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My Impressions = Heathkit WA-1 with two Low DCR, Low H, Stancor C-2708 choke , power supply upgrade

Posted by wpod (A) on July 17, 2007 at 12:47:54

Greetings-Since I first learned of these chokes, rather than speculate on their "sound", I've been wanting to give them a try in an existing circuit, and finally an ideal platform came my way in the form of a pair of Heathkit 807 PP poweramps.The other "addition" to the power supply which really seemed to make a difference was the addition of a 40K "bleeder" non-inductive resistor (to ground) after the last cap in the power supply. This really seemed to make a big difference to me, unless I was/am hearing something else. I had emailed Jeff with my listening impressions, and rather than try to transcibe the whole thing, I find it easier to just cut and paste. I hope that Jeff is not offended that I am posting this without his permission, but his damn emailbox is full AGAIN and I can't wait forever. Here goes:
Jeff-
Thanks for your patience, I am now back in the womb (music room) and
listening and hearing things that I wouldn't have believed possible for a
mere $20.00 upgrade ( two Stancor C-2708 chokes) Wow!.

To be honest, in my first attempt, probably because it was rushed and not
optimised, I really couldn't hear a big difference. However, upon installing
(into the system) an old McIntosh MX110 tube preamp with mono and L+R speaker
reversal switches, the change is not subtle and very easy to distinguish.

I have a handfull of "demo" albums that I play when trying to evaluate a new
component or tweak . These range from Miles Davis "Tribute to Jack
Johnson" all the way to Stravinsky "The Rite of Spring" with some good
mono stuff in between . I use the Miles album to listen to Bill Cobham's
drums which are recorded exceptionally well. The bass ( kick ) drum is tighter
and more refined/defined and the snare has a "snap" to it .......that wasn't
there before.

The midbass in particular has a more precise sound to it now.
I also put on various "classical" pieces that contain very complicated
piano passages which will sound like shit on a poor system. This is where
the power supply really shines !

I really noticed a big difference, there is more of a "blackness" between
individual notes and certain chords, played with and without the sustain, I can
actually hear precisely when the pedals are depressed.

wpod / Paul

Hi Paul,

GLAD you actually built and readily heard it !! I assume you went L/C/L/C on
one mono amp, C-2708s and 40 to 50 uF for Cs.

As I pointed out to you previously, you have gone from the WORST possible
configuration, a C-input filter, to the BEST possible, a L/C/L/C filter that
has low storage time and speed, DYNAMICALLY precise / correct, and .... you
have also beneficially eliminated DCR from the amps stock high HY and high DCR
inductor.

You now have, what Dennis and I like to call, a " direct access to the music "
power supply, ...........just like a 2A3 can be a " direct access to the music
" amplifying device. That descriptive verbage " direct access to the music "
is my mentor Robert Fulton's words to me, 1975.

IMHO, I have NEVER heard a better sounding, more wider-band choke, than these
.32 HY, 10 ohm, 600 mA devices, in ALL my years of audio listening. These
C-2708s, and probably the Triad C-40Xs, ( as explained previously - on how to
employ them ), SMOKE all other Ls in existence on a pure audio / listening /
performance basis. Nothing I know of will touch them, or even approach them .

The bleeder resistor is important, as it draws constant current through the
supply, and allows it to perform better vs: the modulations / pertebations of
the music load. I must warn you however, you ONLY want to use one ( or two ) MILLS MRA-12s as a B+ to Ground bleeder, no other R will do as well there, drawing
current. The Mills MRA-12 is absolutely wonderful in that application, the BEST
possible known to me, use it !!

Do the other amp, listen in stereo for awhile, and get back to me / us all, and
I will see about additional things to try. Ohh.... do this : temporarily add
clip leads in parallel to the B+ and Ground runs, to see if more wire gauge is
needed. Slagle ( hes the very best ) it. Enjoy this supply in STEREO next.
Have fun listening. I come on-board 8-3-07 on the Forum.

Jeff Medwin

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