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    mark 3 hum

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    wedg714

    Posts : 74
    Join date : 2011-11-23

    mark 3 hum

    Post by wedg714 on Tue Dec 06, 2011 3:09 pm

    i have a pair of mark 3's which both have issues. #1 has an earsplitting noise when turned on with my preamp connected. with the preamp not connected it doesn't have a hum unless you put your finger or any other part of your body next to the rca jack. you can stop that hum by grounding the rca jack. #2 has a hum with the pre connected that you can stop by grounding the rca jack. with the preamp not connected i get a very slight hum when you touch the rca jack and grounding the rca stops that. the can caps are new. all of the cords to all of the system are new 2 prong with the exception of the power strip. the pcb's are stock but upgraded versions. the rca's are new gold plated. i've switched back to the original rca jacks but it doesn't help. because of the location of my closest elec outlet, i've had to hook up a power strip to a power strip to reach the system. both of these are 3 prong. any help will be appreciated.

    wedg714

    Posts : 74
    Join date : 2011-11-23

    Re: mark 3 hum

    Post by wedg714 on Tue Dec 06, 2011 4:12 pm

    i forgot to mention that the hum is at the speakers not the amps

    stewdan

    Posts : 160
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: mark 3 hum

    Post by stewdan on Tue Dec 06, 2011 7:19 pm

    Hi --

    There were a couple of POSTS back in 2010 or 2009 by DANF on the forum where he talked about hum and what he did to get rid out it on his Mark3/VTAs. (He did a bunch of different things including (1)running a ground lead on the underside of the Amp, from the speaker COMMON Terminal to one of the screw posts that connects the VTA board to the chassis and (2)running another ground lead from one of the unused VTA board's ground holes back to one of the twist tabs that grounds the Quad Cap to the chassis.)

    You can do a Forum Search, take the Advanced Search and under author, use/type DANF, seach in Basket and Posts.

    Also, it might be easier to debug your hum problem if you don't use a preamp and power strips. Do you have a Tuner with a volume control or an IPOD that you can plug into one of your Mark 3s(you will need a cable with 2 RCA's and a subminiature plug for the IPOD)? Then just use a 2-wire extension cord between the amp and the wall outlet.

    Can you play a music source thru the amp and get music on the speaker, or just hum?

    Hope some of this info helps!!!





    Nicola

    Posts : 12
    Join date : 2011-11-20
    Location : Roma (Italy)

    Re: mark 3 hum

    Post by Nicola on Tue Dec 06, 2011 9:00 pm

    I've a similar problem touching my Stereo-70 (whith rca cables disconnected). Touching it with one finger makes it hum. No hum touching it with two fingers. No hum touching it with rca connected.

    wedg714

    Posts : 74
    Join date : 2011-11-23

    Re: mark 3 hum

    Post by wedg714 on Thu Dec 08, 2011 11:08 am

    thanks to all those who helped. i've found the problems and fixed the amps. sound great and are dead quite.

    stewdan

    Posts : 160
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: mark 3 hum

    Post by stewdan on Fri Dec 09, 2011 3:27 pm

    Hi --

    I am still working on my pair. Have one that is dead quiet and one that sounds like its got a faint AC Hum, but reversing the power cord in the AC socket does nothing, Hum is still there.

    What worked for you in quieting your pair?? The grounding that I mentioned from DanF or something else?

    Please let me know,
    Stew

    wedg714

    Posts : 74
    Join date : 2011-11-23

    Re: mark 3 hum

    Post by wedg714 on Fri Dec 09, 2011 4:18 pm

    the rca's didn't have plastic washers on both sides. simple but stupid on my part

    denny9167

    Posts : 152
    Join date : 2011-05-09
    Age : 49
    Location : Texas

    Re: mark 3 hum

    Post by denny9167 on Sat Dec 10, 2011 6:36 pm

    wedg714 wrote:the rca's didn't have plastic washers on both sides. simple but stupid on my part

    Don't feel bad, I did the same thing myself,I upgraded the RCA jack on my Mark IV's,not realizing the sheild was grounded to the chassis,forgeting about the washer. I had this awful squeeling noise!! I then took my trusty soldering iron and soldered a wire from the jack, to the star ground,problem solved!!

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