Help! Weirdest ground loop yet!
SolidSqual
Posts: 5,218
I have the issue described below.
http://wiki.slimdevices.com/index.php/BalancedPowerAmps
Balanced Power Amps
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If you decide to connect your Squeezebox directly to a balanced power amp, you may well encounter a grounding issue that causes a loud hum.
Let's first consider the traditional way to connect an unbalanced output to a balanced input. The signal from the output goes to one of the signal inputs (usually the "hot" input on pin 2 of an XLR, but it could just as easily be to the "cold" input on pin 3). The ground from the source is connected to the other signal input. The screen of the interconnect cable is usually only connected at the balanced input end (on pin 1) and is left floating at the source end in order to avoid ground loops.
This arrangement causes the balanced input to regard the difference between the signal and ground as the signal (and since the ground is nominally at 0V, this difference is indeed just the desired signal).
In most systems where an unbalanced source drives a balanced power amp, the source is a preamp, and preamps tend to have a ground. But if you use a source which has a floating ground, such as a Squeezebox, then any mains ripple on its ground line doesn't get shunted to earth and appears to the balanced power amp as part of the signal and gets amplified along with everything else. The result is a loud hum.
The solution would appear to be obvious: connect the screen of the interconnect to the ground at the source end. This will shunt the Squeezebox's ground to earth via the power amp's ground. And in many cases this will indeed solve the problem.
But there is an added subtlety. Some balanced power amps don't have the screen of their XLR inputs connected directly to ground. (For example, the power amps in my ATC speakers have a 47 Ohm resistor between pin 1 of their XLR inputs and ground. I don't know why this is so - I'm not an amplifier designer, but I'm sure ATC have good reasons for including it). So connecting up the screen at the Squeezebox end only establishes a partial shunt to earth. The hum is reduced, but not eliminated. The solution here is to connect the ground plane of the Squeezebox to the mains earth - preferably the same one used by the power amp. I used the screen of the Squeezebox's COAX SPDIF output, which was not in use in my system, for this purpose.
First, What is a screen? Second, can someone tell me how to do or what to do in regards to the paragraph above?
http://wiki.slimdevices.com/index.php/BalancedPowerAmps
Balanced Power Amps
From SqueezeboxWiki
(Redirected from BalancedPowerAmps)
Jump to: navigation, search
If you decide to connect your Squeezebox directly to a balanced power amp, you may well encounter a grounding issue that causes a loud hum.
Let's first consider the traditional way to connect an unbalanced output to a balanced input. The signal from the output goes to one of the signal inputs (usually the "hot" input on pin 2 of an XLR, but it could just as easily be to the "cold" input on pin 3). The ground from the source is connected to the other signal input. The screen of the interconnect cable is usually only connected at the balanced input end (on pin 1) and is left floating at the source end in order to avoid ground loops.
This arrangement causes the balanced input to regard the difference between the signal and ground as the signal (and since the ground is nominally at 0V, this difference is indeed just the desired signal).
In most systems where an unbalanced source drives a balanced power amp, the source is a preamp, and preamps tend to have a ground. But if you use a source which has a floating ground, such as a Squeezebox, then any mains ripple on its ground line doesn't get shunted to earth and appears to the balanced power amp as part of the signal and gets amplified along with everything else. The result is a loud hum.
The solution would appear to be obvious: connect the screen of the interconnect to the ground at the source end. This will shunt the Squeezebox's ground to earth via the power amp's ground. And in many cases this will indeed solve the problem.
But there is an added subtlety. Some balanced power amps don't have the screen of their XLR inputs connected directly to ground. (For example, the power amps in my ATC speakers have a 47 Ohm resistor between pin 1 of their XLR inputs and ground. I don't know why this is so - I'm not an amplifier designer, but I'm sure ATC have good reasons for including it). So connecting up the screen at the Squeezebox end only establishes a partial shunt to earth. The hum is reduced, but not eliminated. The solution here is to connect the ground plane of the Squeezebox to the mains earth - preferably the same one used by the power amp. I used the screen of the Squeezebox's COAX SPDIF output, which was not in use in my system, for this purpose.
First, What is a screen? Second, can someone tell me how to do or what to do in regards to the paragraph above?
Post edited by SolidSqual on
Comments
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It's the mesh part of the XLR cable that usually goes to ground.
On the squeeze box, connect the outer part of any of the RCA's to the outlet ground. Which squeeze box do you have?Gallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i -
I have the duet. What wire should I use to make the connection? How should I connect it to the RCA?
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This will make you cringe
Since you're not using the digital output, plug an RCA into it, then attach the ring of the RCA to the Pin on the wall outlet. Least, that's what those instructions are telling you to do. Before you try that, put the ring on that RCA to any bare metal on your amp and see if it does the trick.Gallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i -
Wait, but the digital coax is plugged into my DAC.
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I wonder if an Apple TV or Sonos would have this same issue?
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and your balanced amp is hooked to what?Gallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i -
My amp is not balanced.
The SB goes to my DAC which goes to my battery pre which goes to my Behringer External XO (uses XLRs) which goes to my amps. -
Ok. You don't have the issue described in the wiki you posted. You DO have a ground loop- probably between the pre and the DCX2496. Get some bare wire and attach it from a spare input on the pre to bare metal on the XO and see what happens.Gallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i -
When I unplug the SB, the system is dead silent.
I'll try your suggestion though. -
Typically you don't get ground loop over a digital connection... are it's analogs hooked up to anything?Gallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i -
nope nothing.
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Ok, that's just weird. Anyhow, the easiest way to find it is to just take speaker wire and connect it to the ground on a component to the frame on the next one up the chain till you hear the hum drop.
The only other thing I can think of is that you're not hearing ground loop, but rather the SqueezeBox is throwing out EMI that something else is picking up. With the efficiency of your speakers, that's a definite possibility. Can you swap out the Coax for optical? If it's ground loop, then the SqueezeBox will be electrically isolated with an optical conection.Gallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i -
I just hit all my stuff with a hammer until the hum goes away...
Nick -
nikolas812 wrote: »I just hit all my stuff with a hammer until the hum goes away...
Nick
I'm getting there . . . -
Ok, that's just weird. Anyhow, the easiest way to find it is to just take speaker wire and connect it to the ground on a component to the frame on the next one up the chain till you hear the hum drop.
The only other thing I can think of is that you're not hearing ground loop, but rather the SqueezeBox is throwing out EMI that something else is picking up. With the efficiency of your speakers, that's a definite possibility. Can you swap out the Coax for optical? If it's ground loop, then the SqueezeBox will be electrically isolated with an optical conection.
Thanks for your help. I'm gonna give these suggestions a try.
On a side note, I checked out an Apple TV and an Apple Airport today. IMHO, Apple dropped the ball on both those units in terms of quality and features. Oh well . . . if this doesn't work, I'm buying a transport and sit down for a long drink with my Havana DAC. -
Ok, I'm going to take the whole system apart and build it up one component at a time. If this doesn't work then there will be a Duet for Sale with a massive Polk discount.
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No prob. Definitely start by using an optical cable to go to the DAC. That'll tell you right off if that's the source. It's possible that the DAC has a muting function when there's no signal. This could make it seem that the problem goes away when you unplug the SB, but it's really just the mute kicking in.
Have you considered going directly to the DCX and cutting out the digital-analog-digital and 2 pieces of gear in your signal chain? You can easily set up a preset for this- you could leave the SB hooked up to into input A (and have that set as a digital input), then your other sources would go through the preamp and into Input B and C on the DCX. All you'd have to do is switch between two presets on the DCX.
Just DL the remote software from here:
DCX Remote SW
Copy your configs to a new slot and set up an identical one w/ digital input from A.
If none of that made sense, if you can get as far as saving the current configs (for whatever distances you use), send them to me and I can make you a digital/analog config that you can swap between.Gallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i -
Ok here's what I found out.
When the Digital Coax is used on the Duet, the ground loop is amplified.
Unplugging the coax results in a much quieter hum.
A ground loop still remains.
So, I unplug my new DAC, the ground loops goes away. I plug it back in, the ground loop returns.
I put a cheater plug on the DAC, the ground loop remains.
In addition to all this stuff, I'm getting noise from the Elevator next to my apartment through my power cords. I can actually hear the noise increase and stop as the elevator goes up or down and then stops. This was never an issue when I had my PS Audio PPP.
So, one thing is for sure, I need to invest in another power conditioner. But, what I'm not sure about is how to get rid of the low hum coming from the DAC?
elevator noise -
For Duet/DAC hum, try putting the Duet to ground- put the ring on the analog RCA to the power outlet ground (or attach it to the frame of the DAC).
For the DAC hum, make sure that it's ground loop and not the tubes picking up EMI. Do the same thing with your pre-amp. put a spare RCA ring to the power outlet ground and see if the hum goes down. The problem is that you've got a bad mix of "Floating" ground gear, XLR and SE which is always a recipe for ground loop.Gallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i -
Just remembered this paper from passDIY on ground loops- great reference to have around:
http://www.passdiy.com/pdf/articles/ground-loops.pdfGallo Ref 3.1 : Bryston 4b SST : Musical fidelity CD Pre : VPI HW-19
Gallo Ref AV, Frankengallo Ref 3, LC60i : Bryston 9b SST : Meridian 565
Jordan JX92s : MF X-T100 : Xray v8
Backburner:Krell KAV-300i
