CLC PSU for SymAsym

[beetle]

They there!

I´m wondering if someone here didn´t do this before. The thing is that I´m planing to build a CLC Powersupply for the well known SymAsym. No big deal so far. Well... since some guy told me that might be no good idea, as this could cause some nasty oscilation.

Other then with pure Class-A amps (as far as I understand), the PSU is not seeing a constant impedance from the amp.

One symmetric PSU would be 4x 22mF with 2mH or more.

What do you guys think?

[Holger Barske]

Even on Class-A amps, power consumption is not constant. It just doesn't change as much as with AB amplifiers. So it is a good guess that your supply voltage variation will be higher with an AB amplifier as it would be with an A amplifier.

[EUVL]

Balanced Class A draws constant current as long as they are not clipping.
If you are worried about oscillation within the L-C's, you can either use CRC, or a cap multiplier (see Nelson Pass Zen Version 4, if I am not too drunk....).


Patrick

[Holger Barske]

If you are worried about oscillation within the L-C's...

Is there a good reason to be?

[darkfenriz]

Undamped LC will oscillate like hell, keep in mind, that class AB amplifier of high PSRR is nearly infinite impedance for PSU.
A well tailored snubber could be a cure here, but is there really a good reason for a LC filter?

[Holger Barske]

We are talking about rectifier - C to Gnd - L in series - C to Gnd configuration. What exactly will oscillate like hell and why?
Even an AB amplifier draws current, so why is it a nearly infinite impedance?

[darkfenriz]

Hope you know how to calculate resonance frequency and characteristic impedance of an LC filter and its response to step current waveform.
Such filters are only justified if tailored to resonate below double the mains frequency or better below 20Hz.
Also it would be good to have characteristic impedance of around the same as capacitor's ESR.

Class AB amplifiers' current consumption does very little depend on power supply voltage, within the limits. Therefore the delta V by delta I is in the range of kiloOhms. Now compare it with Z0 of the off-the-shelf LC filter for the supply. Huh?

[beetle]

I have:
C: 10x 22000µf, ESR 0.02Ohms => 22mF, 2mOhms
L: 2mH, 400mOhm

1/(2*4*a(1)*sqrt(0.402*0.022))
1.69237174006746332190


For RL=0

fr sould be slightly below that.

Or is it twice the capacity as I have 2x C? For that it is:

1/(2*4*a(1)*sqrt(0.402*0.044))
1.19668753369018047091

[Zen Mod]

do not use any Pi filter with B class amps ;

you'll have voltage drop , swinging with music ......

unless you exactly want that .......

[beetle]

Can you explain that a bit more exactly. I was not paying to much attention in EE class at university.