[Akku]

Hello, this is my first post here (sorry for my bad english). I’ve almost built a PPA that sounds really good already (I have failed to bias it in class A due to a defective 2N5457 – I am waiting for a new one). Now, to test it, I am powering it with the psu of my phono stage (a 27v single linear PSU based on LM317) but I need another PSU if I want to listen to my vinyls. So I ordered a Wellborne PCB where, I guess, I will be able to build a TEPS from the bridge on populating just the positive half. My idea was to put this PSU PCB (the DC section) in the same case of PPA and build in another small case an AC PSU with choke, transformer and filter. My questions are:

1) A good idea?

2) Can I use a project board to build the AC part of the PSU? I mean, are project boards rated for AC mains?

Thank you.

 

[tangent]

Quote:

So I ordered a Wellborne PCB where, I guess, I will be able to build a TEPS from the bridge on populating just the positive half.

Well, you'll build half a PS1. A TEPS is the name of a specific board, not a circuit. The circuit is generic.

Quote:

A good idea?

I'd make the external box an unregulated supply: transformer, bridge, filter caps. If you wanted to add an AC line filter ahead of that, fine, but since it's in an external box I'd just use a standard iron-core transformer; they don't pass high frequency very well, so an AC line filter isn't really necessary.

Then, take the Welborne board and hook the unregulated supply up to where the filter caps go. You could install some of the filter caps on the Welborne board, too, if you wanted.

 

[Akku]

Thanks for the answer.
Is there any technical reason for not putting the bridge inside the amp enclosure?
You say that with an iron core trasfo I don't need the line filter.
So, if I put everything else inside the amp I will keep the external box really small and easily hide it (I already have too many things stacked in my gear).
And the snubber?

Do I still need the snubber with an iron core?

 

[ITZBITZ]

What about using a cheap $10 24VAC power supply into a board like the Velleman kit and mounting it to the inside of the PPA case?

Kinda like a linear regulated power supply with the AC portion in the Wall Wart..

$10 24 VAC Wal-Wart
$13 Velleman Kit

Stick it inside the PPA case, mount it on the standoffs or something and you've got an internal power supply PPA.

 

[tangent]

Quote:

Is there any technical reason for not putting the bridge inside the amp enclosure?

By doing the filtering outside the amp case, you reduce the possibility of inducing 60Hz hum. This could include inducing hum into your interconnects.

Quote:

Do I still need the snubber with an iron core?

I'd add one myself, but you could get away with leaving it out.

 

[Akku]

Originally posted by tangent
By doing the filtering outside the amp case, you reduce the possibility of inducing 60Hz hum. This could include inducing hum into your interconnects.

I am not sure I understood your reply. What do you mean for "filtering"? Common-mode filter and RC filter are in the AC part of the PSU. Maybe you refer to the big filtering caps

That's why you advised to put only the regulator inside making and external unregulated DC PSU?
But, in that case, can I still use an iron-core trasformer or do I need at least to shield it?

For ITZBIZ:

That's exactly what I want to do but I want to understand if I introduce some signal degradation.

 

[tangent]

Quote:

What do you mean for "filtering"?

I mean the big filter caps. I've been careful to say "AC line filter" when I meant that.

Quote:

Common-mode filter and RC filter

There is no RC filter in the TEPS. It's an LC filter. The resistor is just there to bleed off charge from the caps when the power is removed.

Quote:

can I still use an iron-core trasformer or do I need at least to shield it?

The best shielding is putting distance between the regulator and the transformer, which is exactly what you're getting in this situation. You might worry about where you place the unregulated supply box amongst your audio components, but that's it.

 

[Akku]

Thank you very much, I will do it that way.
And thank you and to all PPA team for this amp. Mine, even not finished (no class A biasing and just one buffer for channel), sounds gorgeous.