Audio amplifier design tool

This is a modelling tool for A/B class audio stereo amplifier power calculation. Based on input variables it calculates the maximum peak-to-peak and RMS voltage that the amplifier would be able to achieve, then applies that voltage to output impedance to get the RMS output power and peak current numbers. Next it calculates the total supply power and RMS current required from transformer. Basically you pick the transformer voltage and the tool will tell you how big the transformer and heat sink will need to be for building the maximum power amplifier at that supply voltage. You can then play with other input parameters to see what happens at different load impedances and allowable heat sink temperatures

The model is somewhat simplistic. For example, the power supply ripple voltage is calculated for maximum power and then applied only once to de-rate the available output voltage. The transformer no-load voltage drop to rated voltage at full load is assumed to be linear. The only input you can really use for oversized transformer is no-load voltage coefficent Ripple calculation is done for 50 Hz mains, 60 Hz would have less ripple.

Heat sink required thermal resistance calculation just looks at ambient temperature and max allowed heat sink temperature, and assumes free air environment. Junction temperature requirements of output devices are completely ignored.

Do not trust any of the numbers to be absolutely correct, at best this tool will place you in the right ballpark with transformer, capacitor and heat sink sizing.

Input variables
Transformer single rail winding voltage at full load VAC
Transformer no load voltage coefficent %
Load impedance Ohms
Final stage dropout voltage at full load (each rail) V
Rectifier voltage drop on single rail (2xdiode drop) V
Filter cap capacitance per rail uF
Ambient temperature degC
Maximum heat sink temperature allowed degC
Transformer parameters required for Max RMS power
Max winding current A
RMS winding current A
Power required for Max RMS (two channels) W
Heat sink parameters
Maximum heat loss W
Maximum allowed thermal resistance degC/W
Power supply characteristics
Winding voltage at no load (each winding) VAC
Filtered supply rail at full load V
Filtered supply total at full load V
Filtered supply rail at no load V
Filtered supply total at no load V
Total supply difference from no load to full load V
Ripple voltage on rail (RMS) V
Ripple current on rail (RMS) A
Single channel output parameters
Max clean P-P voltage on load V
Peak current on rail A
Max RMS voltage on load V
Max RMS current through load A
Max output RMS power W
Max consumed RMS power W
Efficiency at full power %
Maximum power dissipated as heat W

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