Does a "stiff" PSU rely on a beffy transformer?

[pixworld]

I built a First Watt B1 pre-amp using parts I had in stock, which included a rather small 24V/75mA (1,8VA) power transformer.
First I figure this small transformer was just temporary, needed to be changed for a more powerfull one, ones I got my hands on it. But then I start thinking.

Since the B1 works under close to constant curent (12 mA), and I have a CCS/TL431 based shuntregulator (32 mA contant current CCS and 20mA drained through the shunt) with a very low output impedance (0,2 Ohms), is there any need for a beffyer power transformer?

 

[PRR]

The load is like 18V and 18mA, so 1k.

There is (on Pass's plan) a 15,000uFd capacitor on the rail.

1k with 15,000uFd is a 15 second time-constant. MUCH longer than typical audio events.

If this were a class B stage we would need more thinking. But it is Pure A. The preamp current averages to no-change over each signal cycle.

"beef"

 

[pixworld]

Is this correctly understud?

Thanks PRR
Did you ment that a small transformer is okay as long as it can suply with voltage and current with no signal applyed (quescent current) ?

And that is because the last cap is acting a charge resevoar to take care of (if any due to the class A working point) current swing.

 

[Nelson Pass]

A B1 draws about .02 amps, or about 0.4 watts, and it's very constant.

 

[KatieandDad]

A beefier transformer has lower output impedance. The large C on the board also has low impedance. I think it is case of diminishing returns. It probably does make a difference but whether or not you could hear it ???

 

[res07njc]

Honest question - I was under the impression that the best C, is the one that eliminates hum, and no more. Is that wrong? (ed. that's probably not stiff I'm guessing.)

 

[PRR]

In the plan in the first post: there is a "CCS" between transformer and amplifier. This makes deliberate SAG ("un-beefy"). Your only concern is to get enough DC from the rectifier to cover losses in resistors and CCS to get the design voltage at the amplifier.

> best C, is the one that eliminates hum, and no more.

Hum is never totally eliminated. You can only "make it too small to hear".

I have a feeling we are using magic spells instead of actually understanding.