12SN7 Inverting Preamp

A Simple Tube Preamp

The need for a simple  tube preamplifier was realized with this project.

It started with a PT that has similar specifications used in the Bottlehead Foreplay preamp kits.

A FWBR into a typical CRCRCRCR filter provides low ripple B+ for the signal circuit. The UF4007 diodes are snubbed and the on/off switch is bypassed by a .1uF /250VAC  rated line cap to mitigate any unpleasant power on disturbances with my subwoofer.

The signal circuit is simple : cathode biased , resistor loaded 12SN7 twin triodes cap coupled to the RCA outputs.  There are a single set of RCA inputs for line level devices.  A dual 100k ohm pot provides a means of attenuating the input signals.

Output Z is about 8k ohms. The phase inverts 180 degrees on the output of this preamp.  

I might revisit the idea of a simple 12SN7 tube preamp using a choke load and higher B+.

DT 667


12AU7 MJE340 emitter follower headphone Amplifier

Low Voltage Headphone Amplifier


This circuit originally used an IRF510 Mosfet as a source follower as seen on www.diyaudioproject.com .

I have also tried a linear PS with this circuit that puts out about 34VDC.

PT 90-0-90 > 5U4G FWR > 320mH > 44uF > 2H > 1100uF / 200K bleeder .

Subjectively, the circuit seems to sounds  better at higher B+ voltage than the original schematic calls for when using the MJE340 follower.

DT 667   12/11/2019