OP Amp Big Muff Fuzz help

[TheKingRat]

Hi guys, I'm having some real difficulty trying to diagnose what's going wrong with my Big Muff breadboard circuit. I've been running from this schematic -

http://gaussmarkov.net/layouts/opbmp/opbmp-schem.png

And a few bits from this one -

http://img129.imagevenue.com/img.php?image=943090632_V5ICBIGMUFFVERIFIED_122_741lo.jpg

I've been using my audio probe and it seems to lose signal from the 330k resistor at pin 1 of the first IC. Resistor is fine, IC is fine. It's a LM386, I've tried a UA741 too. Any help would be massively appreciated as I'm still pretty new to the whole pedal building thing. I've attached a few pictures of the breadboard.

Cheers!

[nick d]

     The first IC should be a dual op-amp , like a TL 072 . A 741 is a single op-amp , a 386 is a low-power audio amp , which is not suitable here . A 741 would be fine for last op-amp ( the one with the diodes ) . The first two ( IC 1a and IC 1b ) need to be a dual .

[GibsonGM]

Hey Rat, welcome to the forums!  Looks like you're having fun tossing this one together...you'll get it going, just need some pointers I think.

Ok...first, the LM386 isn't an opamp, it's an "audio amplifier chip". It works differently and isn't a replacement for an opamp, altho it IS a very useful chip that you can use down the road!   So put it aside for later.  

The 741 is a SINGLE opamp...one amplifier section.  The 7448 they call for is a DUAL opamp, and has 2 amplifier circuits on the chip.  This means the PINOUT is different!  So you have to either use 2 single opamps and redraw how the pins are wired, or get yourself some 4558's.   I suggest getting a few dual opamps!    I think everyone has done this when they were new!    I made a .jpg of a few chips, and their pinouts...4558, 1458, TL072 and 82 have the same pinout...little cheat sheets...

Other dual opamps you can try would be the TL072 (very commonly used) and the LM1458, which is a dual 741 and not so commonly used anymore (old model).  

The TL071 is the single opamp 'upgrade' for a 741.    Better performance in these newer ICs, and lower noise...better input impedance, etc.  Sometimes they still use them for their characteristics, tho ("grit" and so on).

Good news is that if you are wired correctly, and you just take out the first single opamp and replace it with a 4558, you'll be in business  
And the 741 IS the right opamp for the 2nd part on the schematic, as long as it wasn't damaged when you tried it in the wrong spot...that would happen from it being accidentally connected to power in the wrong way, something like that.

Happy building!

[TheKingRat]

Ahhhhh I see, rookie mistake  Thank you for your help! I've just ordered some, will let you know how it goes. Thanks!

[duck_arse]

[edit :] sorry, theking

king, instead of waiting, how many 741's do you have left over? if you answer "2" or more, try drawing out the dual-opamp section as two single opamps sections, using the pin #'s for the third stage. (there will be some pins not needing connecting on the 741's, 1, 5 and then bung em in, fire it up.

and this is why we always buy loads of different stuff we think we might one day maybe in the future actually use whan we do our orders, because you can always adapt things to other things, especially on the breadboard.

[TheKingRat]

Thanks Duck. I've got 2 741's and a 071. Sorry to be so dumb but how do I draw out the dual-opamp section into two single opamp sections? Thanks!

[duck_arse]

referring to the gaussmarkov diagram, all you really need to do is copy the original and change the pin #'s on the first 2 stages. all your (+) inputs (on the left of each triangle) will become "3", all the (-) inputs will be "2", all your outputs (the pointy end) will be "6". supply pins for the first 2 stages - pin 4 to ground and pin 7 to "VA" on each. just as in the third stage, IC2. you'll need to rip-up your dual opampsection, and spread out your 2 new 741's so you can see what you're doing.

you can pretty much interchange the 071 and the 741, don't get hung-up on which where, not this build. make sure you draw out the whole thing, with additions/corrections, so you know what to point to while building it.

[TheKingRat]

Got it working  Thanks Duck, your instructions really helped. It's oscillating like mad though and is fairly quiet, any ideas? I might try to see if I've got a couple of different op's about.

[duck_arse]

excellent. I'm sure you'll agree, "oscillating like mad" is better than "I'm waiting for a dual opamp".

you can try add a 100pF or so cap across R3 330k, to reduce the high freq response of that amp (as C6 is doing on the 741). you can also try increasing C12, try 1uF ~ 10uF, see if anything happpens. if you have the switched tone bypass thing added, try lifting the ".22uF" connected to the 47k, see if you gets volume.

there is another diagram by Gottfried Divos with some mod info contained, you might googoo for that.

but really, your fist step should be to go and follow the instructions here:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
and come back with yr results.

[TheKingRat]

Will do, thanks again Duck!

[TheKingRat]

Hi guys. Still having a problem with this one. I re-did it on the breadboard several times using Gauss Markov's schematic and using the right op amps too ( http://gaussmarkov.net/layouts/opbmp/opbmp-schem.png ) but I'm still having huge oscillation problems. There's a constant background oscillation when I stop playing the guitar. On the breadboard all the components are the same as the schematic and also the wiring is too. The only difference is I'm using all linear pots. I'm also using shielded wire for both my input and outputs. Any help would be much appreciated!

[MaxPower]

Maybe try connecting some capacitors to the op amps's power supply pins?

http://www.learningaboutelectronics.com/Articles/How-to-prevent-oscillations-noise-in-op-amps

[antonis]

A 100nF ceramic (disk) should be a good idea...

A resistor of 10 -100 Ohms in series with Vcc and Vee connections should supplement to PS decoupling...

Perhaps you need to add a 1k resistor in series with the output of LM741 (outside the feedback loop) for load resonance damping..
(although I think that - if this is the cause - it's due to breadboard's long conneting wires..)

[TheKingRat]

I can't seem to get anything to work! I put a 220nf capacitor in pin 5 (+in) and it cut out the noise but also dropped the volume/gain massively too.

[Brisance]

put it across the power rails!

[antonis]

Pin 5 at 741 is for offset nulling (as pin 1 also)...

Have you coupled pin 8 of 4558 and pin 7 of 741 with 100nF capacitors without any improvement..??

P.S.
I comeback to breadboard's many long cables..