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    pas 3 hum after tubes4hifi zmod power supply mod

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    rolliers

    Posts : 6
    Join date : 2015-03-28

    pas 3 hum after tubes4hifi zmod power supply mod

    Post by rolliers on Fri Apr 24, 2015 3:10 pm

    After replacing power supply in stock PAS 3 with a tubes4hifi z mod supply, the amplifier
    has a small hum in one of the channels. Hum is not affected by volume. Any ideas

    Guest
    Guest

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by Guest on Fri Apr 24, 2015 3:52 pm

    check all your ground connections again, to and from the power supply upgrade kit, as well as all remaining ground connections in your PAS3

    rolliers

    Posts : 6
    Join date : 2015-03-28

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by rolliers on Fri Apr 24, 2015 5:00 pm

    tried that all connections are ok and all ground connections check out ok

    Guest
    Guest

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by Guest on Fri Apr 24, 2015 5:36 pm

    I very much doubt that the problem lies with the power supply, 100's have been sold and are in use with no issues.
    Ground connections may 'look' ok, but the solder joint could be dry.
    Also the fact that only one channel has hum, tells me that it is not the power supply, otherwise both channels would more than likely hum, since the power supply runs both channels/the whole amp.
    All I can suggest at this stage is to check it all again, especially your solder joins, then...check it all again Smile .....you'd be surprised what you find after checking things over two or three times, it is the nature of the beast with electronics and building kits!

    rolliers

    Posts : 6
    Join date : 2015-03-28

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by rolliers on Fri Apr 24, 2015 5:52 pm

    Roys instructions say to connect B+ P ground to eyelet 4 but on the board itself say to connect to eyelet 10 Are these both ok to use as b+ P ground

    Guest
    Guest

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by Guest on Fri Apr 24, 2015 6:20 pm

    eyelet 4 and 10 on the phono preamp pcb, if that is what you're referring to, are 'identical', they both are ground connections. From the GND connection on the Z-mod power supply, one wire is enough to either eyelet 4 or 10, I am pretty sure about that.
    Lets see if Roy can chime in here as well.

    rolliers

    Posts : 6
    Join date : 2015-03-28

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by rolliers on Fri Apr 24, 2015 6:37 pm

    thats what i thought the amplifier plays fine, but a noticeabe hum from right channel that was not there prior to changing out original selenium rectifier and quad cap. i thought the same as you as to why in only 1 channel. nothing else was done to the amp

    Guest
    Guest

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by Guest on Fri Apr 24, 2015 6:48 pm

    rolliers wrote:thats what i thought   the amplifier plays fine, but a noticeabe hum from right channel that was not there prior to changing out original selenium rectifier and quad cap. i thought the same as you as to why in only 1 channel. nothing else was done to the amp  

    thats why i am pretty certain that it has nothing to do with Z-mod psu, but something else has shown up.
    Have you tried swapping tubes from the 'hum' channel to the other and see if the hum 'follows'

    rolliers

    Posts : 6
    Join date : 2015-03-28

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by rolliers on Fri Apr 24, 2015 7:10 pm

    tried changing tubes had no affect is there a list of the voltages for all the connections on the upgrade board i have the original manual with all the pin voltages

    akimball442

    Posts : 1
    Join date : 2017-01-28

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by akimball442 on Sun Feb 05, 2017 1:30 pm

    Did you ever sort this out? I have exactly the same problem, a slight hum only on the right channel after upgrading the power supply board.
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    Peter W.

    Posts : 546
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by Peter W. on Sun Feb 05, 2017 3:27 pm

    rolliers wrote:After replacing power supply in stock PAS 3  with a tubes4hifi z mod supply, the amplifier
    has a small hum in one of the channels. Hum is not affected by volume. Any ideas

    I would suspect wire-dressing - did you stretch any connections or move any of the twisted pairs? Remember, many of the twisted pairs have a 'ground' connection only on one end. Did any of those come loose?

    But, wire dressing could affect only one channel.
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    Bob Latino
    Admin

    Posts : 2583
    Join date : 2008-11-26
    Location : Massachusetts

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by Bob Latino on Sun Feb 05, 2017 3:27 pm

    Two things on a PAS preamp in regards to hum ..

    1. Make sure that when you test for hum you have the top cover on. If the top cover is not on, a PAS preamp may hum a little.

    2. Try using "shorting plugs" on the unused RCA input jacks on the back of the preamp. Sometimes if these are left open, the preamp may pick up hum/noise from these open RCA jacks. See below for shorting plugs ..

    RCA shorting plugs - 10 pieces

    Same thing but 20 pieces ..

    Bob
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    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: pas 3 hum after tubes4hifi zmod power supply mod

    Post by tubes4hifi on Fri Feb 17, 2017 6:38 pm

    right channel wiring is closer to the power transformer. Reroute wires, use either tightly twisted pairs with one wire grounded, or use shielded cable.

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