[SOLVED] Ground loop between grounded Hypex NC400 DIY amp and ungrounded Denon 3700X

[KMO]

Now, this looks potentially promising. (And the only one I've found so far).

Ultimate Pro Audio Ltd

Custom made to measure pro audio leads. Van Damme KLOTZ & HQ cables, Neutrik connectors for high end quality that lasts and out performs many other leads.

www.ultimateproaudio.com

Security measure

www.ebay.co.uk

They are listing custom RCA->XLR cables (all the lengths and all the colours!), but they're using single-wire cable (Van Damme Pro Grade Classic XKE Instrument Cable).

But they do also have twin-conductor Van Damme Tour Grade Classic XKE Microphone Cable in all the colours for their XLR->TRS cables. (And even 4-wire Starquad cable!)

So they could make correct RCA->XLR leads using the bits they have, and should hopefully be about £12 each (1.5m).

Might be worth a look. I've got an Apollon Pure 5 multichannel amp on the way, and that has switchable RCA inputs, so maybe my RCA cables will work fine. But if I do have noise problems, I might turn to them.

I'm a sucker just for the thought of getting a properly colour-coded set of white/red/green/blue/grey cables and/or XLR plugs.

 

[MASKINEN]

I use a Purifi 3 channel amp with a hum/ buzz and trying to solve it by modifying the Monoprice RCA-XLR cables.

Would it be safe to cut pin1 so the shield is floating on XLR side?


This is the Monoprice RCA-XLR cable inside the RCA side.
Hot is signal, cold is tied with shield and drain (?)


I shortened the cables to 75 cm and resoldered the same way as before.


Untouched XLR side with pin1 connected to cable shield (cable housing ground).
I later removed the bridge between pin1 and cable housing ground).
That didn’t make any change.


I made the cables a little more attractive…

 

[DonH56]

Strange design decisions from Cordial right there.

1. Why did thy uses Twisted pair in this cases.
2. Why did they doubled up the signal conductor
3. If they have a 3 conductor calculable to start with why don’t they do it the proper way and make the GND to negative connection on the CRA side.

They probably have bulk star-quad cable they use for everything instead of stocking different cable for different applications. Cheaper to buy 1000 feet of one cable than 100 feet of ten different types. That would explain (1) and (2). As for (3), shield does not always tie to signal ground, particularly with a balanced connection. It may be OK on the input side, but you generally do not want to short the (-) output of the source to ground unless you know it will not upset things.

 

[Lambda]

to 1. they have and sell a whole selection of different Coaxial cables.

Bulk Cables

www.cordial-cables.com

2. is also not relay answered with this. If i would double up a conductor i would double up on ground not signal.

3.

, shield does not always tie to signal ground, particularly with a balanced connection. It may be OK on the input side, but you generally do not want to short the (-) output of the source to ground unless you know it will not upset things.

I’m nut sure if getting your answer there correctly.?
they are connecting (-) to ground. they just doing it on the XLR side not on the RCA side.

 

[KMO]

I use a Purifi 3 channel amp with a hum/ buzz and trying to solve it by modifying the Monoprice RCA-XLR cables.

Would it be safe to cut pin1 so the shield is floating on XLR side?

View attachment 172927
This is the Monoprice RCA-XLR cable inside the RCA side.
Hot is signal, cold is tied with shield and drain (?)

View attachment 172926

Looks like they're well wired. The shell->pin 1 connection is debated - to the extent I think that it doesn't really matter.

But even with that wiring, you can still have ground loop problems, particularly if the destination device has pin 1 connected to signal ground. What amp are you using? (Not in your sig?)

This Rane document suggests your next move is to disconnect the shield at the RCA end.

It is true that connecting both ends of the shield is theoretically the best way to interconnect equipment -- though this assumes the interconnected equipment is internally grounded properly. Since most equipment is not internally grounded properly, connecting both ends of the shield is not often practiced, since doing so usually creates noisy interconnections.

(As I understand it, in a symmetrical cable you would rather disconnect the input end, but in this case as the input is the only end that separates the shield and signal, you disconnect at the output, to keep the shield from the signal.).

 

[MASKINEN]

Looks like they're well wired. The shell->pin 1 connection is debated - to the extent I think that it doesn't really matter.

But even with that wiring, you can still have ground loop problems, particularly if the destination device has pin 1 connected to signal ground. What amp are you using? (Not in your sig?)

This Rane document suggests your next move is to disconnect the shield at the RCA end.


View attachment 173004
(As I understand it, in a symmetrical cable you would rather disconnect the input end, but in this case as the input is the only end that separates the shield and signal, you disconnect at the output, to keep the shield from the signal.).

What is said about pin1 and RCA shell?

I’m going to test to float pin1 on XLR side but if pin1 is connected to RCA shell, would the idea of floating pin1 on RCA shell work as intended? What you write makes sense keeping the shield from the signal pin2.

I know that Hypex for one mentions that if you have a hum with pin1 connected at XLR then you can just float it. But I don’t know if that’s only for XLR-XLR.

I use a Purifi based amplifier with only XLR inputs.

Just made three new cables using Neutrik connectors and the microphone cable from Monoprice. Connected like original Monoprice RCA-XLR but I’ll test with pin1 floating on XLR side during the weekend.

 

[KMO]

What is said about pin1 and RCA shell?

I’m going to test to float pin1 on XLR side but if pin1 is connected to RCA shell, would the idea of floating pin1 on RCA shell work as intended? What you write makes sense keeping the shield from the signal pin2.

I know that Hypex for one mentions that if you have a hum with pin1 connected at XLR then you can just float it. But I don’t know if that’s only for XLR-XLR.

I use a Purifi based amplifier with only XLR inputs.

Just made three new cables using Neutrik connectors and the microphone cable from Monoprice. Connected like original Monoprice RCA-XLR but I’ll test with pin1 floating on XLR side during the weekend.

I guess you meant to write "would the idea of floating pin1 in the XLR plug work as intended"?

Maybe. Which I think is the best answer you're going to get for any mod. Depends on the rest of the system. It's got a better chance of working with a balanced input rather than this unbalanced setup, unfortunately. The earth currents will at least have to find a different path, and maybe the effect will be less bad.

You may as well also test disconnecting shield at the RCA end instead too and compare.

 

[notabenem]

Since my new SVS PB-2000 arrived, I started to deal with issues, like this here.
As soon as I turn my sub on, i hear a constant hum/buzz. I have it connected to 3700x using RCA cable. The noise gets stronger with the volume. If I disconnect either end of the cable, the noise is gone. A spectrum analyzer has shown a clear 50Hz sound coming out of it, which matches the mains frequency.
Tried to move the cable away from power lines, but it had no effect. Changed the cable to a dual-shielded RCA, and it helped a bit - i think, but not too much. Both devices are in separate outlets, but those outlets are literally next to each other, so I figure they must share cabling... (!= they do, I just don't know). The amp has a single HDMI input connected: Chromecast with Google TV. Will try disconnecting that one next, but if it's that one, I wonder, what are my options?

 

[anphex]

When exatcly does the Hum/Buzz first appear? When you turn on the Sub? Even when it isn't connected? Does the Hum/Buzz "move" to other speakers when you connect the sub?

 

[MASKINEN]

I guess you meant to write "would the idea of floating pin1 in the XLR plug work as intended"?

Maybe. Which I think is the best answer you're going to get for any mod. Depends on the rest of the system. It's got a better chance of working with a balanced input rather than this unbalanced setup, unfortunately. The earth currents will at least have to find a different path, and maybe the effect will be less bad.

You may as well also test disconnecting shield at the RCA end instead too and compare.

Yes that’s what I meant to write. Was busy cooking and soldering while writing

Thank you for your thought. Appreciate it since I haven’t tried to float a pin on a cable before. Need all the advice and thoughts I can get.

If floating pin1 at XLR doesn’t work I can try to remove shield at RCA but keep it connected on XLR side to pin1 I suppose.

 

[KMO]

If floating pin1 at XLR doesn’t work I can try to remove shield at RCA but keep it connected on XLR side to pin1 I suppose.

I'm not sure why you think the XLR pin 1 disconnection will be better. The sources you've seen talking about doing it at the input are all (I'm pretty sure) assuming XLR->XLR or possibly single-conductor RCA->XLR.

For XLR->XLR you could disconnect either end's pin 1, and it's marginally better to do the input end (apparently, I don't recall why!)

For single-conductor RCA->XLR, there's no choice - the only thing you can disconnect is XLR pin 1.

But for your specific case of double-conductor RCA->XLR, disconnecting the shield at RCA end should be better - by more of a margin than the XLR->XLR end choice, I believe.

 

[MASKINEN]

I'm not sure why you think the XLR pin 1 disconnection will be better. The sources you've seen talking about doing it at the input are all (I'm pretty sure) assuming XLR->XLR or possibly single-conductor RCA->XLR.

For XLR->XLR you could disconnect either end's pin 1, and it's marginally better to do the input end (apparently, I don't recall why!)

For single-conductor RCA->XLR, there's no choice - the only thing you can disconnect is XLR pin 1.

But for your specific case of double-conductor RCA->XLR, disconnecting the shield at RCA end should be better - by more of a margin than the XLR->XLR end choice, I believe.

I’m not thinking I would be better, I was mostly interested in actually testing both ways of floating the shield. I don’t know if there would be any real difference by floating it on the RCA side or at XLR side. Probably not.

To the matter I will try to disconnect the shield and see if the hum gets removed. Both my processor and the Purifi amp is grounded by 3 prong mains IEC. If that would matter.

 

[notabenem]

When exatcly does the Hum/Buzz first appear? When you turn on the Sub? Even when it isn't connected? Does the Hum/Buzz "move" to other speakers when you connect the sub?

Shortly (~3s) after I turn it on. It's not there if I unplug the RCA cable. No, it does not move to other speakers.
The buzz is also there even if I completely turn off the AMP (but not the sub). It is there if I unplug the AMP and all the connected devices to it from the plug. It is simply enough if the RCA cable connects the AMP and the sub and the sub is on.

 

[DonH56]

Shortly (~3s) after I turn it on. It's not there if I unplug the RCA cable. No, it does not move to other speakers.
The buzz is also there even if I completely turn off the AMP (but not the sub). It is there if I unplug the AMP and all the connected devices to it from the plug. It is simply enough if the RCA cable connects the AMP and the sub and the sub is on.

A line-level ground isolator will probably solve the problem. Numerous ones available on Amazon, Parts Express, Monoprice, etc.

 

[notabenem]

Tried another (better shielded) cables. buzz is much more silent.

 

[MASKINEN]

I'm not sure why you think the XLR pin 1 disconnection will be better. The sources you've seen talking about doing it at the input are all (I'm pretty sure) assuming XLR->XLR or possibly single-conductor RCA->XLR.

For XLR->XLR you could disconnect either end's pin 1, and it's marginally better to do the input end (apparently, I don't recall why!)

For single-conductor RCA->XLR, there's no choice - the only thing you can disconnect is XLR pin 1.

But for your specific case of double-conductor RCA->XLR, disconnecting the shield at RCA end should be better - by more of a margin than the XLR->XLR end choice, I believe.

I disconnected pin 1 on the XLR connector and that did not help...
Next I will desolder the shield on RCA side but keep pin 1 on XLR.

 

[peng]

The Monoprice RCA to XLR cable works great when I tried it with the HA-1 and Hypex amp. I have not tried it with a Denon AVR yet, will so later now that you got me curious. My bet is it will work because the Monoprice cable is wired correctly.

I have finally tried it (on two occasions) with the Hypex NC502MP (Buckeye amp) with the Denon using a RCA to RCA connector to the Monoprice 6-ft RCA to XLR of the Hypex amp. The amp was plugged to the outlet used for the 2 channel system. The noise (hiss and hum) with volume of the AVR-X4400H at higher than 0 was audible within may be up to 18 inches to 2 ft at volume setting +18. That was about the same when I did it in the other room on my AV8801 using XLR to XLR and have nothing else connected vs the AVR-X4400H that has just about every connectors connected including 6 HDMIs, optical, and analog inputs, plus 3 external amps.

I wasn't happy with the slightly increased noise though in the first trial about a week ago, so this morning I moved the amp to the HT set sup, sat it on top of the Anthem amp so the power cord could reach the same power bar where most of the HT gear are plugged into. The difference was huge, then the noise became so negligible that even at volume +18 I could consider it silent.

That little experiment tells me that a) the Hypex amp is silent for all intents and purposes in my room with the HVAC off, b) it is quiet enough to allow me to compare the noise of the AVR-X4400H pre out (the AVR is fully connected with like at least two octopus attached to it) and the AV8801 preamp processor with nothing connected except the XLR analog inputs and outputs, and finally c) the Monoprice Premier series RCA to XLR interconnects are good, no need to pay more for the March Audio and Benchmark's. I was a happy to know my Buckeye amp's gain is on the high end of the tolerance, that is 26 dB.

 

[peng]

So in my case, there is no need to use any ferrite coupling and/or adding resistor/cap to the connectors of the Monoprice cable.

 

[andy497]

Looks like they're well wired. The shell->pin 1 connection is debated - to the extent I think that it doesn't really matter.

But even with that wiring, you can still have ground loop problems, particularly if the destination device has pin 1 connected to signal ground. What amp are you using? (Not in your sig?)

This Rane document suggests your next move is to disconnect the shield at the RCA end.


View attachment 173004
(As I understand it, in a symmetrical cable you would rather disconnect the input end, but in this case as the input is the only end that separates the shield and signal, you disconnect at the output, to keep the shield from the signal.).

If folks are still having trouble after lifting pin 1 at the xlr end the above diagram is key. You won't find these cables online anywhere (they always connect the shield side to black on the rca end). I tried lifting pin 1 on the xlr in of my balanced minidsp and still got a lot of hum. Finally soldered together an xlr cable to rca end like the above diagram (shielding lifted on the rca side), and my six subs fed by two different amps on separate outlets are all finally silent even with gains all the way up and my ear in the cone.

I got this idea from esteemed user Notnyt over on avsforum:
https://www.avsforum.com/threads/mysterious-ground-loop-hum.3107256/post-58918630
He runs Hypex NC400s and has a ludicrously low measured noise floor even using a Denon with rca outs as source, so I'll do what he's doing.

 

[MASKINEN]

If folks are still having trouble after lifting pin 1 at the xlr end the above diagram is key. You won't find these cables online anywhere (they always connect the shield side to black on the rca end). I tried lifting pin 1 on the xlr in of my balanced minidsp and still got a lot of hum. Finally soldered together an xlr cable to rca end like the above diagram (shielding lifted on the rca side), and my six subs fed by two different amps on separate outlets are all finally silent even with gains all the way up and my ear in the cone.

I got this idea from esteemed user Notnyt over on avsforum:
https://www.avsforum.com/threads/mysterious-ground-loop-hum.3107256/post-58918630
He runs Hypex NC400s and has a ludicrously low measured noise floor even using a Denon with rca outs as source, so I'll do what he's doing.

That’s interesting that you mention that. I will try that later this week. Just haven’t got to it yet.

I bought an Ifi gnd defender and the hum went away completely on my center but only lowered the hum level on my fronts.

I still wonder why both Hypex and Purifi (and others) consider disconnecting the shield on RCA side to be the incorrect way of fixing hum.

Also are you connecting an unbalanced source to a balanced input? Actually a RCA-XLR cable? Not the opposite? XLR-RCA.