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    Pas 3 Aikido hum and scratchy volume

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    gdlen1

    Posts : 17
    Join date : 2012-03-18

    Pas 3 Aikido hum and scratchy volume

    Post by gdlen1 on Sun Jan 19, 2014 5:41 pm

    Hi all, just finished an Aikido mod for my Pas 3 and while everything sounds great, I am getting a bit more hum than the stock line stage and there is a rustling sound on the volume pot which starts about 11 o'clock, there is measurable DC on the pot, it goes from 0mv at "0" to 62mv at "10" where would DC be coming from? there is nothing before the pot except the selector switch and tape monitor. any ideas? thanks

    Elrick

    Posts : 71
    Join date : 2012-09-02
    Location : Bellingham WA

    Re: Pas 3 Aikido hum and scratchy volume

    Post by Elrick on Thu Jan 23, 2014 9:30 am

    I had both of your symptoms on my PAS 3 w/ the Aikido board. For me the scratchiness was completely eliminated and the hum was knocked down substantially by systematically trying different tube combinations in the Aikido board. Ggood luck.

    gdlen1

    Posts : 17
    Join date : 2012-03-18

    Re: Pas 3 Aikido hum and scratchy volume

    Post by gdlen1 on Fri Jan 24, 2014 2:31 am

    Great, thanks for the response, I don't really have many other 12au7 types, what did you end up with in yours?, just so I have starting point

    Elrick

    Posts : 71
    Join date : 2012-09-02
    Location : Bellingham WA

    Re: Pas 3 Aikido hum and scratchy volume

    Post by Elrick on Fri Jan 24, 2014 9:14 am

    I originally started out trying various used, older 12AU7A's and 12AU7's pulled from old shortwave receivers and test equipment that all tested good on my emission tester. I was surprised to see that I just couldn't find a quiet combination. Ended up buying 4 new Electro Harmonix 12AU7A's that turned out to be much quieter and eliminated the scratchiness in the volume pot. The hum level was reduced significantly as well but not entirely. Keep trying.

    gdlen1

    Posts : 17
    Join date : 2012-03-18

    Re: Pas 3 Aikido hum and scratchy volume

    Post by gdlen1 on Sat Jan 25, 2014 3:47 pm

    I tried a couple of Valvo ECC82's, but they made the scratchiness worse, so the tubes I have in there now are the quietest, the hum is not very loud, I can't hear it from where I am sitting but it shouldn't be there, and I wasn't having either of these problems with the stock line stage.

    gdlen1

    Posts : 17
    Join date : 2012-03-18

    Re: Pas 3 Aikido hum and scratchy volume

    Post by gdlen1 on Sat Feb 01, 2014 3:56 pm

    The scratchy volume problem has been solved, turns out I had a very early version of the Aikido board that had a missing trace for one of the tubes B+ voltages, so the other tube for that pair was getting twice as much pate voltage as it should have been, easily fixed by running a wire, that eliminated any measurable DC on the volume pot, slight hum is still there, but is very quiet so not that concerned, but I will try a few things at some point. thanks for the help

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