DIY Tube Preamp for SS-Poweramp

[FrancisInter]

Hi. I had to build a solid state poweramp for school. Its about 100 Watts and works fine. Now i need some kind of preamp for it. And because I like the sound of my Orange Micro Terror i thought a 12AX7 preamp should work fine. Are there any real simple low voltage preamp schematics with a 12AX7. I just need volume, tone and gain. I have +- 35 power supply in the amp.

I would chase the signal in my Orange but the PCB is so tiny and with all the SMD parts its hard to figure out whats going on.

[PRR]

Look at what a tube needs and gives.

You need 6V or 12V at *high* current for the heater. Say 12V at 0.150A. You "can" get this from the 35V, but you must waste-off 24V at 0.150A or 3.6 Watts. A 150 ohm 10W resistor will do it, but it needs space and air.

Tubes sound different below ~~100V plate supply. 35V is really pushing it.

SS amp inputs are often quite low impedance, even 10K. Optimum load for a happy tube is over 100K. Even higher when you go lower supply voltage (current falls-off faster than voltage).

It would be more logical to study/plagiarize the many-many solid-state preamps found in commercial guitar amps. Millions of players are very happy with them.

[Somicide]

Look into the preamp emulations that are floating around here (Fetzer Valve, Black Forest, Dr Boogey), and see which suit you.  Build a nice clean preamp and have it switchable to whichever dirty preamp emulation you like, just an A/B type switch even.  www.runoffgroove.com has a few different emulations, and the black forest thread has multiple high-gain style layouts in it.

[FrancisInter]

I think the ROG Thor sounds very nice in various YouTube videos. Could I use it as preamp ?

[PRR]

The preamp part of the amp in this recent thread would be an excellent choice for your power amp. The FETs have a semi-tubey sound. The topology is classic. The preamp eats +32V which can easily be gotten from your +35V rail with an R-C filter such as is shown (you might drop 680 to 470).

http://www.diystompboxes.com/smfforum/index.php?topic=101517.0