How to Dimension a Power Supply for an Audio Amplifier ?

user134450, 8 months ago (edited 8 months ago)

Acording to the datasheet the TDA7294 uses -Vs and +Vs in the block diagram so i would assume it is intended to be used with DC power. If the module is specced for use with AC as well as DC, then this just means what you already suspected: it has an integrated bridge rectifier and most likely some sort of low pass for the rectified power (read: a bunch of big capacitors).

You could just go with a big transformer core that powers them all at the same time; many commercial amps do that and it works fine in general, provided you have enough margin for power spikes and the modules will not influence each other when connected in parallel to power.

In my opinion using separate transformers would be paranoid but it would work of course.

Edit: dont forget that this thing will produce heat. If you really go with an 800W transformer then you have to be able to cool about 400W in the worst case (going by the data sheet power dissipation of the chip and assumed transformer + rectifier efficiency of 90%).

Fermiverse, 8 months ago

When I look around then this amp, taking your statement with the rectifier, needs symetrical AC supply as an input.

For a mono amp the transformer would be 120W / 2x25V per amp. You need more because of the loss the amp includes

Depending on your setup and build maybe several transformers would be better. Or you add all up to 960W trafo.

megrania, 8 months ago

The idea is to have an 8-channel power amplifier in one box …

I still have to source the right trafo, but one large one would be both lighter and cheaper (new) than, say 4 small ones. An argument to use multiple would potentially be that peaks on individual channels might have less impact on the other channels. Still working on it …

ignotum, 8 months ago

Disclaimer: not at all an expert on this, this is just my thoughts based on what i’ve heard, please correct me if i’m wrong

• Normal power supplies are CV, so you don’t have to worry too much about that, CC supplies are a bit more niche
• If you want to be able to run the amps at full power, you’ll have to add up all their rated powers and find a psu that is rated for that, it could also be wise to go with one slightly larger as well, as power supplies tend to get a bit noisy when they’re close to the limit (the voltage they give out gets noisy that is) which reduces the audio quality
• what are the input for the amps? You say they have built in rectifiers and everything? Can they be aupplied by mains directly? What is the max input voltage?

megrania, 8 months ago

Hmm they are rated for 12V to 32V, and the seller recommends using a toroidal transformer to achieve the symmetric power it needs.

Max_P, 8 months ago

There will be loss in the process so you should go a little above. You also need to account for the efficiency curve of your power supply: is it best efficient at 80% load? 90% load? Can it handle 120% momentarily in case of a spike?

CV power supplies are the standard: constant voltage. It outputs say 12V, and trips when overcurrent. A CC supply would limit current to say, 20A. It does so by dynamically adjusting the voltage output to match that target. That’s a lot less common and usually used for battery charging or testing/troubleshooting. So, I guess, don’t plug it on a battery charger.

It should come with specs as to what input it can take. Follow the recommendations. If it says DC give it DC unless you’re absolutely sure of the circuit in there. The presence of a rectifier and caps doesn’t tell you much given it’s an amplifier, it could be part of the amp circuit for the MOSFETs and not its power supply.

megrania, 8 months ago

Well, it says to use a toroidal transformer between 12V to 32V output, and looking at pictures of other people who bought it, it seems to work on AC directly, so I have high confidence that that’s what it is.