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Old 8th August 2002, 10:20 PM   #1
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Default Dyna Pas 3X?

I decided to start spinning some vinyl again and am going to rebuild a Pas 3 I have lying around for a phono section. I would like to do to it what the 3X does, in that the tone controls are defeated when set in neutral. Is it a matter of pots or an extra piece or 3 that I can add when I recap and clean this thing up?
At this point I would rather leave the abilty to adjust the tone if I want an option, so I don't want to just bipass that section. This might have been brought up before but the search engine will not let me use 3X, or 3 or X.
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Old 8th August 2002, 10:56 PM   #2
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Hi
I'm no tech, but I've always heard that those are special pots and that they are unavailable.

Good luck on the preamp and let me know if you need some good European 12AX7's. I've accumulated quite a few.

Gotta love vinyl....
Lee
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Old 8th August 2002, 11:27 PM   #3
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hi

here's a few links

overview:
http://home.indy.net/~gregdunn/dynaco/schneider.html

some details:
http://home.netcarrier.com/~rstevens/pas.html

more rebuilding than you're possibly in the mood for:
http://www.normankoren.com/Audio/Spice_preamp.html

otoh, if it ain't broke - don't fix it! i have 2 of the the PAS-3X's one which is reasonably stock (only the power transformer has been replaced by an off-board beefy UTC unit and some AC filtering + Selenium stack replacement + scratchy volume knob replaced with rat-shack pot), and the other one rebuilt so much that it is barely recognizable as a PAS-3X (most of the modifications in the 3'rd link above have been implemented).

although they do sound a tiny bit different, i *still* can't decide which one i prefer more! i believe that the PAS-3X is one of those classic designs, where the merits of the design means that choice and quality of passive components makes only marginal difference to the sound.

to summarize, i would recommend only
- safety upgrades (i.e. a fuse + IEC power cord + selenium rectifier replacement),
- a beefier transformer to extend the tube life (the original PA-211 is very noisy and leaves the tubes current starved)
- possibly faulty components like scratchy pots replaced etc.

also the original telefunken 12AX7's *ARE* an integral part of the PAS-3X's sound so i'd recommend hanging on to those. i've tried many other tubes but the original telefunken's are simply the best by far. NOS 5751's are also nice (much lower noise, useful in the phono stage) but have distinctly different dynamics.

sorry for the long rambling post....

-pradeep

ps: also curcio audio , van alstine etc sell most of the replacement/upgrade parts and a lot of their mods are downloadable off their web-site.
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Old 9th August 2002, 05:54 AM   #4
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Thanks for the info, I was basically going to replace and beef up the electrolits or if I have enough room cause there is only the electrolitics and the rectifier in that quarter if I remember correctly is maybe add some good high voltage oils and a choke. Maybe slap some Wimas on the boards. But if the X is because of special pots, I'll just have to make do with the pots that are on it. I have a ziplock full of Tele smooths and a few ridge plates. Guess I'll trade a couple with good labels for some black plate 5751s for the preamp section and stick with the AXs in the phono. I'll get the gain there and quiet it down in front.
Thanks again,
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Old 9th August 2002, 07:38 AM   #5
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hey now
in case you're looking to swap - i have a bunch of extra RCA NOS 5751's which i wouldn't mind swapping for telefunken 12AX7's. let me know offline by email if you're interested.
-pradeep
(i'm in cambridge, MA and my email address is sarin@mit.edu)
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Old 9th August 2002, 07:38 AM   #6
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hey now
in case you're looking to swap - i have a bunch of extra RCA NOS 5751's which i wouldn't mind swapping for telefunken 12AX7's. let me know offline by email if you're interested.
-pradeep
(i'm in cambridge, MA and my email address is sarin@mit.edu)
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Old 9th August 2002, 01:33 PM   #7
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Default Re: Dyna Pas 3X?

Quote:
Originally posted by Thatch_Ear
I decided to start spinning some vinyl again and am going to rebuild a Pas 3 I have lying around for a phono section. I would like to do to it what the 3X does, in that the tone controls are defeated when set in neutral. Is it a matter of pots or an extra piece or 3 that I can add when I recap and clean this thing up?
At this point I would rather leave the abilty to adjust the tone if I want an option, so I don't want to just bipass that section. This might have been brought up before but the search engine will not let me use 3X, or 3 or X.
Hi David,

Dig up some copies of the early 80's Audio Amatuer and get the POOGE articles for it by Walt Jung for both the PAS and the Marantz 7C. They were pretty extensive for their time, and kept the basic topology, but did all the standard mods like passives and regulators etc. The PAS was more radical than the 7C. If you can't find the articles and you're interested in the, I can arrange to photocopy them and mail them to you.

The other option would be to rebuild the phono stage as per Allen Wright's circuits in the TPCB, or even an FVP5 stage. The PAS is a really average, old fashioned 'tubey' sounding circuit, even with premium tubes like TFKs in it, and unless you're going to just give it a basic tidy up, I would think your time might be better spent on rebuilding it completely with a better circuit, utilising as many of the original PAS parts as possible to keep the cost down.

In the tone stages, clean and lube all the pots (replace if neccesary) and upgrade all the passives. I'm not sure how much gain the stage has in the centre position for the controls, but you might have enough to be able to put a bypass switch in.

Cheers
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Old 9th August 2002, 08:47 PM   #8
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Acually, the "Last PAS" article was by Dave Vorhis. Also, the Pat Amer article in the later 80's was fairly comprehensive.
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Old 9th August 2002, 08:57 PM   #9
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Quote:
Originally posted by CharleyW
Acually, the "Last PAS" article was by Dave Vorhis.
I stand corrected, it was Dave Vorhis that wrote the articles I mentioned. I was just too lazy when I posted it to get up and check. I haven't seen the Pat Amer article.

Cheers.
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Old 9th August 2002, 09:02 PM   #10
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'87, I think. I'm too lazy to go downstairs and look.
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