Op-Amp Big Muff Tone Mods??

[bradberry00]

Hey,

I recently built an op-amp big muff. It sound pretty good when the tone control is up to about 9-10 o'clock but after that the sound is way too brash/trebly. what caps should I look at the remedy this? would it be the 120n from the tone pot to ground?

thanks,
-david

[bradberry00]

Maybe a low pass filter between the tone and volume pot? wonder what a good resistor/cap value would be??

[Scruffie]

Download Duncan's Tone Stack Caculator and select the Big Muff style and then you can enter the original values and play with them until you find something you prefer the look of and experiment.

There already is a Sallen Key low pass filter in the middle of the circuit which you could tweak or the much easier option of increasing the value of the 150pF cap in the feedback loop of the 741 which will also roll off more highs.

Or... don't turn the tone control past 9/10 o'clock.

[Mark Hammer]

The component values are different, but the basic design of the BMP tonestack is preserved for the op-amp version, as shown below.

R11/C9 provide the lowpass side, and R12/C8 provide the highpass side.  The calculated highpass rolloff is at 1326hz, which suggests that at max treble you should get something that appeals to mosquitoes and dogs with sensitive hearing, but not to anyone who expects to hear a guitar.  BY contrast, R11/C9 yield a rolloff at 237 hz, leaving a reasonably big midscoop.  Since the two sections have fairly shallow rolloffs, the scoop is not that big, but it's there.

One way to make more of the Tone control range usable is to let in a little more upper mids for the bass side, as well as for the treble side. 

Making R11 3k9, instead of 5k6, will raise the rolloff of the bass section to 340hz.  Making R12 2k2 instead of 1k2 will lower the rolloff of the treble side down to 723hz.

Because the two sections only have a 6db/oct slope, and since 723hz is just a bit over an octave above 340hz, putting the Tone control at midpoint should get you a balanced tone with no scoop.  Rotating treble-wise from there should get you something with a little more bark to the buzz, and rotating bass-wise from there should get you something a little throatier than muffled.