SMPS questions

[gaplessophile]

I'm about to build my first Gainclone, and have just discovered the option of using SMPS computer power supplies, through the Decibel Dungeon website. I have a couple of questions about them:

Are all computer power supplies SMPS? If I just pick up a random computer power supply, will it be?

Is there anything to look out for when selecting an SMPS power supply, apart from the voltage and current ratings? I guess that some will just sound better than others due to their components? Any tips you could give me would be helpful since I'm planning on buying some cheap used power supplies.

Thanks

[N-Channel]

Gapless-

try these 8 threads. Should answer most of your questions....

Can i use a computer power supply to power audio amplifiers?
Computer Power Supply for chip amp?
Using ATX PSU trans for 12V SMPS?
computer power supply
DC/DC converter using parts from PC PSU
ATX (computer) power supplies for power amp
Computer SMPS and Gainclone
PSU from a PC



gl,

Steve

[gaplessophile]

Thanks for your help, I had a look at each of those threads.

I get the idea that any computer power supply is an SMPS one, and if it's marked ATX, I can be even more sure. But I'm still not 100% on this, if anyone could offer me any more info about which computer power supplies are suitable, that would be great.

Nuuk, on his Decibel Dungeon website, says that he preferred the sound of an SMPS power supply (or several used together) to any other kind he'd tried. I'd be grateful for any other comments on the sound of computer power supplies.

Also, I've just ordered an Audio Sector Classic Gainclone Kit. Would it be suitable, if using an SMPS powersupply, to hook it straight up to the 1500uF decoupling capacitors used in this kit? Or should I be using something different?

Thanks again

[N-Channel]

All AT & ATX boxes are switchers. Some are single-ended forwards or even Flybacks, but the overwhelming majority of both ATs & ATXs are half-bridge forwards. Some use separate windings for the +3.3v section, while others use the +5V windings, with a saturable reactor core inductor in series with one of the rectifiers to achieve the +3.3V regulation. OK, I digress.

As they sit, most Computer PSUs, be they ATs ot ATXs, are unsuitable for audio applications, as they sit. This does NOT mean that they can not be modified to be able to do so. Mods can be as simple as changing one of the sense resistors for the +12V output to give +13.5V or +13.8V, or whatever voltage suits your needs without having to rewind the transformer. Some units may have a potentiometer to allow for adjustment, but for either case, to achieve regulation, the +5V line must be loaded to about an amp or so. This waste of power kind of defeats the whole purpose of having the SMPS in the first place- higher efficiency with smaller size.

The other option is to rewind the transformer to put out the voltage(s) desired. And, if the board layout will allow for it, bipolar (+/-) voltages suitable for a gainclone or other audio amplifier can be realized.

This is not to say that this will be easy, but it can be done, and great care must be taken because you would be dealing with LETHAL AC & DC voltages (120-240VAC and +330VDC). Several of the threads discuss, at length, and with lively exchanges, the soundness of working with such high voltages.

The best, in my opinion, is given by EVA, who states that, since tube DIYers already have to deal with even higher voltages, they should already be exercising appropriate caution, and sha also points out that she first tries her prrimary sections out on some lower AC voltages, first, like 24VAC or 50VAC, or some safe, or semi-safe voltage before going full-tilt boogey.

There are even a few websites that cover AT & ATX modifiaction. DIYer jackinnj knows an article from about 8 or 9 years ago appearing in QST about just this thing.

Hope this helps you in your decision on how best to proceed. This might be a big thing to do, but, in the end, it will be well worth it.

Steve

[Nuuk]

I have only listened to the Skynet modules but one of the guys who bought some off me reported that they were the best of several kinds of SMPS that he had tried.

I don't push the Skynets but if you are not experienced in working with high voltages, and given the low price of the Skynets, using a modifed computer SMPS may be false economy!

I currently use one module per channel (ie 2 volt rails) on an inverted GC with 1000 uF caps on each rail (soldered to the chip pins). I could try other cap values but to be honest, it sounds so good, I haven't even been tempted to change it in over six months!

[gilbodavid]

Hi. my experience here is minimal. I'm using one of Nuuk's SMPS's to power a much-modded, rehoused S Impact amp, and have found it to be better than mains or battery power, in that it gives more life, makes for more musicality (within the SI's limits) and increased scale, clarity and PRAT. I should also add that the slight mods Nuuk's SMPS's need (as shown on his site) are very easy, even for a DIY beginner like me!!!