[Nak Man]

Don't know if this is the right forum to post my question.

Just got a subwoofer that's humming loudly - sounds like ground problem:
• touching heat sink reduced the noise but still audible.
• turning 'phase control' varies hum noise.
• touching rca input made the hum louder.

Tried with no success:
• reversed AC plug, using groundless 'cheater' adaptor
• connect / disconnect rca input from preamp

Any hint what area should I be checking or looking at ? Ground is connected to chassis / heatsink but not to high / low level input's ground. I don't have the schematics but it's using something like off-the-shelf or generic sub amp.

Thanks much in advance. =)

 

[Edwood]

Try using a cheater on the amp/preamp/receiver that is feeding it the signal.

Also, try unplugging everything but the power cable from the sub and see if you can hear the hum.

-Ed

 

[Nak Man]

Thanks Ed ! Yes, it's humming loudly without anything connected, just the sub unit by itself. Perhaps there's a loose ground near phase area. Is ground almost always connected to speaker's (-) terminal ?

Oh btw, the hum is not affected by turning volume and frequency, only phase control.

 

[rellik]

iunno whats going on but i have similar probs with my sub

mine just hums with the source plugged in

sorry for the hijack but hopefully someone knows whats going wrong with both of our subs

 

[comabereni]

Do you have a coaxial cable connected to a receiver that is driving the sub (or to a VCR or DVD player connected to the receiver)? Sometimes that can introduce ground loop issues.

-coma

P.S. Sorry--re-read the original post. Your sub is humming all on its own even when disconnected from everything and with/without the ground prong lifted? Not sure you will be able to fix that using any of the standard methods--the problem (whether wiring or not) sounds like it is inside the amp itself.

 

[rellik]

thats exactly what i got

would a ground loop isolater fix it? i have no idea where to get em either?

 

[comabereni]

Quote:

Originally Posted by rellik thats exactly what i got would a ground loop isolater fix it? i have no idea where to get em either?

I have an old Radio Shack ground loop isolating RCA-RCA connector that killed the ground loop coming from the coax cable connected to my VCR connected to my receiver. I was in the store the other day and noticed they still sell them. Actually, the sub still hummed mildly after that, until I cut off the ground prong on the power cable to the sub amp. Now it's silent.

-coma

 

[Nak Man]

Quote:

Originally Posted by comabereni P.S. Sorry--re-read the original post. Your sub is humming all on its own even when disconnected from everything and with/without the ground prong lifted? Not sure you will be able to fix that using any of the standard methods--the problem (whether wiring or not) sounds like it is inside the amp itself.

Yeah, this one is my problem. I have opened up the amp but wondered whether some others have experienced this circuit problem. Interestingly volume level and xo freq pots have no effect on hum, I thought that might be a good hint for diy gurus here. Still waiting for email reply from mfg.

 

[Garbz]

Try disconnecting the ground from the power to the subwoofer. But do so with EXTREEEEEEEEM CAUTION!!!!!!!! The ground pin is there for a reason, that is safety. If there is a fault and current can flow through the subwoofer case you become that ground loop when you touch the case.

 

[Nak Man]

Quote:

Originally Posted by Garbz Try disconnecting the ground from the power to the subwoofer. But do so with EXTREEEEEEEEM CAUTION!!!!!!!! The ground pin is there for a reason, that is safety. If there is a fault and current can flow through the subwoofer case you become that ground loop when you touch the case.

Thanks for dropping by Garbz, I did try that with cheater adaptor ... still humming happily. Btw it's from Accusound of Kirrawee, NSW. Very impressive and heavy cabinet. You guys really know how to build good looking subs !

I got a pair and my friend's unit is working OK, if everything fails I'll compare point by point voltages. Arrgh.

 

[Nak Man]

Gotcha !

Found a dead culfridh 10R 5W (!) resistor between AC ground and signal ground. Replaced it and no more ho-humm. Have no idea what might shorted that resistor, no burnt out marks, nothing. There's still some DC signal left to drivers at 202mV, isn't that a bit too large ? Anyway now I can enjoy bass shaking music

without that annoying buzz.

Thanks much to you guys for all help and moral support ! This is the beauty which life you just saved, isn't she pretty ?

Cheers,
SM

 

[Garbz]

Looks very similar to Richter subs. 202mV isn't much for speaker drivers. It would be very dangerous for headphones if sustained long enough though.