In the proposed versions of the amplifiers used lateral mosfets because they have the transfer and output characteristics almost identical to pentodes that allows as close to a tube sound. They also have a negative drain current dependence on temperature, which eliminates the need for thermal stabilization. The amplifier is built on the classic "tube" schematics - differential stage and further push-pull output stage that drives the output transformer.
40 W (Primary coil impedance Ra-a = 200 ohms)
Schematics
PCB (ready to transfer)
Upper side assembly
Bottom side assembly
Assembled board
Example of transformer windings for the 20x60 core:
The windings 153 (0,6 mm) - 91 (0,6 mm) - 37 (0,6 mm) - 54 (0,6 mm) - 153 (0,6 mm) - 91 (0,6 mm) - 37 (0,6 mm) -- 54 (0,6 mm) - 153 (0,6 mm) - 91 (0,6 mm) - 37 (0,6 mm) - 54 (0,6 mm) - 153 (0,6 mm). 153 - the primary, all in series. Secondary parallel. 91 - 4 ohm, 91+37 - 8 ohms, 91 +37 +54 - 16 Ohm
Mouted on chassis
90 W (Primary coil impedance Ra-a = 80 ohms)
Schematics
PCB (ready to transfer)
Upper side assembly
Bottom side assembly
Assembled board
example of transformer windings for the 20x30 O-core:
Each coil 232 (0,7 mm) - 217 (1,0 mm) - 90 (0,9 mm) - 127 (0,7 mm) - 232 (0,7 mm). 232 - the primary, all in series. Secondary parallel. 217 - 4 Ohms, 217+90 - 8 ohms, 217+90+127 - 16 Ohm
Assembled in 2U rack with three channel fet version of Ecstasy
Some comments to the schematics:
Potentiometer "Symmetry" used to set equal amplitudes of signal halves.
Resistors R4, R7 (for 40 watts) and R5, R8 (for 90 watts) determine the sensitivity of the amplifier input. If they decrease the sensitivity increases and vice versa.
Resistor R25 (for 40 watts) and R1 (for 90 W) can be connected to the negative feedback from the output transformer with adjustable Presence. You only need to take into account that the resistance of the resistor 1,6 kOhm that is 3 times less than usual in the tube circuits (4,7 kOhm). To get the same frequency response capacitor in series with the control you need to increase by 3 times.
Example of "Presence" and "Depth" schematics:
Output signal limitation
