Dynaco PAS Preamps

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Dynaco PAS Preamps

Postby coolhandjjl » Tue Jul 02, 2013 6:57 pm

I have read that the Dyna PAS 2 & 3 preamps can be a bit thin sounding on their own. Apparently, one has to modify the tone circuitry to unleash the potential of these units. True? I have been looking for a tube pre without breaking the bank. Marantz 7's seem to always be out of my price range.
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Re: Dynaco PAS Preamps

Postby EWBrown » Tue Jul 02, 2013 8:09 pm

The tone circuitry is the preamp's "Achille's Heel", between the wild and unruly rat's nest of wiring behind the front panel, and those annoying pesky little PECs, there is definitely a LOT of room for improvement.

With all the front panel wiring, it is necessary to have the top cover on for complete RF shielding, , otherwise it will pick up every AM broadcast station in the area, and perhaps some of the stronger international SW broadcasters, all at the same time.

/ed B
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Re: Dynaco PAS Preamps

Postby Geek » Tue Jul 02, 2013 9:16 pm

If you have a PAS chassis, I have some 7c clone boards to fit them ;)

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Re: Dynaco PAS Preamps

Postby coolhandjjl » Tue Jul 02, 2013 9:53 pm

So what are better choices for tube preamps?
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Re: Dynaco PAS Preamps

Postby WA4SWJ » Wed Jul 03, 2013 6:40 am

Here's one idea. I bought some of these boards but have not had time yet to put them together and try them out.

http://classixaudio.com/menu.htm

They're nice boards and I would think they will work great. I just have to get busy and build them into an enclosure of some sort.

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Re: Dynaco PAS Preamps

Postby coolhandjjl » Wed Jul 03, 2013 7:37 am

WA4SWJ wrote:Here's one idea. I bought some of these boards but have not had time yet to put them together and try them out.

http://classixaudio.com/menu.htm

They're nice boards and I would think they will work great. I just have to get busy and build them into an enclosure of some sort.

Regards,


Ed, that looks pretty cool. My triamp system has a ss amp for the bass bin, ss amp for the tweeter, and a tube amp for the mid horn. Are those things you linked geared for the classical/opera genre, or any type of music? I listen to lots of classic rock.

Mainly, I use mp3's from a laptop. I really don't need a full featured preamp anyway, I can do tone shaping in my laptop's music player, whether it is iTunes, or Decibel.

I'm looking at JDS Labs ODEC as my DAC. That unit is all ss. The Grant Fidelity Tube DAC11 seems to get mixed reviews, some say it lacks a hefty bass.
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Re: Dynaco PAS Preamps

Postby WA4SWJ » Wed Jul 03, 2013 4:39 pm

My guess would be that they would work with any type of music. I don't know why they wouldn't. I just gotta get time to put them together and find out!!!! I like all types of music except RAP so I could try it on just about anything.

Work gets in the way of fun (but I'm sure glad to be employed by a great company).

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Re: Dynaco PAS Preamps

Postby mesherm » Wed Jul 03, 2013 4:58 pm

I have two PAS-3x units. One is a factory unit that someone on ebay sold as is after trying to pull the line amp board and modify it.
I bought a set of modern replacements and only populated the line amp board and put it back to stock condition. I did add a modern power supply and filament rectifier board.
The other unit I completely rebuilt with modern PCBs and components. I tossed out the whole rotary switch nightmare but kept the special tone control pots.
The phono section was hardwired to RIAA eliminating the tape EQ. The RIAA components were replaced with 1% resistors and 5% polystyrene caps.
The completely rebuilt unit sounds fantastic where as the stock factory unit has noticeable hum even with the upgraded power supply.
I can tell you that the complete rebuild was the most work I have done on any amp or preamp EVER. I completely replaced the rear jack panel with one made from scratch and used shielded wire and a quality rotary switch deck.
I would suggest you only start with a PAS-3X unit with the unobtainium tone pots.
My preference with any preamp is no tone control at all so rarely do I move the tone pots from their center neutral positions.
Sound wise I would stack that unit up against any other unit costing 5 times as much.
The basic design is sound. It just needs a lot of tweaking.
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Re: Dynaco PAS Preamps

Postby coolhandjjl » Wed Jul 03, 2013 7:08 pm

My ability to rebuild is somewhat limited as I have no test equipment. Tweaking a PAS3X may be out of my league. I'd have to find one already tweaked by someone who knew what they were doing.

I can build however. The kits linked above look interesting. But once I add a cool looking case, connectors, pots, etc, etc, the cost could be more than a tweaked PAS3X.
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Re: Dynaco PAS Preamps

Postby soundbrigade » Thu Jul 04, 2013 10:48 am

I'd recommend a Bruce Rozenblit GroundedGrid.

The other problem with the PAS amps are that there's some passice circuitry after the OP tube loading the output, raising output Z.
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Re: Dynaco PAS Preamps

Postby coolhandjjl » Thu Jul 04, 2013 4:56 pm

Does the Van Alstine Super PAS3 mod do the "correct tweaks", especially to the tone controls, and the sensitivity to RF noise? The articles I read made no mention of that.
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