Ground loop feedback - cable wire issue

agree with @fuzztone - it's likely related to cable and those products address those problems quickly if the cable ground is the root cause.

If for some reason that doesn't work it means that your new amp is interacting poorly with another component connected to it and sharing the same ground.  I just went through this with a SET amp I acquired.  Turned out the interaction was with my preamp.  I diagnosed the problem and ultimately resolved the problem using a Hum X to float the ground on the preamp.  

Besides floating the ground on the preamp I found that I needed to make sure my DAC wasn't sharing the same power strip/conditioner with the amp because my single ended ICs connecting the DAC to the preamp enabled the ground loop to remain intact.  Yes, it took several hours to track this issue down.

Also I don't think it's a good idea to float the ground on the amp or use a Hum X -type device directly on the amp (even though it will remove the hum).  The Hum X is only safe up to 6A draw and many amps can spike above that.  My 48W SET amp was drawing 4.5A at idle for example.  It's better to float the ground on the low draw component that's cause the poor amp interaction.  In my case my VAC preamp only draws 0.5A according to my measurements. You certainly don't want to create a safety hazard while addressing the ground loop/

An unusual trick that can work wonders is to flip the AC supply polarity of the offending device, in this case the preamplifier. Chassis to ground potential difference due to internal transformer current leakage can alter considerably with changing AC supply polarity and can potentially reduce hum/noise.

One can also measure this with a multimeter to determine the optimal polarity.

An unusual trick that can work wonders is to flip the AC supply polarity of the offending device, in this case the preamplifier.

You can only do this if the preamp employs a 2-prong AC connection!


Ground loops occur when different parts of the system share a ground in such a way that noise in the ground is imposed into the signal at an earlier part of the circuit. The best way to eliminate it is to break the common ground- usually at the amplifier end as this is where most of the current usually is. If you can float the amplifier's AC ground at the power cord (using a ground cheater available from a hardware store) and that eliminates the buzz, then there are steps you can take to shut things up.

 the marantz avr I have lacks a third prong vs the external amp which has a third prong.  Why is this?

The Marantz must be an older unit. All consumer electronics are required to have a grounding pin in their AC cord **unless** there is no metal of the product exposed to the outside world.