Hum through AC mains in subwoofer (not ground hum)

[JustJones]

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.

Yet, somehow you ended up with 4 that have the hum? Coincidence, bad luck?

 

[GXAlan]

Oh really?

Tom Vodhanel, President, Power Sound Audio

Tom Vodhanel is president and founder of Power Sound Audio, an Ohio-based company that specializes in subwoofers and sells direct through its website. Tom is also known as the “V” in SVS, another company that started out as a subwoofer specialist, and which he co-founded. Excerpts from this...

www.soundandvision.com

 

[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.

I did go poking around the best I could with my multi meter and verified the hot and cold do not connect to chassis ground at all. Only pin 1 and the ground/shield of the rca eventually make their way to chassis ground.
I also did a brief rewiring of the XLR to mirror "proper" pin 1 of Hypex amps, where pin 1 of the XLR input goes to chassis ground and the ground wire of the PCB input board/amp modules goes to chassis ground near the XLR body...no change.

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. But once a source is connected, hum comes back (this is with all wiring back to original config and no shorting used).
Attached a ground wire from the plate amp chassis to an earth ground significantly increases the hum.

So as of right now, the three "fixes" are either of the following:
- leave all wiring stock and short one RCA input and one XLR input (no hum)
- swap the hot and cold of one XLR input (no hum)
- disconnect the internal RCA wiring harness and short just the unused XLR input (no hum)

Of those three scenarios, any thoughts as to which is a better long term solution (if the underlying problem is never found)?

 

[Chromatischism]

Over the years I've read quite a few comments/complaints about humming PSA subs from either the ICE amps or the drivers they are using, or a combination of the two. Never with Rythmik.

- leave all wiring stock and short one RCA input and one XLR input (no hum)

I can't offer insight as to the best/safest solution. But doesn't this give a clue as to what could be happening internally?

 

[Buckeye Amps]

I forgot a third option as a "fix":

- Disconnect the internal RCA wiring harness and short just the unused XLR input

 

[Sokel]

Over the years I've read quite a few comments/complaints about humming PSA subs from either the ICE amps or the drivers they are using, or a combination of the two. Never with Rythmik.


I can't offer insight as to the best/safest solution. But doesn't this give a clue as to what could be happening internally?

How can a driver produce hum of it's own?
That's the first time I ever heard this.

Has to do with shielding for specific applications (near EMI/RFI sources for example) or in general?

 

[Chromatischism]

How can a driver produce hum of it's own?

It is a combination of the two. The amp plus the sensitive driver making it more audible.

 

[Sokel]

It is a combination of the two. The amp plus the sensitive driver making it more audible.

That makes sense.
But sensitive to what?That's what I'm trying to learn.

 

[Chromatischism]

That makes sense.
But sensitive to what?That's what I'm trying to learn.

Sensitivity to input signals; sensitivity in the traditional electrical/audio sense of the word.

 

[Buckeye Amps]

One more piece of information:

When I swap the hot and cold wires for the unused XLR input, the RCA wiring harness becomes highly susceptible to noise from the IcePower module.

What I mean is with all wiring as it came from PSA, if I move the RCA wiring harness close to the amp module itself the hum barely increases, if at all.
But as soon as I swap the XLR hot and cold on the unused XLR input, the RCA wiring harness is the sole factor for the hum. Positioning it about 6 inches away from the amp module, no hum. Putting it within 1 inch of the module, severe hum.

 

[Buckeye Amps]

Without a schematic (which I will not be able to get), I'm going to settle one of the below workarounds. Any opinion on which is the best of the bunch in terms of not having possible detrimental side effects, let me know:

A) Disconnect the RCA wiring harness internally and use an XLR shorting connector on the second/unused XLR input

B) Swap the wiring for Pins 2 and 3 (hot and cold) of the second/unused XLR connectors

 

[Sokel]

But as soon as I swap the XLR hot and cold on the unused XLR input, the RCA wiring harness is the sole factor for the hum. Positioning it about 6 inches away from the amp module, no hum. Putting it within 1 inch of the module, severe hum.

If I got that right and if RCA wiring is according the usual way,tip - hot/sleeve - cold+ground swapping XLR's hot and cold is something you may don't want to do.

 

[sam_adams]

Without a schematic

Can you post a few pix of their board and the wiring from the board to the amp in stock condition?

 

[Buckeye Amps]

Can you post a few pix of their board and the wiring from the board to the amp in stock condition?

See attached

 

[Sokel]

That's what interests you.
Now work your way backwards:

(@restorer-john better not see the solderwork of the input board )

 

[Speedskater]

Balanced signals are/may be Positive & Negative not Hot & Cold.
"Cold" implies at the audio circuit 'common' potential.

 

[Buckeye Amps]

That's what interests you.
Now work your way backwards:

View attachment 395265

(@restorer-john better not see the solderwork of the input board )

Will try getting back to this later. Taking a break to get my own work done.

Regarding the input board, all I have found out is it was designed by a lab out of Canada (with a contact name of Jim).

 

[Salt]

Just halluzinating, but if the - (negative) of the XLR is simply fixed to ground ('common') for ease of unbalancing, and then the inputs are inverted: could this introduce hum?

 

[Speedskater]

That's not good engineering practice. In fact, it's stupid.
And even thou it has an XLR connector, it's not a balanced input.

 

[Salt]

And could this be the reason for hum?