Comparing wiim amp ultra to wiim amp pro

[wordsum]

Just received the wiim amp ultra and was surprised by the difference in sound compared to the wiim amp pro. Particularly, my bookshelf speakers sound brighter. I found this much preferable at lower volume. The sound is more crisp and detailed at lower volume whereas the wiim amp pro just sounds somewhat muted at lower volume. Even more surprising, I found I prefer the sound of the wiim amp pro at higher volume. It seems to maintain more bass and midrange compared to the wiim amp ultra which seems to overemphasize treble at higher volume. I am not sure whether this is due to some inherent property of my speakers or if it's strictly the amp changing the frequency response. I had assumed the wiim amp ultra would offer a more accurate response from my speakers.

Other things I noticed, I like the volume knob better on the pro. It feels heftier and turns smoother. Also for some reason, the ultra detects my wifi but will not connect to it unless I place it right next to the router. The pro didn't have this problem, nor has any other device I have used. Not sure if this is due to a defect or model design.

 

[Wiimer]

. Also for some reason, the ultra detects my wifi but will not connect to it unless I place it right next to the router.

Hi,
My Amp Ultra is located 4 m away from the router, with two walls between the router and the Amp. However, the Amp Ultra's Wi-Fi reception is fine.


Moving or re-orienting the router (or device) slightly may improve the situation.

 

[wordsum]

I did try moving the router a little closer but didn't help. I assume there might have been a defect but ultimately didn't want to fool with it and returned it. However the difference in sound produced was surprising. I ended up returning my last speakers because they seemed to not have enough treble but I wonder if the wiim amp ultra would have produced a much brighter sound from them.

 

[dominikz]

In case it is interesting, recently I did a suite of equivalent measurements on the Amp Pro and Amp Ultra.

These are the measurable differences between the two that I've found so far:

1. Amp Ultra has approx. 2,4dB higher output voltage compared to Amp Pro when set to the same output volume and using the same input signal level.
   • This difference in output level will be clearly audible, but might appear 'different' rather than clearly 'louder' to some listeners.
   • This means that direct listening comparisons of the two amps will likely be tainted by the loudness difference.
   • This difference can be equalized in several ways, but probably the easiest that is reasonably precise is to feed both amps with the same 100Hz sine wave, and measure the output at the binding posts with a true RMS multimeter. Adjust the output volume on either amp until the measured output voltage is identical on both amps.
2. Amp Ultra preserves absolute signal polarity while Amp Pro inverts it on the loudspeaker output binding posts.
   • Interestingly the polarity is not inverted on the Amp Pro subwoofer output. I've opened a support ticket regarding all this and got the answer that loudspeaker output polarity will be corrected in one of the future Amp Pro firmware updates.
   • Until the firmware update is released, the polarity inversion issue of the Amp Pro can of course be worked-around by switching the loudspeaker cable polarity at the binding posts.
3. Amp Ultra is a tiny bit less load-sensitive above 10kHz compared to Amp Pro.
   • With my Revel M16 loudspeakers there's 0,2dB maximum difference between them at 20kHz, and no difference at all below 10kHz.
4. Amp Ultra's power supply has a ground connection, while Amp Pro's does not.
   • This means that one might pick up ground loops and 50/60 cycle hum where the other doesn't.

The above measurable differences might well explain some of the listening impression reported by people on the forum.

After I find time to consolidate my work I will create a new thread and post my findings in a bit more detail.

Hope this is interesting!

 

[cooky560]

I find this comparison interesting because some reviewers have said the Amp Ultra has more bass than the Amp Pro!

 

[wordsum]

Now I'm totally confused. I'm relatively new to audio equipment so I'm not understanding all the science behind it. I switched back and forth between the two amps to ensure I was not imagining it. The results were the opposite of what I was expecting. I expected there to be little difference between the two at low volume and I expected the ultra to sound better at high volume (due to the higher watts if nothing else).

Until the firmware update is released, the polarity inversion issue of the Amp Pro can of course be worked-around by switching the loudspeaker cable polarity at the binding posts.

So you are suggesting to connect the positive cable plug to the negative terminal on the amp and vice versa? In what way do you expect this will change the sound produced?

 

[canard]

In case it is interesting, recently I did a suite of equivalent measurements on the Amp Pro and Amp Ultra.

These are the measurable differences between the two that I've found so far:

1. Amp Ultra has approx. 2,4dB higher output voltage compared to Amp Pro when set to the same output volume and using the same input signal level.
   • This difference in output level will be clearly audible, but might appear 'different' rather than clearly 'louder' to some listeners.
   • This means that direct listening comparisons of the two amps will likely be tainted by the loudness difference.
   • This difference can be equalized in several ways, but probably the easiest that is reasonably precise is to feed both amps with the same 100Hz sine wave, and measure the output at the binding posts with a true RMS multimeter. Adjust the output volume on either amp until the measured output voltage is identical on both amps.
2. Amp Ultra preserves absolute signal polarity while Amp Pro inverts it on the loudspeaker output binding posts.
   • Interestingly the polarity is not inverted on the Amp Pro subwoofer output. I've opened a support ticket regarding all this and got the answer that loudspeaker output polarity will be corrected in one of the future Amp Pro firmware updates.
   • Until the firmware update is released, the polarity inversion issue of the Amp Pro can of course be worked-around by switching the loudspeaker cable polarity at the binding posts.
3. Amp Ultra is a tiny bit less load-sensitive above 10kHz compared to Amp Pro.
   • With my Revel M16 loudspeakers there's 0,2dB maximum difference between them at 20kHz, and no difference at all below 10kHz.
4. Amp Ultra's power supply has a ground connection, while Amp Pro's does not.
   • This means that one might pick up ground loops and 50/60 cycle hum where the other doesn't.

The above measurable differences might well explain some of the listening impression reported by people on the forum.

After I find time to consolidate my work I will create a new thread and post my findings in a bit more detail.

Hope this is interesting!

It's not normal that you're the one who notices this phase thing...and not check it beforehand...

 

[dominikz]

Now I'm totally confused. I'm relatively new to audio equipment so I'm not understanding all the science behind it.

Don't worry about it. It is not a trivial field so it naturally takes time to learn.

I switched back and forth between the two amps to ensure I was not imagining it. The results were the opposite of what I was expecting. I expected there to be little difference between the two at low volume and I expected the ultra to sound better at high volume (due to the higher watts if nothing else).

Let me start by saying that I don't doubt that you perceived a difference.

However, the cause of the perceived difference can't be determined without designing a more formal test, because many things can influence our perception and we'd need to rule out any factors that we're not interested in (to avoid them tainting our results). Some may be obvious, but some much less so.

Note that even having some expectations of the results doesn't protect us from various physical factors affecting the listening test (e.g. tiny output level differences), or a number of unconscious biases (which all humans are subject to).

Unfortunately, it is not trivial to setup a listening test where the variables are sufficiently controlled to be certain that that the perceived difference is caused only by some intrinsic characteristic of the device being listened to, and not some unknown external factors.

Here's some of the basic things that need to be controlled in listening tests:

1. Ensure that the configuration and layout of both devices under test is equivalent (especially if any kind of signal processing like EQ is used)
2. Ensure that the output signal level from both devices is identical (i.e. aligned to less than 0,1dB difference)
3. Ensure simple, quick and seamless switching between the devices (but you should be free listen to either device for as long as you want/need).
   • When attempting to compare speaker amps, that means you'd need to have a switch box that allows you to connect both amps to the same pair of loudspeakers.
   • You'd also need to feed both amplifiers with the same source signal (including time-aligned playback)
   • Note that manually disconnecting and connecting cables takes too much time to ensure valid comparisons, and using a different pair of loudspeakers for either amp would just introduce additional variables.
4. Listen blind - i.e. without knowing which device is playing.

Could you perhaps describe how you connected and switched between the two amps for your listening test, and did you already try to introduce any of the controls listed above?

So you are suggesting to connect the positive cable plug to the negative terminal on the amp and vice versa?

Doing this would invert the output signal polarity seen by the loudspeaker, yes. It would be a 'dirty' workaround to a bug that currently exists in the Amp Pro. In principle the two inversions (one due to the bug, and the other due to inverted cable connection) would return the signal to original polarity (no inversion).

The polarity of the Amp Ultra is correct out of the box so the loudspeaker cable should be connected normally (i.e. positive cable plug to positive terminal).

In what way do you expect this will change the sound produced?

Some people claim to be able to hear absolute polarity inversion, but up to now I personally never bothered to test this on myself so can't offer any personal experience or insight into it, sorry!

But in any case, if you can align output signal level and polarity to be identical between the two amps you will be a step closer to an "apples to apples" comparison.

It's not normal that you're the one who notices this phase thing...and not check it beforehand...

I agree, it is quite an unexpected omission in product quality control, which I haven't seen mentioned in any Amp Pro review.
I found it so unexpected that I retested in several different ways because I originally thought that it was perhaps an issue in my measurement setup somewhere.
However the issue persisted every time, so I opened a support ticket to WiiM and got a confirmation it is indeed a bug in the Amp Pro that will be fixed with a future firmware update.

 

[wordsum]

Could you perhaps describe how you connected and switched between the two amps for your listening test, and did you already try to introduce any of the controls listed above?

I used the same settings in the wiim app for both devices along with the same layout. I simply switched the speaker cables and optical input between the two devices. I did not measure the dB output of either, simply listened to them at different volume settings and observed the sound.

 

[dominikz]

I used the same settings in the wiim app for both devices along with the same layout. I simply switched the speaker cables and optical input between the two devices. I did not measure the dB output of either, simply listened to them at different volume settings and observed the sound.

That’s very understandable, as anything else would be much more complicated to do.
If you managed to make a decision you're happy with, all is good!

It is just good to recognize that such informal listening comparisons have limitations, and that the perceived differences may or may not persist in more rigorous listening test protocols.
Consequently, the same experience may or may not be shared by other people doing a similar test.

In my personal opinion the WiiM Amp Pro and Amp Ultra are both really great devices, without significant performance issues.
Even the polarity inversion thing in the Amp Pro isn't really the end of the world, IMHO!