Hum through AC mains in subwoofer (not ground hum)

[restorer-john]

It looks like the RCA outer is insulated from the plate amp chassis by coloured plastic washers. Whereas the XLR will likely have its outer shell tied to the plate amp chassis.

How they have implemented the single ended (RCA) input to the amplifier modules (which are differential) vs the XLR is something we don't know. It's most likely the whole front end (filters/gain etc) is single ended in topology and the XLR input is converted immediately to single ended. But that floating "shield" on the RCA means the sub plate "chassis" could be floating or have a "nuisance" voltage on it from any leakage/X caps in the SMPS which is likely also bolted to the "chassis".

The XLR outer may be at "chassis" potential, but where is the XLR Pin1 to chassis actual physical connection? Is it right at the point it enters the plate or does it run down some tracks to a "star" earth/ground?

Combining both RCA and XLR inputs (especially two of each) where a physical switch doesn't disconnect one set or the other set means the potential for injected noise is high, especially where the "grounds" of the two jacks may be different, floating, or have some mains potential (leakage) on them.

If you want to keep the subs and solve the problem, we need either some documentation (manuals/schematics) or we need to have a really close look at (reverse engineer) the front end and study the connections (drive diff/se) to the power amp itself.

 

[Buckeye Amps]

It looks like the RCA outer is insulated from the plate amp chassis by coloured plastic washers. Whereas the XLR will likely have its outer shell tied to the plate amp chassis.

How they have implemented the single ended (RCA) input to the amplifier modules (which are differential) vs the XLR is something we don't know. It's most likely the whole front end (filters/gain etc) is single ended in topology and the XLR input is converted immediately to single ended. But that floating "shield" on the RCA means the sub plate "chassis" could be floating or have a "nuisance" voltage on it from any leakage/X caps in the SMPS which is likely also bolted to the "chassis".

The XLR outer may be at "chassis" potential, but where is the XLR Pin1 to chassis actual physical connection? Is it right at the point it enters the plate or does it run down some tracks to a "star" earth/ground?

Combining both RCA and XLR inputs (especially two of each) where a physical switch doesn't disconnect one set or the other set means the potential for injected noise is high, especially where the "grounds" of the two jacks may be different, floating, or have some mains potential (leakage) on them.

If you want to keep the subs and solve the problem, we need either some documentation (manuals/schematics) or we need to have a really close look at (reverse engineer) the front end and study the connections (drive diff/se) to the power amp itself.

Pin 1 of the XLR goes directly to the PCB board they have the gain/DSP knobs on. Without taking the entire plate amp apart so I can visually trace everything, I cannot tell where at or even if at all Pin 1 reaches chassis ground.

Regarding keeping the subs: since shorting one of the RCA inputs and also shorting the unused XLR input has removed all traces of hum, can I just simply run the subs like this indefinitely?

Would disconnecting the RCA harness internally and only shorting the unused XLR be a more bullet proof solution?

 

[GXAlan]

The AVM 90 is grounded and has been for app of this as there was normal ground loop hum with the AVM 90 and one of my amps that was solved once I grounded the AVM 90 to my power strip.

The subs is just a completely different issue

Darn. Just lost my $5 bet.

Nice work on solving the problem, though!

 

[Salt]

Pin 1 of the XLR goes directly to the PCB board they have the gain/DSP knobs on. Without taking the entire plate amp apart so I can visually trace everything, I cannot tell where at or even if at all Pin 1 reaches chassis ground.

Regarding keeping the subs: since shorting one of the RCA inputs and also shorting the unused XLR input has removed all traces of hum, can I just simply run the subs like this indefinitely?

Would disconnecting the RCA harness internally and only shorting the unused XLR be a more bullet proof solution?

Is a soloution, but no explanation (that was asked for by Yourself and John gave an answer to).

 

[Buckeye Amps]

Darn. Just lost my $5 bet.

Nice work on solving the problem, though!

Well waiting to see if I can consider it solved. I'm not exactly sure what, if any, long term ramifications might arise from the shorting method. Hoping John has an opinion.

 

[Buckeye Amps]

Because I'm taking each plate amp off to tidy up internal wiring, I'm going to try one sub where the RCA harness is completely disconnected internally and also disconnect the unused XLR input internally, see if that "solves" the issue without any shorting needed.

 

[Buckeye Amps]

Well s**t

I think I may have actually solved the issue, not just fixed it.

 

[Buckeye Amps]

Ok. Here is the latest.

I wanted to see what would happen if I disconnected Pin 2 and 3 from the unused XLR. Doing so didn't change the hum. However, when I hooked the wiring back up to the unused XLR the hum was completely gone. Didn't need to short any inputs. Didn't need to disconnect the RCA wiring. It was just completely gone.

After using my multimeter I realized I had switched up Pin 2 and 3 on the wiring harness for the unused XLR.

So, for some reason if I swap the hot and cold wiring for just the unused XLR input, no more hum.

Without access to a schematic to verify if for some reason the original wiring harness/layout had hot and cold reversed accidentally, I can't really be sure how or why this would get rid of the hum.

Any thoughts?

 

[restorer-john]

Ok. Here is the latest.

I wanted to see what would happen if I disconnected Pin 2 and 3 from the unused XLR. Doing so didn't change the hum. However, when I hooked the wiring back up to the unused XLR the hum was completely gone. Didn't need to short any inputs. Didn't need to disconnect the RCA wiring. It was just completely gone.

After using my multimeter I realized I had switched up Pin 2 and 3 on the wiring harness for the unused XLR.

So, for some reason if I swap the hot and cold wiring for just the unused XLR input, no more hum.

Without access to a schematic to verify if for some reason the original wiring harness/layout had hot and cold reversed accidentally, I can't really be sure how or why this would get rid of the hum.

Any thoughts?

Perhaps their "XLR" input is not differential at all. And maybe they have their XLR hots and "colds" (being the floating chassis) are around the wrong way.

Check what is connected to what with your DMM/continuity beeper/ohms range. They may have the "XLR" cold shorted to gnd or via a resistor.

You'll get there.

 

[Buckeye Amps]

Perhaps their "XLR" input is not differential at all. And maybe they have their XLR hots and "colds" (being the floating chassis) are around the wrong way.

Check what is connected to what with your DMM/continuity beeper/ohms range. They may have the "XLR" cold shorted to gnd or via a resistor.

You'll get there.

The only issue is the XLR wiring goes into their own larger input board (which has all of the other stuff on it like Gain, Crossover, Delay, 12v triggers) and it is mounted sideways and partially glued onto the plate. Only way to get to the front of that PCB to start tracing would be to completely remove it. I'm not entirely sure I'm that dedicated.

I guess my question would be if I just leave the wiring as I have it (where hot and cold are reversed on the unused XLR input but left as is on the XLR input I'm using), there shouldn't be any performance issues, no?

 

[sam_adams]

This is the balanced input buffer schematic from the 700AS1 amp (700AS2 is the same):

From what has been discovered, the issue lies largely with what PSA did on their input board and wiring—not with the amp module. I would agree with @restorer-john that you probably don't want to run the amp with a shorted RCA and an XLR signal input.

 

[Buckeye Amps]

This is the balanced input buffer schematic from the 700AS1 amp (700AS2 is the same):

View attachment 395151

From what has been discovered, the issue lies largely with what PSA did on their input board and wiring—not with the amp module. I would agree with @restorer-john that you probably don't want to run the amp with a shorted RCA and an XLR signal input.

I asked PSA if they might send me a schematic of their board but was told the engineering house who designed the board had told them how to connect everything and since there isn't a hum reported for a vast majority of users, it isn't something they want to necessarily tackle as fixing it could (in their view) cause issues for other users.

So far the best work around I have found is simply swapping the hot and cold wire on the unused XLR input.

 

[Sokel]

Icepower universally suggests this as Balanced/unbalanced :

Balanced

semi-balanced

I have used both any way imaginable mixing and matching modules and I/O's and never had even a hint of noise.

There's something wrong in there.

 

[ivanj]

Sorry I don't know how to post the link but it seems others on ASR have had problems with this sub 'designer'

Got a Wiim Amp but my PSA TV1513 sub will not go into standby and stay there... PSA TV1513 SUBWOOFER​

Does't seem to happen with his Hsu.

 

[Descartes]

Get rid of them and buy new ones!

 

[Buckeye Amps]

Get rid of them and buy new ones!

The subs themselves and there performance are great. Plus I have four of them at a steep discount that would be a hell of a hassle to box up and freight back.

I really don't mind the work around. I just need to know if it's going to affect actual performance.

 

[jamesdyson]

@Buckeye Amps Apologies for this question, it may come across a bit pointed, but from this thread and the questions you are asking, can I assume you are not an electronics engineer and you are not involved with the design work on your amps?

 

[GXAlan]

Power Sound Audio is sort of like the Topping/Fosi of subwoofers, except it’s made in the USA.

What I mean by that is that they take electronics from ICEpower, speaker drivers from B&C in Italy (and now another supplier in China), build enclosures, DSP the heck out of it and sell it directly at a very reasonable price. So they take best of breed technology, integrate it for consumers and deliver a lot of value and performance.

The founder, Tom Vodhanel, is active on forums and responds to questions and he is the the “V” in SVS.

 

[Buckeye Amps]

The founder, Tom Vodhanel, is active on forums and responds to questions and he is the the “V” in SVS

Oh really?

 

[Buckeye Amps]

@Buckeye Amps Apologies for this question, it may come across a bit pointed, but from this thread and the questions you are asking, can I assume you are not an electronics engineer and you are not involved with the design work on your amps?

I'm not an EE but I am definitely very closely involved in the amp design work