big muff super mods

[cd]

Use this schematic, as far as I can tell, it's the same as the board pic you posted (except for a cap missing from pin 3 of the 4558, but that shouldn't make any difference), and all the pinouts and whatnot are correct.  I simulated it and it works as expected.

http://img17.exs.cx/img17/9039/EH_BigMuff_OpAmp.gif

[cd]

Another thing, if you want to start messing around with it (provided everything works, no traces cut, etc.) I'd start with the tone control values.  Stock (as per the schematic I posted) the tone control doesn't have a lot of range - but you may like the sound, so play it by ear.  Also, in simulation the Sustain control only seems to go on or off - the sweep isn't very smooth - does it sound that way with the actual pedal?

The stages work something like this (I think - feel free to chime in if I'm wrong):

1) Guitar >
2) inverting stage with 6x gain (also lows cut but it's out of the audio range so it doesn't matter >
3) non-inverting gain stage with 10x gain and bandpass filter (lows cut slightly out of audio range, but highs cut dramatically) >
4) sustain control >
5) inverting clipping stage with 57x gain (enough to clip even with a tiny signal)
6) tone control (standard BMP high pass/low pass blend >
7) volume control >
out to amp/other FX

[petemoore]

Should there not be a voltage divider for 1/2V since it's running 3 opamps?

[cd]

Should there not be a voltage divider for 1/2V since it's running 3 opamps?

Look again, there are two of them in there.

[gdmart]

on my pedal there is a toggle switch what is it supposed to do? mine is disconnected

[cd]

on my pedal there is a toggle switch what is it supposed to do? mine is disconnected

Probably a tone stack bypass.

[Travis]

By toggle switch, do you mean the slide switch on the back of the unit?
That is definitely the tone stack bypass.  Those switches go bad with surprising frequency, as do the power input jacks.  If you are lucky, the "mod" may be nothing more than a disconnected switch.

The opamp versions that I've heard are far superior to the discrete versions.  Significantly less mush, but still fully capable of going into over-the-top, out of control fuzz.  They also have all had the EH, "we'll put anything in here" thing going on: 250V caps, etc.

[jmusser]

I'm not sure that after hearing the "Whisker Bisquit" sample I wouldn't have left the big Muff on E Bay! I have a Russian Big Muff, and it doesn't have near the sustain that thing has. It has the tone to be sure, but the WB has the sustain beat hands down. I'll have to build the bisquit for sure!

[gdmart]

is there a wiskerbiscut pcb to be had or just schematics??

[B Tremblay]

Here's the Whisker Biscuit article, complete with perfboard and PCB layouts:
http://runoffgroove.com/whisker.html

[gdmart]

can some one verify the exact location of the 9v+ lead on the picture of the board i posted?  also on the board it says n.p. is that the same as neg ground? I assumed this was pos ground thanks.
    can I test componets on the board? how do I best test everything on the board to see whats good and whats not??

[petemoore]

Use this schematic, as far as I can tell, it's the same as the board pic you posted (except for a cap missing from pin 3 of the 4558, but that shouldn't make any difference), and all the pinouts and whatnot are correct.  I simulated it and it works as expected.

http://img17.exs.cx/img17/9039/EH_BigMuff_OpAmp.gif

Jumper...add additional cap...what's that mean? J1 gets what exactly and J2 gets what exactly...between the text and J's these things are never real clear to me...sezz add 'an' additional 10uf cap...but there's two J places there. Also says jumper J2 to ground?...that would defeat the 10uf just to it's right...hmm :?

[Tobias Karlsson]

Here's a schem of the Little Bib Muff (OP).
It's also a pic of the pedal so you can compare with your if it's the same. I believe this schem is correct.

You can also see what's difference to the "big" Big Muff (OP)

http://www.diystompboxes.com/pedals/lbm.gif

Tobias Karlsson in Sweden

[petemoore]

I tried an LBM and gave up, tiring of the 'stupid' question and answer quandreis...[ I couldn't phrase the questions well or make heads or tails of the answers...texted help of the forum] :oops:
 The text/jumper schematics sections are not clear to me...I see two 10uf caps [opamp BM prelim schem], and text reference to one, the wiring in the jumpered areas are just hard for me to make heads or tail of.
 I'm going to try a third BMP [OA version], the transistor version 'worked' but was muddy and I wasn't so good at modding and debugging at that time.
 If I can't figure it out somehow on paper, I'll simply build it so I can wire it a number of different ways fairly easily.

[Mike Burgundy]

The opamp BMP I had in for repairs had two clippers, like the transistor one. Perhaps there's more than one version of this circuit as well. Didn't think to trace it though ;(

[Mike Burgundy]

Pete, it's not that hard!
Combined with the text, this:



means you have this:



but should replace that with this:



J1 and J2 stands for jumper 1 and 2, a jumper is a copper trace or wire that is either optional - as in this case, or a 0-Ohm resistor you sometimes need to make a layout work. Optional means you have the option between to circuits - not that the trace can be used and/or omitted without making other adjustments, o'course.
That clear enough?

[gdmart]

tobias can you tell me from the same schematic/pics i posted previously.Where the 9volt + attaches to the board?.i think its the same board pete is also refering to  thanks

[petemoore]

Ok...so here's my take on it...
 Leave J2 and J3 disconnected, and insert a 10uf between the bottom of R9 and ground...R9>[47E] ...['E'=ohms?]
 insert a 10uf where J1 ---- 'isn't'.

[Tobias Karlsson]

tobias can you tell me from the same schematic/pics i posted previously.Where the 9volt + attaches to the board?.i think its the same board pete is also refering to thanks

In mine it's connected here.


We have almost the same board and both is used by EH for both the Big Muff abd Little Big Muff (OA). I've converted mine to the BM :-)

I also have to confess that by opening mine up I discovered a small error in my schem, not a biggie but...
Not only IC2, the IC1 connects to the 47ohm resistor then to +9v.
So both the VS supply pins off both the Op amps connects together and then to the 47ohm that connects to +9v.

I don't think this will change anything drastic but I will uppdate the schem and send it to Aron

Tobias

[gdmart]

i cant seem to get any noise from this thing.I believe the board works.I think the off board wiring is wrong.The 9 volt battery seems warm to the touch.Is this thing pos or neg ground???.If some one could make a drawing of the off board wiring using a 3pdt fuller type switch,9volt only and no bypass or led,pertaining to the board Ive posted that would be most helpful.  
           :cry: