OpAmp Big Muff Reissue - Adding a Mid knob

[Bananagab]

Hello guys!

I have some experience building pedals and eurorack stuff, but I never really modded anything. I want to try to add a Midrange knob on my OpAmp BMP but I don't know where to start. Obviously there is a couple of tutorials but mainly for the classic Big Box Muff and I dont think it applies to the op amp version?

Can you point me in the right direction? Thank you

[idy]

You have a schematic for OPamp Muff? And you are looking at the page about regular big muffs?
And both have that distinctive tone control, overlapping HP and LP, right?
Bass side is C to ground, R in line
Treble side is R to ground, C in line?

And the common passive mid "adjustment knob" is just adding a Pot in series with the (adjusted smaller) R to ground, right? Changing the response of the HP, bigger R=lower HP, the high pass side is letter more mids through.

A "regular" Muff might have 3.9 n in line with 22k to ground for the HP
and 20k in lie with 10n to ground for LP

The Opamp schematic I am looking at shows 100n in with with 1.2k to ground for HP
and 5.6 k in line with 120 nf fo ground for LP, but there's a series "blocking" cap, 1 uf. In series with the 120n that makes... 107nf. (the blcking cap is "moot"...ish)

So, the Rs are smaller, yes? The Old style, AMZ suggested changing the 22 k to ground for 3.3k plus 25k pot. But the change he suggests is from 22 to a new maximum, 28.3k, about 25% greater. Maybe the Opamp muff could use, instead of 1.2k a 1k pot with 500ohms, or nearest thing you've got....
also the cap for bigger, from 4n to 12n. So up from 110n to 330n or so.

These are easy thing to play with....
Next more aggressive plan is active mids....

[GibsonGM]

Hi Banana, if they haven't said 'welcome', then - welcome

Question: is the Muff a commercial product or one you made?   It's not 'impossible' to mod up a factory unit to do what you want, but it will change it and maybe make it worth less if you resell it (worthless perhaps).   If you don't care, carry on.

This might get you started...many useful mods to the BMP tone stack!  http://www.muzique.com/lab/tone3.htm

[idy]

I added an edit. The AMZ mid control also upped the series cap x3....

[Bananagab]

You have a schematic for OPamp Muff? And you are looking at the page about regular big muffs?
And both have that distinctive tone control, overlapping HP and LP, right?
Bass side is C to ground, R in line
Treble side is R to ground, C in line?

And the common passive mid "adjustment knob" is just adding a Pot in series with the (adjusted smaller) R to ground, right? Changing the response of the HP, bigger R=lower HP, the high pass side is letter more mids through.

A "regular" Muff might have 3.9 n in line with 22k to ground for the HP
and 20k in lie with 10n to ground for LP

The Opamp schematic I am looking at shows 100n in with with 1.2k to ground for HP
and 5.6 k in line with 120 nf fo ground for LP, but there's a series "blocking" cap, 1 uf. In series with the 120n that makes... 107nf. (the blcking cap is "moot"...ish)

So, the Rs are smaller, yes? The Old style, AMZ suggested changing the 22 k to ground for 3.3k plus 25k pot. But the change he suggests is from 22 to a new maximum, 28.3k, about 25% greater. Maybe the Opamp muff could use, instead of 1.2k a 1k pot with 500ohms, or nearest thing you've got....
also the cap for bigger, from 4n to 12n. So up from 110n to 330n or so.

These are easy thing to play with....
Next more aggressive plan is active mids....

Thank you! You pretty much told me exactly what to do. I just disassembled the pedal to compare to the available schematics online. The values are not exactly the same but close enough. I will order what I need and try it out!

[Bananagab]

Hi Banana, if they haven't said 'welcome', then - welcome

Question: is the Muff a commercial product or one you made?   It's not 'impossible' to mod up a factory unit to do what you want, but it will change it and maybe make it worth less if you resell it (worthless perhaps).   If you don't care, carry on.

This might get you started...many useful mods to the BMP tone stack!  http://www.muzique.com/lab/tone3.htm

Hello! It's the standard EHX OpAmp Big Muff Reissue. I wasn't planning on selling it anyway, just want to make it better and learn in the process :p

[antonis]

Next more aggressive plan is active mids....

+1