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Suitable for all power amplifiers. This output level is designed for my Ultimate Hi-Fi Class B Amplifier v3.1 circuit which has an input sensitivity of 1.8Vmax. Some of the parameters are:
- Input Impedance - 10Kohm
- Output Impedance - can be pretty low but my power amplifier has an input impedance of 56kohm, so i left it at that. Current amplification carries less noise than voltage amplification, so THD-wise it shouldn't increase it, with lower loads. I guess down to 1Kohm will be the minimum.
- Frequency response - 10Hz-100Khz^
- Ripple rejection - good at -49.1dB. Will get to that later.
- THD+N@1khz - 0.002%, which is the ideal value and will depend on many things, such as type of transistors used and ripple filtration. I recommend BC549 and BC559 as low noise transistors, but any other LN transistors will do.
Tips:
- Use very good ripple filtration. I can't stress enough, the importance of this. Even 3-4mV of ripple hum remaining at the output, will result in a very audible hum from the power amplifier. I've posted a few circuits, one of which is ,,HumLess PSU Revised'', and will be the perfect regulator for the preamp. You can alternatively use an LM7820 regulator, for the job. The end result will be similar.
- Be sensible about grounding. Ground loops are unacceptable here! Keep this away from the ground paths of the power amplifier. Significant difference is observed with the correct grounding.
- Use only the best of materials, avoid cheap components, and be sensible about the layout. Try to restrict long wiring to a minimum and place a few 100nF capacitors along the supply rails, for stability improvement.
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