PAS 3 REBUILD: CURCIO OR VAN ALSTINE?
Ronald Norris
of a Dynaco 70 (Welborne Labs). Which is the better upgrade Curcio or
Van Alstine?? I've seen a few Van Alstine rebuilds on Ebay but never a
Curcio rebuild PAS 3 for sale.
Ron
rl1...@my-deja.com
experience with Curcio; second hand reports indicate the sound is "just
ok", maybe not good enough to justify the cost and effort involved.
As a VA owner (Super PAS-3), I can say the the end result is an order
of magnatude better than 40yr old stock. Tighter and deeper bass,
clearer and more extended treble. Midrange looses the "tube lushness"
however. To my ears the VA sounds closer to SS than tube. The design
is sensitive to tube choices. Be carefull not to stray from a 12ax7 in
the phono stage. Using a 5751 (~30% lower gain), causes a slight
reduction in treble extension due to an alteration of the RIAA eq
designed into the circuit. I ended up with Tele <> 12ax7 in the line
stage and GE mil spec 5751 in the line stage. VA specifies Chinese
tubes as stock- harsh harsh sound.
If you are handy with a soldering iron, I would aquire the manual and
then worry about picking up the necessary parts- also alows you more
choice with regard to cap and resistor choices. The VA rebuild does
include a new ceramic source selector switch. Whether you go for the
gold RCA jack option is up to you.
If you end up going either route, or even just rebuilding on your own,
please report back to the group as I am sure many readers will be
interested in your findings.
Good Luck,
Ross Lipman
In article <3912EB57...@wwdc.com>,
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Before you buy.
AMitch9448
modification, it seems to keep the good points of the pas, and improves the
weak.
AMNYC
Jerry Young
mine has the newer one with SS buffers & likes it.
Tim Reese
>Curcio is a total redesign. VA is a rebuild to stock. No direct
>experience with Curcio; second hand reports indicate the sound is "just
>ok", maybe not good enough to justify the cost and effort involved.
>
Maybe I can fill in the Curcio side of the story ... my PAS-2 was a
gut job - looked like it had been through a fire. I replaced all
three boards with Curcio's "PWBs" (printed wiring boards) to a mixed
outcome. I haven't compared the original PAS to my rebuild since I
felt at the time (maybe mistakenly) that there was little to salvage
except the chassis and transformer.
Most negative - the Curcio phono board, with 2 6922s, has way too little
gain. At 30dB (32x) it's much lower gain than the RCA phono stage with 43dB
(150x) for example, and likely the PAS phono board too. The PAS claims
60dB (1000x), but I expect that approximately divides between the phono
stage at 40dB (100x) and the line stage with 20dB (10x). You may want to
keep the original phono board and upgrade the parts.
Most positive - the power supply board is a clever use of the space available
on the chassis. It offloads the filament load from the main transformer
by adding a new filament transformer and supplies IC series-regulated
voltage (LM317 with a TIP50 pass transistor, 7812) for both the filaments
and the B+.
The line stage board is a tube-transistor hybrid that uses one-half a
12AT7, one jfet and one mosfet per channel. The high output impedance is
one fault of the PAS, and this hybrid board addresses that problem. It
isn't particularly "tubey", although I don't have a stock PAS to compare to.
If I were to do it again, I'd keep Curcio's PS board and upgrade the
stock boards first (it's likely that my original boards are useable with
cleaning and parts replacement). I'd use quality but not boutique parts
and carefully match the components side-to-side, especially the RIAA
feedback caps. I'd pay close attention to wiring quality and routing to
avoid introducing any hum.
You can sub any of a number of circuits for the existing PAS boards by
building on a plain piece of FR4 (that green glass-epoxy, FR = fire
resistant) and wiring point-to-point. You probably shouldn't exceed 30mA
total from the B+ supply (although it has been done) so many of the
more popular phono stages that use WE417s and 6DJ8s are out. However,
this is likely too ambitious for the first-time builder.
You might get ahold of Norm Koren's series of articles on PAS upgrades
from Glass Audio. His solution is adding another tube for a cathode
follower on both boards (be forewarned that cathode followers have both
advocates and detractors whose opinions can be strongly held), and
some power supply upgrades.
>If you end up going either route, or even just rebuilding on your own,
>please report back to the group as I am sure many readers will be
>interested in your findings.
Yep - my PAS is a continuing project, soon to receive its parafed output
stage using one of those yucky 12AU7-incompatible 6085s, and at least a
couple of phono stages planned. Let us know how it turns out.
cheers tr
--
----------------------------------------------------------------------
Visit http://www.nmr.MGH.harvard.edu/~reese MRI, tube audio, reptiles
Tim Reese, MGH NMR Center re...@nmr.MGH.harvard.edu
RDL
and liked it. I think it sounds like an Audio Research D-79B I once
had: Very detailed while inoffensive highs (feathery), controlled bass.
I notice nothing unusual about the mids. I think you'll agree it's a
vast improvement on the stock PAS.
I use Nichicon metallized film caps and Telefunken tubes.
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DJLee01
>I built the Norman Koren phono section upgrade (Glass Audio magazine)
>and liked it. I think it sounds like an Audio Research D-79B I once
>had: Very detailed while inoffensive highs (feathery), controlled bass.
>I notice nothing unusual about the mids. I think you'll agree it's a
>vast improvement on the stock PAS.
>
>I use Nichicon metallized film caps and Telefunken tubes.
>
Ok, a preamp sounding like a power amp. Very interesting observation.
djl
joe1...@my-deja.com
rl1...@my-deja.com wrote:
> Curcio is a total redesign. VA is a rebuild to stock. No direct
> experience with Curcio; second hand reports indicate the sound
is "just
> ok", maybe not good enough to justify the cost and effort involved.
>
Actually, a small correction: the AVA rebuild is not really "stock".
While the audio circuits are close to stock, the power supply circuitry
is enhanced.
In my opinion (as an owner of an AVA Super PAS 3i -- basically the PAS
rebuild in AVA's own chassis) it is a really nice preamp. Have fun!