Tube Screamer FullDrive Flat Mids Mod Solved...

[ShadSunsCrash]

I wanted to do the Flat Mids mod for my TS9 instead of a bass boost mod id been using along side a diode lift and asymmetrical/symmetrical switch. But everywhere i looked people were saying to run a 47K resistor in series with a .01uf (10nf) cap in between the output of the 2nd opamp stage (pin 7 on JRC4558) and the wiper of the Gain pot. But that just doesn't work, like at all. Zero Change.

Everyone who tried it said i just wasnt the same as their fulldrive Flat Mids position. So i looked at the fulldrive schematic and scratched my head for awhile and the answer only became clear once i looked at the TS9 schematic side by side. Ill post both below. So whats happening is the Fulldrive Gain pot is wired differently from the TS9. On the TS9 youd want to wire the series 47k and .01uf in-between opamp pin 7 and the gain pots 1st lug. Its obvious now but i assure you for some reason it went over my head and everyone elses whos tried to do this mod that ive encountered. On the fulltone lugs 2 and 3 are connected but on the TS9 the third lug is left open and it doesnt need to be jumpered for this mod to work correctly. Anyways just thought id share this.

If im missing something or in error please dont hesitate to share your wisdom so more of us can do this mod to our Tube Screamers correctly lol.

Both Schematics below, youll see the difference in the gain pots and if you follow the circuit youll see that to be in between the gain pot/diodes and pin 7 as on the Fulldrive youll have to be connected to pin 1 on the TS9. I know at least a few people who tried this mod but gave up because it wasnt correct. Hopefully this ill help to stop the incorrect mod information being circulated. And if anyone would like to further explain why this only works in this orientation in more detail please do!


The Fulltone has many variations so I just had to choose one that was easy to read but they should all have similar gain pot connections.




Courtousy Of ElectroSmash, check out their Classic Pedal Analysis if you havent already. They are full of useful info.