One single triode as a PI for rack/stomp tube preamps

[Roberto]

Hi all,

During the last days I was wondering about a very simple preamp to be used together with a rack system, including a PI to be more or less saturated.

The first draft design is attached. They are two preamps, one based on a Komet 60 and the other on a Trainwreck (or AC30, that's not so far).

The last stage of both preamps is half a LTPI, of course with the cathode values doubled being one only triode.

Then the signal is taken from the plate, with a voltage divider and a pot to reduce the gain to a suitable value (to be checked, not even sims done yet), and reduce impedance at the same time.

Has anyone tried something similar (maybe with a more common Marshall 1959 or 2203 preamp)?

Thanks in advance.

[Zozobra]

I've got nothing to add, other than this could potentially be a neat trick to add a bit of "power amp dirt" to a hybrid amp. I'll see if I can sim it this afternoon if nothing crops up.

[Roberto]

Thanks zozobra, I will do the same.

[Zozobra]

I have 10 minutes to play now. I can't really get it to distort like an LTPI. It kinda looks more like a cathodyne in the trainwreck implementation!

[Roberto]

Thanks Zozobra,

I will check if simulating a depletion mode mosfet instead of the second triode of the PI, halfing all the resistors to ground, can be of any help.