Need schematic for modding my Big Muff for better cutting.

[Picassochild]

Hey guys...there are so many mods for BM so I need to ask you, what schematic will be better for modding my Big Muff for better cutting in band and to make it more distortion sounding than fuzz...discrease fuzziness in sound. Cheers.

[amz-fx]

Take out the second set of clipping diodes and it will get a LOT more guts.

regards, Jack

[Mark Hammer]

The old Sola Jumbo Tonebender was essentially the BMP circuit but it had no diodes in the Base-Collector path for Q2 (i.e., th first clipping stage was simply a gain stage without deliberate clipping).  This is opposite to what Jack suggested.  This is not "wrong" or "right" or even "better", but I'm wondering if anyone has experience with potential sonic differences between the two approaches to changing over from 2 to 1 clipping stage.

My sense is that with situation of the clipping around Q2 (as Jack suggests), rather than Q3 as in the Sola case, the lesser cumulative gain up to that point will produce a less fuzzier sound, and the situation of two clean gain stages after Q2 will produce gobs more output level.  By contrast, providing two gain stages before clipping at Q3, and only the tone control gain recovery stage afterwards, will produce a different quality of heavy fuzz, but not more output level.

Conceivably, the "ideal" unit is one where there is a diode-lift toggle for each stage so that different sonic configurations can be achieved.

[Dragonfly]

could also "preamp" it by adding the EH LPB1 or Screaming Bird booster in front of the circuit...adds definition and a bit more gain and guts....

[Dragonfly]

Conceivably, the "ideal" unit is one where there is a diode-lift toggle for each stage so that different sonic configurations can be achieved.

yup

[Dragonfly]

Conceivably, the "ideal" unit is one where there is a diode-lift toggle for each stage so that different sonic configurations can be achieved.

another idea....

you could use a dual gang pot on the clipping diodes, wired so that as the 1st stages clipping increases, the second stages decreases, and vice versa...should make for some interesting variations. kind of like a wierd take on jacks "warp" controls....

hmmm....

[Yun]

Hey there mr.P , 

i think that you don't need "more distortion"  as more dist, or clipping, makes it more fuzzy. 



as far as resistors go; i replace the following:

-100 ohm resistors with 2.7K
-10K resistors with 12K-15K
-390K resistor with 470K

Diodes:

-try replacing them with germanium, or 2 on one side and one on the other (assymetrical clipping).
-Add caps in there for a creamier tone

You can also play around with the tone stack to "atchieve" different tones (of course)

[amz-fx]

Take out the second set of clipping diodes and it will get a LOT more guts.

The reason for modifying the second clipping stage instead of the first set is that removing the first set won't change the sound hardly at all....  you get a big signal that is hard clipped by the second set of diodes and the output is square-wave-like as in the stock BMP.  OTOH, if you remove the second set of diodes, the first set does some clipping and the following gain stage will also distort but with less hard clipping.

You want to change just the character?  Make the emitter resistors of the second and third stages 2200 ohms instead of 100.  This will reduce gain, noise and sustain, but the box will be more controllable overall.

regards, Jack

[psst]

It doesn't cut because there is a mid-scoop. It's tipical in the BMP.
Here's the frequency diagram:



Yo can clearly see the mids being cut at 1kHz.


As you say, in the context of playing with a band, the BMP "disappears", cause the highs are lost in the cymbals and the bass in the bass guitar. As we don't have mids, there's no guitar.
People usually fixes it with a equ after the BMP, making the mids stronger (think David Gilmour).
There's another solution I used, take a look at my BMP:



As you see, I have an extra pot, labelled "presence". What it does is adding mids as you turn it right.

This is the graph of my BMP with the presence at 9 o'clock:



As you see, pretty similar to a "normal" BMP.

If I turn the presence all the way to right:



You see the mids are there again.
Of course, you have the whole range with the pot, so you can dial anything between.

Instructions:
In the BMP schematic there's a 22k resistor going from the tone control to earth.
Replace it with a 3k3 and a 25k pot (linear). That will be your presence pot.
Around there you see a 4 nF capacitor too. Replace it with 10n.

That's it.

Keep in mind, though, that most of the schematics (the real ones I think) have that 22k resistor, but the generalguitargadgets schematic uses a 100k resistor there, so the freq graph is totally different:



And last, there's another thing you can do, bypassing the whole tone control. In very old BMPs there was a switch to bypass it. The result is very similar (almoost equal) to my presence at max.
In my BMP you can see both modifications, although what I suggest is installing the presence pot. That's enough and you'll get a pretty versatile BMP that cuts prefectly through the band.

Most of these ideas taken from "AMZ presence control" article.

[amz-fx]

AMZ Saturation Control:

http://www.muzique.com/lab/tone3.htm

regards, Jack

[SaBer]

Why not just stick in a baxandall instead of modding the hell out of a BMP tone control 

http://www.duncanamps.com/tsc/index.html

[Mark Hammer]

I suspect because the baxandall will eat up too much signal, or rather will eat up signal differently, necessitating some rejigging of the signal level and gain recovery.  The changes based on Jack's mod ideas are simply, don't need a change to anyone's board layout, and don't require adjusting the gain anywhere.

Another mod I have sugegsted a few times is to use two "Sustain" pots, rather than one.  The stock BMP has an attenuator pot between the first gain stage and the first clipping stage.  The signal level going from clipping stage 1 to clipping stage 2, however, is unattenuated.  Sticking a second 100k attenuator pot between the 1st and 2nd clipping sections will permit a much broader range of moderate to hard clipping, by letting you produce less "reclipping".