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How to replace volume pot in Dynaco Pas

I have just aquired a Dynaco Pas 2 preamp. I would like to replace the funky volume pot.I have a alps style pot and I also have a stepped attenuator to use.Both the Alps and the Stepped Atenuator have 6 lugs for connecting.The stock Pas pot has 12 lugs. Normally there would be R-in,gnd.,R-out,L-in,gnd.,L-out.That's six.
The pas has 12 and a couple of caps connected as well. Can anyone enlighten me on how to change this out?

thanks in advance.

e
emorrisiv
viridian's avatar
viridian
4,184 posts
 
Great job! I hope that you are enjoying it. I installed the SDS power supply board in my PAS and it made a world of difference for the better. I just used cheap mylars as the bypass caps on the power supply, I may switch them out for something more ambitious.
emorrisiv OP
312 posts
 
Viridian: I was thinking I would just purchase on of the upgraded power supply mods from Audio Regenesis. Here is there link:
http://www.audioregenesis.com/projects/index.html

Not expensive and a easy conversion and makes the amp much safer and with better power supply.

I am also going to try my 25k stepped attenuator.I will let you know how it goes in the next day or so.

e
viridian's avatar
viridian
4,184 posts
 
I used this board and am quite happy with the outcome, if you prefer there is an option to delete the tube rectifier and use diodes (I did not do this). There is also film bypass caps:

http://store.triodestore.com/sdslacabofor1.html

I imagine that any replacement board is going to kick the snot out of the stock setup.

Do you use the phono? If so you will have to change values if you go with a 25K pot. I would be interested in what the measured input impedance is with this value, if you can measure it. Please post back, or contact me off the board.
emorrisiv OP
312 posts
 
Viridian: Do you think I should use a 100k pot? I am not using the loudness feature.I have been looking at the math and I am unsure.
The low level input is 50k and the high level input is 250k and the output is 1k.

I have been reading up on pots and attenuators and I will admit that I am a little confused.I was never very good at math and the equations (as expressed in the white paper I am reading) are beyond me.I understand the concepts but am having a problem putting numbers to formulas.

If you or anyone has experience with this or a recommendation I would be very grateful.

rank beginner hack

e
viridian's avatar
viridian
4,184 posts
 
I would, and have, gone with a 100K pot. The problem being, if you use the phono stage, you will have to replace several of the caps and resistors on the board with different values to return the RIAA curve to being flat. This is not a bad idea, as the original design pretty much sucks and even with the upgrades, you will find that it is probably not up to the quality of the line stage.
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