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Stefano 3rd February 2006 12:19 PM

inductors on the AC line
"Large inductors in series with the transformer primaries and secondaries
can be used to stretch the duration of the charge pulse to the power
supply capacitors, improving regulation and reducing noise."

Has anyone tryed to do it? How much inductance is really needed for a zen v4 or a bzls?

Stefano 3rd February 2006 12:28 PM

...From Nelson's "Power Supplies: Commentary for Consumers"

audionut 3rd February 2006 01:48 PM

I just completed an Aleph 30...the transformers are large 28v x 16a signal transformers. The rails from these transformers after a capacitor filter would be far too high for an Aleph 30. (recquiring 25volt rails)My solution was to put air cored 14ga. 2.5mh inductors after the rectifiers and before the capacitors...

this is called a choke input filter. The inductors "buck down" the voltage from the rectifiers, and convert the access voltage into current. The rails, loaded by the Aleph 30 circuit come in at 26 volts.

This implementation is supposed to be easier on the rectifiers, and I note that the rectifiers and the transformers run very cool. The inductors however get very warm.

I notice that the ripple, under load is at 30 mv per rail...this is much better than the ripple on my aleph 3's which use a CLC filter.
My Aleph 30 (using Brian Bell's wonderful boards and parts list) draws 360 watts out of the wall. This is high for an Aleph 30 and is the cost of using higher voltage transformers and bucking the voltage down. (transformers were $5 apc.)

Amazingly, on start up, the voltage on the rails takes 3 or 4 seconds to build up. I don't think the voltages come up perfectly evenly, resulting in 2 or 3 seconds of 10 volts of DC heading out to the speakers. I fixed this with a muting circuit.

I like the idea of a choke input seems to provide quieter rails for the circuit.

Nelson Pass 3rd February 2006 06:37 PM

Re: inductors on the AC line

Originally posted by Stefano
Has anyone tryed to do it? How much inductance is really needed for a zen v4 or a bzls?
Works like glue. The value of the inductor is dependent on the
current draw and how much drop you want. Feel free to

jackinnj 3rd February 2006 10:09 PM

and if you're looking for the article:

Stefano 4th February 2006 06:29 AM

Thank you Nelson, thank you all guys! I've asked because I'ven't got any inductor and so I have to buy 'em.
But if I've understood it means that the inductors lower the ac voltage, it is correct?

balthazard 7th February 2006 12:06 PM

coil size
try this simulator for your coil calculation and voltage loss ...


jackinnj 7th February 2006 12:49 PM

you can do much the same analysis with LTSpice (SwitcherCad) from Linear Technology or TINA from Texas Instruments -- and these have bode-plotters which will make dynamic analysis of power supply stability much easier.

there is an LTSpice support group on Yahoo.

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