# Hum problem.



## sportflyer (May 2, 2010)

I have been pulling my hair out trying to figure which component is generating a slight hum. I finally located it to the Energy External XO unit. Its power source is a 18V AC wall bug. I moved the power bug to various places and still cannot eliminate the hum . I tied the XO chassis to the preamp to no avail.

I am thinking of using a LiPo as power source eliminating the wall bug altogether. But I would like to try a simpler less drastic solution before doing that. 

Any suggestions?

Tks

I spoke too soon ! I decided to remove the XO and connect the preamp directly to the power amp to be sure . Unfortunately the Hum/buss came back


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## lcaillo (May 2, 2006)

Test the unit for leakage current. If it is higher than 500uA it is defective.


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## sportflyer (May 2, 2010)

I isolated the problem even more. I found that the hum is from the the left ch of the preamp. There is no hum component from the right channel only low level hiss. The left channel has both hum and hiss. The left ch spl is about 6db louder than the right . Power amp is totally silent by itself without the preamp connected. I also swapped left and right Preamp tubes hum still on left ch . Not sure how to proceed next.
Advise ?


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## informel (Jun 21, 2011)

disconnect every source from the preamp.
then you could connect 1kilohoms resistors let say to the input of CD and select CD from your preamp, if you still hear hiss, then your preamp needs repair.


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## sportflyer (May 2, 2010)

I did as you said . There is still hum and hiss on the left channel. Right channel has only std tube hiss. There is definitely a hum component on the left speaker when I put an oscilloscope on it . It is a 120hz hum . It looks like I need to send the preamp back to the mfg since this is only 4 months old .


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## hjones4841 (Jan 21, 2009)

120Hz sounds like a power supply problem.


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## sportflyer (May 2, 2010)

I think so .


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