What's going on in in an Ampeg V4 preamp?

[Guitarist]

I've often looked at my Ampegs' design and am yet baffled by what's really going on; anybody?

The main area in question is the 6K11.

Massive plate resistors, feedback (or is it feedforward) and smaller blocking caps - but they still sound clean and bassy. I'm about to modify the duplicate channel for distortion by adding 820 R/1 UF to the cathodes and then 100K R to the plates and move the volume pot after the 2nd gain stage.

! Sorry the images wont upload so here: http://www.drtube.com/schematics/ampeg/vt22-v4-74.gif

~I'm trying to get a Fender preamp to trickle out tubey vibe at -10 dB. What could we learn from Bill Hughes and Roger Cox to this end?

[Merlinb]

Well, the input stage has the biggest anode resistor, which is complemented by a lower anode resistor and unbypassed cathode on the 2nd stage, so negligible overdrive there. Then you have a tone stack, so there's a good deal of loss. Then a ring-of-three (the three valves with feedback), so that greatly reduces the effective gain of that lot, then a cathode follower (gain of 1), then the power amp, which also has feedback.
Altogether it certainly should sound clean!

And most of the couling caps are 10nF which isn't exactly small, giving a roll off around 14Hz, depending on where you are, so no loss of bass then!

[daz]

I've never seen a preamp with values anything like that.

[Guitarist]

'wondering if anyone can 'X out" or erase the mid's circuit (and reverb but that's easier) so as to make it buildable. It would be a nice alternative as a clean channel.

The "ring of three" is the wonder...

[Suusi M]

in an Ampeg V4 The 6k11 section has unity gain with the mid pot in mid and some +- 26 db gain at the LC frequency.

[mike_mccue]

Does the mid control get hooked up to an inductor in that amp?

[Diablo]

Does the mid control get hooked up to an inductor in that amp?

Yes, look at the schematic shown above for the toroidal inductor.

[Suusi M]

just for the information the inductor is 800mH tapped at 100mH 300mH