My acoustic research hd510 has a loud humming noise

If you've replaced the LM4766 ICs and the humming sound returned, there could be a few possibilities to consider:

1. Grounding Issues: Humming sounds in audio systems can often be caused by grounding issues. Ensure that all components are properly grounded and that there are no loose or disconnected grounding connections.
2. Power Supply Problems: The rapid loud hum could be related to power supply issues. Make sure the power supply is stable and within the correct voltage range. Also, check for any issues with the power cables or connections.
3. Filter Capacitors: Check the filter capacitors in the power supply section and around the LM4766 ICs. Faulty or aging capacitors can lead to noise issues in audio systems.
4. Signal Interference: Electrical interference from other devices or cables can sometimes cause humming sounds. Make sure the audio cables are properly shielded and not running too close to power cables.
5. Speaker Connections: Double-check all speaker connections, ensuring they are secure and properly connected. Loose or damaged speaker wires can lead to noise issues.
6. Board-Level Problems: There could be other components on the circuit board that are causing the issue. Inspect the circuit board for any signs of damage, burn marks, or soldering issues.
7. Magnetic Interference: Make sure there are no strong magnetic fields or sources of interference near the system that could be causing the humming sound.
8. Professional Help: If you've exhausted your troubleshooting efforts and the issue persists, it might be best to seek the assistance of a professional audio technician who has experience with Bose systems. They can perform more advanced diagnostics and repairs.

Remember that working with electronics and audio equipment requires technical expertise and can involve risks, including electrical hazards. If you're not comfortable or experienced with electronic repairs, it's advisable to seek professional assistance to avoid potential damage to the equipment or harm to yourself.

The loud humming is the sound of AC mains - clearly your amplifier is receiving an input from somewhere and possibly into the front end.

The hum could be induced by radiated energy from nearby unshielded equipment, it could be the result of an accidental hum-loop or could be because the amplifier power supply has a fault.

It is usual practice with amplifier construction to ensure unused inputs are shorted to ground by switching or by additional contacts and wiring at the input sockets. High gain high impedance inputs can cause a great deal of unwanted noise if they are not shorted.

I suggest you read the instruction manual and perhaps Google a few hints and tips about amplifiers and stuff.

Make sure that the input connection ground is good. If that does not cure the loud hum then you have a power supply issue.

what happened just prior to the sub failure? Have you tried a continuity test across the sub speaker coil?

Humming noise could be an indicator of bad capacitors in the amplifier. You can take the amp out, pull the cover off, and look at the capacitors. If they appear to be swollen at the top, with some brown ooze coming out of them, then they need to be replaced. You can actually do this yourself from radio shack parts, just get the proper sized voltage and uf capacitors, desolder the old ones, and solder the new ones back in.

I have to do this every 5 years, or so, to my old MTX home sub amp.

be more specific, what type of noise? Humming noise or cracking noise or pop noise? can you still hear noise without signal input line connected?

Did you check the operating power needed for this Subwoofer. I guess I saw one that operates only at 230V-240V 50Hz. Could that be the problem?

If I understand this correctly: with NO input or cable attached it hums; with an RCA cable attached it works. (What does 'some' mean in this regard?)

You say that connecting the RCA cable improves its sound. That tells me you're supplying a ground through the RCA cable for stray voltage in the sub.

It seems there may be a basic power issue if it hums with no input. Sometimes a given power source in a home may be wired differently than others or may insufficient grounding, which can result in hum. Try reversing the sub's power plug or move it somewhere else.

Since the sub contains its own electronics it is also susceptible to strong external magnetic fields. Keep it and any signal cables leading to it some distance away from other electrical devices like TV's.

I fixed the same issue by replacing the original AC power supply with a 13.8 volt DC power supply (Radio Shack) It seems to be more consistent at high SPL and no hum , as the Boston acoustic unit accepts either AC or DC power.

Bad amp

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