60 Hz Hum from Powered Sub

I'm with you @yogiboy!

G

Stop spinnin’ your wheels tryin’ to figure out what’s wrong with that 20 year old subwoofer. Break open your piggy bank and get a new one. There are many out there at all price points to choose from!

Huh? Two electrolytic caps, you must be kidding. One I serviced, I replaced 42 electrolytic caps and the problem still existed. Only switching to the high level inputs stopped the hum.

The 2 prongs on a plug, one is hot the other neutral, aka utility ground. The third is earth ground and is redundant.

My first thought when reading this was to not respond. But then after thinking about it for awhile I would be remiss if I did not.

/ /

NEC article 100 definitions.

Neutral Conductor. The conductor connected to the neutral point of a system that is intended to carry current under normal conditions.

Grounded Conductor. A system or circuit conductor that is intentionally grounded.

Informational note: Although an equipment grounded conductor is grounded, it is not considered a grounded conductor.

Grounding Conductor, Equipment (ECG). A conductive path(s) that is part of an effective ground-fault current path and connects normally non-current carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.

The Grounded Conductor (neutral) and an EGC, (Equipment Grounding Conductor) are not interchangeable with with one another. The two serve entirely different functions.

The 2 prongs on a plug, one is hot the other neutral, aka utility ground. The third is earth ground and is redundant.

"utility ground" ???

"The third is earth ground and is redundant." No it is not a redundant ground ... It is an EGC as defined by the code...

The neutral conductor is a current carrying conductor and should never be used as a safety EGC.

A circuit neutral conductor is only grounded if it is connected to the electrical service Grounded Conductor.

Open Neutral:

An open neutral is where the neutral connection to the electrical service Grounded Conductor is broken, open.

An energized open neutral is dangerous and can be an electrical shock hazard or worse lead to death.

An energized open neutral? Where there is a connected load on a circuit (branch circuit wiring) and the neutral connection is broken, open, upstream (source end) from the connected load.

There will be a 120V difference of potential between the two broken conductors of the neutral. 120V as well from the load side open neutral to any grounded object.

As you can see it would be a bad idea to use a current carrying neutral conductor also as an EGC connected to the EGC ground terminal screw on a wall outlet or directly to the chassis of audio equipment.

( Existing 2 wire branch circuit wiring, (no EGC), 2 wire duplex receptacle is replaced with a 2 pole grounding type duplex receptacle outlet).

.

It definitely "developed" the hum. It has been in the same location for about 6 months and it's just begun making the noice in the past 2-3 weeks. From all of the comments collectively, it would appear that the amp has caps that are failing. I'm not sure I have the time or interest to mess with it. It will probably be retired.

Thanks to all of you for the great responses!

G

Spacecadet3;
moving it around to rule out ground loops is nonsensical.  ground loops will occur whenever there are two different paths to ground. By moving it you guaranty a different path!

Every single solitary component in your sonic chain must b grounded to the same circuit, preferably to the same outlet.  The best way i know to achieve this is to have a 20A outlet, and buy the biggest, heaviest duty outlet strip you can get and plug everything into that.
if you need to daisy-=chain them do so. But use heavy strips with heavy cables and preferably upgraded or even hospital plugs.  Why? solid, high current contacts.  the $15 is well spent.

However, you said it "developed" a hum. You didn't say "i rearranged stuff and suddenly there was a hum". Be clear which was it?  if it just developed with no changes then indeed you likely have a problem in the woofer and it requires service. A loose ground, bad connection, or failing capacity or among myriad other reasons....

I doubt its a big deal, but qualified labor is not cheap.

Good luck, noise issues can be buggers.
G

If you added a new electrical device, it could be anything from a cooktop to a heater. This device could be causing a DC on mains issue which causes  the transformer to buzz. So you need to isolate the noise. If the driver is making the noise, it is most likely a ground issue somewhere, aging components or aging sub cable with deteriorating connector. If the transformer is buzzing, it is most likely the DC on mains issue. Emotiva makes a specialty filter that works if that is the issue. If the sub is old, its not worth fixing unless it has a special connection for some reason.  

I assume the DC power supply uses full wave rectification.

: a rectifier that converts alternating current into continuous current and that utilizes both halves of each cycle of the alternating current.

120 ripples per second.
I would think if it is a bad electrolytic cap in the DC power supply the hum buzz would sound like this:

120Hz Hum
https://www.youtube.com/watch?v=pC4Uzt0qm2E

or this,

Like a 120Hz buzz
https://www.youtube.com/watch?v=pf-vULfjYK8

If you're going to open it, be careful to discharge all large electrolytic capacitors through a resistor. These caps can store some high and potentially lethal voltages for a long time. All plate amps I've worked on use 105C capacitors.

Hey,

If you get the hum with NO audio connections and just plugged in you need to have it serviced. It’s probably a power cap that’s going. Get them all replaced before it blows.  If you can afford it and they are available, get higher temp caps than you originally had.  They'll have a much longer lifespan.

Best,

E

OK. So I was wrong about one thing. The permanently attached power cable is a 2-prong, polarized version, where you can't invert it in the wall socket. So there was no way to use a cheater plug to get out of this. 

@jea48: It is definitely the middle YouTube video hum. Great videos, BTW.

This is a pretty old unit. $400 gets me a basic 12" Emotiva sub that will run rings around it. I may open it up and take a look at the caps. If it looks like there's something obviously amiss, maybe I'll try to do a repair. It's not worth paying someone to work on it given what it is...

I really appreciate all of the advice!

nob and tube

Knob and tube. Cost me a fortune to replace after some flood damage.

Have not read all responses. So at the risk of repeating, the most common cause for a subwoofer hum is cheap cable or a cheap cable that eventually went bad. Poor shielding is the most common exact culprit on a cheap cable. Power cord is also a possible culprit. Solid copper 75 ohm Quad Shield RG6 terminated with a RCA plug is an inexpensive alternative to all the other types of subwoofer cables that are offered, sold or recommended as being the best. None of those offerings will be quad shielded. The solid copper coax RG6 cables are easily found and are probably the least expensive of all the options.   

Funny, I was using my sub's Line Input/LFE connection via RCA cable from my loop out right/left connections on my power amplifier and all was well.

Now using the high level speaker input connection with the amps plug adaptor off my speaker terminals and I get the 60Hz hum.

Need to mess around with it more, but why would the power amp to the LFE be fine, but not the high level speaker terminals (producing hum)?

spacecadet65   said:

08-30-2021 9:13am

The hum is present whether there is an audio source connected or not.

Power your sub from the mains plug which is also connected to your other devices. Basically, all the earth potentials of all the devices must be on the exact same potential. If there is even a few millivolts difference, you will get the dreaded hum. Every device must be on a STAR connection, meaning plug everything into the SAME mains outlet with the shortest possible power cables.

Are you using the low or high level inputs to the sub? If you're using the low, it's probably a bad cap in the subwoofer. You might just try the high level inputs if you have them. I know that cured the hum in my older Sunfire sub years ago. I replaced all big electrolytic caps and it still hummed, no matter what I did. This just might work? It would be a temporary cure until you either upgrade to a newer and better sub, or decide to send it in for repair. Good luck.

Almost all subs have a "plate amp" with a switching power supply and are very prone to this type of problem. Check with Tannoy and see if they have an exchange program where they send you a rebuilt plate amp, which you can change out yourself. If not, some repair shops will work on the removed plate amp, saving a lot of shipping cost. Also if you remove it, sometimes it is easy to spot a split cap.

@ spacecadet65,

Which sound best describes the hum you hear from the sub?  

60Hz hum  
  https://www.youtube.com/watch?v=SVZ2P0KsLic     

60Hz buzz  
https://www.youtube.com/watch?v=FBRPHojSGAs

120Hz hum  
  https://www.youtube.com/watch?v=pC4Uzt0qm2E


Did you try a 3 wire to 2 wire cheater plug yet?  
Make sure you insulate the ground tab on the cheater so it does not contact the 6/32 trim screw that holds on the outlet cover plate. The 6/32 screw is grounded.

Thanks cleeds I got a phone call from a city official I been waiting on.. I got excited, only took a month for the call back. :-)

Excuse me, I meant to say sub panel, and must be bonded at the main.

At the a sub a jumper can be between the TWO. It will work but I separate and have found it to be a source of noise in my house wiring.

I check ground and commons for amperage to ground. It always amazes me what I find there and the difference between the TWO.

A 220/240 sub panel, with a blower motor using L1 and L2 and in the same sub panel, stereo receptacle (s) being uses on one or the other hot rails. That is a no no in my system for noise..

My house is quiet and I have a  mix of nob and tube on the old AND Romex on all the new construction.  SOOW 4/3/g feed both shops, and 12/2/g for all shops, basement, kitchen and attic outlets..

The house is 14/2/g and nob and tube.

Bottom line OP shared grounds can make noise..:-)

oldhvymec

... A common and a ground CAN (not should) share the same bus with a jumper in the main. I keep them separate. That jumper can be the source of a lot of noise in house wiring ...

It isn't clear what you're saying here. All neutrals and grounds must be bonded together at the main panel - and only at the main panel - for safety. That is very a basic NEC requirement. No exceptions.

Why does that work?

If the source and preamp are on one circuit (L1) in the main, and the sub is plugged into the other side of the main (L2), the difference between the two is the hum you are hearing. Lifting the ground with a cheater removes the common difference between the two. A ground is for fault protection and a drain to ground vs YOU.

A common on the other hand completes the circuit. A common and a ground CAN (not should) share the same bus with a jumper in the main. I keep them separate. That jumper can be the source of a lot of noise in house wiring..

You can get a hum using the same side of the bus if a two component have a slight difference in voltage but share a common cable like a RCA or XLR, (good place for a ground loop eliminator). Cable boxes are notorious for it, so are laptop computer supplies.

Regards

Thanks Miller! Great advice.

G

The 2 prongs on a plug, one is hot the other neutral, aka utility ground. The third is earth ground and is redundant. Sometimes earth ground is your hum inducing ground loop. Removing the extra ground is an easy way to improve cheap power cords and many components. Silversmith's Jeff Smith carries one around to demo and did so here at Chuxpona. 

In this case since the problem developed over time and occurs on every outlet and even when not connected to anything else this all argues for the caps going bad. Caps are cheap, the values printed right on them, making this an easy DIY fix.

Is it time to just move on or is this something worth repairing? Could this be something simple, and if so, how can I diagnose it?

Probably electrolytic capacitors failing caused the 60Hz hum, you can find a good condition PS110 for less than $150!
If you want to diy, replace all electrolytic capacitors.

Will do! Why does that work? Sorry, I'm an electrical noob here...

G

Try a cheater plug and see if the hum goes away!
https://www.amazon.com/GE-Polarized-Grounding-Adapter-14404/dp/B00B7PK1TC/ref=sr_1_8?dchild=1&ke...