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373 posts

Ultimate Geek


#265596 30-Jan-2020 13:04
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We've got a home theatre system - Newish Marantz amp / receiver and 5 wharfedale speakers (incl sub woofer)

 

everything works fine and after we replaced the Marantz last year there have been no problems

 

Except on Saturday morning 25/01 just after 9am the power went off.... we thought nothing off it and went out to do our planned activities, came back 11-ish and power still off, so went out again to do some shopping - saw the Vector trucks near our street so asked them about the power outage and they said might be another 3 hours before power is back on..... power was back on when we got back so all good.

 

I sat on my chair on the lounge and could hear there was a big 'hum' somewhere - immediately thought it was the sub and was correct. As I reached around behind it to turn it off and I accidentally touched the back of the sub (on the metal grill thing) and the hum got way louder - gave me a fright actually. took my hand away and the hum went back to being at a low-ish volume.

 

Anyway I managed to turn the sub off, waited about 10 seconds and turned it back on..... hum still there..... I repeated this a couple more times with the same result (the amp / receiver was 'off' while I was doing this). So then I unplugged the sub from the power board - identical to this one but older https://www.belkin.com/au/p/P-BV108130-3M/, waited a couple of minutes, plugged it back in, turned sub on and hum still there.

 

I then turned it off, unplugged it and disconnected the RCA red and white leads that connect it to the Marantz.... plugged it all back in the next day and turned it on and the hum still there

 

The Marantz and other 4 wharfedale speakers all work fine, as does the TV and My sky that are all plugged into the same power board

 

Would the sub be stuffed?? or is there something else I can try?

 

Any advice would be appreciated


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145 posts

Master Geek


  #2410158 30-Jan-2020 13:09
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Is the sub still woking when you play sound through it? the hum is usually from the input not being terminated and picking up noise, normally it stops once the connection to the amplifier is made. Or is it possible the receiver somehow "forgot" the sub was there and needs to be set up again?

 

Not much else to offer from me.


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  #2410161 30-Jan-2020 13:13
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Maybe a stuffed neutral causing it to return by the earth and now exposing a groundloop that you didnt notice before?





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  #2410162 30-Jan-2020 13:15
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Sounds like a ground loop hum, weird that it only kicked off after a power outage.

 

Does it hum without being plugged into the Marantz, but turned on?

 

Is the sub plugged into the same power circuit as the Marantz? If not, can you try that? Also, try it straight into the wall if you can.


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  #2410165 30-Jan-2020 13:19
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I got my Sub Repaired by a guy in Auckland. It was very reasonable. Certainly thrashed replacing mine which would have been $2K.

 

Let me know if you want the details.

 

 


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  #2410166 30-Jan-2020 13:21
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If you take away all input except power, does it hum?

 

 


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  #2410169 30-Jan-2020 13:23
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I had something similar happen to a M&K sub I had a few years back. In the end it was diagnosed as a faulty gain potentiometer that was causing the ground loop. A $2 part from Jaycar had it resolved quick smart.

 

 

 

I would ask a local repair technician to have a look at the amplifier.




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Ultimate Geek


  #2410245 30-Jan-2020 14:42
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ShinyChrome:

 

Sounds like a ground loop hum, weird that it only kicked off after a power outage.

 

Does it hum without being plugged into the Marantz, but turned on?

 

Is the sub plugged into the same power circuit as the Marantz? If not, can you try that? Also, try it straight into the wall if you can.

 

 

 

 

I've not tried that - all the times I have tried / tested it the RCA's from the Marantz have been plugged into the sub

 

I did unplug everything, leave it for a day and try again, but the hum was still there

 

I'll test it without the RCA's being plugged in and see what that does.

 

it's not possible to plug it straight into the power point, as the only one near the TV / stereo has everything plugged into it


 
 
 
 


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  #2410252 30-Jan-2020 14:51
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I've got an ever-growing problem with a sub as well (it'll turn on randomly by itself and, when the amp is off, there's a lovely ground loop hum), so appreciate the irritation factor!

 

OnceBitten:

 

ShinyChrome:

 

... Also, try it straight into the wall if you can.

 

 

...

 

it's not possible to plug it straight into the power point, as the only one near the TV / stereo has everything plugged into it

 

 

Even if not feasible when it's in use, just try ShinyChrome's suggestion above to test whether the hum remains to help rule out what may be causing this - ie, unplug the multibox and plug the sub directly into the wall socket.




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Ultimate Geek


  #2410264 30-Jan-2020 15:20
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jonathan18:

 

Even if not feasible when it's in use, just try ShinyChrome's suggestion above to test whether the hum remains to help rule out what may be causing this - ie, unplug the multibox and plug the sub directly into the wall socket.

 

 

 

 

what I was trying to say is TV / Blueray DVD player / Marantz / Chromecast / My Sky / Wifi Modem / landline telephone are all plugged into the same multibox and they are all working fine, but I'll plug the sub into another power socket without the RCA leads and see if it still 'hums'


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  #2410270 30-Jan-2020 15:35
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OnceBitten:

 

what I was trying to say is TV / Blueray DVD player / Marantz / Chromecast / My Sky / Wifi Modem / landline telephone are all plugged into the same multibox and they are all working fine, but I'll plug the sub into another power socket without the RCA leads and see if it still 'hums'

 

 

Subs are particularly susceptible to electrical noise, so the idea is just to remove any potential source to isolate it to nothing but the sub and a power point. It's probably not the power board, but never hurts to ensure the it's not adding electrical noise that your sub is now picking up on.

 

I'm inclined to agree with the others' suggestions that the outage caused something to go bad in your sub, but no harm in doing a few preliminary checks yourself.

 

To be honest if the sub performs fine otherwise, and the hum isn't loud enough that you will hear it during particularly quiet parts of a sound track, then I wouldn't bother spending money to fix it. Both my S12 and PB12 have both had a little bit of a ground hum, presumably from my house wiring, but you could only hear it in a completely quiet room.


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  #2410277 30-Jan-2020 15:47
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Subs should be on a balanced signal since they are usually distant from the receiver and have quite a bit of gain, but beancounters decided that the top end is the only place that get done, so this is quite common with ground differences between the sub. It shouldnt just appear after electrical work however.

 

I had to run an extension to the same circuit that the amp and stuff was on to get it to quieten down when I had my HT set up, otherwise it was bad enough that the sub would wake up with any electrical transient and buzz for a while before going back to sleep.





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  #2411519 2-Feb-2020 12:50
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Try temporarily running an earth wire between the sub and the amp. Either look for a chassis earth connection or just use a screw that goes into the chassis. It worked for me. 

 

 





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  #2411540 2-Feb-2020 13:46
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I'm assuming the hum is from the actual speaker?


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  #2411582 2-Feb-2020 16:28
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Since the problem occurred after a power outage I'd be suspicious of the subs power supply, but first I'd do as suggested earlier and see what happens with no audio leads plugged into the sub. Then I'd also try it with the audio leads plugged in to the sub and the amp, with the sub powered separately from everything else, via an extension cord to a plug that's only powering the sub.

 

If the hum disappears with the sub plugged into it's own 230 socket then you need to be looking at the multi points, one of them has developed a fault or one of the devices plugged into the multi points has developed a fault on the earth lead.

 

If the hum is still there I'd be looking at the sub power supply. How is is it powered? 230v supply to an internal power supply or a power pack which delivers the voltage to the sub? If it's a power pack try another power pack. If the sub connects to 230 volts and has it's own internal power supply I'd be suspicious of the filtering capacitor.





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Ultimate Geek


  #2411709 2-Feb-2020 20:34
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Ok unplugged sub completely and plugged it in to another power socket and turned it on.... no hum
Plugged it back into marantz as it was pre-power cut and all works 👍

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