SMPS powered small cl. A amp

[marconi118]

In case you use 2 SMPS for symmetrical PSU how do you synchronise them?
There is always one of the 2 that will power up faster. This could lead to a short Brust of DC at the speaker...

 

[TungstenAudio]

Unless the SMPS have a dedicated synchronization feature, there is no way to get them in sync, either in power up or switching frequency. You might use a speaker protection circuit for the power on issue, but the supplies will still oscillate at different frequencies; the difference will appear as a ‘beat’ frequency riding on the supply rails.

 

[ElFishi]

Depending on the circuit you want to feed a two-step power up may even be a blessing.
I have this effect in one of my amps and I get a DC hump at powerup, but it isn't a problem as the speakers are cap coupled. A two step power-up rather reduces the power-up thump.

 

[marconi118]

I was thinking of one relai per rail controlled by the other rail. (sort of X) So that all rails get power simultaneously. And in case of failure of one psu both rails go to 0V

 

[lonepine510]

Is there some kind of protection circuit in the Sony VFET Amp? At least for failure?

 

[Mark Johnson]

Have a look at the schematics. They are attached to post #1 of the following thread

DIY Sony VFET pt 1




_

 

[vdi_nenna]

Using a dual -/+ supply for power amps has been discussed before, but there's always an objection to using them because if one side fails it's catastrophic.
What's the call on this? Is it practical or a case of F.A.B. syndrome? Fearless Amp Builder- take it to the limit and see what happens!

Seriously though, I'd like to know. I have an amp I'd like to resurrect on the cheap.
I've had good luck with Meanwell as single ended power supply in a few amp projects.

Thanks.

 

[rayma]

Just use an output coupling capacitor, and no worries.

 

[vdi_nenna]

Thanks rayma. Quick solution. A cap at output would protect the speaker. Any protection needed for the amp circuit itself?

 

[Mark Johnson]

It's pretty easy to design a protection board that detects one sided failures and switches to a safe configuration ... in milliseconds.

Not so simple to do the same thing ... in nanoseconds.

Try it! You'll have fun and it'll be new design work you haven't done before. Therefore, double fun.

 

[rayma]

Thanks rayma. Quick solution. A cap at output would protect the speaker. Any protection needed for the amp circuit itself?

Think I'd try to make the circuit robust against such a fate, but still use rail fuses anyway.

BTW, that output coupling capacitor should be bipolar, since the DC fault could be either pos or neg wrt ground.
But, a typical bipolar power supply can still lose one polarity also. The rail fuse blowing is most the common reason.

 

[vdi_nenna]

Roger that...

Thx.

 

[chede]

The basic topology solutions are either bipolar supply, or unipolar with output cap or output transformer.

If you already have a bipolar supply, I wouldn't add an output cap, but just a speaker protection board (as Mark recommended) if you want to have some reassurance.

Regards, Claas

 

[Vunce]

Thanks Vunce!

Would love to see your M2 in action with the SMPS too.

Its been a while, but wanted to add my SMPS powered Class A Pass M2 clone (Prasi pcb layout).

I’m using the same Micro-Audio SMPS500-CLA for power as Meanie. Each channel has it’s own 40,000uF cap bank, sort of a “poor man’s” dual mono psu setup.
I don’t have experience with any other type of M2 amplifier, but this set up is dead quiet, zero noise/hum from the speakers with my ear right up to the drivers. I couldn’t be happier with this combo. I’m closer to curing my fear of SMPS based power with builds like this.

 

[meanie]

Nice work Vunce!

I didn't use a shielded enclosure for the Edcors, it is as quiet too.

 

[Cresnet]

Very nice work!

 

[jacques antoine]

My version of the Class A Alpha Nirvana uses two Meanwell SMPS.
The SMPS required a fan transplant with low noise Noctua's.
Works great, very quiet.

 

[brian.goodman]

My version of the Class A Alpha Nirvana uses two Meanwell SMPS.
The SMPS required a fan transplant with low noise Noctua's.
Works great, very quiet.

Jacques,

What are the part numbers of the Meanwell SMPS and Noctua fan you used.

Thanks,

brian

 

[jacques antoine]

Hi Brian,

Noctua NF-A9 FLX 92mm
MEANWELL LRS-350-24 (trimmed to 27V)

The Noctua fans are powered directly from the same 12V pins as the original noisy fans.
The transplant required some heavy butchering

Cheers,
Jacques

 

[cloudalmasai]

Hi everybody!! Mr Juma I was wondering if the amp in post #1 can be made for single supply use? Let´s say 24V switcher. Thanks for all circuit you have shared over the years, in the past I build a composite amp of "the wire series", but always read your post about class A amp. Sorry for my bad english.