Hi,
I recently bought a few pre-made amplifier modules for an 8-channel amplifier project (for a sound installation).
The amp is based on the TDA7294 chip and is rated 85W nominal. Now I’m looking for a power supply, but I’m a bit lost (this isn’t really my strongest field, to put it mildly).
Do I just need to add up the output power, 8*85W = 680W, or could I get away with using something smaller, like a 300W or 300VA?
Also, the seller said that you need to use CV power supplies, CC won’t work and kill the circuit. Does that mean a switching supply can’t be used?
It looks like the module has a rectifier and smoothing caps integrated, so I could potentially just use a transformer, right?
Best, N
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.
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 …
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.
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.
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%).
