My WiiM Amp tests, chapter 2

[onlyoneme]

It would be amazing to hear of any known differences between PCB 5 and version 4.

I cannot help because I have no access to pcb 4 unit.

 

[Jay]

I cannot help because I have no access to pcb 4 unit.

Completely understand and I am grateful for what you have shared. I just wanted to comment for others who have PCB 4 in case they are curious about any known issues or have any other input to this. For info my RCA inputs are reversed like your PCB 5 version but I have no class ll mark.

 

[Yoku-San]

there is an obvious high pitch continual whine from the unit itself

I would open a ticket and return/exchange the Amp. Otherwise you might regret that in the future even though there might be nothing else wrong with your device.

 

[Smartplug]

@onlyoneme, I’m glad to see you posting measurements. I haven’t seen you posting here in a while. I had ver 2 but return it and purchase again and got ver 5. No hum unlike the first one.

 

[onlyoneme]

Tonight I will update the main post with some measurements taken over the speakers output. And there will be another break, a bit longer maybe.

 

[onlyoneme]

New measurements added.

 

[canard]

A new unit is with me. Because new device is too cold to be powered, I can focus on external differences. Both units are almost undistinguishable.
One difference is reversed channels on RCA inputs. Second one is a class II power supply mark printed on the bottom.

I've seen units with reversed RCA plugs in some recent YouTube movies, so this change was probably applied in the meantime.

There are also subtle differences between outside boxes, like the mentioned class II mark. Another one are black and white icons of the music services vs colorful ones for the box of old unit.




First things first, as the full set of measurements and tests takes a lot of time, I will verify known issues at the very beginning.

PSU noise - absent, it's (almost) deadly silent. I can hear something only when my ear touches the chassis directly. Well, I know it could be pretty risky idea...

PCB_version - 5.

HF switching signal on sub out - absent.

Low frequencies / multitone bad performance - seems to be greatly improved in my quick and dirty measurements. I will provide more details tomorrow.

SMPTE, 5W:

View attachment 4658

Multitone, 5W:

View attachment 4659

Differences are huge.

Another example of improvement, this time for THD+N vs level at 100 Hz, 4 ohm load as before:

View attachment 4674

An old unit starts to distort much earlier.

THD+N vs level measurements at different frequencies finally look like for other TPA3255 implementations, 4 ohm:

View attachment 4680

Below the same measurements but for V1 unit:

View attachment 4681

Yet another comparison vs old unit, for multitone measurement at different load levels:

View attachment 4683

THD at 5W/4ohm load, related to frequency, for both units:

View attachment 4724

Surprisingly slightly worse performance for higher frequencies in case of the new model.

It can be also seen for lower 1W load:

View attachment 4725



Measurements - optical in to speakers out

All tests here were made with an external LPF. More details: https://forum.wiimhome.com/threads/my-wiim-amp-tests.1873/

Although the new revision is a clear improvement over an old one, the most basic SINAD measurement for 1 kHz sine signal will not reflect it at all in case of 4 ohm load.

4 ohm / 5 W, an old unit:

View attachment 5035

And the new one:

View attachment 5036

For 8 ohm load there is a measurable improvement.

8 ohm / 5 W, an old unit:

View attachment 5037

And the new one:

View attachment 5038


Nothing has changed in case of the load dependency:

View attachment 5039

Crosstalk, left to right and right to left, 4 ohm / 5 W:

View attachment 5040

THD+N vs output voltage, for 4 ohm and 8 ohm load:

View attachment 5041

And details for different frequencies, 4 ohm:

View attachment 5042

and 8 ohm:

View attachment 5043

THD vs frequency, for 4 ohm and 8 ohm:

View attachment 5044

Stay tuned.

in the case of using this type of amplifier it is still interesting to observe the effective impedance curve of the speakers concerned.....
the situations when going up in frequencies are so variable...

 

[Yoku-San]

in the case of using this type of amplifier it is still interesting to observe the effective impedance curve of the speakers concerned.....
the situations when going up in frequencies are so variable...

This is typical of entry level Class D. However, PFFB will be integrated into new amplifiers by Aiyima and Fosi Audio. I hope that WiiM incorporates PFFB into the next version of the Amp to eliminate load dependency.

 

[harkpabst]

in the case of using this type of amplifier it is still interesting to observe the effective impedance curve of the speakers concerned.....
the situations when going up in frequencies are so variable...

The rise into 8 ohms load is less than 2 dB at 20 kHz (edit: closer to 1 dB, I think). Not nice for sure, but also not reason for too many concerns.

Implementing the TPA3255 with post-filter feedback would have improved on that noticeably.

It's important to understand that these measurements are taken with a purely resistive load. Just from looking at this one graph you cannot say for sure what's going to happen with inductive (or even capacitive) load.

In other words: Just because a loudspeaker is sold as being nominally 8 ohms or even because the impedance trace shows an absolute value of 8 ohms at high frequencies doesn't necessarily mean the rise in SPL will be as seen in this graph.

 

[onlyoneme]

I’m leaving the hospital today so hopefully I’ll publish more details about the improved performance of the sub out in upcoming days.

 

[onlyoneme]

Few graphs added, better late than never I guess.