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Subwoofer buzz/hum revisited…what is best solution?

Saturn94

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Some years ago I noticed a buzz/hum when I was near my sub, a Power Sound Triax. I didn’t notice it at the listening position, particularly when playing content. I added a BJC Isolation Transformer and the noise went away. I assumed this meant there was a ground loop issue?

I recently came across the Amir’s review of the BJC Isolation Transformer and was horrified by the poor performance. I’m surprised and confused about why I didn’t noticed a huge degradation in sub performance when I added it. This new knowledge is bugging me enough to want to look for other solutions.

For reference, my current sub connection looks like this;
Anthem AVM20 pre/pro sub RCA out > BJC isolation transformer > RCA to XLR adapter > sub (sub only has XLR input). If it matters, distance from the pre/pro to the sub is about 22ft.

My first thought was to replace the BJC with a better quality isolation transformer, perhaps this one?


The comments about it making noise worse is concerning though.

The AVM20 pre/pro does have balanced/XLR outputs, though I’ve never used them. Would just connecting the pre/pro to the sub via XLR, eliminating the isolation transformer and RCA to XLR adapter entirely, work to eliminate the buzz/hum? If this would work, then it seems the best solution to assure best performance.

I did some reading and found conflicting information about whether or not using an XLR connection would likely be an appropriate solution. Unfortunately, I don’t have an XLR cable to try, so I would have to buy either a long XLR cable or a better isolation transformer. I was hoping to avoid having to buy both to try (I’m retired on a very tight budget).

I would greatly appreciated some guidance.

Thanks!
 
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droid2000

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I'm pretty sure connecting the amp to the sub with XLR would be the simplest, cheapest, and best sounding option. Throw away the RCA to XLR adapter and the isolation transformer. You don't need them if it's a pure XLR connection.
 

solderdude

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When your output is not balanced (XLR) perhaps use an isolation transformer (the mentioned Jensen) or DI box that is performing better.

Also an option could be to use an active DI box. Chances are an active one might also work here despite offering no isolation.
 
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Sokel

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When your output is not balanced (XLR) perhaps use an isolation transformer (the mentioned Jensen) or DI box that is performing better.

Also an option could be to use an active DI box. Chances are an active one might also work here despite offering no isolation.
His output is balanced,he just don't use it until now.
Thing is that maybe in theory the balanced connection eliminates noise but in practice we have a new thread every week about noises despite the balanced connections.

avm20-presurround-sound-processor-v21-mint-condition.jpg
 
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Saturn94

Saturn94

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His output is balanced,he just don't use it until now.
Thing is that maybe in theory the balanced connection eliminates noise but in practice we have a new thread every week about noises despite the balanced connections.

View attachment 304452

Yes, the Anthem AVM 20 does have balanced outputs, but I have not tried using it for the sub (the only channel with the buzz/hum issue).

I’m trying to figure out if I can expect using the balanced sub output to eliminate the buzz/hum.
 
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Saturn94

Saturn94

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When your output is not balanced (XLR) perhaps use an isolation transformer (the mentioned Jensen) or DI box that is performing better.

Also an option could be to use an active DI box. Chances are an active one might also work here despite offering no isolation.
Do you know if just using the balanced connection from my pre/pro to my sub would eliminate the buzz/hum?

I’m assuming since the BJC isolation transformer eliminates the noise that it’s caused by a ground loop. Would this be a safe assumption?
 

solderdude

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Do you know if just using the balanced connection from my pre/pro to my sub would eliminate the buzz/hum?

It could/should

I’m assuming since the BJC isolation transformer eliminates the noise that it’s caused by a ground loop. Would this be a safe assumption?

Yes.

Ground currents AND audio signal ground are the same so ground currents enter the signal path.
With balanced the signal is between 2 wires and not referenced to ground.
The ground currents should simply flow between the grounds of both devices and not enter the signal path.
Assuming all is designed properly....
 
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Saturn94

Saturn94

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Is low level ground loop buzz/hum in a sub a risk to anything, or is it strictly an annoyance?
 
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Saturn94

Saturn94

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Is low level ground loop buzz/hum in a sub a risk to anything, or is it strictly an annoyance?

Anyone?

Btw, I did some additional testing.

I removed the BJC transformer and sure enough the buzz returned. However, it’s pretty low level and not usually noticeable past a foot or two from the sub. I say “usually” because it does become louder if I turn on a floor lamp (with a built in dimmer) in the same room (different outlet than the sub, but likely the same circuit at the breaker panel). With the lamp on, I can just barely hear the buzz at my listening position 8ft from the sub, providing the room is really quite (HVAC not running, etc) and no content playing.

It‘s still bugging me that the BJC transformer may be introducing significant distortion, so I won’t reinstall it, even if just for peace of mind. I didn’t spend all that money on a great sub just to feed it a crappy signal, lol.

I may try using my pre/pro’s balanced connection instead of the current unbalanced connection to see if that eliminates the buzz. Anyone have experience with this cable (25ft length)?


Is it well built? Or would one from BJC ($72 vs $12 for the Monoprice cable) be much better build quality?

Thanks again for any feedback.

EDIT; I just read some concerning reviews of the Monoprice cable concerning high incidence of improper construction. Perhaps I should splurge for the BJC cable. I’ve never had an issue with a BJC cable, but have had an issue before with Monoprice (to their credit, they promptly refunded my money).
 
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sam_adams

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The only thing that you need be concerned about with any prebuilt cable made with a name brand wire that you buy is the quality of the terminations of the connectors. You can always open the connectors and examine the workmanship to see if there are any poorly done solder joints or stray wires. You can return it if it is not up to your expectations.
 
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