I am thinking about using some cheap TPA3255 amps in an active speaker project. These are readily available from Fleabay (choose carefully!) but come without a power supply. The tricky bit is that a power supply with the right voltage and current capability is not cheap or readily available due to the voltage and current involved.
Being a bit of a hoarder I happen to have some of the ubiquitous dual-output 500W SMPS power supplies lying around that can also be purchased on eBay. I have a pair of these with +/-50V outputs and I am wondering if they could be used to each power a PAIR of the TPA3255 stereo amps. Here is my thinking:
Normally one would need a circa 50Vdc supply for a stereo TPA3255 amp. The PS is single ended, so the inputs are capacitor coupled (reference: the typical application circuit in the datasheet). Could I not connect one of the amps to the +50V supply and PS ground, and connect the other amp between group and the -50V supply? When using the -50V supply, the ground must be connected to the amp's (+) terminal, and the -50V to the (-) terminal.
Assuming this works, I could use the PS with two amps to get 4 channels of amplification on the cheap. As long as I limit the load on any channel to a minimum of 8 Ohms the power demand for two amps should be able to be accommodated by the 500W rated PS. Seems like a very cost effective way to get 4x100W per side.
I just wanted to run this by the forum in case I am setting myself up to let out the magic smoke...
Being a bit of a hoarder I happen to have some of the ubiquitous dual-output 500W SMPS power supplies lying around that can also be purchased on eBay. I have a pair of these with +/-50V outputs and I am wondering if they could be used to each power a PAIR of the TPA3255 stereo amps. Here is my thinking:
Normally one would need a circa 50Vdc supply for a stereo TPA3255 amp. The PS is single ended, so the inputs are capacitor coupled (reference: the typical application circuit in the datasheet). Could I not connect one of the amps to the +50V supply and PS ground, and connect the other amp between group and the -50V supply? When using the -50V supply, the ground must be connected to the amp's (+) terminal, and the -50V to the (-) terminal.
Assuming this works, I could use the PS with two amps to get 4 channels of amplification on the cheap. As long as I limit the load on any channel to a minimum of 8 Ohms the power demand for two amps should be able to be accommodated by the 500W rated PS. Seems like a very cost effective way to get 4x100W per side.
I just wanted to run this by the forum in case I am setting myself up to let out the magic smoke...
Correction to third paragraph above:
Anyway, I think the question comes down to this:
Is the SMPS created by internally tying two independent, floating SMPS together? If so I think they could be operated independently. I don't know for sure, because I am not all that familiar with all the various SMPS topologies and variations.
Can anyone comment on this?
should read
Anyway, I think the question comes down to this:
Is the SMPS created by internally tying two independent, floating SMPS together? If so I think they could be operated independently. I don't know for sure, because I am not all that familiar with all the various SMPS topologies and variations.
Can anyone comment on this?
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No, you can not use these SMPS in this way!
Also it is not recommended to use only one of the rails to power the amplifier.
Also it is not recommended to use only one of the rails to power the amplifier.
OK. Thanks for the reply.
My next question is WHY is that?
I believe that most of these cheap audio SMPS units are half-bridge. That is an isolated type. But I have not been able to find an explanation, schematic, or circuit diagram of such a supply that provides DUAL, SYMMETRIC +/- voltages PLUS A GROUND like you use for an audio power amplifier (e.g. class AB, etc). If the SMPS is isolated all terminals will be floating, no?
Please help me understand what is going on under the hood!
You can buy SMPS with grounded and ungrounded secondaries.
Using one rail on SMPS could mess up regulation feedback if its taken from other rail.
Using one rail on SMPS could mess up regulation feedback if its taken from other rail.
Your ground of amp 1 is 50V higher than amp 2.
When you connect your signal cables the grounds will be linked.
BANG!
When you connect your signal cables the grounds will be linked.
BANG!
I am using this one with a TI 3255 EVM board and it works very good
Amazon.com: MEAN WELL LRS-350-48 350.4W 48V 7.3 Amp Single Output Switchable Power: Industrial & Scientific
Amazon.com: MEAN WELL LRS-350-48 350.4W 48V 7.3 Amp Single Output Switchable Power: Industrial & Scientific
Yes, thanks for posting about that. I have come across this PS during my search.
I have a question: how loud is the fan? When does it come on (I think only above 50C internal temp or something), if ever? I was wondering if you can open up the case and use an external (quiet) fan. I would be building these into another enclosure anyway.
I will probably just make a linear supply at this point. I have some 400VA 33-0-33 toroidal transformers. I will dig out the center tap connection and separate the windings to give two independent 33V secondaries, which I can connect in parallel. This should give me about 46Vdc with zero current draw after rectification and smoothing.
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Good point.. I hadn't thought about the grounds, only the signal input (which are AC coupled).
Anyway, it's pretty clear that the answer to my initial question is "no!". 🙂
My amp and power supply are boxed in a compact enclosure with fair sized air
vents....it is performing home theater duty with some occasional
use for soft / classical music - I can't say I can hear the SMPS fan even
during the quietest moments.
But then I am no spring chicken, so my ears are probably suspect too.
I am sure you could open up the case, but I preferred to leave it on for the additional
EM shielding it (hopefully) provides.