What does the Flat Mids mod really do?

[Unclerny]

Hi Forum, this is probably covered somewhere in here but I cna't find it.

What does the Fulldrive Flat Mids Mod really do?

I can see it's injecting some of the signal from one place into another but past that I'm stumped.

Thanks UE

[Unclerny]

Okay, so I 've played with this a bit and I hope that this post gets maybe someone to give me a more technical explanation.

I noted that the 47k and .1uf cap are wired between the Gain pot and resisters of the feedback loop to the output of the tone stage opamp.

I first just wired it placed between the stock 51k resister and the gain pot to the opamp output.  It does work but is only noticable after the note begins to decay and can't be heard at all while the notes are being attacked.  Not really a useful thing.  It did change the gain structure some.

Then I decided to wire it as the Fooldrive2 drawing and placed it between two 22k resisters that replace the 51k.  This made a marked difference clearly adding more highs.  The gain structure doesn't seem to be as affected.  Apparently what it's supposed to do! 

Can anyone explain what I just learned?  Why did the placement between the two resisters make such a difference?

[petemoore]

  If this is a TS type circuit, GEO has a nice article on 'tubescreamer'.

[Unclerny]

Yes the TS circuit and I have the GEO work.  I'm mostly trying to understand what's happening with this mod.

UE

[Projectile]

Bump.

I've got a TS circuit breadboarded and I've tried out just about every mod under the sun, but I don't really understand what is going on with this one, and it doesn't seem to be working right for my circuit. Any help would be appreciated.

[aziltz]

i was wondering this lastnight myself.  i think it might be bypassing the low pass filter between the clipping stage and the tone stage by adding that feed forward line.  That low pass filter is what creates the mid hump, because its centered in the mid frequencies, and then the tone control can add/subtract treble afterwords.  The the only thing i could think of without actually doing a derivation of the signal flow and impedances.

[Andi]

Got a link to a schematic?

[Projectile]

This is the best one I could find:

http://img5.imageshack.us/img5/1426/fulldrive22004withmods.jpg

I've got a pdf file also with basically the same mod, so it seems it's drawn correct. I tried it and it did flatten the mids out a little bit, but at the cost of a DRAMATIC loss of gain. Just seemed like a silly kludge that totally screws with the normal operation of the pedal.  The tone control doesn't function properly anymore, the gain knob loses most of it's range, and all for a tiny bit of a flattening of the frequency response? This is a stock mod on a popular commercial pedal? Really? I don't get it.

[Gila_Crisis]

just look here:
http://wlst.jp/effector/fulldrive2/Full-Drive2-Rev.G.pdf