Op Amp Muff Fuzz overdrive mods?

[MuffinFlop]

Hey, all

I'm rather new to building pedals and electronics in general, so I was hoping you could help me out.
I've been tinkering with the  op amp Muff Fuzz, and was wondering if it was possible to mod it to lower the amount of distortion to put it into more of a lower gain overdrive territory.

Thanks

[Mark Hammer]

The first stage has a gain of 5x, so not much to tinker with there.  The 2nd stage is quirky in that there is no gain-setting feedback resistor.  Rather, the diode pair serves as the gain-setting element that the negative feedback comes through.  I can only suggest sticking maybe a 50k variable resistance (pot) in series with the diodes, and see if that does what you want.

Alternatively, since there is no treble-taming anywhere in the circuit, try this and tell me what you think.  Connect the wiper of a 50k-100k pot to the inverting input in stage 2, and one of the outside lugs to the diode pair (the leg of the pot goes between the inverting pin and diodes, right?).  Now run a cap - and I'll pull a value out of my hat and say 1000pf - from the output of that stage to the other outside lug of the pot.  Rotating the pot in one direction should reduce the clipping action of the diodes while increasing the treble-cutting action of the cap.  Rotating the other way opens up the treble and increases the clipping.   Presumably, settings in the middle give you something that is a little dirty, and not so raspy.

I would recommend building it with an LM/MC1458 dual op-amp, rather than something higher quality.  The 1458 will keep the super high-end reined in.

[MuffinFlop]

Thanks for the suggestions, Mark. I've gotten desirable results using a 10k-50k resistors in parallel with LEDs, almost Guv'nor like, though the noise floor has raised significantly. Swapping between 4558 and TL072 doesn't change anything other than a tad more treble with the latter (I actually enjoy the high treble content of this circuit). I'll try the resistors inline with the LEDs tomorrow to see if that helps with the noise.

Also of note, nothing in the second feedback loop creates a huge, piercing gated fuzz that was pretty fun to jam on.

[antonis]

I've gotten desirable results using a 10k-50k resistors in parallel with LEDs,

Consindering that the original closed feedback loop gain is 470k/(82k+Fuzz pot+47k) you've reduced it dramatically...
(in practice, you've attenuated the incoming signal a lot..)

[MuffinFlop]

I've gotten desirable results using a 10k-50k resistors in parallel with LEDs,

Consindering that the original closed feedback loop gain is 470k/(82k+Fuzz pot+47k) you've reduced it dramatically...
(in practice, you've attenuated the incoming signal a lot..)

You're thinking of the op amp BIG Muff... I'm working on the op amp Muff Fuzz.


I am also building another op amp Big Muff, but the only things I'll be changing from stock are the coupling caps, removing the tone stack, and fixing the sustain at max.

[Gus]

something I posted before

[MuffinFlop]

something I posted before

That looks pretty fun, but I'm trying to keep this a one pot kinda deal.

[MuffinFlop]

Alright, so as far as amount of distortion is concerned, I've settled on a 1meg resistor in line with back to back LEDs, parallel with a 50k resistor.
It still seems to have a ton of noise. It's so bad that stacking with other pedals is almost unusable. Any suggestions as to eliminating some of that?  I've checked and rechecked all ground connections. Single coils and humbuckers make no difference, neither does placing it on it's own power supply. Neither of my Big Muffs have anywhere near this amount of noise.


EDIT: This is the kit I'm using - http://pedalparts.co.uk/docs/FuzzyMuff.pdf

[Gus]

Try a jfet input opamp TL072 etc.  I like LF353s in circuits like this.

The circuit I posted sounds very cool.  Try it with a passive bass with .0047uF and 470K at the first stage.

[Mark Hammer]

Does that threshold control provide anoise-gate type function?

[Gus]

Does that threshold control provide anoise-gate type function?

Yes but IMO more for fun than noise reduction

As I wrote on the schematic it is a mix of muff fuzz and ultra fuzz (gating/threshold)
I like the tone control values
The two switches are fun open loop or feedback
diode clipping or opamp clipping
Values are good starting point for passive Ps and Js does sound nice with an active Stingray bass

[MuffinFlop]

I am using a TL072 right now, but it doesn't change the amount of noise vs the stock 4558. I'll swap out the 10n for a 4.7n and see if that helps. If not, I suppose I'll rig up the threshold gate control.

[Gus]

Is the fuzz in a metal box or on a breadboard?

[MuffinFlop]

Is the fuzz in a metal box or on a breadboard?

Right now, it's completely unboxed, but on a PCB.

[MuffinFlop]

Still unboxed (waiting on an order from ebay), but I've gotten most of the noise sorted. First, I swapped the input cap for a 4.7n, then added a 100n coupling cap inline with the 100k resistor between the two stages. That seemed to clear a bit of noise and give me some more treble, which is good as I was wanting a tinnier, brittle kind of overdrive similar to Andy Gill's. It seems just about perfect now. I also added some extra power filtering with this - http://shop.pedalparts.co.uk/Humlininatorator_-_power_supply_hum_reducer/p847124_6807259.aspx. Almost all of the noise is gone. I'm hoping once it's in the folded steel enclosure I have on order, the hiss and hum will be all but gone.

I'll get some clips up next week once the enclosures are here.

EDIT:
Just realized this is the first dirt box that actually responds to the strangle switch on my VI with the bridge pickup.

[MuffinFlop]

Here's a schematic with the mods I've put in place


EDIT:
The inverting and non-inverting inputs need to be swapped on both op amps.

[Mark Hammer]

If - with the exception of the flipped inputs, that you corrected - the circuit is exactly as shown, you won't get much clipping out of it.  Stage 1 has a gain of 5, as does Stage 2, yielding a combined gain of 25x;  not really enough to produce more than a bit of coloration, let alone overdrive.

[MuffinFlop]

If - with the exception of the flipped inputs, that you corrected - the circuit is exactly as shown, you won't get much clipping out of it.  Stage 1 has a gain of 5, as does Stage 2, yielding a combined gain of 25x;  not really enough to produce more than a bit of coloration, let alone overdrive.

Hmm... it's certainly giving me a decent amount of dirt and noticeable treble boost. I'll get clips up as soon as I can.

[Mark Hammer]

I'm always open to being corrected, and obviously you hear what you're hearing, but the values shown predict something different than what you're hearing.

[MuffinFlop]

I'm always open to being corrected, and obviously you hear what you're hearing, but the values shown predict something different than what you're hearing.

Oh, I don't mean to doubt you- you're leagues more knowledgeable on the subject than I, but it's definitely giving me some dirt. I'll check it tomorrow to make sure the LEDs/ 1m are actually functioning. It's giving me about the same amount of dirt as the 50k alone, so perhaps I overheated the LEDs.

Now, after hooking it up to a footswitch, I get a loud pop when engaging the effect. What would be the recommended way to remedy this?

And, thanks again for all the help.