switch mode supplies

[Zero One]

I have been experimenting with computer switchmodes on my lm1875 based clones and after several test sessions find I definitely prefer the sound, it really is far more tube like and the bass seems more tightly controlled. The power is adequate with my efficeint system so thats no problem.

I am building a low-gain clone with very short paths, some surface mount components etc, so far the test amps/circuits sound superb on the regular transformer supply and as I said better again on the smps.

The problem is the computer supplies have a very limited -12V output, the two I'm using are only 1 amp on one and .8 on the other, and I cannot find anything stiffer, heck I can't even find another 1 amp job to match the one I have. The 1 amp is probably OK, just, but I think more margin would be better.

The other problem is that the supplies have noisy fans which are most annoying considering the whole system has such low noise floor levels, they do intrude in the quite passages so a fanless option or a very quite one would be better.

So I need an alternative, all of the commercial smps have only the positve rail output as far as I can see.

Is it possible to create a dual 12V supply out of one 24v smps, there are plenty of these around with adequate output, or can 2x 12V supplies be rigged up to give the +/- supply. I don't know much about these things and it took me a while to work out how to get the computer ones to do the business, so explanations will need to reasonably straight forward.

[Khron]

Me and my dad are in the process of building a 2x30V ~10A smps. If you're interested i could keep you posted regarding the progress.

Right now, progress is somewhat frozen, as i'm at uni, about 150km from home But my holiday's coming up in about 1,5 months, so... Can't wait to get my hands "dirty"

[janneman]

Originally posted by Zero One
I have been experimenting with computer switchmodes on my lm1875 based clones and after several test sessions find I definitely prefer the sound, it really is far more tube like and the bass seems more tightly controlled. The power is adequate with my efficeint system so thats no problem.

I am building a low-gain clone with very short paths, some surface mount components etc, so far the test amps/circuits sound superb on the regular transformer supply and as I said better again on the smps.

The problem is the computer supplies have a very limited -12V output, the two I'm using are only 1 amp on one and .8 on the other, and I cannot find anything stiffer, heck I can't even find another 1 amp job to match the one I have. The 1 amp is probably OK, just, but I think more margin would be better.

The other problem is that the supplies have noisy fans which are most annoying considering the whole system has such low noise floor levels, they do intrude in the quite passages so a fanless option or a very quite one would be better.

So I need an alternative, all of the commercial smps have only the positve rail output as far as I can see.

Is it possible to create a dual 12V supply out of one 24v smps, there are plenty of these around with adequate output, or can 2x 12V supplies be rigged up to give the +/- supply. I don't know much about these things and it took me a while to work out how to get the computer ones to do the business, so explanations will need to reasonably straight forward.

Possibly you can connect two +12V supplies in series, use the common tap as ground and then have + and - 12V. It will wotk if:
- the +12v of each are isolated from mains earth/neutral (to be checked);
- you need to physically keep both metal boxes from touching each other!

May not be a final thing but would allow you a quick try on your amp.

Jan Didden

[Stocker]

The fans can be disabled entirely unless the music is holler-to-be-heard loud all the time

Yes they can be connected in series if the outputs are isolated from each other. Practically it means lifting all the "ground" connections from the chassis in one supply if using two. This has been covered here and elsewhere on the net... search...

[eLarson]

Are there really no +/-12V SMPSes out there?

I've looked and not had success so far, but then again maybe I'm fishing the wrong end of the lake, as it were.

[Igla]

The only thing to do with SMPS is to cut connection between PCB and chasis.Then you can wire two SMPS together to get +- 12V each at 10amp.
Usualy there is a cooper ring and track under one of the screws holding the PCB on place and connecting PCB ground to chasis.
I've just scratched this connection on my both SMPS.
You can also disconnect the fans.My SMPS are not hot at all.

Check this link:
http://myweb.tiscali.co.uk/nuukspot/...clonesmps.html

Regards;
Igla