Zero Feedback Impendance Amplifier.

(Following Susan-Parker Zeus Amplifier Idea)

This amplifier is based on Impedance Amplification and has similar distortion characteristics to valve triode designs.

As you can see, the amplifier is constructed in such a manner that uses the mosfets Q2, Q3 and Q4 as Source Followers, not as amplifiers. Therefore the transformer arms follow the gate input voltage minus the mosfet bias level - the actual gain is about 0,9. All voltage amplification is carried out by the first stage mosfet Q1.

Interstage SE transformers (EI or UU type) is hand wound, with quad-filar 180 x 0,56 mm wire. With quad filar winding the coupling is very good, far better than a conventional winding topology. Two wires (primary) connected in series as in pic4 shown (2:1:1). Core (8-10 cm^) assembled with air gap. This is necessary in order to bring the operating point of the core to the correct region on its B-H curve. Paper spacer 0.05 mm thickness is applied.

Output autotransformer (transformer with only one winding) is using a 200 VA core recovered from a regular mains transformer and then quad-filar wind about 150 turns of 0,8 mm wire. All winding connected in series with grounded central point.

There is no overall negative feedback. The only feedback mechanism is within Q2, Q3 and Q4 as they operate in voltage follower mode and regulate the voltage across the source / drain to match that of the gate.

Amplifier had a special combination of fluidity, detail and dynamics. It is tested with the following CD and LP:

1. Bizet - Shchedrin, Carmen Suite, Moscow Virtuosi	LP and CD
2. Mike Oldfield, Tubular Bells	CD
3. Keith Jarrett, Standards Live, 1986	LP
4. Getz/Gilberto, 1963 (Grammy)	LP and CD
	.

So I'll simply say it sounds wonderful.