Op Amp Big Muff redux

[Gripp]

Just my 2 cents...
I actually have an op amp little big muff and it doesn't look the same as Tobias', Anubics' or Phipott's. I'm at work right now and don't have the differencies in my head but the input cap is different, so is the V+ supply and the "bypassed" output isn't taken from the first half of the 4558 and so on.... Oh, the clipping diodes are silicon.
Somebody did the worst soldering job I've ever seen on this one and the tone switch didn't work so I decided to give it a workout but was puzzled by the differencies in the schematics. It did however work and gave a nice Robert Frippish distortion. Just wanted to fix the tone and use shielded input wire (was extremly noisy) and perhaps put pots for dist. and tone. It is presently dismantled in the to do pile on my workbench :wink:  

Best!/
Pelle Garpebring

[Gripp]

Sorry, I wasn't clear in my earlier post :oops:
It is just the in/out/switching wiring that someone has butchered with a soldering iron. This needs a rework. The pcb/components are most likely original.
Best!/
Pelle Garpebring

[Rodgre]

Okay, I took my original BMP home from the studio last night. I started to trace the circuit and it seems similar (I'm not done checking values) to the posted Little Big Muff circuit. I'll do a thorough trace and see if I can't post it.

I was tracing the PCB as well, and I may just go with tightening up that layout and making a clone using the same layout, just slightly smaller to fit into a 1590D.

I think mine had been modded before I bought it, as someone swapped out the input cap for another value, and the in and out wires are shielded.

Everywhere I turn, it's frustrating, though. I hate to whine, but years ago, I used to do PC layouts in my sleep using CorelDraw. I loved it. I could do a decent layout in a couple of hours. Now, I'm using an Imac (which crashes constantly, despite the fact that it's always in the shop) and I've shoehorned Illustrator on it to do PC layouts, and I'm nowhere near as used to using Illustrator, so it's a total pain.

I've downloaded a mac-based PC layout program and couldn't figure that out for the life of me, either. I come from a graphic design background, when it comes to computers, so zipping around with Corel was a breeze. Someone have an old PC they want to get rid of?

Back to the workbench before my next session.
Roger

[Rodgre]

This is one of the most frustrating things I've ever tried to do.

I just perfed a circuit, copying the layout of the original Big Muff that I have and I still get nothing. I must be doing something completely stupid because this is the fifth time i've tried to do this.

the next thing I can do is to make a 1 to 1 copy of the board layout and etch it and try it that way, but honestly, I don't have that kind of free time for awhile... a week or so.

Now I know why people who know how to DIY their own pedals STILL pay $200 for a boutique box. I've probably spent about that much in time in parts trying to clone this blasted thing.

That being that case, I'd just as soon buy another vintage op-amp big muff and repackage that (I still want at least ONE original one) to put on my pedalboard. Anyone have one they'd part with? I just won't eat this month, and I'll give you the next $100 that passes through my hands.

It's not like I'm trying to clone a friggin' Microsynth. It's a fuzz box! It's not that complicated.

I hang my head in shame and I hang up my soldering iron. Time to go to work.

Roger

[RDV]

Roger:

Have you done much with OAs in the past? Pinouts can be a bitch, also: what are the OAs in your original unit?

Regards

RDV

[Rodgre]

Yes, I've done a lot of stuff with OAs in the past. I can recite the pinouts of 741s and 4558/1458s in my sleep! That's why I feel like such an idiot!

My original has a 4558 and a 741.  I'm using the same, and I've even swapped out different ones in case the first ones I tried were defective.... no difference. I must be doing something ridiculously stupid. Can you sense my frustration? I've been DIYing pedals for seventeen years now! What about this am I missing? It would be comical if I wasn't so seriously frustrated about it.

I'll try again when I get home from my session tonight, but I feel like it's a losing battle.

Several times I've tried to build this one step at a time.... meaning put together the first section of the first op-amp and see if it's passing signal. I lose it somewhere after the first section.

Roger

[RDV]

This may sound crazy, but try going into the non-inverting input on the first opamp section, just reverse it. Maybe both sides of the 4558 need to be running into the non-inverting or + inputs like on a tube screamer. It could be whats making all your attempts go bad. Forget the schematic! Inputs into + & feedback loops into - like a tube screamer.

Regards

RDV

[Winged Eel Fingerling]

Hi Rodger,
I once had an Op-amp Little Big Muff which I cloned so I could have a mini Big Muff. Any way I still have the diagram I did from the Little Big Muff if it's any help.
I also encountered crazy oscillation in the second stage of the 4558 with the clone and recall having to raise the value of the 0.01uf cap to something like 0.047uf or even 0.1uf.

-Dave

[Gripp]

Dave, could you please mail me a copy of the diagram you did for the little big muff? As stated in my earlier post, I have a little big muff that doesn't seem to exactly match the known schematics. I'm really curious of what I have here. Is it modded or are there several versions of the op amp circuit? Plus, I need to remove it from the to do pile and onto the pedalboard.  
Thanks in advance!
Best!
/Pelle Garpebring Grillbeppe@hotmail.com

[Tobias Karlsson]

Yes, I've done a lot of stuff with OAs in the past. I can recite the pinouts of 741s and 4558/1458s in my sleep! That's why I feel like such an idiot!

Is there anything that you want me to check on my Little Big muff that can help you?

i still have the pedal around.

Tobias Karlsson in Sweden

[Gripp]

Thanks Tobias! Tackar!
If yours look exactly the way it does in your schematics then I'm still confused. Mine is just a little bit different, have to draw it up in order to point out the specifics...  It has a different input cap, the V+ supply goes after the 47 resistor to the other points, not straight from the 9V, other different caps and so on. It doesn't look like its modded on the pcb though. Anyhow, it is working, it just needs a resoldering of the in/out/switch. When already having it open on the bench, I thought of improving it a little. Shielded cable on the input (it is good sounding but noisy as...), true bypass ( another thing that is different, mine doesn't have the bypassed signal taken after the first 1/2 4558 but from the input of the entire circuit), maybe tone/dist controls and try original values IF there is such a thing  So I'll get back when I have thought some more.
Best!  Ha det!
/Pelle Garpebring

[petemoore]

Maybe I shouldn't type on behalf of the other OA muff wanterz.
 But I would like to see something tonally close to an OA Big Muff WithOut the buffer bypass, or any other schematic anomolies.
 I guess I'm easily confused, but still prefer to build ckt's without Any bypass switcheing on them...
 I can get past them usually, but sometimes they're 'folded' so many times, they're very difficult to follow [Bear Face] or tied to the ckt in a way [BM] that makes it necessary to re-sort that entire portion of the ckt.
 I think most of us prefer TB on our ckts, to prevent altering or tone sucking off of  the signal path, all that other stuff becomes a moot nuisance except for the repair of original aspect.

[Rodgre]

Okay, I found a stupid missed connection so the 741 wasn't getting power.

Now I have fuzz, and the controls do what they should. The only problem now is that it oscillates like crazy.

Any ideas? Could it be the layout? I followed the general layout of the pcb of the original, trying to avoid this. What would cause oscillation? Is there a cap value I should tweak?

Roger

[Rodgre]

I increased the value of the cap between pin 5 of the dual op amp and ground and that took care of the oscillation. It's pretty much working now, except it doesn't sound quite as chewy as my original. It could be tolerance of components. There were a few that I changed the value of because I didn't have the correct on on hand, but I kept it close. The fact that I did this build-up on solderless perfboard and it's finally sort of working...well now I have to build it again on a more permanant board.... Time to try to PCB layout. I won't have time to do it right until next week.

At least it's sort of working, even if it doesn't sound 100% yet. Thanks for all of your help.

Roger

[RDV]

How different from Tobias' schem is what you did? I'm dying to do one myself and I want to take advantage of all your hard work :wink: .

Regards

RDV

[Rodgre]

I think it's the same as Tobias' schem.

R17 is definitely a 47 ohm on mine.

I didn't do the "dotted-line" suggestions, as I followed the layout of my original.

Roger