Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Re: Trade off between transformer & capacitor sizes?

Posted by jneutron (A) on April 23, 2003 at 13:12:28

In Reply to: Trade off between transformer & capacitor sizes? posted by Ehien on April 23, 2003 at 10:43:49:

Assume a power output and load..ex:100 watts, 8 ohms, vpeak=40.

Add for drops in pass elements..say, 2 volts. Add in pre driver say 2 volts, means rail has to be 44 volts minimum.(bipolar example)

The cap bank can't droop below that...So, choices are a billion farads at 44.1 rail voltage, 10 uf at one million volts, or something in between..This neglects PSRR of course..

Your output stage dissipation will depend on the rail voltage..Less heat with the lower rail voltage, just requires more capacitance..There's the tradeoff..

Your xfmr will be rated for a current, the windings will heat up otherwise. So the current is already set...The voltage, hence VA rating, will depend on the peak voltage you need the rail to be at so the music will not pull it below required PS voltage.

When you get caps, look for newest, as has been stated..And, look at the freq response of the cap...There will be a capacitance vs freq graph on the good sites, capacitance at 20Khz will be bout half that printed on the can..and I bet the older ones are even worse..

And also correct is the bridge lifetime for high turn surge currents.

Cheers, John

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