anode follower

[Andy Le Blanc]

I spent a little bench time today playing with an anode follower volume control.

Fun feedback based gain control, there is a insertion loss, and a loss of presence
in the simplest form of the circuit that I was noodling with, but if its used in
a situation where that is needed or desirable, it could be just the thing.

[tubeswell]

Hi Andy,

So you put this in a signal path? (And if so, did you make any soundbytes?)

TIA

Pete

[ChrisM]

What else goes on in the grid? How is the triode biased?

[Andy Le Blanc]

yes in the signal path, to replace a volume control, just to see...
I found a paper on it once, a excerpt from a magazine, I'll dig around for it...

I have it between a 6sj7 and a 6j5, reference a 1M vol. pot. to after the
coupling cap instead of ground, it works as a volume control.

I guess the stage can biased normally, you could give it its own coupling cap
Its always neat to try out uncommon things, I didn't make any clips, but it
sounds pretty good. The feed back cleans it up a low volume.

[Andy Le Blanc]

heres the pdf. There other petty familiar circuits based on it.

Active tone controls, RIAA networks, its a precursor to OP amp designs
you see it all the time, just not so much with tube gear

[Andy Le Blanc]

A little more bench time with it... I tried referencing a simple vol/tone circuit
to the output instead of ground, as with the anode follower, it works as a vol/tone.

wasn't fully practical in this simple attempt, but it functions and has an acceptable tone.
Anybody else playing with active tube based tone circuits? I'd like to find a
few more good references and practical circuits.

[pdf64]

Burman used active tone controls - some folks really love them.
I've not tried one in 20 years.
Credit to Tracy Norton on Plexi Palace for tracing the schematic.

[Structo]

Merlin has a section on anode followers and anode mixers in his preamp design book.
I thought it was used sometimes to help tone stack insertion loss.

[Andy Le Blanc]

Ive seen the active banbaxal for years, kind of fun that it starts so simply with that volume control
Theres a Impedance relationship there, that'll be fun to sleuth...
In early tube OPamps, I've noticed that they look like the circuit isnt much
more than a diff. amp feeding a cathode follower, or a high gain stage(s)
with a low imp. out, IC based circuits seem to follow the same general form.

thanks for the burman sheme...