PA4 - 2x300W/4ohm Solid State Power Amplifier

This amplifier was inspired by conversation with John Curl in a ‘Blowtorch thread’, as well as by his thoughts ( http://www.parasound.com/pdfs/JCinterview.pdf ).

The aim was to build a reliable, solid, good sounding amplifier. Topology of the amplifier is complementary differential, with JFET input, MOSFET cascode and VAS, and BJT output stage with 4 pairs of 15A transistors.

Simplified, basic schematics is shown in the following image:

Description

Solid state, dual mono design, stereo power amplifier. Inputs: 1 pair balanced (WLR). Outputs: 2 pairs binding posts. Protection circuits: DC output, AC current overload, DC current overload.

Specifications

• Output power 2 x 300W/4 ohm, 2 x 150W/8 ohm
• Input impedance 94kohm balanced
• Frequency range 0.5Hz - 130kHz (-3dB)
• Harmonic distortion <0.03%/100W/8 ohm
• CCIF 19+20kHz intermodulation distortion <0.03%/40Vp/8 ohm
• Slew rate >80V/us
• Gain 27dB
• Dimensions 450 x 440 x 190mm
• Weight 30kg approx.

Measurements

Distortion spectrum at 50W/8 ohm

The PA4 amplifier photos

Pavel Macura, 10/2009 - 09/2011