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.