OP
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Another piece to the possible puzzle: lowering the Crossover setting on the subwoofer plate amp reduces the hum.
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Hum through AC mains in subwoofer (not ground hum)
- Thread starter Buckeye Amps
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OP
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I'm going to try a few more things today:
- taking one of the subs to a friend's house to see if hum still happens
- shorting one RCA and ome XLR input while connecting my source via XLR
- using a ground wire from the plate amp body to a ground source near the amp
Depending on what works/doesn't work, I may open up the plate and start looking more closely at the wiring and pinouts chosen.
Based on responses from certain people over in the AVS official PSA thread, I'm kind of committed now as I really don't think the answer of "just turn the Gain down until you can't hear it from the seating" is acceptable.
- taking one of the subs to a friend's house to see if hum still happens
- shorting one RCA and ome XLR input while connecting my source via XLR
- using a ground wire from the plate amp body to a ground source near the amp
Depending on what works/doesn't work, I may open up the plate and start looking more closely at the wiring and pinouts chosen.
Based on responses from certain people over in the AVS official PSA thread, I'm kind of committed now as I really don't think the answer of "just turn the Gain down until you can't hear it from the seating" is acceptable.
OP
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@restorer-john
I know you're busy but would love if you can chime in as I piece together results. You always seem to have a nack for sniffing out issues it seems.
Thanks!
I know you're busy but would love if you can chime in as I piece together results. You always seem to have a nack for sniffing out issues it seems.
Thanks!
Agree.
It doesn’t happen to everyone with PSA subs, so you definitely need to figure out what’s up. When I was doing my run of measuring gear, how often grounding n needed to be done.
Two prong electronic under test with laptop on battery power and I would still get a 60 Hz spike to disappear by grounding stuff. (phono lug of the integrated to the XLR ground pin)
My Meyer Sound gear is silly sensitive to ground. I can be running XLR to XLR and have issues too!
Post in thread 'Balanced interconnection and ground'
https://audiosciencereview.com/foru...interconnection-and-ground.51570/post-1857877
100% of these were solved when I grounded things with an extra wire
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Stop moving around the sub to different houses. That is pure non-sense.
You seem to ignore the gain setting from the primary source to the subs final (D-) amp stage.
First you have to bump the souce output as high as possible without clipping. If you miss that, you simply sabotage the system. There should be no amplification of the signal after that. Any amplification will add noise, reducing level will reduce noise too.
The gain has to be reduced in the last option to do so, before it is sent from the sub's internal DSP to the amp. This whole chain has to be matched to the maximum SPL you will have in your room.
I have seen even sound people with decades of experience, that stuggle to get a mixed digital-analog-digital-analog chain right.
You seem to ignore the gain setting from the primary source to the subs final (D-) amp stage.
First you have to bump the souce output as high as possible without clipping. If you miss that, you simply sabotage the system. There should be no amplification of the signal after that. Any amplification will add noise, reducing level will reduce noise too.
The gain has to be reduced in the last option to do so, before it is sent from the sub's internal DSP to the amp. This whole chain has to be matched to the maximum SPL you will have in your room.
I have seen even sound people with decades of experience, that stuggle to get a mixed digital-analog-digital-analog chain right.
OP
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Results so far:
- Moving the sub to a completely different electrical source (house), hum is still present
- With JUST the power cord plugged in and one of the RCA inputs shorted, the hum disappears
- With JUST the power cord plugged in and one XLR input shorted, hum is still present
- With the power cord and XLR cable from source (Anthem AVM 90) connected while shorting one RCA input, hum is still present
- With the power cord and just a short XLR cable connected (no connection to source) while shorting one RCA input, hum is still present
Interesting observation:
- With JUST the power cord plugged in, if I simply touch the XLR jack push tab (tab used to release an XLR cable), the hum increases significantly
I am really starting to suspect an internal grounding issue. My next step is to attach a simple ground wire to somewhere on the internal side of the plate amp (bare metal) and then to a grounding lug externally/ground screw on an electrical outplate plate.
- Moving the sub to a completely different electrical source (house), hum is still present
- With JUST the power cord plugged in and one of the RCA inputs shorted, the hum disappears
- With JUST the power cord plugged in and one XLR input shorted, hum is still present
- With the power cord and XLR cable from source (Anthem AVM 90) connected while shorting one RCA input, hum is still present
- With the power cord and just a short XLR cable connected (no connection to source) while shorting one RCA input, hum is still present
Interesting observation:
- With JUST the power cord plugged in, if I simply touch the XLR jack push tab (tab used to release an XLR cable), the hum increases significantly
I am really starting to suspect an internal grounding issue. My next step is to attach a simple ground wire to somewhere on the internal side of the plate amp (bare metal) and then to a grounding lug externally/ground screw on an electrical outplate plate.
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More results:
- Grounding the plate amp chassis increases the hum
- Disconnecting the internal XLR cable (so the XLR input PCB is no longer connected to the main amp module/PCB interface) significantly decreases the hum to nearly inaudible at full gain
At this point I am fairly convinced the issue is the XLR grounding approach.
- Grounding the plate amp chassis increases the hum
- Disconnecting the internal XLR cable (so the XLR input PCB is no longer connected to the main amp module/PCB interface) significantly decreases the hum to nearly inaudible at full gain
At this point I am fairly convinced the issue is the XLR grounding approach.
AVM90 has a chassis ground screw and is two prong power.
If you had a Panamax power center you could just connect a wire from the AVM90 to the Panamax and fix your problem.
$5 bet it fixes your problem.
You should be able to just connect the AVM90 chassis ground screw to the ground pin of an actual outlet since that’s all that is happening internally on the Panamax but I don’t know what counts as code.
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This is all 100% completely independent of the AVM. I'm not even doing my current testing on the same breaker panel as my HT room right now.
“Disconnecting the internal XLR cable (so the XLR input PCB is no longer connected to the main amp module/PCB interface) significantly decreases the hum to nearly inaudible at full gain“
The amp receiving no signal is OK.
Once you have the input PCB, it is picking up noise because there XLR is picking up noise.
“With JUST the power cord plugged in and one of the RCA inputs shorted, the hum disappears”
When the ground is solve, no problem.
“ With JUST the power cord plugged in and one XLR input shorted, hum is still present”
Are you just shorting the +/- or is the -/ground connected?
All I am saying is that everything you are describing to me sounds like my own experience with Meyer Sound (XLR) and both Arcam (RCA) and Yamaha (XLR) sources and both my Arcam and Yamaha problems disappeared when I grounded them to my Panamax surge protector (Arcam is black speaker terminal and Yamaha is the phono ground screw).
Can you lift the ground of the sub and test connected to the AVM90?
(hides from stones being thrown)
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There is no ground to lift (2 prong power cord)
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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
Do you have a mains DC remover? Something like the iFi DC Blocker+?
ifi-audio.com
(again hides from stones being thrown)
DC Blocker+
Say goodbye to transformer hum and enjoy a pure audio experience with the DC Blocker+. This advanced DC offset filter is engineered to eliminate unwanted noise and interference, making it essential for high-fidelity audio systems. With the DC Blocker+, your amplifiers and DACs can perform...
ifi-audio.com
(again hides from stones being thrown)
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Yea. I had to use such a thing on my Rythmik subs. No dice hereDo you have a mains DC remover? Something like the iFi DC Blocker+?
DC Blocker+
Say goodbye to transformer hum and enjoy a pure audio experience with the DC Blocker+. This advanced DC offset filter is engineered to eliminate unwanted noise and interference, making it essential for high-fidelity audio systems. With the DC Blocker+, your amplifiers and DACs can perform...
(again hides from stones being thrown)
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I think I got it, just need to make a cable to double check.
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So the RCA AND unused XLR input on the plate amp are indeed acting as antennas.
Once I hooked the subwoofer back up to my Anthem AVM 90 via one XLR cable (using the LFE XLR input on the sub amp), shorting one of the RCA inputs and the unused XLR input results in a hum that is only audible from 6 inches away at full gain. At half gain it is dead silent.
Shorting both RCA inputs brings the hum back. Only shorting either one RCA or the unused XLR alone and the hum is still there. You have to short both one RCA and the unused XLR. Voila, silence.
Dumb question but is this safe/non-performance damaging to do long term?
Once I hooked the subwoofer back up to my Anthem AVM 90 via one XLR cable (using the LFE XLR input on the sub amp), shorting one of the RCA inputs and the unused XLR input results in a hum that is only audible from 6 inches away at full gain. At half gain it is dead silent.
Shorting both RCA inputs brings the hum back. Only shorting either one RCA or the unused XLR alone and the hum is still there. You have to short both one RCA and the unused XLR. Voila, silence.
Dumb question but is this safe/non-performance damaging to do long term?
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Attached is a picture of what I mean by shorting one of the RCA and the unused XLR.
For the RCA, I just cut an existing RCA cable I had short and then simply tied the two wires together (so the ground and hot of the RCA are tied together).
For the XLR, I did the same approach but only tied the Hot and Cold (Pin 2 and 3) of the XLR cable together. The ground and shield of the XLR should NOT be tied to anything (so pin 1 and the shield should be floating).
On High gain, the hum is gone completely.
A side note I shared with Tom is on the one plate amp I took off, I noticed the RCA and XLR wiring harnesses were wrapped together and the RCA wiring was loose (not twisted or wrapped). By separating the RCA and XLR wiring and twisting the RCA wiring tightly, this allowed for the zero hum at High gain (when also using the shorting connectors). By comparison, just using the shorting connectors on a sub I did not open up, there is a very slight hum at High gain.
For the RCA, I just cut an existing RCA cable I had short and then simply tied the two wires together (so the ground and hot of the RCA are tied together).
For the XLR, I did the same approach but only tied the Hot and Cold (Pin 2 and 3) of the XLR cable together. The ground and shield of the XLR should NOT be tied to anything (so pin 1 and the shield should be floating).
On High gain, the hum is gone completely.
A side note I shared with Tom is on the one plate amp I took off, I noticed the RCA and XLR wiring harnesses were wrapped together and the RCA wiring was loose (not twisted or wrapped). By separating the RCA and XLR wiring and twisting the RCA wiring tightly, this allowed for the zero hum at High gain (when also using the shorting connectors). By comparison, just using the shorting connectors on a sub I did not open up, there is a very slight hum at High gain.
