A question regarding hum in the amplifier

[wullymc]

hi there,

I currently have a Quickie 1.1 and have some Paramounts on order.  I am using my Quickie right now connected to a cheap Lepai LP-2020A+ to Fostex FE126en speakers.  There is a hum but without the Quickie in the chain there is  no hum .  Now when I connect the Quickie to my Crack there is no hum.

What contributes to the hum?  It is the Lepai but am wondering what tech specs to look at that I could say ah... the hum is because...  Is this why there is a hum pot on the Paramounts to eliminate any hum that might show up?

Sorry if this is a very basic question but just want to know.

Thanks.....Dave

[Grainger49]

Let's try an experiment to see where the hum is coming from.  Build a pair of shorting plugs. 

Try them in the input of amp where you feed the Quickie.  If you have hum it is the amp and maybe that input.  If no hum, remove the shorting plugs, add the Quickie and cables.  Turn on the Quickie and put the shorting plugs into the Quickie's inputs.  If you have hum, swap the cables.  If that cures it the problem was the cables.

If no hum, remove the shorting plugs and add your source and cables.  Again, if you have hum, swap the cables.  If that cures it the problem was the cables.  If it persists the source is the problem.

You may be chasing a ground loop.  The source and amp might not have a common ground.  Try just running a wire from the chassis of the source to the amp. 

[Paul Birkeland]

I concur that it's likely a grounding issue.  It's a little tricky with the Quickie, since the chassis plate isn't metal, but a clip lead from the shell of an RCA jack (above or below the chassis) to the chassis of the Lepai may just do the trick.

[wullymc]

Thanks guys I will give that a try grounding the Quickie to the Lepai

although I do notice that if I put the Quickie to the Crack I don't experience some hum.  Perhaps it is because i am using high 600ohm headphones?

[Paul Birkeland]

although I do notice that if I put the Quickie to the Crack I don't experience some hum.  Perhaps it is because i am using high 600ohm headphones?

No, the Crack makes the ground connection that you need to manually make with your clip lead to the Lepai.

Headphone impedance is not really a factor in this instance.

-PB

[wullymc]

Thanks Paul,

Much appreciated!  I guess I won't have to worry about this when the Quickie is connected to the Paramounts


Take care.....Dave