Power supplies

Of utmost importance for good sound quality is the power supply. Not only the power amplifier should be able to deliver sufficient peak power but also the pre amplifier and associated filter need stable and noise free power supply.
The pre-amplifier has a separate power supply built in. Each opamp in the design is separately buffered with 22-220uF. The whole amplifier is symmetrical. Even more important in pre amplification is the decoupling of the power supply lines to ground. Every stage in the pre-amplifier is decoupled using 100nF ceramic capacitors. Most opamps in the design are designed to behave as buffer. Where gain is needed, larger buffer capacitors are used.

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Since the pre amplifier is controlled by a microcontroller, supply for digital parts and analog parts are completely kept separated to avoid digital noise on analog signals. The analog supply is symmetrical and built around low noise voltage regulators with high output ripple rejection (80dB). Voltage levels are set to the upper range of the opamps to make the highest voltage swings possible. With this setting a headroom of 23 dBu (defined at THD+N < 0.01%) is possible at 1V input signal.
All components carrying analog signals are fed from one low noise power supply. Components not carrying analog signals are fed from a different source (digital parts, LEDs, display).

photo of preamp supply, click to see an enlarged view

Each satellite speaker contains the filtering for its speakers. Also these are low noise power supplies. Since each channel uses his own supply, channel separation is improved. Also for these satellite speakers, the required buffering and decoupling is used. The bass speaker in the satellites are equipped with a 80VA transformers and a total of 30000uF capacitance. The very low end is filtered for correct matching, this reduces also the load on the power supply.
The subwoofer amplifier is comprised with a much heavier supply. The transformer is 300VA with a total buffer capacitance of 60000uF. For a 140W amplifier this is sufficient to reproduce every bass peak while maintaining a clear, controlled and distortion free bass.

 

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