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View Full Version : Bad Amp? Bad reciever output? Grounding Problem? I Need Help



The8thst
02-23-2005, 06:06 PM
I finally got time to go back to a job and add the custom subwoofer built into the floor joists today, and the day ended with nothing but problems.
The reciever is a HK AVR335 with Paradigm Monitor Speakers.
The amp I have for powering the sub is an AudioSource Amp 5.3A.
The sub is an inexpensive driver in a bandpass box being ported through the floor.

Everything worked fine without the sub amp.
Plug in power for the sub amp and turn it on and everything is fine.
Connect the sub cable to the output on the amp and everything is perfect.
Connect the sub cable to the input on the amp and there is a terrible BUZZ that doesn't sound like 60 cycle.
Unplug the input on the sub amp and everything is fine again.

There are two other things that lead me think there is a problem with the amp:
1. Pressing the button to invert the polarity to the sub makes the buzz about half as loud.
2. To get any decent output at all the input sensitivity has to be practically maxed out.

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I have tried two different outlets for the sub amp.
I tried a new sub cable.
The only thing I haven't tried is lifting the ground on the sub amp.
I also have not been able to plug the sub amp into the same outlet as the main equipment rack, but if all else fails I may have to try to fish an extension cord up behind the main equipment rack (since it is a dedicated branch circuit).


I am going back to the house tomorrow and friday to load CD's into the Escient Fireball, so please give a few thoughts?

Ground problem? Fixes to try?
Bad amp? Bad output from the Harmon? How should I test these?

Thanks in advance for the help.

Jerry
02-23-2005, 07:53 PM
Sounds like a ground problem to me.
Powering from the same circuit would be a good start.
As far as cable goes, premade, or handmade?
If hand made, lift the shield at the amp end. (assuming twisted w/ shield is being used.)

LarryFine
02-23-2005, 07:57 PM
My first guess is as you deduced, the ground loop; I also agree with the ground-lift and/or the extension-cord experiment.

Also, eliminate the possibility of malfunctioning equipment: try using the AudioSource amp to feed full-range to a full-range speaker.

vwpower44
02-23-2005, 09:13 PM
First lift the ground on the amp. If that takes away the buzz, you know it is a ground problem. Then, run an exentions cord to plug into the same circuit/outlet that the equipment rack plugs into. We had a similar problme once on a center channel. A transformer from a LV light was causing the sepaker to fuz out at high volumes, then through the amp into protect. Bypass the ground, and plug the amp into the same outlet as the equipment. This should then tell you where you stand.

Mike

AHEM
02-23-2005, 10:32 PM
Does the customer have CATV? Have you tried unhooking the CATV feed to the system?

mr2channel
02-28-2005, 08:06 AM
when I have encountered ground hums, it has almost always been because of one of two devices, CATV systems or subwoofer amplifiers.

The8thst
02-28-2005, 11:51 AM
I narrowed it down to a faulty amp.
The noise is not a ground hum it is a higher pitched mechanical buzz.

Hopefully the new amp will make it go away when I get back in town.