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Bad Hum Coming Through Amp, What Happened?

I've been running a Primare I21 amp for over a year now, and have been quite happy with the fact that there is no audible hum that comes through the speakers at any volume output. Out of the blue a couple of weeks ago, a nasty hum has started to emit from the amp through the speakers, audible starting at 20-25% of the volume output and louder as the volume increases. I've changed AC receptacles to a Cryo Hubbell one, I've upgraded my power conditioner, and I've switched the stock power cable to a Magic Power cable (which makes the hum even louder).

I am only using 2 of the 4 inputs on the amp, CD and Line 1 (turntable). The hum only occurs on the inputs that have something plugged in to them, and the hum goes completely silent when switched to an input that doesn't have anything connected to it. I've tried rolling the other components to the other inputs (the hum followed the components), and have tried the upgrade power cable on both of the components (no change). The hum occurs whether the components are off, on, or in standby.

What happened here? How do I make this hum go away? It's driving me crazy! Is there something inside of the amp that can be replaced/upgraded to kill this problem? Thanks in advance!

I posted this in Misc Audio last night, sorry for the double post! I realize now this was a better spot for the question, and I can't seem to figure out how to delete my other post.
maha0098
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almarg
9,670 posts
 
Rtn1, my Sunfire poweramp has 2-prong connector and everytime I try to touch any of my equipment pieces I grab a great piece of the static charge especially during the dry seasons or winter when heater is always on. So figure to have the same with cheater plugs.

As long as at least one of the interconnected components has its safety ground connected, the chassis of all of the components will be at ground potential. So the static discharge you feel would be due to the static voltage on your own body discharging to ground (static buildup being at its worst in dry wintertime conditions, and especially if you have been walking on carpeted surfaces). The same thing would happen whether or not cheater plugs were used on some components, as long as at least one component has a 3-prong plug which is not defeated.

If no components have 3-prong plugs, or if the safety ground is defeated on all components (which are situations that should be avoided, as I indicated above), then the chassis can "float" to substantial voltages which could cause a shock (typically a mild one).

Regards,
-- Al
magfan
1,583 posts
 
Longshot and maybe some help....long term.
Go to home multi-mart and get an outlet tester. Not one of the 'does it have voltage' types, but one which will show various hookup faults, including hot to neutral or ground reverse and various 'opens'.
They are cheap and should be in anyones parts box who has any work done on there power.
goldeneraguy
442 posts
 
Rtn1 and Almarg,I just want to be sure of the procedure in taping the ground post.When using a turntable do you connect
the grounding lead from the turntable to the grounding post on the preamp and then wrap the grounding post with Electrical tape.This is the first time I have heard of this method to eliminate hum.
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almarg
9,670 posts
 
Goldeneraguy -- No, don't use any tape at all on that connection. We were referring to power cords only (and isolating the safety ground of the ac wiring from the component's ac power connector), not to the ground connection between turntable and preamp. Defeating the connection of turntable ground wire to preamp ground post will most probably increase hum significantly.

Regards,
-- Al
rtn1
535 posts
 
On the AC IEC inlet located on the component, I tape the grounding prong to block its connection to the power cord. This is the same as adding a cheater plug at the opposite end of the power cord, or pulling the grounding prong out of the IEC.

I also have star grounding of all components from wires connected to the chasis, to the Tripoint Troy. Tripoint Troy is a RF/EMI filter that grounds everything through an outlet.
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