• a couple of comments, mods, tubes - rodney 12:50:42 10/30/03 (0)
  In Reply to: Cheap PAS 3 Upgrade posted by kozzmo on October 24, 2003 at 12:04:36:

  Hey David,

  Russ makes some good suggestions. I would like to add a little info and some of my experiences.

  First, there are a couple of articles out there on the net that discuss PASS mods, one called "SPICE and the PASS" or something like that and an article by Audio by VanAlstine on the power supply. These gave me some good hints.

  Second, I just redid a PASS power supply and phono section. I run this into my Foreplay line stage. I redid the power supply and filament supply as Russ57 suggested. However, I used two Angela (Solen) 60uF caps for first two caps and two 180uF electrlytics each bypassed with 10uF Angela caps for the next two caps. This got rid of all residual hum in the circuit (I modelled the supply first to get the values). In the phono section, I removed the positive feedback resistor. I replaced the plate resistors with metal film types. I then replaced the cathode resistor in the second stage with a diode (BEWARE- the tube manuals recomend that 12AX7's NOT be diode biased). Finally, I installed a 30pF "Miller" capacitor (grid to plate) on the input of the first stage.

  These mods proved quite worthwhile. The bass is is well defined and articulate, but not overblown. Overall the sound is much cleaner and more airy. I like it allot and I think it is a better phono stage than my previous rebuilt Fisher 400C.

  I have bee lucky enough to obtain a bunch of 12AX7s over the past few years. I would say the best in the phono section are "smooth plate" Telefunkens, "box anode" Mullards, and "bugle boy" Amperexes (never put in the "orange globes" so I can not comment). Anyway, in my setup the Amperexes are clear winners in the phono stage, yielding better detail and focus than the others. I have been using the Tele's in the line stage, BUT I have not rebuilt this stage so my preference could change. Moreover, in its current state, the PAS line stage is crushed by my actively loaded Foreplay. However, there is much room for improvement in the PASS line stage (Russ57 indicated some of the easier stuff), so I withhold my final judgement untill I finish up my mods.

  Good luck,

  Rodney
  
  

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• Re: Sure...try the following - Russ57 13:02:53 10/24/03 (7)
  In Reply to: Cheap PAS 3 Upgrade posted by kozzmo on October 24, 2003 at 12:04:36:

  1) Redo the heater supply. Pick up some diodes and get rid of that selenium rectifier and replace the caps with bigger ones or at least newer ones. Then remove the on/off light from the socket front left of the preamp. Might want to get a terminal strip. Costs around 3-5 bucks total
  2) Radio Shack sell an Alps 100K stereo pot for the volume control. Remove and replace old one doing away with the loudness circuit. Costs around 3 bucks.
  3) Remove tone controls. Costs nothing
  4) Clean all the controls you plan on keeping such as the selector switch and balance pot. Costs whatever you have to pay for contact cleaner.
  5) Replace quad cap. You can make one 10 uF/450VDC and three 40 uF/450VDC caps work. Mount the little 10 uF directly on the rectifier and mount the three 40 uF where the old quad cap was with the leads insulated and going throught the chassis. You can use a hose cap to hold them all together and maybe some silicone to glue them in place. Costs around 10 bucks.
  6) FIRST, download the instructions for the above work from Joe. Costs nothing:)

  Next time don't pay so much. I got my PAS for 40 bucks:) After you get done with the above you might question building one from scratch. I like the PAS better than the Foreplay personally. Next round of modes would be replacing resistors and caps which can be done for under 20 bucks.

  Good luck,
  Russ
  
  

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  • Re: Sure...try the following - Flyquail56 05:16:39 10/25/03 (0)
    In Reply to: Re: Sure...try the following posted by Russ57 on October 24, 2003 at 13:02:53:

    David,
    I would also second what Russ suggests; excellent advice. If you have a turntable, remove the 47K positive feedback resistor in the phono section (from pin 3 to pin 8) for improved sound. You also might want to consider replacing coupling caps sooner than later, there are some good inexpensive ones. Many people like the Illinois caps from Antique Electronic Supply. I also like the Panasonic caps from DigiKey. I don't recall which series, but they are metallized film with copper leads, IIRC. I can look them up if you're interested.

    You will likely be very pleasantly surprised at how good the PAS is after these tweaks. Good luck!

    Mike
    
    

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  • Re: Sure...try the following - sinewave 14:48:06 10/24/03 (0)
    In Reply to: Re: Sure...try the following posted by Russ57 on October 24, 2003 at 13:02:53:

    Russ suggestions are good ones, I would only add that you replace the output .22 caps in the line stage with 2.0 / 200v multicaps. I did that to my preamp and result was very good.
    
    

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  • Re: Tubes - kintyre695 13:54:10 10/24/03 (4)
    In Reply to: Re: Sure...try the following posted by Russ57 on October 24, 2003 at 13:02:53:

    You don't mention what tubes are in it. I just changed to telefunken's and they are amazing. I hear that there are new tubes from JJTesla that are very good, but are much cheaper.

    One other thing you might consider is to touch up any bad solder joints on the PC boards, or other connections, which costs you nothing.

    Good Luck

    David
    
    
    

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    • Re: Tubes - Kozzmo 09:57:24 10/25/03 (3)
      In Reply to: Re: Tubes posted by kintyre695 on October 24, 2003 at 13:54:10:

      Thanks!! Everyone. I will try some of these suggestions and post my results.

      
      David
      
      

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      • Re: Original tubes are Telefukens and... - Russ57 15:58:01 10/25/03 (2)
        In Reply to: Re: Tubes posted by kozzmo on October 25, 2003 at 09:57:24:

        because the heater voltage is so low chances are in your favor that they are fine. Bottom line, don't let the original tubes get away from you as NOS replacements of same quality would be a staggering amount belive it or not.

        And yes, if you could afford the caps, and for that matter resistors as well, it would be a "sound" investment.

        
        Russ
        
        

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        • Re: Original tubes are Telefukens and... - Kozzmo 20:26:56 10/25/03 (1)
          In Reply to: Re: Original tubes are Telefukens and... posted by Russ57 on October 25, 2003 at 15:58:01:

          I did not know that when I bought the thing. I got the thing from a HIFI resale shop here in Chicago. They have SOVTEKS in them. Oh well.

          I'll try some JJ's or EI's. Don't feel like buying Telefunkens at the lovely ebay price$$$$.

          David
          
          

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          • My Experence/Tubes/Mods - marcus2114 08:36:57 10/26/03 (0)
            In Reply to: Re: Original tubes are Telefukens and... posted by kozzmo on October 25, 2003 at 20:26:56:

            Hi David,
            I also have the Dynaco PAS Pre Amp units.
            I have 3 of them.
            If you ever run across the Telefunkins and can afford them, By all
            means get them, They are the best.
            I have a matched quad of the JJ's and EI's, The (JJ's) sound good but the (EI's) in them sound very close to the Telefunkens.
            Russ and David are also correct about the mods for the unit as I have preformed the same mods on mine using the Illinois caps and such.
            Definitely remove the pilot light as that will give you some more current and will be a tad better on your transformer.
            You might consider putting a LED in lew of the pilot light if you want to know when it's on.
            If you want to know how to do the LED?, Let me know.
            I hope this helps.
            David
            
            

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