Op Amp Big Muff redux

[Rodgre]

Okay, I have tried to build this thing three times to no avail.

Has anyone actually managed to build one from one of the schematics out there? To refresh, I have a real one and I would LOVE to have a clone in a smaller box so it will fit on my pedalboard.

Has anyone designed a PC Board for it? I could try yet one more time, copying the board from my original, but it's at the studio, not on my workbench....

I'm getting very very frustrated with this project and I keep revisiting it every three months or so, thinking that it will work one of these days, but it ain't happening...

By the way, the sound that I just got out of the circuit I just built passes a garbly futzy signal. I put a test probe to the circuit, tracing where things start to go awry, and when I tap off pin 1 of the first op amp, it sounds scratchy and bad. Pin 5 is even worse. I'm assuming the issue is there in the first op amp. I'll check the power again and make sure that's happening.

Roger

[RDV]

Which schem are you using?
Are you perfing or PCBing?
Is your Vr correct & going to the right place?
Do you really gaze at your shoes while you play?

Regards

RDV

[Rodgre]

Which schem are you using?
Are you perfing or PCBing?
Is your Vr correct & going to the right place?
Do you really gaze at your shoes while you play?

Regards

RDV

I'm perfing, but should be breadboarding.... I believe the power supply is hooked up right... +9v at pin 8 on the 4558 and pin 7 on the 741 and pins 4 to ground.....I don't gaze at my shoes, I stare at the ladies and make them crazy with my wild Fuzz Probing.

Or something.

Roger

[Darren N]

I also tried to build the op-amp big muff some time ago with similar results. At the time I assumed I'd just built it wrong (and sometimes breadboards can lie!)

Looking at the schematic I find myself suspicious of the Fuzz pot wiring, intuition tells me the 47k resistor should go to ground or the first Vr but I'm just guessing here, it's probably right.

Pin 1 of the first op-amp (through a cap and resistor) is used for the bypass so if you're not getting a clean signal there, you're in trouble.

What I find most interesting about this pedal is why and how EH created a pedal that sounds pretty much the same but has a completely different circuit.

Anyone actually got one to work?

EDIT: are you using this schematic? I only had the philpott one before
http://members.chello.at/anubics/html/schematics/EH_BigMuff_OpAmp.gif

[Rodgre]

I've tried both the Phillpott and the Anubics and haven't get either one to happen yet.

Roger

[RDV]

I'm perfing, but should be breadboarding.... I believe the power supply is hooked up right... +9v at pin 8 on the 4558 and pin 7 on the 741 and pins 4 to ground.....Roger

I guess I meant the Vr or half the supply voltage(at pin 3 of both OAs) that OAs must have to do their thing.

I've got a 'Fuzz Probe' too, but I won't go into that.

Regards

RDV

[Rodgre]

I guess I meant the Vr or half the supply voltage that OAs must have to do their thing.

So maybe that's the issue? These schematics don't establish that I need to devise a Vr from the 9v supply. Actually, that Anubics schematic doesn't even include power supply connections, so what's the deal there?

Roger

[RDV]

Have you tried this one? I'm going to.

Regards

RDV

[Rodgre]

nevermind,
I'll try that now

Roger

[petemoore]

Let me know how it goes.
 I don't know that my Transistor BM is 'right', but it IS muddy.
 The OA versions I try never worked out either...
 A while back I was trying the OA muff stuff.
 I would like to hear that somebone's actually sorted this out and gotten a usable [Similar to Orig.] Muff typ tone from one of these OA, BM schematics.

[Rodgre]

Okay, bit by bit, I'm trying the circuit from the Little Big Muff schem.

So far, I have wired up the first dual op-amp. Now, just to see that I'm in the ballpark, I have tapped off of the output of that op-amp (pin 7) just to see that I'm getting signal.

I am getting a sick fuzz, but I'm also getting an unstoppable, unchangable oscillation. The oscillation is at a lower note.

What's the deal? any ideas?

Roger

[RDV]

add the 1uF and the 8.2k and listen from there

[Rodgre]

I forgot to mention that. I do have those two components hooked up. It's still oscillating. Hmmm..... Very very frustrating.

Roger

[RDV]

Maybe the 741 stabilizes the circuit.
It seems like it shouldn't be fuzzing at all since all the diodes are in the second OA.
You've got the first OA grounded, right?

[Rodgre]

The super fuzzout/oscillation is occurring on the far side of the 10K that's coming off of pin 1. Pin one gives a clean signal. As soon as we pass the 10K, it's mahem.

Thank you so much for walking me through this.

Roger

[RDV]

What voltage are you reading at pin 3 ?

[RDV]

from the 10k on the far side of pin1 you are going into pin 5, right ?, cause I think pin 6 would cause some oscillation.

[Rodgre]

At pin 3 I'm getting 4.68v from a brand new alkaline battery.

I just doublechecked and it seems like all is right. It's just super saturated fuzz (not a bad fuzz either) with a crazy oscillation.

Maybe my problem is that I need to build this circuit on a board the size of my head so things aren't so close to eachother. My layout is nothing crazy, as far as parts shorting against eachother, but it's such a pain to troubleshoot when I've soldered everything on this perfboard. I need to breadboard this.

I just have no patience. This is a box that I've wanted on my live pedalboard for years now and I figure, "hey, build it once, and if it works, box it up and take it to the gig." Ugh.

Roger

[ErikMiller]

I can offer no help other than to say my hat's off to you for taking another crack at it.

I've tried (I think) 3 different schematics, including the one posted above, and none of them worked correctly.

What got me wanting to build one was that I bought a factory fresh Big Muff about 20 years ago (probably right before Mike shut the doors) after trying my friend's and falling in love with it.

Mine sounded good, but not the same as his. I did some repair work on his (broken wire or switch or something) and was very surprised to see chips on the PCB where mine had transistors. I would have thought that the older one would be transistors and the newer one IC's, but it was the other way around.

The difference in tone was similar to the difference between a silicon and germanium Fuzz Face. In this case, the opamp Big Muff sounded more germanium-ish. Leads me to think that maybe they used germanium clipping diodes in the one I tried. EH were surely not picky about what components they used. If someone got Mike a closeout deal on a truckload of germanium diodes, he would have used them.

I'm really rooting for you. Good luck.

[Somicide]

That's crazy stuff, from EH.  I only wish I'd heard an OA Big Muff, I've only heard reissue sovteks with transistors.