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Einric 18th July 2012 01:46 PM

SMPS for DIY Audio F5c
I am planning to build an F5c with the newly announced DIY Audio chassis.
I already have my input FET's and will be placing my parts order soon.
I am planning on paralleled output FET's and cascoded input FET's

I originally figured on using a CRC power supply for this project but now I am wondering about a SMPS.

What should I look for?
Any suggestions about a good manufacturer or specs I need?


Osvaldo de Banfield 18th July 2012 02:23 PM

I work in SMPS repairing, and clearly, the best of them are Lambda. Specifications will be according to your requeriments, like voltage(s), current(s), external fault relays, remote on/off, etc. The 2 firsts are the most important.

Nelson Pass 18th July 2012 07:20 PM

I advise that you get a supply current rated much higher than your projected


Einric 19th July 2012 04:49 PM

I was anticipating around 600VA worth of Toroid for the project.
The SMPS would be of similar capacity.

What differences could I expect with the SMPS V.S. Unreg. CRC?

Nelson Pass 19th July 2012 04:53 PM

I haven't tried it on the F5 for lack of time. In general, I think they are
workable, especially if you give them some passive filtering. Often this is
a problem as the start-up circuits of many SMPS sense the filter capacitance
as a short on startup.


Zen Mod 19th July 2012 05:24 PM

bingo! opportunity to use common mode choke

2x30mH at least , then drekload of 33mF buggers


flg 19th July 2012 06:49 PM

The big deal with these things is that they work with switching behaviour. This is something like a high voltage high current transient. This transient will send high speed load source and sink currents down the line to your amp. It will be reduced by the time it gets there due to R and C and L on the way to your amp, but also, the amp won't actually be abble to get a clean transient and will likely sag momentarily. You can get something that won't, but, I guess that was the suggestion, to get something bigger than you need. There are levels of transient response performance that can be had. I work with Intel based processor SMPs and we test with 100k-1M square wave loads per Intel spec. At over 100A!
But, there is much more to it. those big switching transients cause gobs of High freq and RF noise on the Rail. Yes, passive filters can smooth that. But, the supply itself will radiate RF EMI etc. etc. it will generate noise back into the mains if not built correctly and screw up your pre, your source, and anything else close to the same mains wire. It will radiate between component cases and across you interconnects etc. etc.
Having said that, and scared everyone away. Make sure the suupply is a couple feet .5M away from any audio interconnect or circuitry. Use Highspeed Polystirene or Polyprop or goood caps in your filter...
Actually, half the equipment and appliances in your home probably have SMPs supplies in them that are messing up your mains now :eek:

AudioSan 19th July 2012 07:18 PM

at least one:) everyone has a TV i guess:) and a PC.

Anchan 22nd July 2012 01:39 AM

Supposedly the Vicor brand smps are supposed to be really good. They go for about $500, but can be routinely had for $50 on eBay. With the "ripple attenuator module" supposedly ripple down to 4mv. I haven't used them in an amp yet, so just passing info along. Worth a look.

JZatopa 9th August 2012 04:41 PM

John65b built an F5 using laptop power supplies, I have heard it and it sounds very good. One problem you might run into is the need for a dual rail smps, they are not that common. You may have to use 2 power supplies to build a dual rail power supply.

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