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    Dynaco PAS 4 Modifications



    Posts : 2
    Join date : 2009-01-14
    Location : Pa.

    Dynaco PAS 4 Modifications

    Post by GMD12 on Thu Jan 15, 2009 3:47 am

    I am looking for any modifications that may be available for the PAS 4 preamplifier.
    I a using two Telefunken smooth plate 12AX7's in the phono stage and four 6N1P's in the line stage.
    Bob Latino

    Posts : 2644
    Join date : 2008-11-26
    Location : Massachusetts

    RE: PAS-4 modifications

    Post by Bob Latino on Thu Jan 15, 2009 10:23 am

    I have heard the Dynaco PAS-4 and in stock form it is a MUCH better sounding preamp than the PAS-3. You did the right thing on the phono stage with the Telefunken 12AX7's. On your 6N1P's in the line stage. > They are good sounding tubes but in those Russian tubes the 6H23 tube is considered to be more of a direct replacement for the 6922/6DJ8. The 6N1P has slightly more current draw than a 6922 but in most applications this won't cause any problems. If you ever get a chance to try 6H23 tubes in your PAS-4 - try them. Amperex 6DJ8 Bugle Boys might be worth trying also if you want to roll tubes in there and note any improvements or changes in the character of the preamp.

    As to modifications you may want to locate the two 1.0 Mfd 400 volt main coupling caps that feed the output jacks of the two channels and try replacing them with an higher quality coupling cap (VCap, Auricap, Mundorf, REL etc).



    Unbelievably Nice Results from Coupling Cap Mod

    Post by michaelm on Sat Mar 26, 2011 11:25 am

    I went with the coupling cap replacement mod for the 1 mfd caps and the results have been very plentiful in my system. I upgraded the stock caps with Mundorf Silver and Oil, and the PAS 4 now sounds extremely open with a much darker background. I cooked the Mundorfs on a Marantz solid state amp with FM radio fuzz for 150 hours to burn them in. Some of the results I noticed right off the bat are as follows.The stage is larger and more dimensional. The bandwidth is a lot more linear. The resolution is much more accurate and detailed. There is a lot more spacial aspects to the music. My system now has a much more laid back and natural feel to it. The list goes on, but all in all the preamp just sounds even more amazing than it did before. I think this modification would help it to stand even firmer with higher priced preamps.The caps cost 95 or so dollars from Madisounds, but I can equate the sound quality gain as being just as big of an improvement as going from an entry level Movign Magnetic Cartridge to upgrading to a three hundred dollar Ortofon 2M Bronze (that I got within a couple of days of doing the modification.) I recorded the same songs' beginnings from the tape output and from the main output for my ST 120, and even though both of the outputs have different circuitry paths, I still feel that the differences are so vast that the caps are the main reason for the increase in fidelity. To further reduce any ideas that one may have on the improvements being subjective, my girlfriend that is hardly a fidelity enthusiast noted that she definitely heard an improvement with the Mundorfs. When she doesnt hear much of an improvement she usually just looks at me blankly and tells me that she cant tell a difference. Hah. I am really happy with the results minus one little road block. The Mundorf caps had larger leads coming out of them than the holes in the circuit boards would allow. I had to use a tiny file to shape them to where they would fit. I suggest replacement of the coupling caps with higher end caps for any preamp that it is possible on. Different caps have different presentations, so if you consider a mod like this, look into them for a while and research to find out what would sound best in your system. I chose the Mundorfs because a lot of the info suggested that they would help balance out my system. Music sounded a little too analytical and mechanical, before, and these caps really made it more 'musical' WHILE adding more detail. I am extremely happy with Bob's suggestion now that I have applied it.

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    Re: Dynaco PAS 4 Modifications

    Post by StereoGaryo on Sat Apr 02, 2011 7:16 pm

    I think I'm going to try some new output coupling caps in my PAS 4 real soon.
    Any other users out there with modded P 4's?


    Posts : 5
    Join date : 2009-07-18

    Dynaco PAS4 Mods

    Post by Thx1326 on Fri Oct 07, 2011 1:32 pm

    I replaced all the original electrolytics with new low ESR where possible. Replaced all diodes with stealth diodes and the rectifier bridge with discreet stealth diodes. Removed all the WIMA caps (very over rated) and replaced them with a combination of Russian PIO's bypassed with Solen FasCaps. Vastly improved the warmth and detail over the more expensive boutique caps and about 1/10th the cost. Right now am working on having a replacement cover fabricated that will have an "indented island" in the center portion to allow all of the tubes to be exposed - moving most of the heat outside of the cabinet. The sound of this preamp in stock form was fabulous for the money... with the mods - it's a killer. Currently running it with 2 highly modified Ella's. Sound comes out of pitch black silence with the warmth and liquidity that only tubes can deliver. It's a shame this classic piece went away - it way outperforms the other PAS series preamps. Good luck.


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    Join date : 2012-05-03

    Re: Dynaco PAS 4 Modifications

    Post by Rws62 on Mon May 07, 2012 1:41 pm

    Hi is it possible to post a pic of your cap mod. Thanks

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    Re: Dynaco PAS 4 Modifications

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