Author Options:

What to be aware of when considering power supply for a 100 watt amplifier? Answered

I have a TDA7294 IC and want to know what kind of power supply should I build for it so that it can work safely. I heard that even though it works on 12V DC there are other things to take into consideration when choosing the tansformer and designing the AC to DC converter, like amperes and watts.

My current set up is the following: a transformer (input: 220V AC; output: AC2*12V) a rectifier and a 35V, 2200 uF capacitor. I know this is very cheap and low quality but can you explain why in principle wouldn't an amplifier like the above work properly with such power supply?

How do I calculate the ideal values of these factors for a 100 watt amplifier?

5 Replies

steveastrouk (author)2014-06-23

What everyone else says, but look carefully at the spec for the amp. What is its "power supply rejection ratio" (PSRR) ?? That tells you how much ripple will appear in the output. Modern amps usually have extremely high PSRR, which is a good thing.

So don't be too afraid of a little ripple,

Select as Best AnswerUndo Best Answer

Josehf Murchison (author)2014-06-23

Well If your transformer can handle 10 to 12 amps output when you convert the 12 volts AC to DC you will actually get about 19 volts DC ripple.

The reason for this is 12 volts AC is a mean average of 38 volts peak to peak between 19+ and 19-.

Even with the capacitor there will be a ripple in your 19 volts, ripple can come through your amplifier.

This must be checked under load, without a load the 19 volts ripple may be small, however under load the ripple can be much higher. So the smother your ripple under load the better.

As long as the ripple under load doesn't drop below 14 to 15 volts you can use a high current 12 volt regulator to give you a nice 12 volts 10 amps and no ripple. The regulator for 12 volts 10 amps you will need to build.

Is this what you were asking?


Select as Best AnswerUndo Best Answer

mpilchfamily (author)2014-06-22

Power supply design is an advance thing that most electronic engineers would prefer to avoid if they can. It's best to buy one rather than trying to build you own.

There are a great many problems with your current configuration. This PSU has to supply more than 100W of power at 12V to run the amp. So it should be able to offer around 10A. Can your transformer support that much current from the secondary coil? You'll also want a good clean 12V going into the amp. The more ripple on the 12V the worst your audio will be. So you'll need to figure out better filtering than a single cap. There are some fairly advanced calculations involved for determining the right cap. They you'll have to test multiple brands to find one that works best with your setup. The calculations are beyond me. Like i said just buy a good 120W or better 12V power supply and be done with it. You could even use a PC PSU as long as the 12V rail can support 10A or more.

Select as Best AnswerUndo Best Answer

rickharris (author)2014-06-23

100 watts at 12 volts is 8.3 amps. Can your power supply provide this much?

PSU Ripple is translated into hum in an amplifying circuit, this often calls for more sophisticated filtering to ensure a good DC supply.

What are your current problems I assume you have tried the amp on this PSU.

Select as Best AnswerUndo Best Answer