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    PAS 2 Issues

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    Drugolf

    Posts : 25
    Join date : 2014-12-29

    PAS 2 Issues

    Post by Drugolf on Fri Jan 16, 2015 8:57 am

    Hey guys.  I have a PAS 2 preamp that I have paired up with my ST70.  I have some odd behavior with the left side being weaker than the right and when I turn the volume all the way down, I still get a fair amount of sound, especially from the right side.  Any thoughts where to start?  I would not have bothered to post anything on it with just the weak left side but the odd volume thing I figured would be a good one to throw out at you all.  Caps related to the volume pot?  If there is something you think I should test, all I have is a good multimeter and a small brain so keep that in mind. jocolor

    peterh

    Posts : 680
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: PAS 2 Issues

    Post by peterh on Fri Jan 16, 2015 12:11 pm

    Drugolf wrote:Hey guys.  I have a PAS 2 preamp that I have paired up with my ST70.  I have some odd behavior with the left side being weaker than the right and when I turn the volume all the way down, I still get a fair amount of sound, especially from the right side.  Any thoughts where to start?  I would not have bothered to post anything on it with just the weak left side but the odd volume thing I figured would be a good one to throw out at you all.  Caps related to the volume pot?  If there is something you think I should test, all I have is a good multimeter and a small brain so keep that in mind. jocolor
    replace the volume pot. tubes4hifi has this, get a 250k ( as the original ) is what you need.

    corndog71

    Posts : 454
    Join date : 2013-03-19
    Location : It can get windy here

    Re: PAS 2 Issues

    Post by corndog71 on Fri Jan 16, 2015 1:04 pm

    The first thing I would do is swap the tubes to the other channels to see if the problem follows them.

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: PAS 2 Issues

    Post by GP49 on Fri Jan 16, 2015 2:03 pm

    A customer unit came in with this complaint. It always had it but was slowly getting worse.

    I found that the original kit builder hadn't soldered the ground end of the volume control.

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: PAS 2 Issues

    Post by Drugolf on Sat Jan 17, 2015 8:09 pm

    Volume pot measured 0-245 on one side and 0-289 on the other.

    Bob Latino
    Admin

    Posts : 2415
    Join date : 2008-11-26
    Location : Massachusetts

    Re: PAS 2 Issues

    Post by Bob Latino on Sat Jan 17, 2015 10:29 pm

    Drugolf wrote:Volume pot measured 0-245 on one side and 0-289 on the other.

    Try cleaning the volume pot with contact cleaner. See if you can get some contact cleaner inside the crevases of the pot and then work the pot from one end to the other for a few minutes. The pot may have some rust inside that is causing the high reading (289K) on one channel.

    Bob

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: PAS 2 Issues

    Post by Drugolf on Fri Jan 23, 2015 12:21 pm

    Tested the pot again and came up with a reading that confirms the pot is bad on the one side. Ordered from Tube4hifi. Going to replace the power supply board too while at it.

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: PAS 2 Issues

    Post by Drugolf on Mon Jan 26, 2015 11:01 pm

    So I got the new volume control and it is of course entirely different than the old original. It is labeled to tell me what attaches where but the problem is I don't know what wire is which on the existing pot. How do I determine this?

    tubes4hifi
    Admin

    Posts : 1292
    Join date : 2008-11-30

    Re: PAS 2 Issues

    Post by tubes4hifi on Wed Jan 28, 2015 5:58 pm

    most of those old kits used green wire for the left channel and red wire for the right channel, although, some used black wire for everything.
    Which channel is which isn't going to matter on the volume control anyway, both channels are identical.
    But if you (or anyone) takes something apart, mark the wires first!

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: PAS 2 Issues

    Post by Drugolf on Thu Jan 29, 2015 11:45 am

    Okay then, on the new ALPS volume control things are labeled well enough.  one side has lout/gnd/rout/GBD.  The other inl/gnd/inr/gnd.  The question I have now is how does that correspond to the positions on the old control?  The Dynaco manual does not identify what the wires are.  It just says connect this to that.


    Last edited by Drugolf on Thu Jan 29, 2015 11:46 am; edited 1 time in total (Reason for editing : spelling)

    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: PAS 2 Issues

    Post by tubes4hifi on Thu Jan 29, 2015 12:30 pm

    you can download the manual from my website here
    www.tubes4hifi.com/downloads.htm
    all volume controls I've ever seen are all wired the same, something I can do intuitively even in my sleep,
    but I can't explain it in words, so you'll probably need to look at a wiring diagram (last two pages of the PAS manual)
    With a meter, if you set the volume control at halfway point, it should measure around 10-15% of the total value, from ground.
    So that's how you know which end is ground. (around 25-35K on a 250K volume control).

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: PAS 2 Issues

    Post by Drugolf on Sat Jan 31, 2015 11:39 am

    So a few questions for those with experuence in installing these new volume pots. With your help maybe I can get this right without too much trial and error.

    Will I be able to install the new alps unit without taking apart other aspects? The original was installed on the front panel and wires attached to it early in the build process so I am wondering if I will be able to get good enough access for soldering. This is compounded by the different shape of the new pot.

    Is there an install orientation of the new control that seems to be best or correct? Horizontal,vertical etc?

    Thanks

    peterh

    Posts : 680
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: PAS 2 Issues

    Post by peterh on Sat Jan 31, 2015 12:27 pm


    Myself soldered wires on the pot before installing, using color-coded cables to ease identification.
    Then after fastening the pot it's an issue of cutting and soldering the wires.
    as regards to orientation, i _think_ there is a small hole that locks the pot in position, this will
    prevent the pot from working itself loose during the years.

    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: PAS 2 Issues

    Post by tubes4hifi on Sat Jan 31, 2015 12:45 pm

    a photo is probably worth a thousand words, here's one:

    although usually the center pins on the TAPE/SOURCE switch would go to the inputs of the BALANCE control first,
    this photos shows them going to the VOLUME control first, then to the balance.   Easy enough to do it the other way.



    Last edited by tubes4hifi on Mon Jan 25, 2016 6:31 pm; edited 1 time in total

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: PAS 2 Issues

    Post by Drugolf on Sat Jan 31, 2015 2:04 pm

    Cool, thanks guys. Yes a picture is worth a thousand words.

    Of course the loudness control connections add quite a bit to it beyond the above.

    There is no guide hole and pin for orientation, at least on the front panel of the Pas2.

    I guess I should have also asked if I should be replacing the old original caps attached to the loudness connections?

    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: PAS 2 Issues

    Post by tubes4hifi on Sat Jan 31, 2015 2:18 pm

    replacing 50 year old capacitors is a good idea, and modern capacitors are so much smaller in size


    Last edited by tubes4hifi on Mon Jan 25, 2016 6:32 pm; edited 1 time in total

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: PAS 2 Issues

    Post by Drugolf on Sat Jan 31, 2015 3:35 pm

    Thanks. Iv'e been using photos from my original too but it is nice to see a better looking neat wiring job.

    What is the spec on the original wire used in these? Oddly the manual never identifies it. Can I use stranded like you suggest for the PSB?

    tubes4hifi
    Admin

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    Re: PAS 2 Issues

    Post by tubes4hifi on Sat Jan 31, 2015 7:40 pm

    I always recommend 22g stranded wire. All Dynaco kits were supplied with 22g solid wire, which as far as I'm concerned does NOT solder well.
    The only nice thing is it will stay straight and make nice square bends. Bob supplies solid wire in his amp kits, but it is pre-tinned.
    However, my opinion is that one wire will never make as good a connection as a dozen or more smaller strands.

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: PAS 2 Issues

    Post by Drugolf on Mon Mar 02, 2015 1:07 pm

    Update........Success!
    Worked on installing the new Alps volume control throughout the weekend and once I figured out how to go about it, it went well.Kinda hard to get at some of the connections so I had to be very purposeful as I went. Connected as many wires as possible to the control prior to installing it. Also ended up taking out the Loudness switch, making those connections between it and the volume control(which were the most complex with new caps etc) and then reinstalling each. Then did all the black grounds followed by the green and reds.

    Nice to have the ability to turn the volume all the way down. Cool Cool

    The only thing that caught me was the length of the Alps control shaft. It is about 3/16" too long so now I need to cut it back.

    Roy helped with advice additional to what everyone added on this thread along the way. Thanks for letting me bug yo so much Roy!

    Next is the power supply. Right now I just want to use it a bit.

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