Compact power supplies


2010-09-28 2:52 pm
Hi all, I'm new to putting together amplifiers and have been inspired by some compact/lightweight designs out there and am looking to put something together to suit my specific purposes, though I am finding the power supplies to be a bit larger than I expected -- often as large as what I think of as full size desktop computer power supplies. I'm not sure if that's a matter of necessity or if that's just typical for instances where size isn't a primary consideration.

I had hoped for an internal power supply but if that's simply not an option within my design requirements then I can live with that. But specifically my question is, what are my options as far as power supplies that will power something like 200-300w RMS (mono) that are designed with size in mind? Am I going to be better off putting something together myself for this, or are there reasonable PSU options on the market?

Any info or links appreciated, thank you.
I bought this the other day:
200W 36V 5.5A Single Output Switching power supply AC to DC SMPS | eBay

36V but I adjusted it down to 32V - took about 10 seconds with a screwdrive, and it's wonderfully quiet too - 300mV spikes only. Good transient response into 63W (three 21W car lamps in series) too.

Building your own SMPS takes bravery but is possible. The easiest way would be to find a good one and have a more compact PCB made for it, then transfer the components across. Some are more compact, but how they (or any) perform is in my experience a lottery.

The one above is not very compact.
How small is small enough for you? To get that kind of power in a small footprint likely demands a switch-mode PSU. Full size desktop computer power supplies (I assume you mean ATX form-factor) are indeed large, though, there are smaller form factors in pretty big power ranges. Look at 1U power supplies, FlexATX, etc. (I'm not suggested computer power supplies are necessarily good for audio, but trying to use what I assume is a reference point for you.)

I've had good luck with the (intended for audio use) SMPSes from ConnexElectronic. For example, the SMPS300RS is a single-rail 300 watt PSU in a 100x100 mm form factor.


2010-09-28 2:52 pm
Thanks for the link, I think that is the kind of thing I've been looking for.

Ideally I want something that ends up around 150x150 with a height of 60mm or so. This is just a rough visualization, not exact measurements so it's a little flexible.. but that's an example of what I'm picturing. Most other power supplies I've seen that claim to be designed for the purpose of powering little class D amps are larger than that, just on their own.

What got me thinking about it was this thing: BH250 - Micro Bass Head with TonePrint and Tuner | TC Electronic

Now, that's designed for a bass guitar so in addition to the amplifier it has a preamp, some digital modeling hardware, and a bunch of pots/knobs. I don't need any of that stuff. I just need a mono input, one speaker output, and maybe something like this 06A2D Delta Electronics | Mouser to keep the power input/switch simple. And I guess a volume/input attenuation knob would probably be useful. Basically just what you'd expect to see on a very simple powered P.A. speaker.

So anyway, it seemed that if they could fit all that in this little bass amp then I should be able to go even smaller when I don't need the preamp, tone controls, or other doodads.
I just re-read your original post, where you mentioned 200-300w RMS. The tpa311x amps won't do that. So those might be out, unless you can live with less power than you originally suggested. Did you mean 200-300w out of the PSU, or out of the amp?

As far as the Connex power supplies and heat: I've never had any issues. With my tpa311x builds, I've never even worried about it. But, my power requirements are pretty modest. The tpa311x amps are upwards of 90% efficient, combined with generally lowish volumes, so heat just isn't a concern.

That said, if you're planning on an application where you really push the PSU, you may need to get a little fancier with heat management. Most of those Connex SMPSes have a link to a PDF document that is more detailed that the web store's overview page. IIRC, they usually have a note about adding some kind of heatsink if your application calls for continuous high power operation. Ultimately, it might just be a "test and see" kind of thing. On the extreme end, you might need to acquire a decent heatsink, and make sure your enclosure is adequately ventilated (and potentially add a fan). But, I'm guessing, more realistically, you might just need to mount the PSU in such a way as to use the chassis itself as a small heatsink.
You could also find a ampboard that already includes the psu. They can be very small indeed. I have some monoamps from audiopower. They are not tiny, but they are quite small. Just remember that if you need to push them hard, and get 200 watt, you also need som space around the amp module, otherwise it will not be able to get rid of the heat.

Yuanjing, Connecelectronics and Sure also makes som very small amps with smps psu.