Power supply for two LM1876


2008-02-25 5:35 pm

I'm designing an amplifier with two lm1876 chips. The thread can be found from chip amps category.
Now I have to decide how big trafo will I need. I understood that 160 VA is enough, but can it be smaller? For example 120 or even 100? The chips will run with +-25V so the trafo secondaries will be 18V.
Wow. I'm surprised that somebody didn't answer that question.

All of those can work.
The 120va looks good for a production model.
The 160va looks good for personal enjoyment.
The 100va is workable, but costs of employing it don't give it a pricepoint advantage.

Anyway, for LM1876(5) the bare minimum is 1 amper per channel, and that would also need 4700uF per rail, per channel. That's why the 100va is the most expensive option.

However, less reliance on power caps may make a nicer sounding chipamp at cooler temperatures (less expensive heatsinks). Less reliance needs larger transformer (144va minimum). So that additional opportunity exists with the 160va.

The above applies to unregulated power supplies (no regulator onboard), because you need a power source strong enough that the voltage won't droop during audio programme transients--the 120va. Its even better if its strong enough that it isn't recharging caps during audio programme transients--the 160va.

Well, that's all I've got. I probably botched the explanation, but I think the figures are right.