SMPS supply for CD Player or Clock


2008-06-12 4:18 pm

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 ?

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.


2008-06-12 4:18 pm
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 :cool:
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



  • Monovolt pic.jpg
    Monovolt pic.jpg
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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.
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!
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