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Hum through AC mains in subwoofer (not ground hum)

And could this be the reason for hum?
 
That's what interests you.
Now work your way backwards:

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(@restorer-john better not see the solderwork of the input board :facepalm: )
I did some poking around with my multi meter.

From the input of their input/dsp board to the output of that same board, I can't find continuity of any of the XLR or RCA inputs.

So I can trace, say, the positive of the XLR input to the input connector of their input board, then there is no continuity of it from the input to the output of their board.
I can then pick the continuity back up from the output of their board to the input of the amp module.

This is regardless whether amp is on/off/source input connected.
 
There is seldom continuity from signal input to output on a PC board that has, tubes, transistors or op-amps.
I suppose I'm just used to our input board designs as I can easily trace continuity from input to output.

Without a diagram/schematic there isn't much left for me to do it seems.

I'm likely going to opt with just leaving the RCA connectors disconnected internally and then if need be also short the unused XLR.
 
If I really feel like it tomorrow I might hook one of my 2ch amps directly to the subwoofer driver just to see what happens
 
Final solution I settled on is disconnecting the internal RCA harness and using an XLR shorting plug (pin 2 and 3 tied together) on the unused XLR input. Zero hum now.

Wanted to continue looking into the cause to hopefully offer suggestions to Tom at PSA, but he has made it clear on AVS that the issue is dirty mains power and there is nothing to be seen here. So not going to waste any more time on it.
 
Oh, that dirty mains power issue ... all that rubbish within it .... someone really should clean this up ... :cool:
I'm going with my original theory, faulty design or faulty manufacturing.

Sometimes you might find friends from which to borrow a power quality analyzer which can find harmonics, noise, or glitches. Generally they are data center engineers. They would be a common text equipment rental item. I doubt on scientific/engineering analysis you will find it is a power quality issue.

There are some questionable electricity companies in Ohio and questionable energy policy. Usually I would say write a strongly worded letter to the public utility commission. Your stellar electric utility was responsible for the great blackout of 2003. It is a classic story: https://www.nerc.com/pa/rrm/ea/August 14 2003 Blackout Investigation DL/NERC_Final_Blackout_Report_07_13_04.pdf Then came the bribery scandal.

If it is a Hypex OEM plate amp, maybe your buddies at the ampco can slip you a schematic and PCB layout by a back channel. There is probably a part number inside.
 
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I also think I need Tom to clarify what he means by dirty mains. In his responses he references how there are "many variables" connected to home circuits that could be causing the hum people sometimes experience, such as "projectors, fridges, cable boxes" etc. Even giving examples of how someone disconnecting an HDMI cable from their receiver makes the hum go away. Which we usually know as ground loop hum. That would make sense, except I have been trying to reiterate that the hum I have is with no source cable connected (only the AC power cord).

Unless I am missing something and a hum inducing anomaly can exist via the hot and/or neutral AC wiring (no ground wire involved)?
 
If it is a Hypex OEM plate amp, maybe your buddies at the ampco can slip you a schematic and PCB layout by a back channel. There is probably a part number inside.
It is an Ice Power 700AS1 (x2) amp design.
 
Note to self: Never buy a PSA subwoofer (I was actually considering upgrading my dual SVS SB2000 to dual PSA's S1512M). I've now decided to go with four SVS SB1000 Pro instead for nearly the same price...
 
Note to self: Never buy a PSA subwoofer (I was actually considering upgrading my dual SVS SB2000 to dual PSA's S1512M). I've now decided to go with four SVS SB1000 Pro instead for nearly the same

Note to self: Never buy a PSA subwoofer (I was actually considering upgrading my dual SVS SB2000 to dual PSA's S1512M). I've now decided to go with four SVS SB1000 Pro instead for nearly the same price...
Not sure you can say that as a definite answer. Many company's have problems which they don't even know about and when it comes to their attention they fix it. Some don't but real company's do.. let's see what happens and then make judgment .

Remember the PSA guy is part of SVS . Hopefully they catch wind of what's going on and they address the problem.

Cheers.
 
I also think I need Tom to clarify what he means by dirty mains.

We've all heard that term before and it is largely just a marketing term to get the unwary to part with money for something that doesn't really do anything. @amirm's reviews of power conditioners show us that all AC mains have a spray of harmonics and noise—they are an unavoidable fact. Normally, in a properly designed power supply, that noise doesn't get into the signal path. Here it seems, that's not the case.

The signal wiring for both the unbalanced and the balanced inputs should be shielded twisted pair—it's not. There also seems to be a problem with the ground layout on their input board that is causing a lot of noise to be induced into the signal ground:
Only other interesting thing I found is if I don't have any XLR source connected to the inputs and I touch my hand to the plate amp chassis, the hum nearly disappears.
You touching the plate amp chassis drains away the circulating currents enough that the noise is reduced.

This is a chance for them to take a look at the design and fix it. It is now on them to take action—or not.
 
@Buckeye Amps, I see the mentioning of DSP noise-gating here and over on the AVS support forum. We can see the DSP on your input board pics along with the micro-USB port. Has there been any offer to make that DSP software and instructions for use available to you to change the noise gate setting?
 
@Buckeye Amps, I see the mentioning of DSP noise-gating here and over on the AVS support forum. We can see the DSP on your input board pics along with the micro-USB port. Has there been any offer to make that DSP software and instructions for use available to you to change the noise gate setting?
I asked to try it myself but was told no. Tom did offer to send an amp with a different nosie gate which has worked for others in the past. BUT the caveat is that sometimes the sub will shut off during content and people who have used the stricter noise gate have reported it sounds "worse" then distortion when it happens. So from what I've read/been told it isn't the best fix as it has its own drawback.
 
It's a cop-out.
Yea. I'm finishing my convo on the PSA thread as it is just turning into Tom coming back to "Well how can you explain some people how moved to a new house and the problem is gone" or "I can't reproduce any hum issues in my workshop" sprinkled in with "Every house has a different mixture of devices so you can't say mains issues are not affected by all these variables".

Good news is the subs are all in place and preliminary quick measure shows they are going to perform nicely, after all the hassle.
 
To be fair I don't think Tom is making a bad product. By all measures, they seem stellar. To address these issues though, which have been going on for literal years, he could go to a different amp. He could use Hypex or go custom like Brian at Rythmik, but the subs would get more expensive. I am sure there are other options but he likely gets the best bang for the buck with the modules he is using, and he really needs and relies on the DSP capability. Even if it is the house, there may be other options to modify the existing amps to make them more resilient but I'm no expert there. Just playing devil's advocate.
 
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