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    VTA-SP-14 Hum

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    Leigh W

    Posts : 45
    Join date : 2013-04-02

    VTA-SP-14 Hum

    Post by Leigh W on Fri Jan 24, 2014 10:15 pm

    Hi all. I have the SP-14 preamp custom built by Roy himself with all the best parts. It has the Mundorf caps on one output channel and the KY's on the other. I have a multi amp set up that includes the VTA-120 power amp. I have a noticeable audible buzz from the speakers on all amps except the VTA-120. I'm thinking it's about at 120hz or so as it's not a 60hz hum. I have changed cables, outlets for the power source etc..., re-routed audio cables to no avail. I have hooked this amp to a Sony ES55 power amp, a Transcendent Sound OTL tube amp, a Harmon Kardon and a Heathkit power amp with the same results with all. I have even taken everything to a different room but the results are still the same. A low level (more a buzz than a hum) that is clearly noticeable. My speakers are Klipsh with an spl of around 95db but in the other room using some speakers in the 85db range the buzz is still present. Roy supplies Tung-Sol 6SN7's which are fine but I have changed them out for some vintage Sylvania 6SN7's from the 50's (clearly Superior). The noise level is the same regardless of which tubes I use. What puzzles me is why the VTA-120 has no noise at all but all other amps do. I wouldn't think the SP-14 is designed to be "perfectly" matched to the VTA-120 amp and nothing else. Could it possibly be the rectifier tube that's causing the issue? I'm using the supplied one provided by Roy. Anyone with a possible solution would be of great help.

    Thanks,
    Leigh

    Zimmer64

    Posts : 112
    Join date : 2013-01-29
    Age : 52
    Location : Switzerland

    Re: VTA-SP-14 Hum

    Post by Zimmer64 on Sat Jan 25, 2014 1:47 am

    Hi Leigh,

    When I build mine I also had a buzz issue. In my case I was able to track it done to a missing ground connection.
    Since you do not have the issue with all you amps, you can try to run a ground wire from the SP 14 to the amp and see if it goes away.

    Best

    Michael

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: VTA-SP-14 Hum

    Post by Bob Latino on Sat Jan 25, 2014 10:44 am

    It is possible that you have a "ground loop" somewhere in your system. Try floating the ground on every component in your system that has a 3 wire cord. Try using a 3 wire to 2 wire "cheater plug" on any and every component with a 3 wire plug.

    Another thing .. If your stereo system is on the same AC line as your cable TV, sometimes unscrewing the cable wire can reduce a stereo system's noise level ..

    Bob

    Leigh W

    Posts : 45
    Join date : 2013-04-02

    Re: VTA-SP-14 Hum

    Post by Leigh W on Sat Jan 25, 2014 7:25 pm

    Thanks Michael/ Bob.

    Bob. I did what you mentioned about the cheater plugs on "all" 3 prong plugs and it "has" made a difference for the better. There is still a buzzing in the speakers though, but not quite as much. I have a considerable amount of equipment running off a dedicated 80 amp "pony" panel (4 separate 20 amp outlets), so I wouldn't be surprised if there is interference somewhere in the chain. I'm also using two "Monster Power" line conditioners in my set up. I wonder sometimes whether these things do more damage than good. Lot's of controversy from what I've read online. The buzz may be something I have to get used too, until I can strip the wall and rewire everything. Thanks guys, for your help.

    Leigh

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: VTA-SP-14 Hum

    Post by Bob Latino on Sat Jan 25, 2014 9:28 pm

    Hi Leigh,

    Sometimes the AC output from some power conditioners is not a true sine wave. What if you tried bypassing the power conditioners and maybe use a few power strips to connect your components to the incoming AC line? Just see if the hum/buzz is reduced from what you have now ?

    Bob

    Leigh W

    Posts : 45
    Join date : 2013-04-02

    Re: VTA-SP-14 Hum

    Post by Leigh W on Thu Jan 30, 2014 6:47 pm

    Bob.

    Thanks for the info. I tried the cheater plugs and at first I thought that helped somewhat, but on removing them for comparison I notice now that there was no real improvement. I took the Monster line conditioners out of the system and plugged all "three prong" components into the same outlet. No change. After reading online I went out and purchased a ground loop isolator and installed it between the SP-14 outputs and the second amp. The hum was magnified 10 fold. I actually bought two of them in case I needed a second in the future. Both produced massive hum. They were from "The Source" here in Canada. Radio Shack in the States. Now I'm really miffed! And again, on the VTA-ST 120 I don't here hum at all. I even swapped the cables between the outputs on the SP-14 and no change so I know the preamp isn't the issue.

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: VTA-SP-14 Hum

    Post by tubes4hifi on Sun Feb 02, 2014 6:51 pm

    definitely some sort of ground problem. At one time I had a customer who found out his house wiring was at fault !!
    Since the preamp was dead quiet here and is quiet when playing thru your ST120, there is obviously something wrong with the grounding connections of the other amps.
    Those types of problems are extremely difficult to figure out . . .

    dougmon

    Posts : 65
    Join date : 2013-11-04
    Age : 59

    Re: VTA-SP-14 Hum

    Post by dougmon on Sun Feb 02, 2014 8:16 pm

    tubes4hifi wrote:definitely some sort of ground problem.   At one time I had a customer who found out his house wiring was at fault !!

    Just curious, what was the problem with your customers house wiring? Was the customer able to fix it?

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: VTA-SP-14 Hum

    Post by tubes4hifi on Sun Feb 02, 2014 11:19 pm

    I can't remember, it's posted somewhere on this forum

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