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Old 19th February 2006, 12:25 PM   #1
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Default Can i use a computer power supply to power audio amplifiers?

Now a days, those computer supplies are very cheap.

I was thinking if is possible to modify to 35 Volts for instance.

Do you think that the oscilating frequency will be captured by our audio amplifiers?

Do you think we can increase the oscilating frequencies to avoid that?

The increase of oscilating frequency will be a good solution?

Can this frequency cross the Supply shield can and be detected by our amplifiers?

Do you think that I can install 30000 uF in the outputs?

Can you suggest modifications to use them as audio supplies?

Do you have some experience?… something practical related that?

Can you suggest filter values?

Do you think that I will maintain the supply power when increase the voltage….. as 240 watts can be 20 amperes and 12volts….will 35 Volts have more than 6 amperes as simple calculations will shown us?

If you can answer to one of more questions, please, go ahead.

Thank you in advance by the cooperation

Regards,

Carlos
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Old 19th February 2006, 12:26 PM   #2
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Default Do you think that this is reliable?

I could not see those supplies in use now a days.....i remember them beeing used in the seventies and eigthies only.

regards,

Carlos
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Old 19th February 2006, 12:29 PM   #3
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Default I have already made some modification to use as a Radio Amateur, 13.8 Volts - 16 amps

But i made it using an sketch...was not my idea, i do not understand those switching supplies very well.

I remember that i gave it to a friend, as it produces some carrier beating with my receptions...alike a frequency marker.....do not remember exactly, but i think was 30 or 40 Kilohertz the carrier generated by that supply.

regards,

Carlos
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Old 19th February 2006, 12:30 PM   #4
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Default As this is not beeing used, i suppose this may have some problem

Do you know what problem is this?

regards,

Carlos
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Old 19th February 2006, 12:32 PM   #5
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Default I imagine that over the output DC voltage may have a superimposed residual

hi frequency tone, not perfectly filtered.

Can we suppress this signal?

regards,

Carlos
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Old 19th February 2006, 12:34 PM   #6
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Default Worst than that, i suppose that 2 supplies will create two signals to beat .

those signals beating one with the other will produce a big mess....well, i do not know...reason i am asking you guys.

I am sure, even with small knowledge, you may be better than i am related those supplies...i do not understand nothing about them...i have an idea of the operational work only.

regards,

Carlos
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Old 19th February 2006, 12:36 PM   #7
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I would be carefull with an LC filter on the output.
SMPSs sometimes have problems when the load turns complex and the regulation loop can become unstable.

If you want to risk it you can try an LC filter, but you might end up with a more dirty supply that you had before.

\Jens
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Old 19th February 2006, 12:42 PM   #8
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Default Thank you Jens, i was suspecting that this may have problems, as not normally used.

And of course, a lot of guys already had this idea before me.

I will be satisfied knowing the reasons, as the price is very atractive, calling my attention for that.

Used ones can be bougth at a ratio of 3 units for one dollar.... really interesting, even beeing 10 years old supplies.

thank you by the cooperation,

regards,

Carlos
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Old 19th February 2006, 01:36 PM   #9
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LC filters in the output of a SMPS are fine as long as they are damped. Only filters with considerable resonance peaks will cause trouble.

By the way, those PSUs may be modified for 35V or even +-35V output, but that will require to rewind the transformer, new output rectifiers and to redraw the secondary side of the PCB.

I have been tempted sometimes to develop some easy to build SMPS with symmetrical outputs in the 500W range (where computer PSU parts and cases could be employed), and publish the schematic, board layouts and all the data for DIY. But I don't know if it's worth the effort, and these circuits have to be built and tested with great care due to the mains isolation requirements, so it won't be suitable for everybody.
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Old 19th February 2006, 01:51 PM   #10
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Quote:
Originally posted by Eva
LC filters in the output of a SMPS are fine as long as they are damped. Only filters with considerable resonance peaks will cause trouble.
You are correct, but I have seen both Buck/Boost and standard buck converters misbehave when a damped output LC filter was Deployed. I had to redesign the loop to compensate for this problem. The loop work is not always needed, but it is possible that it can be necessary when modding something.

You also have to carefully design the filter so that it infact works in the freq area where the noise is present, something that can be difficult without a scope/spectrum analyzer.

I think a modded PC supply could be a nice idea, but I would rather construct something from scratch...

Maybe next year

\Jens
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