The (high-cap.) unregulated PSU for chipamps

[falcott]

Originally posted by carlosfm
On regulators I would rather use an electrolythic bypassed with a ceramic than use tantalums.

Waay off topic, arn't we?


Carlos, do you think bypassing with a ceramic here is better than with a film cap? On my dual bench supply I have just thrown away the 1uF tantalums and fitted 47uF electrolytics bypassed with 470nF MKT. Would 100nF ceramic be good here instead?

(And it doesn't take up too much more space, if the bypass cap is under the board.)

[DigitalJunkie]

Just my .02

I try to avoid ceramics in audio gear as much as possible..*Especialy* in the signal path.. But,PSU bypassing with them might not be so bad..

I dislike tantalums,except as power supply bypassing in digital circuits,they perform well there aslong as you overspec the voltage 2-3x! I've had 16V tantalums explode at 12V...25V caps were okay though (35V would be safer.) I dunno why tantalums are so picky about the voltage thing.

[carlosfm]

Originally posted by falcott
Waay off topic, arn't we?

Yup.

Originally posted by falcott
Carlos, do you think bypassing with a ceramic here is better than with a film cap? On my dual bench supply I have just thrown away the 1uF tantalums and fitted 47uF electrolytics bypassed with 470nF MKT. Would 100nF ceramic be good here instead?

(And it doesn't take up too much more space, if the bypass cap is under the board.)

If the space is small I use multi-layer ceramics.
You can do that across the CAdj. cap.
But the cap at the reg's output, in the case of the LM338 (with LM chips) is the most important, as it has influence on the sound of the whole amp.
Here I use Philips 47nf MKT caps (polyester) with excellent results. Feel free to use polypropilene if you want.

[D_GR8_1]

Ok.

So, why does the software complain that the ADJ pin has no "driving source" when there is a capacitor connected between it and ground?

[SheldonD]

Carlos : did you ever check the voltage regulation dynamically under heavy load.
Using the snubbers and large caps? What voltage sag percentage did you get?

[carlosfm]

Originally posted by D_GR8_1
Ok.
So, why does the software complain that the ADJ pin has no "driving source" when there is a capacitor connected between it and ground?

I presume you have a cap and a resistor from Adj. pin to ground?

[carlosfm]

Originally posted by SheldonD
Carlos : did you ever check the voltage regulation dynamically under heavy load.
Using the snubbers and large caps? What voltage sag percentage did you get?

Yes, I did.
The tests were made with an LM4870 and a weak PSU, made with two 15V/3A trafos, MUR860s and, initially, 3,300uf caps on the PSU, as you can see on the first post of this thread.
The LM4780 has 100uf+100nf on board.
This PSU, under load, produced around 22.5V, and with music playin' LOUD it sagged to around 18~18.5V.
I know, this PSU was just for test purposes, it's weak, and I don't listen to choral music.
Inserting 10,000uf caps the PSU voltage under load decreased some 0,5 volts, to around 22V.
But with LOUD music it very rarely went below 20V.
Better trafos should be used, this was a test.
Anyway, I prefered the sound of the final PSU (with the big caps added and the snubbers) to the initial low capacitance PSU.

[D_GR8_1]

my schematic is exactly the same as the one you posted here on the forum.

[carlosfm]

Originally posted by D_GR8_1
my schematic is exactly the same as the one you posted here on the forum.

You can sell that software on ebay.

[D_GR8_1]

Considering that Protel licenses cost around $10k, i think i will be making myself quite a profit!

if only my company allowed it...