert's Dream Fuzz board just to build a straight-up clone of the recent-ish EHX reissues, but in the meantime I figured I'd work with stripboard and make a mess. It was also an opportunity to try the Pinecil USB iron someone gave me for the holidays. It's actually decent, but the standard Hakko has the edge for sure.

I breadboarded Aion's Corvus, which looks to be pretty faithful to the original other than an Analogguru modification to the Gain control structure and some different values here and there. Really not sure how much I would notice the difference either way, but I think a lot of Aion's tweaks are pretty well thought-out. I say this as someone who knows jack squat, so take that with a grain of salt. I also wanted to integrate the JHS diode mod, which replaces the second trio of Si diodes with a switch offering the original three diodes, no second set of diodes at all, or two LEDs. The two new settings give you moderate gating or strong gating. Pretty cool. I also added what is essentially the AMZ Presence control - another part of the JHS Pumpkin Patch mods.

I changed the Dirtbox Layouts arrangement quite a bit in that I added/replaced several components to match Aion's schematic, took out the Tone Bypass (didn't find it particularly interesting), added the Mids/Presence control, and set things up to swap half of the diodes. I opted for two Green LEDs for the "moderate gating" mode and a Yellow LED in place of the second trio of 1N4148s since the Vf was about the same. Couldn't tell the difference when breadboarding, and it fit well on the layout! At the last minute I tried two infrared LEDs in place of the single Yellow, so that's what you see in the pic. I'd just stick with Yellow next time.

Yes, the enclosure is severely unfinished and yes, it's a bit of a rat's nest. Cleaning flux? Pffffft. This was just an experiment, and I'm sure I'll build a prettier one in the future. Sounds great to me, though! I really, really like the Green LEDs - it just accentuates what I always liked about the sound of this thing. Very quick, crappy phone clip of a little desktop amp below. Better than nothin? Not sure. Diode Switched to the LEDs for a little more crunch and gating.

I'm also including the modified version of the DBL layout if anyone wants to give it a go - by all means, fix what I got wrong! Ha... I noticed there's a section of the forum for Stripboard Layouts which is sadly empty... should I post this there..?


View attachment OpampMuffGinsly.mp3

 

[manuel.marsicobetre@gmail]

Tu compilación es interesante; ¿podrías publicar el esquema? Nos ayudaría mucho a comprenderla mejor y a depurarla. Gracias de antemano, Ginsly.

 

[Chuck D. Bones]

I don't understand why changing the diodes would cause it to gate.

 

[Ginsly]

I don't understand why changing the diodes would cause it to gate.

I had the same reaction, but then again I know a fraction of what you know, Chuck! It does indeed cause it to gate, especially when you simply remove three of the Si diodes entirely. I know you just breadboarded a BM2, but maybe give the OG a shot and see what you think!

 

[Chuck D. Bones]

Going by your Vero layout, the DIODE switch selects either D5+D6 or D7 or none of them. In the D5+D6 setting, there's a good chance that the opamp output is saturating on the positive half-cycle. In the "no diodes" setting, I guarantee that opamp output is saturating on the positive half-cycle. I have no idea how a 741 would react to that, so upsetting the bias and gating is a definite possibility. BTW, Vf for yellow and green LEDs is nearly equal.

 

[Ginsly]

I have no idea how a 741 would react to that, so upsetting the bias and gating is a definite possibility.

Interesting! Do you still have the BM2 on your breadboard? I know it's set up differently, but... maybe see what happens..? I haven't looked at that schematic very closely but seems like there would be more than one place in which to remove diodes...

BTW, Vf for yellow and green LEDs is nearly equal.

Absolutely - the yellow ones I measured were just slightly closer to a trio of 1N4148, but if all I had was green I could have used one for the "normal" and two in the "moderate gating" positions without issue. This is a good way to use those yellow leds that collect dust! Ha...

 

[Chuck D. Bones]

Interesting! Do you still have the BM2 on your breadboard? I know it's set up differently, but... maybe see what happens..? I haven't looked at that schematic very closely but seems like there would be more than one place in which to remove diodes...

The only place I tried it in the BM2 is the 1st stage and it reduced the compression a bit. Completely different circuit, different parts. and I removed both diodes, not just half of them.

And yes, the BM2 is still on the breadboard and is featured in The Boneyard.

 

[Ginsly]

Completely different circuit, different parts.

Yep kinda figured it might not translate. For what it's worth, the two LED setting on the standard IC Muff is quite nice - not a harsh gate by any means - if I built one without a switch I'd make it a permanent change. YMMV!

 

[Chuck D. Bones]

If you want to compare this with a similar circuit, check out the TC Electronics Spark Booster (PPCB Ember Boost) or the Black Country Customs TI-Boost (PPCB Dark Esbat).

 

[Ginsly]

If you want to compare this with a similar circuit, check out the TC Electronics Spark Booster (PPCB Ember Boost) or the Black Country Customs TI-Boost (PPCB Dark Esbat).

Huh! I would not have made that connection, but in taking a cursory look at the Ember’s schematic I see what you mean! I’ve used a Spark on bass for years- it bested many dedicated bass fuzzes, overdrives, and preamps.