[preamp]

Dear TT Forum!

I just finished my 2nd TT amp (PX18) and I am already thinking about the next project (addictive...).

I want it to be a Blackface with much headroom. However, as I mostly play with headphones, I am wondering if it would make sense to build  a BF preamp only, and not an entire amp with power stage.

Explanation: to play with headphones (95% of my time due to house regulations :-), I insert the amp with a power soaker (TwoNotes Torpedo) within the FX loop of my Line6 HX Stomp, then add cab simulation or IRs. I must admit Emma or PX18 sound really nice and sound in my ears already better than Line6 Tweed or Plexi models, and with great dynamics.

Now, I want a Blackface, and instead of adding gain and many watts after a preamp stage and then soaking 99% of that power to get a Line signal level, I was wondering if using a preamp in my HX Stomp FX Loop could not lead to a comparable result. However with the famous 'negative feedback' loop in BFs coming from the power stage, I wonder if some part of the sound character may not be lost.

Questions:
- If I stick to a classic BF Preamp (e.g. Princeton or Vibroverb, by the way all the same!) and use the signal just before the phase inverter stage or gain stage (see attached picture, courtesy of brieskorn.de ), do I have a chance to get a nice Fender-like clean tone?
- If yes, will the signal volume be enough (coming then from only 2 half-valves 12AX7= V1, and I need standard Instrument or Line level), or do I need to add another gain stage (e.g. another half-valve as additional gain stage)?

I will add that I do want to go with the full valve voltage and not use low-voltage (9V) plate values, so that means I will go with the trouble of providing at least Heaters and high voltage from a power transformer and a mini-PSU (partly) just for one or two valves - but I won't need an OT and many other parts, and it is not a matter of saving money.

Any thoughts more than welcome !!!!
Many thanks
Kind regards
David

You might want to look at the Alembic F2B preamp, which is a version of the  BF Showman preamp and was used by Garcia, Gilmour, and others, some with names that don't start with 'G.' It will certainly give you some information, even if it's not exactly what you want. Schematics and information are all over the net.

Steven

Using a BF preamp like shown in your first thread could basically fulfill your requirements.
I would suggest to add a cathode follower stage before the output in order to reduce the output impedance.
Like it was done by Rivera for the Concert II in the effect send unit. Schematic is available in the net.

Regards Stephan

Thank you to both of you, Stephan and Puddnhaid!

I had not figured out that the impedance might be too low indeed. I had found some figures under Bob Robinette with almost 3 V signal level after V1b - which could be too high for LIne voltage and may require a voltage divider.

I will update the next steps, thank you guys!!!!

Kind regards
David