EHX Big muff Ri tone bypass

feneder · Post by **feneder** » 02 May 2012, 00:47

hi there,

This is my first mod and i'd like to bypass the tone stack on a 2012 big muff reissue. Ive found a site that as a schematic of the mod, and i think i get it, but i do have a few questions:

-I have sn50pb50 solder, is that ok?
-Ive opened the pedal, but i cant undo the circuit board....(yes i know, should be easy). Anyway, should i get a really thin wrench to acces the nuts under the plastic knobs on top the pedal? Or should I just pullout the plastic knobs? Ive tried to pullout, and they are really tightly fit, i dont wanna break anything....

thx

Nocentelli · Post by **Nocentelli** » 02 May 2012, 05:57

Lead solder is what I prefer, unleaded is only really a problem if you've got an old iron that won't go hot enough though.

You won't be able to remove the pots unless you take the knobs off, you could try levering them off with a small flat-blade screwdriver, resting it against a thin layer of card to protect the pedal's finish. I've also had success by looping some strong twine or string over the knob and pulling - Just check that the knobs are definitely push-on types and there's no set screw (unlikely with the BMP) - I know thery're on pretty tight, so there is always a tiny risk you'll break a knob pulling them off.

Can you post a link to the mod you're planning to do? There are several methods, one involves actually "true-bypassing" the tone section and inserting a resistor to compensate for the volume boost, the other merely lifting the earth connections. The latter method seems to leave the tone pot still with some small influence on the circuit, which I found weird, whereas with the former method, you can add a capacitor to ground in tonebypass mode if you find the tonebypass a little too bright/hissy (I did). Please post a schem, keep us updated and good luck!

feneder · Post by **feneder** » 02 May 2012, 18:43

Thx man

This is the schematic ive found

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

I guess it's not the "true-bypass" since it doesn't add resistors/cap. I migth try it that wat though and see if i like it. Also, i was wondering if i could use a pot instead of an spdt switch. That way i could blend the signal between the tone stack and the bypass. Kind of a compromise between the std Muff sound (which i like) and the mids needed to be heard. Could i damage the circuit by sending only a portion of the signal through the tone stack, and the other portion in the bypass (with nothing in it,,,)?

thx

Nocentelli · Post by **Nocentelli** » 02 May 2012, 19:44

feneder wrote:This is the schematic ive found

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

I migth try it that wat though and see if i like it. Also, i was wondering if i could use a pot instead of an spdt switch. That way i could blend the signal between the tone stack and the bypass. Kind of a compromise between the std Muff sound (which i like) and the mids needed to be heard. Could i damage the circuit by sending only a portion of the signal through the tone stack, and the other portion in the bypass

That will work certainly, you just need to identify the 10n cap and 22k resistor and lift their connections to ground: You can then connect wires from the disconnected ends of the cap and resistor to one lug of a SPST switch, and wire the other lug to ground (maybe one of the now-empty ground pads). When the switch is closed, the cap and resistor are both grounded and the stack works normally: When the switch is open, the ground connection to those components is broken and the tonestack is effectively bypassed.

If you want to blend mids back with a pot, there are far better ways than creating a bypass path: Search for "big muff mids" and you'll find many different solutions. My favourite is one used by the Earthquaker Hoof fuzz (YABMP): They actually took it from AMZ -

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

It requires you to replace smaller cap (3900pf in the AMZ bypasss chematic) with a 22n cap (or 0.012uF in the AMZ schem in the last link), and replace the 22k resistor to ground with a 3k3 AND a 20/25k pot to ground. You then get the stock midscoop at one end of the rotation, flat mids, and then slightly boosted mids at the other extreme.

I have to warn you, that messing with the tonestack of a BMP can place you at serious risk of developing a pedal modding/building addiction.... The BMP is a very versatile circuit, and you could spend a lot of time messing with values and tinkering with the sound of the tonestack alone, the Duncan tonestack calculator below allows you to change the values of the caps, resistor and pot and see the effect it has on the sweep so you can tinker to your heart's content:

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

You cannot damage a pedal by rewiring it: Please note that this is not the same as saying tinkering with it will not stop it working. If it stops working, you've wired something wrong and will have to find the fault and fix it....

In my own personal experience and opinion, modding commercial pedals can actually be trickier than building one from scratch. The traces on manufactured pedals are often rather thin and can be difficult to unsolder/resolder without damage. If you like the idea of modding a BMP, I'd suggest considering medium/long-term getting a breadboard, laying out your favourite BMP schematic and then just messing around with all of the sections: Try different coupling caps, different clipping options, add extra pots, switches etc, to find your favourite sound. You can then get a standard BMP pcb and solder your own custom personalised BMP, or maybe even make your own veroboard/perfboard or home etch a pcb yourself.

feneder · Post by **feneder** » 03 May 2012, 02:35

nocentelli

thx for your answers, very helpfull

Nocentelli · Post by **Nocentelli** » 11 May 2012, 18:25

I got a pm about this mod, so I thought I'd paste my reply here aswell in case anyone else finds it useful:

Does this mean i wire the ground to both the middle and right pins?

Yeah, you've got it. The pot is wired as a variable resistor, meaning you only actually need to connect two pins, the middle and left (the right-hand pin is connected to the centre wiper by convention, but will work just the same if left unconnected). Incidentally, pins on a pot are usually numbered by a convention whereby if you hold the pot with the shaft towards you and the pins pointing towards the floor, left to right the pots are numbered 1-3. If you connect ground and the 3k3 using pins 1 and 2, the pot acts as mid boost (i.e. turning the control "up" or clockwise) changes the sound from midscoop -> flat -> midboost; If you connect pins 2 and 3, it is reversed and acts as a "scoop" control, i.e. clockwise increases the scoop...

I think that's the right way round... at least that's what Duncan's tonestack calc tells me...