I get a significant hum from the speakers when the receiver puts out a signal to the speakers. I have the receiver wired by HDMI cable from a satellite receiver to the Onkyo to an HD TV. The microphone autobalancing trys to eliminate the hum by setting the speaks in - db which doesn't work.
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Active speakers for a computer contain a high gain amplifier and it is a characteristic of such an amplifier, when the input is open circuit with a lead attached, it will amplify whatever signal the lead is receiving - the open circuit lead will act as an aerial for what has become a crude radio receiver..
The overwhelming signal will be that radiates from the surrounding power wiring - hence the mains hum, assuming it disappears when the volume is turned right down. If it is present with the volume turned down or the input short-circuited it indicates a power supply fault.
A quick test for amplifier functionality is to input a strong mains hum by wetting a finger and touching it to the input.
When I was much younger, one of my amplifiers would receive taxi radios and the police whenever an open circuit lead was connected...
Is the hum in the receiver-attached speakers or the sub?
How is the sub attached - RCA or speaker-level?
Disconnect the input(s) and see if it hums in the absence of an audio source. A bad audio cable shield or unwisely-routed audio cables will allow entrance of unwanted signals from external power sources, magnetic fields, even dimmer-controlled track lights. Sometimes, simply reversing the orientation of the ac power plug can eliminate humming.
If it hums with the sub attached, unplug the sub's power cord. Differences in AC ground potentials will generate hum across linked devices.
jd40, Sounds like a grounding issue. The first two places to look into is the powered subwoofer and antenna. During your last test, did you leave the FM antenna and subwoofer connected? Many times the hum is directly related to the antenna and/or the subwoofer and to how they are grounded; creating a ground loop through the receivers ground on the outlet. If the antenna is grounded to the dwellings wiring, hum is inevitable and sometime you can get a ground loop hum from how or how & where the subwoofer is grounded. Try taking them completely out of the loop.
Also try taking it further back to the basics, start with the receiver plugged into a known good grounded outlet with no surge or line conditioner in the loop and nothing connected to the receiver, nothing. Use one speaker and different wire to test each speaker output while in tuner and any other mode but phono. With no signal, you will either get nothing (no hum or static) or just static in the tuner mode. No hum is a good sign. Some systems will mute the speakers if no signal is connected to eliminate the static from being produced through the speakers but a ground loop hum will most likely still be produced even in mute. If you get a hum when nothing is connected to the receiver, try looking into getting a better grounded outlet, even maybe to a different dwelling.
The hum you hear from the speakers and from the unit itself originate with 60hz AC power. They may not actually be related. Sometimes a transformer will hum slightly and unnoticeably. That you're getting a loud speaker hum says there is an electrical leak or a grounding issue somewhere.
Do all sources produce the hum or, say, just the phono? How about on headphones? Try rotating the AC plug. In those days they weren't keyed with one large blade as they are now.
It is assumed that the hum is coming down the aerial wire it self....The hum should be eliminated
dissappear if you remove the wire from its connector at the rear of the receiver.
If this is the case then reconnect the aerial and try to find a radio station to listen to..
When you find a station you will find the hum dissappears as follows:
When there is no station detected the receiver tweaks up its sensitivity via the Automatic Gain Control, (AGC) and when this happens any thing that is detected on the aerial is reproduced at the speakers and in your case its just a hum.
I have heard this event lots of times and mostly its scrackles or scratchs or other weird sounds which come down the aerial while the AGC is flat out at maximum..
The radio station transmits a sound "carrier" and within this carrier there is the music content.
The receiver detects the "carrier" when you tune to the radio station, and then it sets its receive
level to the setting made by the volume control and then lovely music is presented at the speakers..
So in fact your receiver is working as it should be ,.,,, no worries mate....
Now if the hum is still there when the music is there then you have a fault, but as you havent mentiond this aspect your receiver is in my view quite "normal".
The humming is always there you just can hear it better when the cd is playing. The humming is caused by the electrical system in your car. There is an inline filter you can buy and insert it between the car's power source and the head unit. I had a head unit I bought that was absolutly terrible until I installed that filter.
Also if you did a do it yourself job on your amp wiring it is usually best practice to run your RCA cables on the opposite side of the car as your power cable.
You can also purchase shielded spark plug wires which is a source of noise usually of a different kind tho.
First make sure you have a good ground. This means that you have grounded your amp to bare metal not painted metal.
If that didn't work put in the inline filter on the head deck as they are only $20 available at radioshack.
If that doesn't work, go back an wire your car right this time and put the power and RCA on opposite sides of the car.
If you still have that hum it may be the spark plug wires but that sounds more like static than hum.
You have a text book case of alternator hum...