300 Watt MOSFET Real HI-FI Power Amplifier

Nico Ras, South Africa

Project Summary

My passion for excellence progressed over the past 40 years to developing sonically superior amplifiers to the highest possible standards, providing life like sound performance.

Project Description

I am committed to sharing my experience of the RAS300 with other enthusiasts sharing my passion for perfection. I designed this minimalist amplifier to be durable, simple to operate while offering high fidelity equivalent to the original sound source and would recommend partnering this amplifier only with other products of outstanding quality.

When I set out to design this amplifier, my aim was to create a product most suitable for the reproduction of complex music and speech signals. Although I placed high emphasis on electrical characteristics, the single most important requirement is achieving an audibly superior sound, vivid spatial imaging and superb tonal clarity.

Although the average listening level is normally less than 10 watts, my design approach was to create an amplifier with ample reserve power, but biasing it for class A at average listening levels reducing cross-over distortion to extremely low levels.

There is not one capacitor in the signal path, improved the accuracy of the tonal characteristics of instruments and voices significantly.

The RAS300 has almost zero phase distortion far beyond the audio range resulting in perfect resolution and totally un-coloured sound.

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Amplifier Specification:

• Maximum Output: 240 watts rms into 8 Ohms, 380 watts rms into 4 Ohms
• Audio Frequency Linearity: 20 Hz – 20 kHz (+0, -0.2 dB)
• Closed Loop Gain: 32 dB
• Hum and Noise: -90 dB (input short circuit)
• Output Offset Voltage: Less than 13 mV (input short circuit)
• Phase Linearity: Less than 13° (10 Hz – 20 kHz)
• Harmonic Distortion: Less than 0.007% at rated power
• IM Distortion: Less than .009% at maximum power

The amplifier consists of two completely separate monaural amplifiers each channel has its own power supply, resulting in zero inter-channel cross talk, a common phenomenon in amplifiers sharing the same power supply.

In order to obtain the full output power each supply transformer should be rated at 40VAC – 0 – 40VAC at 640VA. Unlike many designs relying on the reservoir capacitors to supply peak currents, I prefer to have the raw power available from the transformer resulting in much faster transients.

Although the RAS300 specifications are moderate, when listening to it you will immediately experience the massive reserve power available and never have any cause of anxiety that something is going to give in that one would when driving many amplifiers loud.
You will hear nothing but reality with no distortion at any level and I guarantee that this amplifier will divulge the best qualities of any equipment connected to it.

BOM: 

PCB:

PCB Layout:

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