Op amp Muff Tonestack

[kaycee]

I'm having a go at the op amp Big Muff and I'm wondering whether the tone stack has the same scooped mids as the standard transistor  version, of which I am not a fan?

[John Lyons]

It sounds a bit flatter in the mids to my ear.
(Not that I only have one) 

[armdnrdy]

If you are not happy with the mid scoop tone stack you can change it.

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

This is a very easy to use program!

[kaycee]

Thanks, but i don't think thats going to help me as the tonestack as in the op-amp muff isn't the same as the Pi one so its not included in the models featured. Plus, even if it was I'd be just shooting in the dark sticking in random cap and resistor values. Maybe I'll build one stock and maybe one with the Pi version t/s using some of the many mods around to tweak it?

[DiscoVlad]

The topology of the Opamp Big Muff tonestack is the same HP and LP filter with blend potentiometer that the Transistor Big Muff uses except for the 1uF coupling cap on the LP side (which rolls off everything below about 20Hz), and a slightly  different frequency range because of the different component values (mid sweep, that is, the knob at halfway is approx. 600Hz for Opamp, and 1.06kHz for transistor).

Schematic of Opamp, Modified (1uF cap removed), and Rams head Muff Tonestacks.
http://i.imgur.com/90ajWum.png

Frequency Response for each (potentiometer at halfway):
http://i.imgur.com/jDQWPiU.png

The Opamp version uses large caps, and small resistors, while the Transistor version uses small caps, and large resistors - presumably due to the differing drive characteristics of opamps and transistors, or maybe that doesn't make a difference and the important thing is the cutoff frequency (1/ (2*pi*R*C) of each side of the filter (e.g.. R=1k and C=100nF will have the same cutoff frequency as 100k and 1nF... or 2k and 50nF)

The difference in sound between the two families mainly comes down to how each version distorts the original signal than the tonestack.
An Opamp muff set up with a tonestack that covers the same range as any given Transistor muff would more than likely still sound different.

Hope this helps!

[armdnrdy]

Thanks, but i don't think thats going to help me as the tonestack as in the op-amp muff isn't the same as the Pi one so its not included in the models featured. Plus, even if it was I'd be just shooting in the dark sticking in random cap and resistor values. Maybe I'll build one stock and maybe one with the Pi version t/s using some of the many mods around to tweak it?

The tone stack calculator that I posted a link for will keep you from "shooting in the dark sticking in random cap and resistor values".

You can make changes in the calculator and see how it changes the frequencies. It's a design tool!

Now you may say "If I can't hear it.... I won't know what it sounds like"

The lower frequencies are the bassier tones, the mid freqs are the mid tones......and so on.
Using this tool is much better than "shooting in the dark sticking in random cap and resistor values". 

[kaycee]

Ah, thanks guys. I didn't realise the calculator could work from both ends as such, so maybe I can get something out of it after all, that's neat! So, essentially it's the same ts, does sound a bit different to me, I usually can't stand muffs but this isn't too bad after all. Thanks for the help

[kodiakklub]

Triangle version: R1=33k, C1=4n, R2=33k, C2=10n;
Ramshead version: R1=33k, C1=4n, R2=22k, C2=10n;
1975 version: R1=39k, C1=4n, R2 = 22k, C2=10n;
1977 opamp version (1): R1=5.6k, C1=100n, R2=1.2k, C2=120n;
1977 opamp version (2): R1=8.2k, C1=100n, R2=1.2k, C2=120n;
Green Russian version: R1=20k, C1=3.9n, R2=22k, C2=10n;
Late model: R1=39k, C1=4n, R2=100k, C2=10n
Reissue version: R1=22k, C1=3.9n, R2=22k, C2=10n;
Little Big Muff version = reissue version.
And then some different mods:
Swollen Pickle: R1=33k, C1=3.3n, R2 = 22k, C2=47n;
Flat mids: R1=33k, C1=5.6n, R2=33k, C2=5.6n;

its all in the values. socket them and play around. until reading this yesterday, i didnt know you could get a flat filter just from changing the component values.

[garcho]

It's not really flat; it's a high pass and a low pass overlapping each other and being blended with a potentiometer. It's just about the most versatile 1-knob tone stack you can find. If you dislike it, it can be replaced by any tone stack you want (with tweaking, of course). Or no tone stack. I'm not sure what you mean by 'flat' filter. A truly 'flat' filter is called an "all-pass filter", not something you use for tone shaping.

[kodiakklub]

to clarify (and after playing with the tone calc this morning) if both R = 33k and both C = 6.8n (0.0068uf) with the spec 100K pot AND the pot set at 50%, it will CUT all freq's by about 6.75db, and when graphed, yields a flat response "curve". yes i used the word filter incorrectly, my bad. this is the mixture i am going to try next with the added 25k "body" pot as per jack orman.

[garcho]

it will CUT all freq's by about 6.75db

Isn't that what a gain/volume function should take care of?

[kodiakklub]

AND the pot set at 50%,

0%, 50%, 100%. vol/gain knobs dont* shape tone like this: