Hum through AC mains in subwoofer (not ground hum)

[Buckeye Amps]

Hey all,

So I just switched out some Rythmik subs with a quad Power Sound Audio setup using their S1813's. But I've run into a hum in all four subwoofers that IS NOT ground loop and is also not coming from the source. This hum did not happen with the Rythmik subs.

The hum happens even if only the power cord is connected. The subs themselves only use 2 prongs for power, so there is no ground connection to the wall. And the hum doesn't change whether I connect the subs to my source via XLR or RCA.

The subs themselves are on their own breaker/circuit. I did try running an extension cord to try the subs on different outlets connected to different breakers but didn't fix it. Also tried the power conditioner I have (Emotiva CMX2), no change. There is one LED light on the same circuit as the subs and I am planning on seeing what happens if I disconnect it tomorrow. Also going to take one sub to a friend's house and try their power.

I also took the plate amp off one sub and verified Live and Neutral are wired correctly.

Turn the Gain down on the sub to the 9 o clock or lower (so about 25% gain max) lessens the hum to only being audible within about 1ft of the sub. But ideally I'd like to try and get rid of the hum overall.

I'm being told that the drivers in the PSA subs are very sensitive so even a tiny amount of "bad" AC power will cause said hum.

Since it isn't typical ground loop hum and seems to be due to amplifying whatever small issue may be present in the mains power, does anyone have any advice to try besides what I have?
Would wiring a ground wire to the plate amp body/chassis help at all in this instance?

FYI, these subs use the IcePower 700AS1 amps.

 

[restorer-john]

Short the inputs to the subs, turn up the gain and see if the hum is there. Lift the subs up from the floor. Do you have any electrical underfloor heating/wiring near the subs?

 

[Buckeye Amps]

Short the inputs to the subs, turn up the gain and see if the hum is there. Lift the subs up from the floor. Do you have any electrical underfloor heating/wiring near the subs?

There are two RCA inputs and two XLR inputs. Should I short all of them or just the RCA's?

Subs are off the floor. The floor itself is concrete and then wood subfloor, no wiring near subs.

 

[Buckeye Amps]

Short the inputs to the subs, turn up the gain and see if the hum is there. Lift the subs up from the floor. Do you have any electrical underfloor heating/wiring near the subs?

So I just did a quick test.

If I short one of the RCA inputs on the sub without the XLR cable (from source) connected, the hum is gone even with the gain at max.

But if I short the RCA with the XLR connected, it still hums (no change)

 

[sam_adams]

If I short one of the RCA inputs on the sub without the XLR cable (from source) connected, the hum is gone even with the gain at max.

The noise is coming from inside the amp.

 

[Buckeye Amps]

The noise is coming from inside the amp.

I'm all about permanent solution, so would there be a good approach to doing an internal fix or bandaid on the actual amps if I take the plate off?

Also, very dumb question but what's the proper way to creating an XLR short for testing? Hot and cold connected (leave ground untouched)?

 

[Speedskater]

Remove all the RCA & XLR cables from the sub. Does it still hum?
If it still hums, take it (without cables) to another room, or better yet another building. Does it still hum.

 

[Buckeye Amps]

Remove all the RCA & XLR cables from the sub. Does it still hum?
If it still hums, take it (without cables) to another room, or better yet another building. Does it still hum.

Yes. Haven't tried a different building yet though.

 

[Buckeye Amps]

One more piece of information I just got from PSA:

A lot of the time this issue can be mitigated/minimized to inaudibility with a stricter noise gate in the DSP. The noise gate on your subs is very "loose"

 

[ryanosaur]

Filled with nothing but revulsion that a major player in the ID Sub community has this problem.

 

[sam_adams]

The manual for the sub from PSA uses makes no mention of DSP.

The amp manual shows these connection options for unbalanced and balanced connections:

Unbalanced:

Balanced:

Without further info from PSA on how they implemented the two connection types, it's hard to tell what could be causing the issue.

 

[Buckeye Amps]

The manual for the sub from PSA uses makes no mention of DSP.

The amp manual shows these connection options for unbalanced and balanced connections:

Unbalanced:

View attachment 395014

Balanced:

View attachment 395015

Without further info from PSA on how they implemented the two connection types, it's hard to tell what could be causing the issue.

At this point I'm kinda determined to make these work. I can take one of the amps out tomorrow and take pictures of the wiring/pinouts if anyone would like to help me get to the bottom of this.

 

[sam_adams]

At this point I'm kinda determined to make these work.

I admire the determination . . . but . . . if these subs hum like the Mitch Miller Trio—by design—I'd put them back in the boxes and say thanks, but no thanks. Your time is far too valuable to try and correct the engineering mistakes made by someone else.

 

[Buckeye Amps]

I admire the determination . . . but . . . if these subs hum like the Mitch Miller Trio—by design—I'd put them back in the boxes and say thanks, but no thanks. Your time is far too valuable to try and correct the engineering mistakes made by someone else.

I get that. FWIW, with the gain at the level I need it at for proper usage, the hum is not audible from more than maybe 1ft away.
I am just more invested to now eliminate it. Call it natural curiosity coupled with OCD.

Plus it would be a lot more work to box them all up, return, and then wait for a different option from another brand to be ordered and arrive.

 

[GXAlan]

What’s your source? The StormAudio?

Even with two prong electronics when there are three prong electronics in play, I have found that I need to manually ground things occasionally. I have seen this with two prong sources and three prong amplifiers but it probably doesn’t matter.

You can try connecting a chassis screw from one PSA to the StormAudio

Alternatively, find a used Panamax power conditioner that has the ground lug and have the PSA chassis screw go to that ground lug.

 

[Wolf11Man]

Your "problem" seems like a combination of faults.
If you leave the RCA input of an amp open, you will quite often hear unwanted noise. This is simply a user fault. An impedance mismatch amplifying any induced noise in the room. The worst noise is generated by an SMPS near the amp, it's own... So don't switch it to RCA, leave it open and turn up the gain. That is simply asking for trouble.
With the XLR connection, you can use it grounded or ground lifted. This may change the hum.

You should indeed take out the plate amp and check the wires running near it. These may induce the noise. Something like a wire running half an inch nearer to a component can make such a highly integrated amp/ SMPS combination hum or not. Post a picture and we can maybe point to the suspects.

Now there is a second problem, If you do NOT power the sub from the same wall outlet and breaker as the signal source, you are asking for hum. Never do that. You did.

All these causes may produce hum, in single ore combined. They are your faults, exept for the wires inside the amp. These are made by ignorant workers during assembly and or no/ incorrect working instructions.
The ICE amp itself is dead quiet.
You will not solve this problem with any expensive mains cable or power conditioner. That is just rip off like all Voodoo audio snake oil.

Reduce your chain to the minimum and power it from one wall outlet. You should use only one sub first, then add more. If they allow daisy chain, that will only work with XLR from source to the last, but not mixed RCA/ XLR.

 

[EERecordist]

Can you point your measurement microphone at it and run that into a spectrum amplifier like REW? Can you set up a voltage divider, or use a current probe to look at the spectrum of your house power? If you have RF EMF getting into your power line above the capability of REW, you can also sweep up in timebase on an oscilloscope - if you have EMF it can be down converted by the circuitry in the amp, that can be reduced by any decent power line filter.

You should ask the manufacturer how they do QC testing. Maybe a filter/bypass capacitor or a signal connector came loose in shipping? It's always fun to trace through the circuit with an oscilloscope and tap / spray freeze mist to find intermittent problems. Have to agree with others, send them back and let the manufacturer troubleshoot it, then work the root cause into their manufacturing and test.

 

[Wolf11Man]

Loose capacitor or connector? With all 4 of them?

I did not touch the DSP gain problems, if you don't know how to set it. Maybe you use a very low input signal. It has to be as high as possible, then reduced in level inside the DSP!

 

[MCH]

At this point I'm kinda determined to make these work.

Welcome to the club, and good luck.

https://audiosciencereview.com/foru...ate-the-noise-rumble-of-my-svs-sb-1000.46977/

 

[GXAlan]

You will not solve this problem with any expensive mains cable or power conditioner. That is just rip off like all Voodoo audio snake oil.

Reduce your chain to the minimum and power it from one wall outlet. You should use only one sub first, then add more. If they allow daisy chain, that will only work with XLR from source to the last, but not mixed RCA/ XLR.

The only exception I would make is that power centers with ground lugs make it easier to avoid ground loops that seem to occur even when plugged into the same wall outlet.

You can easily ground the system in OTHER ways but it’s pretty convenient to have a product that’s UL listed and feels more reliable than just using a chassis screw or something like that.