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Amp problem

A few months ago I wanted to see how balanced cables would sound going from my pre to power amp.


So I got some XLR cables, plugged in, every thing was good, though not really a big change. 


I then received some RCA interconnects that I wanted to try out.


After connecting them I now get a pop from one speaker when I power up the power amp, the volume from that one speaker is a fraction of the other speaker and there is a hum coming from it. The only remedy I have found is to engage the phase inverse on the pre. The hum is greatly reduced, and both speakers play at equal volume. Also if I engage the mute button on the preamp, I do not get a pop in the speaker when I power on the power amp.


Plugging the XLR cables back in returns everything to normal.


After testing multiple sources and swapping wires around, it seems like the problem is with the preamp. If I swap the output wires on the rca outputs from the left to the right channel on the pre, the problem moves from the left speaker to the right speaker.

 

So my question is, short of taking it to a tech. Is there something I can check in the preamp that I can possibly fix myself.


No I am not a technician, no I do not want to get electrocuted.


Thanks for any insight you can provide. I enjoy the forum.


Rob


System 


Thorens TD 145

K+K phono pre

VTL TL-5.5 (preamp)

Threshold T-200 (power amp)

Proac response 1


robertalger
lowrider57's avatar
lowrider57
5,417 posts
 
Regarding the Pop sound when amp is turned on, there is a power on/power off sequence which must be followed.
Powering up...Preamp ON, Amp ON.
Powering off...Amp OFF, Preamp OFF.

If you're having hum using the RCA unbalanced IC and not the balanced, it could be a ground loop. The XLR cable is a grounded cable while the RCA has no ground. A difference in ground potential between components (impedance) is passed thru the unbalanced cable resulting in hum.
The first step to diagnosing the hum issue is to have all components plugged into the same circuit.


erik_squires
16,185 posts
 
I wonder if your RCA’s developed a short? Turn everything off, replace with a diff. RCA set, and turn on in correct order:

Sources, preamp, wait 10 seconds, then amp.
robertalger OP
8 posts
 
  I’ve tried swapping RCA cables with no luck.

 I do power things off and on in the correct order. 

 I will try changing  the way the power cords are arranged.

Thanks for the ideas
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