Hello community.
I acquired this sub 2nd hand and it does a fair job at moderate volume levels, however it suffers from mains hum.
I'm hoping someone on here can help.
First off, the basics...
With nothing connected except the 3 pin mains lead and switched on the driver hums quietly so I'd rule out earth loop.
It is normally connected via a phono lead to my amp and this makes no difference to the hum.
The amp isn't earthed and is fed solely by optical link from PC.
The crossover and volume controls on the sub make no difference to the hum either.
Thus far I'm thinking the PSU circuitry has issues.
I have the circuit schematics and have a basic grasp of electronics, although very capable at the actual work I am still learning at fault diagnosis at component level.
Can anyone guide my hand through fault finding this unwanted hum?
I acquired this sub 2nd hand and it does a fair job at moderate volume levels, however it suffers from mains hum.
I'm hoping someone on here can help.
First off, the basics...
With nothing connected except the 3 pin mains lead and switched on the driver hums quietly so I'd rule out earth loop.
It is normally connected via a phono lead to my amp and this makes no difference to the hum.
The amp isn't earthed and is fed solely by optical link from PC.
The crossover and volume controls on the sub make no difference to the hum either.
Thus far I'm thinking the PSU circuitry has issues.
I have the circuit schematics and have a basic grasp of electronics, although very capable at the actual work I am still learning at fault diagnosis at component level.
Can anyone guide my hand through fault finding this unwanted hum?
I have 3 of them and they are totally crap. You need to put protection diodes on the inputs before any statics charge or a higher signal will blow the first CI. Anyway, after a while --about 1-2 years-- they'll begin humming and is cheaper to just change all amp module with something else, anything will be better then that, just my two cents.
I'm happy to report I have fixed the humming.
As suspected and as Ola suggested the transformer is both too close to the amp board and moreover the driver.
I extended the wiring to/from the transformer and screwed it to the inside front, immediately above the port.
Important to note that I also rotated it by 90° to further reduce driver influence.
Only a very faint hum is detectable if you put an ear to the driver so it is to all intents and purposes silent.
One problem I will have to address another time though is the physically buzzing transformer, despite being screwed lightly to the box using neoprene foam as cushioning it can just be heard in a silent room... now I'm being fussy!
Thanks to everyone who responded.
I hope this fix gives others an idea if their sub is humming.
As suspected and as Ola suggested the transformer is both too close to the amp board and moreover the driver.
I extended the wiring to/from the transformer and screwed it to the inside front, immediately above the port.
Important to note that I also rotated it by 90° to further reduce driver influence.
Only a very faint hum is detectable if you put an ear to the driver so it is to all intents and purposes silent.
One problem I will have to address another time though is the physically buzzing transformer, despite being screwed lightly to the box using neoprene foam as cushioning it can just be heard in a silent room... now I'm being fussy!
Thanks to everyone who responded.
I hope this fix gives others an idea if their sub is humming.
I've deadened the transformer buzz by screwing it to the box using 4 small rubber grommets taken from a PC where they are used to dampen hard drive noise.
The last issue that concerns me is that the transformer now up at the top of the box has no room to dissipate heat and it can get too hot to handle if left on for a couple of hours. Hopefully it is within design tolerance.
Unless I position it externally I think I have gone about as far as I can to improve on this cheap sub.
One last thing, I removed the safety grille material from the rear of the port and it now breathes freely and sounds just a bit more dynamic.
The last issue that concerns me is that the transformer now up at the top of the box has no room to dissipate heat and it can get too hot to handle if left on for a couple of hours. Hopefully it is within design tolerance.
Unless I position it externally I think I have gone about as far as I can to improve on this cheap sub.
One last thing, I removed the safety grille material from the rear of the port and it now breathes freely and sounds just a bit more dynamic.
After cutting a chunk out of the surrounding filling material, just slightly larger than the transformer. I can say that in 20°C ambient temperature the heat felt on the external surface of the sub where the transformer is situated is barely noticeable, even after hours of hard use so I would imagine the transformer is not running exceptionally hot now it has some room to breathe.
I could open things up to check but that seems unnecessary.
If anyone wants to improve their old A-10 or similar I would recommend this mod without hesitation.
I could open things up to check but that seems unnecessary.
If anyone wants to improve their old A-10 or similar I would recommend this mod without hesitation.
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