The Aleph Design Reloaded

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
OK, here we go.

Last month I collected some "junk" Aleph 30's and 60's from the back shelves
of the storage space (the same one you remember from Raiders of the Lost Ark)
with the intention of salvaging the heat sinks drilled for TO-3 devices for use in
another project (yet another Sony SIT amplifier).

Opening them up, I discovered that they were in good enough shape that they
were worth keeping with a little cleaning and repair.

You will perhaps remember that I previously posted an update to the Aleph 3
which incorporated Toshiba 2SJ109 Jfets on the input stage, and while this
is still a worthy update there are two problems with it; first, it's difficult to
get these parts, and second, they only work on the lower voltage amplifiers
which leaves out most of the other Alephs.

However on these I decided to try my favorite small power Mosfets, the
Toshiba 2SJ313's. Apart from a different package and pin-out in some
amplifier models, they will drop right in as replacements, and they need to
be matched for Vgs at 10 mA.

The Toshiba's are preferred, but you can make do with other comparable
modern Mosfets if you can't get these parts.

Noting that some units had zener noise with R105 at 4.7K, I dropped that
value to 3.3K, and you will note that I optionally deleted Q104, the over-
current protection. Also, I moved the chassis ground connection directly
to the AC Earth ground.

The addition of the Toshiba Mosfets made for an immediate improvement
in power supply noise rejection, dropping it typically by a factor of 4 to 6, to
as low as 50 uV unweighted output. This alone justified the effort.

Also, as a tweak, you can replace the 220 uF caps with the silk caps from Elna.

Listening tests showed a significant improvement over the originals, and I
gave copies of these to my business partners for Xmas.



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witty Pa ........... why I'm feeling that some Greedy Boys are Nassssty dissssssssapointed ......


Not really on my part, just relief! First and the most important is the classic circuit remains; 2nd it's cut-off, desolder, clean holes and replace; and 3rd I've got me a stash of matched 10mA 2SJ74 BLs. Probably replace and refresh the PSU caps as well. Something I can do down the road...

Thanks as always PaPass!