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Re: Low DCR question for Jeff

Posted by drlowmu (M) on July 6, 2006 at 16:38:28

In Reply to: Low DCR question for Jeff posted by electronluv on July 6, 2006 at 14:18:32:

Hi Electronluv,

Well, its not just the chokes that come into the equation. Three things apply, the power transformer, the rectifier system, and the inductors.

You often like to use mercury vapor rectifiers - which ARE relatively low Z. But ...you MUST also consider the power trannie AND the chokes. The whole PSU is designed to act as a WHOLE, a single ENTITY, all low-Z. If the power trannie ain't low Z, ( which is the initial source ), who cares what 'ya do with the L's Z ??

There is a whole OTHER factor on low DCR that I need to post herein, and it comes to me recently from Dennis who mentors me. *** The need for low DCR is more important as the B+ voltages decrease, so a 200 VDC Plate supply will NEED much lower DCR parts than a 550 VDC B+ supply. ***

If you make the 550 VDC supply "ultra low" ( under 10 ohms DCR ) the supply may get sluggish sounding, from the mass of the trannie's wiring, laminations etc., so one needs a balance and ..... NOT always is " under ten ohms " the BEST answer.

But Josh, in GENERAL, a lower DCR supply will sound better in the triode amps you like to buiild, and its NOT a small audible difference to someone sensitive to building and listening.... like you !!

If you try to listen through a "mid fi" ( 40 ohms or so ) power trannie, you will have a very hard time hearing the full effects of some ultra hi fi ( 10 ohm or less ) chokes. Now, IF that PT was 20 ohms ( "good hi fi" ) you will have a lot easier time hearing the differences in those ten ohm chokes. You got my drift??

There is not much available in low DCR Ls and PTs. I have paralleled sections of Lundahls, which halved the DCR ( and the HY's ), just to get lower DCR . In the late 1970's and early 1980s, I used to order L's and PTs from surplus places like Fair Radio Sales and a store in Orlando, Skycraft Surplus, and I would sub in different PTs and Ls and listen to the differences. It was always the same, I got so I didn't wanna listen at all to iron over 20 ohms. In the Mid 1980s I was introduced by Dennis to Dr. Halijack and got his Figure of Merit of a Power Supply letter, ( posted on this Forum ) which pulled all the A-Bing and listening results of mine into a reasonable guideline.

Now there is a new concept - such that I am " coming out of DIY retirement" to explore...low Inductance, in addition to low DCR....ala Dennis. That new amp design is rumbling around in my head...can't wait to hear it.

I hope this helps a little, feel free to repost or email me Josh, anytime. I totally respect the fun and passion you bring to the art Josh.

Jeff Medwin

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