Ampeg GVT15 - What circuit is that?

[Badside]

Really really loved that amp, for the first time a small amp that sounds just like a big amp when cranked except quieter (instead of smaller).
I don't want to clone it (buying it would be cheaper), but I want to study it as a basis for a build.

Although Ampeg does not publish schematic, they do have a block diagram in the manual, through this I learned the following:
- Input
- V1a
- Gain control
- Mid control
- V1b
- Baxandall Bass and Treble
- Master volume
- Loop/Reverb
- PI - Power amp

From what I can gather, it's probably very similar to the non-trem channel of a GU12, feeding into what I assume to be a more classic 12AX7 based LTPI. I think...
The big question right now is: what the hell is that mid control???
Single knob mid control outside of the tone stack. I know

Anyone have an idea?

[marcoloco961]

Take a look at the SVT pre amp http://www.el34world.com/charts/Schemat ... p_RevB.pdf

Keep in mind it is a bass amp, but it also has a stand alone mid control. Uses a coil with several different taps as part of the mid control.

[oldhousescott]

My guess would be a bridged-T filter with the pot in the bottom for more or less mid cut.

If you ask Pyotr nicely, he might just tell you.