Posted by ezragreen on September 27, 2003 at 13:37:18

Ron,this is what I did so far. b+=392v bias=68v 300b(kr)fil=4.54v
other ac fil=6.42vac. w/no input hum/buzz med loud. other amp similar
buzz but only audible frm inch away. buzz stops completley w/shorting
plug in input rca. visual inspection of solder joints;no obvious problems. tapped & pulled gently on all conns w/no chng in hum/buzz.
(In case nearby computer was inducing rf into inputs I moved amp to different room and outlet away from computer but hum still present with open input.) Should amp be silent to a speaker w/input open? Does silence when shorted mean there is no problem? and/or should I go ahead and re-solder all connections? Any and all suggestions appreciated. We talked briefly on phone mon.

• Re: hum/buzz; PS lifted ac grnd w/cheater plug/no chng - ezragreen 13:40:14 09/27/03 (4)
  In Reply to: hum/buzz in new laurel posted by ezragreen on September 27, 2003 at 13:37:18:

  addendum to posted message
  
  

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  • Re: hum/buzz; PS lifted ac grnd w/cheater plug/no chng - Chris O 06:07:28 09/28/03 (3)
    In Reply to: Re: hum/buzz; PS lifted ac grnd w/cheater plug/no chng posted by ezragreen on September 27, 2003 at 13:40:14:

    If your amp is quiet with the inputs shorted, then the amp is not the source of the hum. When the input is open with no interconnect to another component, you are using the input wiring as an antenna for RF.

    You may have a system ground loop. Make sure everything is plugged into the same outlet. Double check all of your interconnects to make sure the grounds are functioning like they are suppose to.

    Make sure you do not have any dimmers on anywhere in your house. AC filters really help here.
    
    
    

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    • clarification - ezragreen 11:22:26 09/28/03 (2)
      In Reply to: Re: hum/buzz; PS lifted ac grnd w/cheater plug/no chng posted by Chris O on September 28, 2003 at 06:07:28:

      Let me backtrack. I am just doing final cks on my amps w/a speaker
      connected to provide a load. Now,testing both amps w/open inputs one amp has more audible hum although it does disappeaar when input is shorted. Does the fact that a shorting plug makes it go away mean that
      the differences between the amps w/open inputs are to be ignored or do
      they still mean something is wrong or differend between the two?
      thanks for the response. this was a p.s. to previous post
      
      
      

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      • The results with unshorted inputs should be ignored - Chris O 17:22:24 09/28/03 (1)
        In Reply to: clarification posted by ezragreen on September 28, 2003 at 11:22:26:

        If they are quiet when shorted, they are quiet. Hook up a cd player and leave it off if you do not like shorting the inputs.
        
        

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        • Agreed - Ron W 21:44:15 09/28/03 (0)
          In Reply to: The results with unshorted inputs should be ignored posted by Chris O on September 28, 2003 at 17:22:24:

          If you have no noise when the inputs are shorted then there is nothing wrong with the amps.

          So the noise is either being generated from a component up stream or you have a system ground loop. Try lifting the ac ground of your preamp or one of the amplifiers.

          Ron
          
          

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