At your risk. Please take all safety precautions. A suitable fuse must be in series with a battery for injury or fire hazard protection.
It is almost one MOSFET, an output transformer and gate biasing arrangment.
Today the cute little IRFS450 MOSFET was mounted on a big black anodised aluminium heatsink about 20 times the area of the transistor itself.
Vb is 12V from a 1.2Ah lead acid battery.
Bias is created as follows. From Vb a potential devider is created with one 47Kohm resistor in series with a multi turn 50Kohm potentiometer. Bias is taken from the wiper of the potentiomer and directly applied to gate.
1st test with a 100 ohm load resistor. Vd=7V at Vg=3.3V
2nd test with 6R8 load resistor. Vd=7V when Vg=3.3V
3rd test with only the primary of the Pleiades 1:1 output transformer with air gap, connected between Vb and drain. The primary DC resistance is 2.4ohms. For given conditions best sound is when Vg=3.7V.
Signal path:
Brothers is Arms - Dire Straits on vintage compilation CD - SONY D-EJ758CK CD Walkman line out - Pleiades IRFS450 - Marantz Imperial 5-G
Yes it worked and sounded surprisingly nice.
Initaly there was some clipping distortion as no volume control had been connected. A potentiometer should always be connected for ear protection anyway. The nearest potentiometr found on the table was a 220Kohms. It worked attenuating the output of the CD walkman but once there was attenuation there was severe treble cut. Possibly form high impedance feeding the high? gate capacitance.
When poentiometer (which must be changed soon to a low K value) was at max, at the begining of the song which is quiet the sound is phenomenal, bright, clear with great bandwidth.
As bias is increased sound is not getting better. There seems to be voltage drop at the small battery.
Heat sink is running hot.
Things look promising. Thank to Panos for giving me the inspiration to try a MOSFET by letting me know of the Suzan Parker zero feedback schematic.
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