My WiiM Amp tests

onlyoneme

Major Contributor
Joined
Oct 20, 2022
Messages
2,883
Well, not finished. Yet. But let's start with some facts.

The Amp seems to be a class D BTL H-bridge amp with a single power rail (find someone smarter than me for an explanation), and with an advanced temperature monitoring through some sensors to deliver "optimal performance and safety" which results in the output power optimizations. It has some consequences for measurements.
First of all, the output signal is modulated by high frequency switching signal, 454.5 kHz in this case:

1700667122641.png

As it shouldn't bother typical speakers, it affects any measurement instruments. Especially noise level increases when BW of the ADC is wide enough.
I will start my measurements with a bare ADC and then I will compare results with the ones when a low pass filter is used to attenuate the switching signal (I hope I will succeed with the build of an LPF).

Second thing is a DC bias on speaker outputs in relation to the amp ground. It's 20V DC which means that the amp is powered internally from 40V DC. That also means that I could burn my ADC AC coupling capacitors as the DC voltage level is too high, when common ground between the amp and ADC is established. I will start my tests with my ADC floating to protect it from the DC bias. I will verify later if using an external AC coupling capacitors brings more reliable measurement results.

And a third thing, those output power optimizations make measurements slightly challenging in case of high output powers as the output voltage may vary and even fluctuate. I've been told that a FW update is incoming with some power related improvements. So far I had to focus on 1W output power results.

Few other facts:
- the Amp can consume as much as 323W AC power for full scale sine signal in stereo at the highest volume and with 4 ohm load. In case of 8 ohm it's reduced to 163W.
- typical consumption is between 11W and 14W when nothing is played, it goes down to 6W for an "idle" mode and can drop to below 1W under some circumstances, in such case the Amp looses its WiFi connection and cannot be awaken with the remote
- max output power is 124W per channel for both channels loaded and 4 ohm load, and 63W for 8 ohm
- USB output can deliver up to 660mA at stable 4.72V voltage
- amplifier gain is around 27 dB


Just one graph for today - some class D amplifiers are known to have a frequency response influenced by load impedance. The same behavior can be seen with the Amp, plot below was made for 1W output power and a sweep with 48 kHz signal:

1700670129397.png

In real life scenarios it can sound "bright" or "dull", but it will depend on the speaker and its impedance for increasing frequencies.


Just one preliminary result I got for 5W/4ohm sine 1k signal, so quite comparable to measurements usually seen on ASR website:

1700682877632.png

Unfortunately both noise related measurements - THD+N and SNR - are lower than expected, even with very limited BW. It can indicate that I will need an LPF for better results.

THD: 95.8 dB
THD+N: 89.3 dB
SNR: 90.4 dB

Above is for single channel only.


A word about some concerns I have so far.
My unit is humming, buzzing, or hissing, no idea which word fits the best but the amp produces some noise from itself. It's more quiet with mediocre volume levels but gets louder for high power outputs. And unfortunately also when in idle. I can imagine it won't bother in daily use, but when it sits on the desk it's simply annoying. Fortunately I've been told that the noise is from the power transformer and it won't happen to production units.
Another thing is that the device outputs high frequency component on the sub out. It's at 520 kHz and -15 dBV level which gives the overall Vpp of 680 mV even when no content is played. It's beyond my expertise level to say if it's safe or not for the connected subwoofer but as it affects the performance of my ADC I can imagine it can have some impact on active subwoofers if HF signal is not filtered out. I've been told that the root cause has been identified and it's the power supply.

There are no DAC selectable filters (yet?), the default one seems to be fast, linear phase one, with responses as below

response.jpg

1700956947595.png

Undithered -90.31dBFS 16 bit sine signal doesn't look very good, but remains undithered

-90.31_16_und.jpg


Measurements - optical in to speakers out

EDIT: since I now have LPF, all content has been revised and corrected where necessary

All measurements here are taken with Cosmos ADC and REW. My dummy load is purely resistive, 4 or 8 ohms. Both channels are always driven. Low pass filter against class D switching frequency was used. Amp's volume is set to 100%.
Using the LPF does not bring a significant improvement. Although its filtering capability is impressive
1701989302069.png
1701989322716.png

it does not translate into measurement results. The biggest observed differences were related to the noise level for higher sample rates

1701990152936.png

Linearity is quite good, with 0.5 dB deviation at 110 - 111 dBFS source level (111 - 112 with LPF)

ezgif-3-a40cd7e15a.gif

SINAD measured for 5W/4ohm 48 kHz sine signal was 88.7 - 89.1 dB. SNR 90.6 dB. SNR jumps to 103 dB for full power signal.

1701990100389.png

Dynamic range calculated with -60 dBFS sine signal reaches 105 dB, while noise stays at 124 uV.

1701990245817.png


IMD distortions measured using SMPTE signal keep low level for 1W signal, but rise significantly at 5W (well, in fact I shouldn't call it IMD, these ones are just harmonics of 60 Hz tone)

1701990409520.png

It affects badly multitone results which are simply terrible for higher output levels, below 1W vs 5W again


1701990475478.png

I've enabled a subwoofer output to verify if it influences results, but no, still horrible

1701990733265.png



The frequency response shows a dependency to the load, as mentioned already. As a result the response within +/- 0.5 dB deviation covers an audible range fully for 4 ohm, but reaches 14 kHz only for 8 ohm load.

1700960225534.png


THD vs power shows similar performance for 1kHz sine signal and 4 vs 8 ohm load

1701991075476.png

THD+N vs power plots for different frequencies show increased distortions at lower frequencies

4 ohm
1701991338807.png

8 ohm
1701991451743.png

Best results at high powers are achieved around 5 kHz, it's also visible on THD vs frequency plot, below for 8 ohm, 5W

1701991658667.png

Harmonic distortions are dominated by uneven ones, below for 1 kHz sine at 4 ohm

1701991894805.png

SMPTE vs power and multitone vs power both show similar total distortion curves, as affected mainly by low frequency issues, 4 ohm

SMPTE

1701992155686.png

Multitone

1701992170546.png

While right channel shows slightly better performance for low frequencies

1701992588632.png

it's opposite for high frequencies

1701992719363.png


My conclusion for this part is that the performance for low frequencies is, again (Pro Plus V1?), disappointing. While the Amp measurements are similar to the ones seen for other 3255 implementations, low frequencies are broken. It's unclear to me if it's an issue of my particular unit or it's a design flaw, as other measurements are not yet available publicly.


Output impedance is as below (using 4 ohm load for measurements)

1702026725270.png

Measurements - optical in to sub out

For this purpose I use 200 Hz crossover frequency and 100 Hz test sine signal.

Just like for speakers output, the subwoofer output is also affected by the HF switching signal at around 521 kHz

1702031631792.png


This signal affects the wave shape of my test tone

1702031853580.png


I've been told that it's related to the PSU and it will be eliminated in the next HW iteration.

Sub out signal is a sum of both channels content and can reach 1.98 Vrms in stereo mode for 0 dBFS sine.

The HF switching component can be eliminated by my LPF for further testing purposes

1702032698451.png

but I didn't see any impact of it on my measurements here, so I'll continue with a combo Cosmos ADC / Scaler. As before both channels are driven.

The sub out performance resembles what I saw during previous tests, below for 0 dBFS input signal:

1702040334199.png

THD, THD+N vs power, this time with LPF due to the gain applied by autoranger in the Scaler

1702052647805.png


ADC - line in
Just quick tests here using Victor's sine oscillator as the generator of the sine 1 kHz wave. In the absence of digital outputs I've decided to use AirPlay cast feature to minimize the amplifier impact.

ADC reaches full digital scale at around 2.12 Vrms. The noise floor elevates before it happens, at around 1.9 Vrms, which results in further decreasing SNR ratio gradually

1702231190150.png

ADC performance seems to be similar to the one in the Pro Plus. It's not a surprise as chip used is the same AFAIK.



Stay tuned. Or maybe that's all, folks :)
 
Last edited:
Well, not finished. Yet. But let's start with some facts.

The Amp seems to be a class D BTL H-bridge amp with a single power rail (find someone smarter than me for an explanation), and with an advanced temperature monitoring through some sensors to deliver "optimal performance and safety" which results in the output power optimizations. It has some consequences for measurements.
First of all, the output signal is modulated by high frequency switching signal, 454.5 kHz in this case:

View attachment 3487

As it shouldn't bother typical speakers, it affects any measurement instruments. Especially noise level increases when BW of the ADC is wide enough.
I will start my measurements with a bare ADC and then I will compare results with the ones when a low pass filter is used to attenuate the switching signal (I hope I will succeed with the build of an LPF).

Second thing is a DC bias on speaker outputs in relation to the amp ground. It's 20V DC which means that the amp is powered internally from 40V DC. That also means that I could burn my ADC AC coupling capacitors as the DC voltage level is too high, when common ground between the amp and ADC is established. I will start my tests with my ADC floating to protect it from the DC bias. I will verify later if using an external AC coupling capacitors brings more reliable measurement results.

And a third thing, those output power optimizations make measurements slightly challenging in case of high output powers as the output voltage may vary and even fluctuate. I've been told that a FW update is incoming with some power related improvements. So far I had to focus on 1W output power results.

Few other facts:
- the Amp can consume as much as 323W AC power for full scale sine signal in stereo at the highest volume and with 4 ohm load. In case of 8 ohm it's reduced to 163W.
- typical consumption is between 11W and 14W when nothing is played, it goes down to 6W for an "idle" mode and can drop to below 1W under some circumstances, in such case the Amp looses its WiFi connection and cannot be awaken with the remote
- max output power is 124W in stereo for 4 ohm load, and 63W for 8 ohm
- USB output can deliver up to 660mA at stable 4.72V voltage
- amplifier gain is around 27 dB


Just one graph for today - some class D amplifiers are known to have a frequency response influenced by load impedance. The same behavior can be seen with the Amp, plot below was made for 1W output power and a sweep with 48 kHz BW:

View attachment 3493

In real life scenarios it can sound "bright" or "dull", but it will depend on the speaker and its impedance for increasing frequencies.


Just one preliminary result I got for 5W/4ohm sine 1k signal, so quite comparable to measurements usually seen on ASR website:

View attachment 3499

Unfortunately both noise related measurements - THD+N and SNR - are lower than expected, even with very limited BW. It can indicate that I will need an LPF for better results.

THD: 95.8 dB
THD+N: 89.3 dB
SNR: 90.4 dB

Above is for single channel only.


Stay tuned.
@onlyoneme,
Thank you so much.

There are some things I don't understand. Does this mean that Amp's DAC doesn't have the right filters set up?

That may not be an ideal spec, but with a SINAD of 87dB, it's still not bad. In the sense that it is equal to or better than many AVRs.

I can't wait to see what happens with DSP. 😊
 
@onlyoneme,
Thank you so much.

There are some things I don't understand. Does this mean that Amp's DAC doesn't have the right filters set up?

That may not be an ideal spec, but with a SINAD of 87dB, it's still not bad. In the sense that it is equal to or better than many AVRs.

I can't wait to see what happens with DSP. 😊
It's not about the DAC part, it's about the amplifier inside. Class D amps resemble the way SMPSes work. That mentioned switching frequency component should be harmless to the speakers but not everybody agrees. It's debatable what should be done with it, when for example this signal can meet HF noise in the environment. BTW I strongly suggest you to read about class D principles as my knowledge is very basic here and you can find explanation in internet much better than the ones I can provide.
 
Well, not finished. Yet. But let's start with some facts.

The Amp seems to be a class D BTL H-bridge amp with a single power rail (find someone smarter than me for an explanation), and with an advanced temperature monitoring through some sensors to deliver "optimal performance and safety" which results in the output power optimizations. It has some consequences for measurements.
First of all, the output signal is modulated by high frequency switching signal, 454.5 kHz in this case:

View attachment 3487

As it shouldn't bother typical speakers, it affects any measurement instruments. Especially noise level increases when BW of the ADC is wide enough.
I will start my measurements with a bare ADC and then I will compare results with the ones when a low pass filter is used to attenuate the switching signal (I hope I will succeed with the build of an LPF).

Second thing is a DC bias on speaker outputs in relation to the amp ground. It's 20V DC which means that the amp is powered internally from 40V DC. That also means that I could burn my ADC AC coupling capacitors as the DC voltage level is too high, when common ground between the amp and ADC is established. I will start my tests with my ADC floating to protect it from the DC bias. I will verify later if using an external AC coupling capacitors brings more reliable measurement results.

And a third thing, those output power optimizations make measurements slightly challenging in case of high output powers as the output voltage may vary and even fluctuate. I've been told that a FW update is incoming with some power related improvements. So far I had to focus on 1W output power results.

Few other facts:
- the Amp can consume as much as 323W AC power for full scale sine signal in stereo at the highest volume and with 4 ohm load. In case of 8 ohm it's reduced to 163W.
- typical consumption is between 11W and 14W when nothing is played, it goes down to 6W for an "idle" mode and can drop to below 1W under some circumstances, in such case the Amp looses its WiFi connection and cannot be awaken with the remote
- max output power is 124W in stereo for 4 ohm load, and 63W for 8 ohm
- USB output can deliver up to 660mA at stable 4.72V voltage
- amplifier gain is around 27 dB


Just one graph for today - some class D amplifiers are known to have a frequency response influenced by load impedance. The same behavior can be seen with the Amp, plot below was made for 1W output power and a sweep with 48 kHz BW:

View attachment 3493

In real life scenarios it can sound "bright" or "dull", but it will depend on the speaker and its impedance for increasing frequencies.


Just one preliminary result I got for 5W/4ohm sine 1k signal, so quite comparable to measurements usually seen on ASR website:

View attachment 3499

Unfortunately both noise related measurements - THD+N and SNR - are lower than expected, even with very limited BW. It can indicate that I will need an LPF for better results.

THD: 95.8 dB
THD+N: 89.3 dB
SNR: 90.4 dB

Above is for single channel only.


Stay tuned.
Is this a typical thd, thd+n and snr on class d amp? On class a/b, we see atlist 110db or more on snr which result on low noise floor. With that said, if you put your ear next to the tweeter without playing anything is there a hiss? Thanks!
 
Is this a typical thd, thd+n and snr on class d amp? On class a/b, we see atlist 110db or more on snr which result on low noise floor. With that said, if you put your ear next to the tweeter without playing anything is there a hiss? Thanks!
ATM my results are typical tpa3255 ones IMO, but you have to understand that the issue I face is a measurement issue. You can see below how the BW will affect measured noise level due to the amp class D nature:

1700722625322.png

I hope that final results are better but I cannot confirm it yet (or deny) without a proper low pass filter.
 
@onlyoneme, @Achim1811,

Thank you.
It's very difficult for me. 😅😅😅


Is this a typical thd, thd+n and snr on class d amp? On class a/b, we see atlist 110db or more on snr which result on low noise floor. With that said, if you put your ear next to the tweeter without playing anything is there a hiss? Thanks!

Yes, I'm interested in that too.
 
Another thing is that the device outputs high frequency component on the sub out. It's at 520 kHz and -15 dBV level which gives the overall Vpp of 680 mV even when no content is played.
Will this prevent a subwoofer with auto on/off going into standby?
 
I have heard this amp chip in many other products from aiyima, fosi and others and it's nothing special it's just ok at best. But with them you can change out the opamps to take it up a notch not sure this can be done with the wiim amp. But that doesn't bug me as the older ess dac being used here I would have gladly paid the extra $200 for having the ak4499 chip in this. I upgraded from the mini to pro to pro plus but I don't think I'll upgrade this time.
 
Regarding load dependence, is there an issue when impedance of the loudspeaker is 6 Ohms? The KEF LS50 Meta has a 6 Ohm impedance at higher frequencies.
 
Regarding load dependence, is there an issue when impedance of the loudspeaker is 6 Ohms? The KEF LS50 Meta has a 6 Ohm impedance at higher frequencies.
One huge advantage this device has over say a Fosi Audio V3 as far as load dependence issues is the PEQ built in - effectively variation in higher frequencies can be fixed with a single filter.
 
I've finally finished my LPF, first results are promising in terms of reduced impact of HF switching signal and reduced noise level. Unfortunately distortion based measurements do not seem to improve.
 
I've finally finished my LPF, first results are promising in terms of reduced impact of HF switching signal and reduced noise level. Unfortunately distortion based measurements do not seem to improve.
there was no real reason for it to change the big problem observed on your device in imd or multitone at 5w...
but it had to be done...
;-)

your machine clearly has a problem....
"

A word about some concerns I have so far.
My unit is humming, buzzing, or hissing, no idea which word fits the best but the amp produces some noise from itself. It's more quiet with mediocre volume levels but gets louder for high power outputs. And unfortunately also when in idle. I can imagine it won't bother in daily use, but when it sits on the desk it's simply annoying. Fortunately I've been told that the noise is from the power transformer and it won't happen to production units."
 

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