Carlos' snubberized Gainclone Power supply, Part II

[peranders]

Thank you both for the input.

It's interesting to see what happens if only SMD caps are used, very little inductance (looked at the irf document).

Can we make any conclusion about how it should look like if we take both impedance curves into accont and also the necessity of a snubber in the first place?

My idea now and also in the beginning is that you should concentrate your efforts close the supply pins if we talk LM3886 and otherwise close to the "power consumer" in general.

[Joseph K]

Mauro,

I don't really understand the low frequency part in this last graph. Could you please show also the according schematics?

Phase shift: I feel like the phase shifts produced by the power supply in a frequency range where there is still enough loop gain left to compensate for it, are getting compensated for by the amp. It becomes critical in the range where the phase margin of the amp diminishes, so it can not compensate any more, and can go actually in oscillation. Then, much above this frequency it does not count again, because though there is a bad phase shift, there is no more gain left for the oscillation requirement. For example, for an LM3875 I would say the "phase margin critical ramge" is the ~500K -1MHz range, as You know it just too well.

Else: I'm not too surprised by the agreement of your sims and my tests. You did make the right simulation with the right values, and that can be closer to reality than a fraction of dB! I've controlled that in the "another" forum

But it is [badly] needed to have the right parameters of the actual part in your hand!! And that is called a network analyzer..

And yes, this was just the marketing dep. blubber leading to a project:Your network analyzer on a shoestring [though only for the bravehearted]!!

http://n2pk.com/

A most beautiful one, seriously

Ciao, George

[Joseph K]

Per,

Yes, real HF [i mean RF] bypassing is done in the range of mm-s.. of the actual power circuit. These two things, short distance [minimal loop] and low rf impedance are unseparable.

Ciao, George

[mauropenasa]

Hi peranders,
I have not details position on this diverged bypass techniques.

I believe that does it main point is analyse well the circuits and "only after" that is they have a concrete elements, are useful to modify to improve.
I believe that a PSU by OPamp is able is different by S.S. , but I don't believe that am great there differences " of method " among diverge OPamp or diverged PSU voltage or power.

The data and my doubts are here to look for a shareable idea on I don't know what to do about it a good PSU, with or without "snubber".

If you have ideas or data to add to my, perhaps we are able help the beginners to understand the problems of the audio PSUs...

SMD caps, ye, very low ESL, different resonance point , but equal principle of use ( and compensation ).
Perhaps the low Q of some types ( film ) in league with the low ESL is able improve the performances in the 100Khz-10Mhz zone.
I will do of the tests....

Ciao

Mauro

[mauropenasa]

Hi George,

I share your analysis on the phase shift.
Some subjective elements make that is noticed in the forums, do me think that are even a phenomenon in league with the audio band, similar to the dynamicses it observes from Graham Maynard in his test " " inverse driven".
I have not done experiment directed to this phenomenon.
I believe that the better condition is that the phase of the PSU is identical in that of the amp circuit...

My Zener mod. circuit :

[Joseph K]

Mauro,

Yes, I forgot about the Zener... Now I got it.

By the way, when you talk about low Q film caps - I have found these quite nicely working, low Q. Was exactly thinking about applying such things in bypassing! I think I have seen these at Schuro.

[mauropenasa]

Bypass film cap:

Wima MKs02: p.2.5mm =~2-4nH ESL (George photo)

Arcotronics R82 p5mm =<7nH ESL (my ordinary use)

Wima MMC: SMD =~1-3nH ESL (good SMD implementations)

All Metallized polyester type, normalized Q ~ 3 - 7


Ciao

Mauro

[NicMac]

Hi P-A,
If you are still watching this thread I have a newbie question:
In the schematics of your optimized supply (also in that of Carlos) there is a 100uF bypass cap before the final "snubber". What is the primary function of this cap? Ripple rejection or fast low-impedance energy storage close to the amp? I have some huge 100u Obbligato film caps (http://www.diyhifisupply.com/catalog...bligatopsucaps) and I was wondering if they could be use here with any benefit (the supply is feeding a Hypex UcD module).
Thanks,
Nic