AUDIO OUTPUT Transformer design

I need to design 250W output transformer for solid state amplifier.
How to start with, please direct me in this.

K.Hariharan

A modern solid state amplifier does not use an output transformer.

It does if you are driving a 100V line?
Frank

As a first estimation, you can give it double the number of turns as needed for a mains transformer of respective voltage , resulting in a full power lower bandwidth corner of 25 or 30 Hz, which should be o.K. for low quality public adress as usually intended with 100 V systems. So the core size is equivalent to a 500 VA 50 Hz transformer.

If upper cut-off frequency of the fransformer above 10 kHz is an objective, you would need to build the transformer different from a standard mains transformer with interleaved sections to reduce the leakage inductance. As far I'm aware of, it's unusual for industry standard 100 V transformers, but it's possible.

Finally, you should check, if your solid state amplifier is capable of driving inductive loads without getting damaged.

P.S.: I noticed, that some 100 V transformers available from catalog distributors are using considerable smaller core sizes related to nominal power. Apparently they are designed for a more restricted frequency range, e.g. > 100 Hz. It's not the quality that has been usual in German 100 V systems of the past.

FvM said:

Finally, you should check, if your solid state amplifier is capable of driving inductive loads without getting damaged.

Click to expand...

Yes, a lot of perfectly robust amplifiers have lost their output devices when driving 100v line transformers !
At the very minimum, connect 2 power diodes to the amplifier's 'hot' output. Use these to divert any positive back-emf from the transformer to the positive power rail and any negative back-emf to the negative power rail.
Its probably worth duplicating this just before the amplifier's zobel network (the RC or LRC network between the output devices and the 'hot' output connection).

An amplifier which uses output devices operating very close to their maximum designed capabilities will not be suitable for 100volt line operation at high power or with long cable lengths.

In Canada the level for PA lines in schools is only 25V so that little kids who are crawling around in the ceiling don't get electrocuted.
The level is 70V everywhere else in Canada.

Apart from electrical safety, 25 V has the great advantage, that you don't need a transformer at the amplifier side. If the rooms have individual cables, the wire resistance is still acceptable.

A 78.1W into 8 ohms amplifier has a 25V RMS output at clipping. Then an output transformer is not needed.
It can drive up to 156 1/2W speakers.

Thanks to audioguru, chucky and FvM.
In india i have seen that the amplifier named AHUJA, designing pushpull amplifier(for PA upto 1000W) with output transformer.