SMPS supply for CD Player or Clock - diyAudio
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Old 14th October 2010, 01:18 PM   #1
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Default SMPS supply for CD Player or Clock

Hi

I have a Monovolt PK 30 smps rated at 5V and 6 amps and I'm wondering if it would be suitable for 5 V rails on my CD player or for powering a clock.

They are around 200 each, are rack mountable and are used in outside broadcast applications.
It's absolutely quiet when powered and is built beautifully.
Ripple figures from the spec sheet suggest < 40 mV pp.
Is this a good figure ?.
Is there a way of removing noise away from audio frequencies of smps ?
CLC' s perhaps ?
Linn are using them in flagship CD players but I assume there's are specifically designed for this purpose.

I've read that smps is a bit of a ' no no ' for some applications and can cause audible and unwanted noise problems.

Anyone have experience of trying this ?

Andrew
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Old 14th October 2010, 05:19 PM   #2
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A lot of DVD / Blu Ray players are powered by SMPS these days.

And as you say, some CD players too.

It just depends how well filtered the example you have is, as I know that poorly filtered ones can create all sorts of harmonic crud through the various supplies that it feeds.

I would test it under a reasonably heavy load, and see what the ripple looks like (bearing in mind you're looking for ripple each side of ~50khz or so..) - of course that depends at what frequency it's switching at.

Harking back to my TV repair days, I remember all manner of weird faults being caused by SMPS ripple. Same on some VCR players too.
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Old 14th October 2010, 09:50 PM   #3
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Tony - thanks for the reply.

I've done some more digging and Mr Nelson Pass himself suggested LC Filtering and keeping the smps away from the equipment - that's easy enough.
He didn't balk at the suggestion at all - I guess he would if he didn't like the idea
Seems, if done correctly and the unit is built properly they can be used.
This unit is far and away better than a PC supply or some of the other smps units I've seen - pic attached.
I hope it works - it'll look great having 5 or six of these side by side powering up my CD player's chips and clock - it could be a dream I'm having here !!

Only way is to give it a go I guess so I'll hook it up to a cheaper victim and not my current pride and joy - to see if it works !!

I'll post what happens if you like

Thanks again

Andrew
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Old 15th October 2010, 01:58 AM   #4
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In my view, the only excuses for using SMPS are cost-cutting & weight reduction, which is also, of course, cost-cutting on shipping weight.
While I have been able to upgrade some dvd players w/SMPS into very fine sounding cd players, the SMPS is positively a liability, and such players end up sounding good *despite* having a SMPS, by putting a lot of extra work/parts into more filtering of the supply lines than would be needed with a linear supply.
Given how terribly easy it is to build a good linear supply, I am absolutely of the opinion that going that route will be easier, cheaper & far less complicated than using a SMPS and dealing with it's noise, and reliability very likely, issues, even if the SMPS was free. And the results will be undoubtably better with the linear supply.
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Old 15th October 2010, 06:19 PM   #5
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I agree with pretty much all that. The PSUs you have may be very good in their field, but a poor choice in this category.

<40mV ripple and noise isn't particularly good at all. A cheap 7805, 3-pin reg will very likely perform at least 100x better (0.4mV ripple and 40uV output noise would be reasonable specs for such a part - check datasheets).

In particular, clocks demand the quietest supply you can arrange - esp. at low frequencies.

Yes a bit of LC filtering may help for less-critical circuit elements. But with a 5v SMPS if you need a clean 5v output there's simply no voltage overhead to run sufficient filtering or a linear post-regulator. If you only need 3.3v supplied then no problem at all!

Last edited by martin clark; 15th October 2010 at 06:24 PM.
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