Mid range flat mod for a tube scramer.

[MmmPedals]

Anyone know an easy way (ie without adding a mid freq. tone control) to flaten out tubescreamer mids. Alot of the new tubescreamer clones have a classic/modern switch which does this.

[Mark Hammer]

Technically, it would be a switch to select between two different RC combinations from the inverting pin of the first stage to ground.  Stock, it is a 4k7 resistor and .047uf cap.  This produces a bass rolloff at 720hz, which makes mids seem more prominent.  Replacing the .047uf cap with a .22uf cap moves that bass rolloff down to 154hz which will result in a less prominent midrange.  Since so much of the signal "lives" in the low end, though, that will also increase the ffective amplitude of the signal to be clipped, resulting in more clipping.  So, to keep the clipping quality the same, while keeping more of the bass, you'll probably want to drop the max gain down from 118x (stock) to something a little more timid, like 100x.  Increase that 4k7 resistor to 5k6, and that will do it.  It will also nudge the bass riolloff down a bit to 130hz.

[MmmPedals]

Got it. i see the keely mod moves it to a .1uf cap.

[Mark Hammer]

.1uf is a reasonable compromise.  Thing is that so much signal lives in the low end that as you move the bass rolloff lower, the circuit starts to distort in a different way.  Remember that shifting the bass rolloff not only restores bass in the output signal but also increases the likelihood that more harmonic content is produced by lower notes.