Choosing a power transformer - diyAudio

Not sure why you would want to artificially limit the swing. Assuming that you are not boosting the rails to the front-end, and a conventional topology, your output swing will be inherently limited anyhow to within a few volts of the rails or so.

A stiff 60VCT transformer will give you around 150W into 4R and perhaps 80W into 8R. If you want to build a stereo amplifier with a single transformer, designed for 150W into 4R then you might choose a unit rated between 300 - 600VA. Of course an even bigger one will not hurt either.

For any transformer >300VA I would suggest using a soft starter in series with the primary windings.

Thanks for the reply. The reason I use low voltage because I want to use high quiescent current to run the first 5W as Class A and lower dissipation.

I artificially limit to swing to 30Vpeak to avoid the increase the CCB loading the previous stage. Of cause, I can choose not to limit the output also. It all depends on the input of the music.

As is, the power calculate from 30V peak is 112W already. It's plenty. I was even debating lowering the rail even more and raise the quiescent current even more to get more Class A power.

I just want to confirm a 625VA transformer is a good choice.

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