A23 AMP THIS IS MY SECOND A23 THE FIRST STARTED TO HUM AFTER 10 MONTHS TRIED ALL USUAL THINGS CABLES SEPERATE MAIN FEED STILL HUMS SENT IT BACK, WAITED 5 MONTHS FOR REPLACMENT ARRIVED 10/08/07 SET IT UP AND YES IT HUMS ANYBODY ELSE HAD THIS PROBLEM.ONE WAS LISTED ON EBAY WITH SAME PROBLEM THANKS GUYS

Try the following steps to stop subwoofer hum.

1. If the subwoofer is plugged into its own outlet, plug the subwoofer's power cord into an outlet shared by the other components. Use an extension cord if necessary.
2. If the hum persists, and your system includes a cable TV, disconnect the cable line. If the hum stops, install an isolation transformer on the cable.
3. If the hum persists, disconnect the remaining component cables one at a time until the hum stops. Install a coaxial isolation transformer on that cable.
4. If the hum persists, install a line-level ground loop isolator on the subwoofer's line-level feed cable. This usually solves most hum problems.
5. If nothing helps, disconnect all the audio cables from the subwoofer. Leave the subwoofer plugged in and switched on. If the subwoofer hums, it points to a defective unit. Contact the company's customer service to technical support.

The hum is likely to be the sound of the ac mains electricity, either because the power supply smoothing has become ineffective in the amplifier or one or more of the audio peripherals or because the audio connections to the input of the amplifier have created a hum loop that is picking up the radiated energy from the mains supply and feeding it into the audio input.

Multiple grounding is often the reason for a hum loop. This is where an audio peripheral is not only grounded through the supply cable but is also grounded through the screened audio lead.

If the hum persists when there is no inputs connected the problem is almost certainly power supply related, otherwise it is likely to be a peripheral that has a faulty power supply or the culprit is a hum loop.

Hi-fi officianados have a number of tricks to deal with hum loops and google could lead you to these.

Grounding is an important safety consideration so appliances that are intended to be grounded must continue to be grounded but the loop could be broken by using special audio leads. The usual lead would use the screening as a conductor and so the screen must be connected both to the peripheral and to the amplifier.
A better lead uses an extra core conductor and the screen then becomes just a screen and is grounded only at the amplifier end and is not connected to the peripheral.

I hope this helps.

Hum is tough. It is often caused by quite a variety of things. First, address the basics:
1. Make sure that none of your signal cables run near to power cabels.
2. If possible, feed all power from the same receptacle.
3. If your plugs are not polarized, try reversing one at a time.

If none of those basic checks uncovers your demon, verify the path of the noise by disconnecting the signal from the preamp at the input to the sub. If is still hums, then look closely at the power feed to the sub, More likely, the hum will stop (along with the music.) In this case, try breaking the shield ground at the sub input (e.g. with a ground isolation adapter.)

You should also confirm that the hum is limited to the sub. Subs tend to exaggerate hum because playing signals in the 60Hz is their forte. So with the sub turned off and bypassed, listen for the hum in your main speakers. If it is there, too, then start checking your sources. Remember, even a source device other than the one selected for play could be the source ... completely disconnect each source at the preamp to track it down.

The issue a floating ground that causes the hum you are talking about. What are you connecting it to that causes the hum?

Generally the hum is one of two things. If a sensor, pickup, per-amp, or mini-amp are too close to the receiver or speaker, Feed-back may occur or a hum and buzz join the audio signal out. The usual problem is: line in port on the instrument can be defective or the male jack is not making proper contact. If a cord is tested and working, the condition is in the input on the instrument. If a terminal has a loose wire inside the instrument the problem can be intermittent ( come and go) and thus a buzz or line noise may be present.

Good day sir, there are several reason why the amplifier hums, but lets go to the common ones,

1. The main power amplifier is defective. Does the volume control affect the loudness of the hum? If no, possibly replace your main amplifier IC. if its transistorized, check the two push pull amp. for shorts.
2. If Yes, check for shorted audio cables. just maker sure you are using a good audio cable. or
3. The pre-amp IC is defective, usually op-amps. try replacing them one at a time. these requires unsoldering and soldering.
4. If you want to find the faulty part, you may need to trace a signal, you may need the folowing, an audio source, sine wave generator, an oscilloscope, or a portable amplifier. This method requires you to be techie. Feed the input with the audio source (disconnect first the speakers so that the hum will not bother you.) check the output of each stage, from preamp to power amp. identifying where the heck the signal dissapper. and where the start humming appears.

The third one requires a lot of work, just bring it to a service center.
Hope this helps, feel free to ask again, let me know your progress. Thanks

Rita's Vintage Audio Repair is a Bob Carver Company & can repairs & updates Subs at a reasonable cost try calling them.

Was not clear .....does the sub have audio output
If not the preamp circuit is bad and this will cause the hum as well

You need a 2 Amp Slow Blow fuse. 250V. Available from eBay

the hum is probably the main pump powered up but not turning. the pump is an induction motor and a usual fault is the motor capacitor. try to access it, find the value of the capacitor and replace. it is a cheap part