WiiM Ultra direct to Purifi amp (Audiophonics LPA-S450ET): audible hiss – anyone else experienced this?

[Corchea]

Hello everyone,
I would like to share an experience and see if anyone has encountered something similar.
My system includes a WiiM Ultra connected to an Audiophonics LPA-S450ET power amplifier (Purifi based).
When connecting the Ultra directly to the power amplifier, I noticed a clear hiss, audible both with music and without music. The noise was strong enough that using the system in this configuration was simply not possible.
At first I assumed that the unit might be defective, so the Ultra was returned and replaced with another one. However, the second unit behaved exactly the same. Since two different units produced the same result, I concluded that it was unlikely to be a defect in a specific device, and more likely some kind of interaction or compatibility issue between the Ultra and the power amplifier.
To check whether the power amplifier might be responsible, I inserted a NAD C320 integrated amplifier used only as a preamplifier between the Ultra and the power amp.
With the NAD acting as preamp the result was complete silence — no hiss at all, both in silence and during music playback. This confirmed that the power amplifier itself was not the source of the problem.
Based on this, it seems that the behaviour may be related to how the WiiM Ultra output stage interacts with the input stage of this Purifi amplifier.
So my question to the community is:
Has anyone experienced something similar when connecting a WiiM Ultra directly to a Purifi power amplifier, especially the Audiophonics LPA-S450ET?
What preamplifiers (tube or solid-state) are people successfully using with the Ultra?
For reference, in my case:
Connection used: RCA from WiiM Ultra to the amplifier
Amplifier gain setting: 20 dB
Thanks in advance for any insights.

 

[EddNog]

Zero hiss for me audible from my main listening position two meters away when I tested using Benchmark RCA to XLR cables to feed my Topping B200 monoblocs directly from WiiM Ultra’s line output.

-Ed

 

[Aquaman]

I have an Ultra directly plugged into an Apollon 1ET9040 BA DM (also Purifi based). No such issues at all.
I‘d try a different cable. XLR / RCA switches set correctly? Or maybe a grounding problem? In any case, I‘d contact Audiophonics. They are the most likely to have a clue of what‘s going on.

 

[Corchea]

Thanks for the suggestion. I checked the connections and the XLR/RCA switches several times and they were correctly configured.
Since the hiss disappears completely when a preamp (NAD C320) is inserted between the Ultra and the power amp, I’m confident the wiring itself was correct.
I appreciate the idea though.

 

[Corchea]

Regarding grounding, I’m in Europe (Spain) where most of my audio devices use two-pin power plugs without a separate ground pin. In any case, when I insert a NAD C320 as a preamp between the Ultra and the power amp the hiss disappears completely.

So I’m fairly confident the wiring and grounding are not the issue.

 

[dtc]

Hiss is usually a grounding issue or a RF interference issue.

I would try some tests just to try to narrow down the problem. You may have already tried some of these. None of these are definitive but it might give you some idea about the problem is.

Try using just 1 input into the amp. Try it on both amp inputs. Then switch to the other Wiim output and check both amp inputs. Is there hiss in both channels with just the 1 input? Try these tests with one side of the cable and then the other side. Does anything change when you change these connections? Try different RCA cables.

If you mute the Wiim does the amp still hiss?

Are all 3 components plugged into the same circuit? Are all three grounded?

 

[Aquaman]

Regarding grounding, I’m in Europe (Spain) where most of my audio devices use two-pin power plugs without a separate ground pin. In any case, when I insert a NAD C320 as a preamp between the Ultra and the power amp the hiss disappears completely.

So I’m fairly confident the wiring and grounding are not the issue.

Another thought. Have you tried turning the plug(s) by 180 degrees in the wall sockets?

 

[harkpabst]

To check whether the power amplifier might be responsible, I inserted a NAD C320 integrated amplifier used only as a preamplifier between the Ultra and the power amp.

Did you try to connect the WiiM Ultra directly into the C320 main in connectors?

If the hiss is still there, then most probably there is still an issue with the second Ultra. If the hiss is gone, something strange between the Ultra and that particular power amp might be going on.

 

[mlsstl]

A couple of questions:
1) Is this a hissing sound like one would hear from a tape recorder or FM tuner in-between stations? Of is it a humming sound? Or static? I know you used the word "hiss" but in the past I've seen the word "hiss" used in other audio forums to describe a variety of different noises.
2) Have you tried a different power amp with the WiiM? You said you used the integrated NAD as a preamp, but have you used it as a power amp?
3) Are there any electronics near the WiiM? RFI works on the inverse square law so if that is the cause of the noise, you probably don't have to move the other equipment very far away to get rid of the problem.
4) How are you using the Ultra -- as a streamer for digital music or a preamp where you've plugged in a turntable or other analog device, using the ADC in the Ultra?

I've got an Ultra that I used with a Vibelink and the pair is silent.

 

[SKApretto71]

Ultra to Audiophonics nCore power amp via RCA is just mute and silent ( until I turn up the volume )

 

[Corchea]

Thank you for the suggestions and questions.
To clarify a few points:
• The noise is clearly a hiss (white noise), similar to FM static between stations, not a 50 Hz hum.
• The NAD C320 is used only as a preamplifier, bypassing its power amplifier section. In this configuration it is placed between the WiiM Ultra and the Audiophonics LPA-S450ET.
• When used this way, the system becomes completely silent, both with and without music.
• The hiss only appears when the WiiM Ultra is connected directly to the Audiophonics LPA-S450ET via RCA.
• I also tried several different RCA interconnects to rule out a cable issue.
• Following the suggestion above, I also tried reversing the power plug (180°), but it made no difference.
• There are no other electronic devices very close to the Ultra that could obviously cause RFI.
So far this behaviour seems related to the direct interaction between the Ultra output stage and the power amplifier input.
Thank you again for your suggestions.

 

[Corchea]

As an additional test, I also tried a small tube preamplifier (Aiyima T20) between the WiiM Ultra and the Audiophonics amplifier.
In that configuration there is only a very faint hiss, audible only with my ear very close to the speaker.
During normal listening and when music is playing, it is completely inaudible

 

[mlsstl]

Sounds like the one thing you haven't tried is a different power amp, using the Ultra as the preamp. If that combo was silent, it'd show there is some weird incompatibility between the Ultra and the Purifi amp. If the new combo continues to be noisy, then you're back to the Ultra One final thought, I assume you've experimented with the various settings on the Ultra, though it is hard to imagine any of those causing a hiss problem.

 

[cnowacki]

My WiiM Ultra is hooked up directly to a Purifi 1ET400A EVAL1 manufactured by VTV. No hiss at all.

 

[Persona Grata]

Hi. I had a similar issue on the wider version HPA-S450ET with the same internals. One of my op amps was defective. Try changing them and test again. I expect you have already tested the RCA cable for faults if you used it connected to the NAD?

 

[Valentino]

Long shot, but anyway: Could the uncommonly low output impedance of the Ultra be a bad match for the Audiophonics input board, causing the noise?

 

[harkpabst]

Long shot, but anyway: Could the uncommonly low output impedance of the Ultra be a bad match for the Audiophonics input board, causing the noise?

I cannot imagine the low output impedance to be anything but useful. Usually we don't want matched impedances in Hi-Fi connections, because we don't want to maximise the power transfer.

@Corchea:

1. Did you try the C320 as the power amp in the meantime?
2. How long are the cables you have been using so far?
3. Can you place the Ultra and the LPA-S450ET close to each other and use short cables? If using long cables, does arranging them in a different way make any difference?
4. Does the loudness of the hissing change when you change the volume setting on the Ultra from 0 to 100?
5. Does the loudness of the hiss change when you change the amplifier's gain, up or down (just for fault finding)?

Depending on the answers it might (or might just not) be useful to get properly made RCA to XLR cables.

 

[Corchea]

Thanks for the suggestion.

If the problem were related to a faulty op-amp in the input stage, would replacing it completely solve the problem?
What makes me wonder is that when I insert the NAD C320 (used only as a preamplifier) between the Wii M Ultra and the Audiophonics amplifier, the system is completely silent.

If an op-amp in the Audiophonics input stage were faulty, I would expect the noise to be present in that configuration as well.
Also, as Valentino suggested, I'm wondering if this could be related to some kind of interaction between the Wii M Ultra's output stage and the Audiophonics input stage.

 

[Corchea]

Thank you, @harkpabst, for the detailed suggestions.
I will run the tests you proposed (using the C320 as a power amplifier, checking cable length and placement, and observing whether the hiss changes with the Ultra volume or with the amplifier gain).
I will report back here with the results.

 

[dtc]

While playing with the cables and volume you might want to try some of the things I suggested above. The idea is to get as much information as possible. Hiss is always hard to track down.