RCA to balanced speakers - background noise problem

[incans]

WiiM Device: WiiM Ultra (Firmware 5.2.730566)
Network: Ethernet (hard-wired)
Speakers: KRK VXT8 (active)
Subwoofer: B&K P12-300SB-PR
Sources: Samsung S95B (HDMI ARC), DLNA Streaming (hopefully)

My new WiiM Ultra arrived today. Having connected it up I notice an immediate problem with background noise from the speakers. The noise is semi-random tics and pops, but it's clearly not actually random because for example changing the volume level on the WiiM causes a stream of audible pops in time with the stepping of the volume level.

The speakers are active studio monitors with XLR/TRS balanced inputs. They are connected to the Ultra via moderately long (~6m) single pole (mono) RCA->TS (jack plug) cables. The whole system is connected to the same mains supply circuit (ring main).

The speaker documentation says they are ok with an unbalanced source, as long as the "cold" (negative) side is linked to the ground. When using a mono jack plug this happens automatically as the single sleeve contacts both the Ring (cold) and Sleeve (ground) contacts in the TRS receptacle of the monitor.

This connection arrangement worked fine with my old preamp, a Rotel 1070 stereo unit, but the WiiM definitely has a noise problem.

The monitors have a "ground lift" option that is supposed to help with noise caused by ground loops, but this has no appreciable effect.

It was the combination of features and price that drew me to the Ultra, so it will be really disappointing if it turns out that it's just not compatible with balanced power amps (even in unbalanced mode), as the nearest comparable devices with balanced outputs are substantially more expensive.

If anyone has experience of mitigating with this problem I would appreciate any ideas.

 

[hgo58]

WiiM Device: WiiM Ultra (Firmware 5.2.730566)
Network: Ethernet (hard-wired)
Speakers: KRK VXT8 (active)
Subwoofer: B&K P12-300SB-PR
Sources: Samsung S95B (HDMI ARC), DLNA Streaming (hopefully)

My new WiiM Ultra arrived today. Having connected it up I notice an immediate problem with background noise from the speakers. The noise is semi-random tics and pops, but it's clearly not actually random because for example changing the volume level on the WiiM causes a stream of audible pops in time with the stepping of the volume level.

The speakers are active studio monitors with XLR/TRS balanced inputs. They are connected to the Ultra via moderately long (~6m) single pole (mono) RCA->TS (jack plug) cables. The whole system is connected to the same mains supply circuit (ring main).

The speaker documentation says they are ok with an unbalanced source, as long as the "cold" (negative) side is linked to the ground. When using a mono jack plug this happens automatically as the single sleeve contacts both the Ring (cold) and Sleeve (ground) contacts in the TRS receptacle of the monitor.

This connection arrangement worked fine with my old preamp, a Rotel 1070 stereo unit, but the WiiM definitely has a noise problem.

The monitors have a "ground lift" option that is supposed to help with noise caused by ground loops, but this has no appreciable effect.

It was the combination of features and price that drew me to the Ultra, so it will be really disappointing if it turns out that it's just not compatible with balanced power amps (even in unbalanced mode), as the nearest comparable devices with balanced outputs are substantially mode expensive.

If anyone has experience of mitigating with this problem I would appreciate any ideas.

What is your line output level set to?



Maybe try another setting?

 

[HansD-NL]

The Wiim Ultra has a floating (class 2 no earth) power supply and interconnecting to a device like your active monitors with a earth connection can have the effect you hear. The KRK's have semi balanced inputs (not real galvanic isolation with transformers) and so you will end up with a difference in earth potential and the ground-lift switch will not do anything in this case because you connect unbalanced. Your Rotel 1070 is also a class 2 (no earth) device with a floating earth like the Wiim Ultra.
The best option is to use a real galvanic isolation device (line level) and all tears will be gone.

 

[HansD-NL]

Never disconnect the safety earth on devices that have them, it will sometimes cure a problem like you have but if the device some day is faulty you'll risk having the whole system under line voltage without your electric panel knowing anything about it.

One more thing: Big (high power) power supply's (linear and mainly switched mode supply's) need the earth connection to offload some leakage current and to keep the filters inside simple and working right.

 

[HansD-NL]

I think the most elegant, great working and affordable solution in your situation is the ART DTI
You can then connect your KRK speakers with standard XLR cables again.

https://artproaudio.com/noisereduction/product/246724/dti​

 

[jed1]

Please check out the following document;

Sound System Interconnection

RaneNote 110 explains the cause and prevention of ground loops and how to interface balanced and unbalanced gear with proper connections and wiring.

www.ranecommercial.com

Configuration #18 is recommended to connect unbalanced RCA output (WiiM Ultra) to balanced TRS input (KRK).

I believe you can ground the WiiM Ultra with ground connector to power strip. Make sure WiiM and KRK share the same power strip.

You may have a gain issue because standard balanced input is 4V while WiiM outputs up to 2V.

 

[incans]

Thanks for all the feedback.

Further prodding and poking has shown that the quiescent noise (when nothing is changing on the WiiM) mostly seems to be affecting one speaker, and that is linked to one physical speaker (i.e. not isolated to either one interconnect cable, or one channel on the WiiM).

I do think there's a ground loop issue (the speakers can't know when the volume is being cranked up or down on the WiiM, so the "pop on volume change" effect must be triggered by the WiiM), I think I may also have a bad connection in one speaker, which is confusing the issue.

I need to see if I can get the speaker issue sorted out, and then revisit the WiiM->balanced devices question I think.

What is your line output level set to?

View attachment 27883

Maybe try another setting?

Output is set to 2V (default). Comments below indicate that theoretically might limit the maximum output from the speakers, but in practice, 100% volume from the WiiM is more than loud enough from these large monitors in a domestic setting, and that's with the speakers set to default (0dB) gain. They can be adjusted up to +6dB of sensitivity, which would enable truly painful levels to be reached I imagine.

 

[incans]

Configuration #18 is recommended to connect unbalanced RCA output (WiiM Ultra) to balanced TRS input (KRK).

Interesting. I see config no. 18 uses the voltage differential between the "hot" and "cold" on the receiving equipment, and takes the chassis ground from that end down the cable shield, terminated only at one end. That would mean me buying/making new cables, but if I can get the problem with my speaker fixed, it's probably worth trying this configuration.

 

[Nanook]

I agree, #18 is the way to go. It's likely, you make a ground loop from speaker to speaker (in case they have Pin1 connected to protective earth (PE).
For class 2 devices leakage current from the switch-mode-power-supply can also cause hum due to the I*R drop along the shield of the cable.

In case you try #18, you can as well try to connect the shield, either directly or via 100R||100nF as proposed here:

Forum

www.soundonsound.com

The WiiM Pro(+) for example is floating and in case there's no connection to PE (via the SPDIF or the analog inputs), the internal ground will build up a fairly high AC voltage due to the leakage current of the wall-wart. This common-mode voltage may not get fully suppressed by the differential input resulting in hum again.
The 100R resistor (I usually ommit the resistor and connect the shield directly to the RCA) makes sure, that the common-mode voltage remains small (Ileakage*100 Ohms).

In any case it's crucial that the differential input picks up the voltage at the RCA end of the cable.

 

[HansD-NL]

I agree, #18 is the way to go. It's likely, you make a ground loop from speaker to speaker (in case they have Pin1 connected to protective earth (PE).
For class 2 devices leakage current from the switch-mode-power-supply can also cause hum due to the I*R drop along the shield of the cable.

In case you try #18, you can as well try to connect the shield, either directly or via 100R||100nF as proposed here:

Forum

www.soundonsound.com

The WiiM Pro(+) for example is floating and in case there's no connection to PE (via the SPDIF or the analog inputs), the internal ground will build up a fairly high AC voltage due to the leakage current of the wall-wart. This common-mode voltage may not get fully suppressed by the differential input resulting in hum again.
The 100R resistor (I usually ommit the resistor and connect the shield directly to the RCA) makes sure, that the common-mode voltage remains small (Ileakage*100 Ohms).

In any case it's crucial that the differential input picks up the voltage at the RCA end of the cable.

Mostly agree with you but still a galvanic isolation removes all ifs and buts and no cable or adapter modifications at all.

 

[Nanook]

Galvanic isolation is the simplest method and 'always' works — I won't argue with that. However, a good transformer is not cheap, and you end up with another box taking up space. The driving device should also have low output resistance; otherwise, the bass level may drop depending on the transformer's inductance. Manufacturers of cheap transformers tend to provide limited information (ART, for example, does not specify the source impedance in their specifications), so it is difficult to predict the performance of the final solution. Jensen, for instance, specifies a maximum load capacitance of 100 pF, which is equivalent to just about 1 m of cable. Of course, in almost all cases there will be no hum anymore.
I have always been able to control hum due to ground loops or leakage currents in other ways. If you have a soldering iron and know how to use it, it's definitely worth a try.

 

[canard]

Just a small step aside... galvanic isolation on the SPDIF, AES (or USB) side is nothing expensive , but very effective and should be present in the future on the Wiim side (if in doubt about whether it's on the receiver side, it's worth having some on each side)

;-)

 

[HansD-NL]

Just a small step aside... galvanic isolation on the SPDIF, AES (or USB) side is nothing expensive , but very effective and should be present in the future on the Wiim side (if in doubt about whether it's on the receiver side, it's worth having some on each side)

;-)

Yes works great these little isolation devices (no transformers but using a chip for this function) Most times not needed but a life saver in some situations.

Note that digital coax (RCA connector) and optical are both called S/PDIF, it's the same protocol. I know that optical can do other protocols but talking about the standard consumer digital connections here. AES/EBU is a professional digital balanced (wire) connection using XLR plugs.

I think it is incredible that Sony and Philips (and some other external engineers) settled on the still in use and great S/PDIF standard and not only that, 16 bit 44.1Khz for the digital format and that turned out to be more than enough for many years after...

 

[Kro]

Not sure that will be of any help but I have been using Wiim Ultra's line out to my fully balanced power amp (hypex ncore) and it's dead quiet, not a single pop, noise or whatever. Basic RCA to XLR cable (cold to shield) but much shorter, 40cm as I don't need any longer.
For the sake of principle, I used balanced cable for each channel and connected cold to shield at RCA's end, this was my understanding of hypex recommandation. Maybe completely useless, no idea.

 

[Kro]

Or same here

 

[Nanook]

For the sake of principle, I used balanced cable for each channel and connected cold to shield at RCA's end,

That's exactly what I do "per default" when I have a balanced input but a RCA output.
The I*R-drop (be it due to Gnd-loops or leakage current) in the cable will normally clearly be dominant and you "subtract" the I*R drop in the cable and get a clean signal. And the longer (and cheaper) the cable, the higher the "R" and therefore I*R.
In most modern and cost-effective devices the RCA connectors are soldered directly to the PCB and it's Gnd-plane. The resistance from RCA jack to the circuit thus is extremely small.

 

[Nanook]

Or same here

Bruno Putzeys has really understood this stuff - I think he just got impatient about the lack of knowledge in the communities and wrote a nice white paper on it.

 

[Nanook]

;-)

https://www.hypex.nl/media/fa/d8/a3/1682342122/The%20G%20word.pdf