(Unofficial) Review of JCALLY JM20 MAX: USB-C Headphone Dongle with High Unbalanced Output Power

[MC_RME]

The specification is an incredible 140dB, although there is no information on load resistance, frequency, or direction.
Even in the best case scenario (e.g., no load, around 1kHz, optimal direction) I doubt this value.

Correct. 140 dB must be some theoretical data sheet stuff, not the real world Crosstalk of the completed dongle with phones connected, its unbalanced design makes this impossible.. But - just checked with not optimal cabling and 100 kOhm load: already -110 dB. My only adapter for this kind of cabling just broke, so I will redo that later.

With a maximum output of 2.5V RMS, 140dB lower would result in 0.25µV RMS. That's below the noise of this device, which should be around 1µV.

Can a sine be measured if it actually disappears into noise?

Easy peasy, and you see it here all the time - FFT.

Even for devices with balanced outputs, I've never read a value of 140dB for crosstalk.

With unbalanced outputs, 120dB might be possible.
But 140dB? Isn't that probably a typo?

Is possible. See here, measured at the XLR outputs.

RME ADI-2/4 Pro SE - Auto-measured with Multitone

Ok, I came across an oddity. Although I hadn't set the zoom levels properly when saving results, I did notice that the Linearity result for my motherboard from the test plan seemed really good. So I repeated it as a single test (I set averages to 32, same as the test plan, if that means...

www.audiosciencereview.com

 

[MC_RME]

Did some first measurements which so far confirm the OPs findings. But also made me totally crazy again - my EU iPhone does not put out 2.5V with the JM20 Max, but only 1.4 V (that is still damn loud, 13 dB higher than with the Apple dongle)! So a similar level reduction as with the original Apple dongle is performed in the EU iPhone in the digital domain (yes, simple as that - they lower the digital level fed to the DAC). I did some more checking - my wife's iPhone (not EU) spits out 2.5 V, as does my iPad Pro. So how does Apple know that this dongle is a dongle for headphones and not a standard DAC (where no digital level reduction occurs)?

When connecting the dongle for the first time you can select headphone or others, but that choice is not making a difference. The JM20 Max also does not feature impedance detection, so again that doesn't matter. The answer most probably lies in the USB descriptors, where Jcally has put the same 'headphone' indication as the Apple dongle (bad idea...):

View attachment 443651

Some more info on this ongoing saga. I had to learn that here on ASR most of the stuff that I tried to find out is already there - just not easy to find. Especially @staticV3 has posted tons of useful infos in the dongle comparison review https://www.audiosciencereview.com/...pple-vs-google-usb-c-headphone-adapters.5541/.

There I learned that there is not only a difference between EU and US (or non-EU) iPhones, but it seems Apple also sells two different dongles, where one spits out a max of 0.5 V (A2155) for EU, and one for the rest of the world (A2049) which maxes out at 1 V.

Luckily I am currently in the rest of the world, so visited the local Apple licensed shop and bought the USB-C dongle, which happens to be the A2049 (MW2Q3ZA/A). And Lo and behold: my EU iPhone is up from 300 mV to 600 mV, Windows and my wife's iPhone are up from 0.5 V to 1V. Can't believe I missed that info for so long!

Now I have no clue where EU residents could buy this dongle version, but the 6 dB higher volume on my iPhone already makes a big difference - as expected! Still crazy to realize that the 'rest of the world' has a 10.46 dB higher output level (1V instead of 0.3V) than EU buyers to play with...

 

[Zek]

This is due to EU regulations on consumer hearing protection.

 

[MC_RME]

Correct. 140 dB must be some theoretical data sheet stuff, not the real world Crosstalk of the completed dongle with phones connected, its unbalanced design makes this impossible.. But - just checked with not optimal cabling and 100 kOhm load: already -110 dB. My only adapter for this kind of cabling just broke, so I will redo that later.

New adapter in house, so here we go:

Fixed new screenshot, label of 300 and 600 Ohm was swapped.

 

[olieb]

There I learned that there is not only a difference between EU and US (or non-EU) iPhones, but it seems Apple also sells two different dongles, where one spits out a max of 0.5 V (A2155) for EU, and one for the rest of the world (A(320∑2049) which maxes out at 1 V.

Interesting. I just checked my Apple dongle that I bought in EU several weeks ago at a certified Apple retailer, it says A2155 and MW2Q3ZM/A on the packaging.
With my Macbook (EU too) I get 1V_rms with my Sennheisers (320Ω) and 1V_rms with Truthear Gate (30Ω). [I recall that the dongle might check for impedance.]
EDIT: I measured the 3.5mm output of the Macbook in comparison. Here I get 2dB more ≈1.24V_rms. Distortion of the output is [a bit] higher (≈-70...-75dB THD).
EDIT II:

The hardwired cable on my Tanchjin Space Lite (not reveiwed) developed an intermittent in its hardwired cable so, toss. The cable on my TempoTec Sonata developed one also but at least that one had a user-replaceable USBC cable- but replacing it didn't fix the loud POP when plugging it into my phone, so I don't use it anymore. It has a little window with an LED so yuu can see part of the curcuitry though.

On the other hand, my '$9 phone dongle' (as it's referred to around here), has none of the above problems and just keeps working.

I used shrinking tube (with glue) to make my dongle sturdier and give it the "form" I seem fit.

 

[MC_RME]

How a MacBook interacts and further confuses these dongle variations - don't know,
But doesn't the MacBook not already have a 1 V output, or even higher, for high impedance headphones? That feature might get lost when using the external Apple dongle. So many variables...

 

[Miley_B]

@MC_RME Is the choice of 100kOhm upper impedance dictated by the impedance of the AP?
Also what would cause the crosstalk to reduce at 300 ohm when compared to 600 ohm in your test?

Big caveat that I don't really know what I'm doing... Testing the JM20 Max using REW, my RME ADI-2 Pro FS R as the AD (Input mono'd) 1kHz, 1v I got -125.7dB, however with a 15 ohm load to represent a set of sensitive IEMs it dropped to -51dB. I'm not sure how significant a factor the RME impedance is.
I also realise now that my test cable is of a Y split with a common return wire join half way, not sure if this will meaningfully affect the result (0.75mm OFC).

 

[MC_RME]

Of course it will. Yes, the AP has 100 kOhm unabalanced. And lower impedances (aka load) reduce channel sparation due to the high current flowing on whatever shared ground line/wire, so that is expected.

 

[MCH]

Interesting. I just checked my Apple dongle that I bought in EU several weeks ago at a certified Apple retailer, it says A2155 and MW2Q3ZM/A on the packaging.
With my Macbook (EU too) I get 1V_rms with my Sennheisers (320Ω) and 1V_rms with Truthear Gate (30Ω). [I recall that the dongle might check for impedance.]
EDIT: I measured the 3.5mm output of the Macbook in comparison. Here I get 2dB more ≈1.24V_rms. Distortion of the output is [a bit] higher (≈-70...-75dB THD).

Amendment 12 applies only to "personal music players" reading the definition, doesn't seem laptops are included.
That could be the reason for this behaviour.

 

[jkim]

New adapter in house, so here we go:

View attachment 445537

Thank you for this. These results make this USB dongle's test even more extensive! I will update my OP to point this out.

 

[Billy Budapest]

I this kind of design is utterly insulting and I will never buy anything that behaves like this. @amirm should implement a standard test for this kind of characteristic. I strongly suspect that this logic, while always running, will affect music in certain situations - I wonder how....

//

I think this feature of the CS43131 chip is ingenious. Clever engineering to address a problem that admittedly may or may not be audible.

 

[CedarX]

I found an interesting phenomenon about this device. I believe this occurs with any DAC built on CS43131 (or CS43198).

View attachment 443074

Is this CS431xx feature what is sometime referred as a "noise gate"?

Another example from a KTmicro chip (quite popular in the dongle world...). The KTmicro tool let you pull (and push) the Gain, PEQ, Limiter, and Noisegate (DRC) settings from the chip:

In that example, the "Gate Volume" is set to -30dB.

Here is what it becomes if I set the "Gate Volume" to 0dB--i.e. a linear gain response:

In addition, it has been hinted that the "clicks" reported on the CS431xx chips may be tied to this feature as well: at very low frequency (<10Hz, rumble noise), the signal may vary at a slow-enough speed to trigger this noise gate / DRC, if the time-based attack & release settings are short enough...

I wonder if these types of features are a lot more common than we may think. Cheating? Not really, but perhaps worth understanding...

 

[jkim]

Is this CS431xx feature what is sometime referred as a "noise gate"?

Another example from a KTmicro chip (quite popular in the dongle world...). The KTmicro tool let you pull (and push) the Gain, PEQ, Limiter, and Noisegate (DRC) settings from the chip:
View attachment 445600
In that example, the "Gate Volume" is set to -30dB.

Here is what it becomes if I set the "Gate Volume" to 0dB--i.e. a linear gain response:
View attachment 445603

In addition, it has been hinted that the "clicks" reported on the CS431xx chips may be tied to this feature as well: at very low frequency (<10Hz, rumble noise), the signal may vary at a slow-enough speed to trigger this noise gate / DRC, if the time-based attack & release settings are short enough...

I wonder if these types of features are a lot more common than we may think. Cheating? Not really, but perhaps worth understanding...

I think it's a similar thing. "DRC" stands for Dynamic Range Correction or Compensation?

The "click noise" reported on the CS431xx may or may not be related to that feature. This Russian webpage describes that it is due to its power saving mode triggering its Class H mode. I do not know how this "power saving mode" is related to the dynamic range enhancement mode.

 

[CedarX]

The "click noise" reported on the CS431xx may or may not be related to that feature. This Russian webpage describes that it is due to its power saving mode triggering its Class H mode. I do not know how this "power saving mode" is related to the dynamic range enhancement mode.

I am not sure this is correct… see this post from @nick_l44.1:
https://audiosciencereview.com/foru...20-headphone-dongle-review.58749/post-2190674

 

[jkim]

I am not sure this is correct… see this post from @nick_l44.1:
https://audiosciencereview.com/foru...20-headphone-dongle-review.58749/post-2190674

I am aware of that post. I don't think anything is conclusive from there.

EDIT. Here is what I know. The JM20 Max does not seem to produce this clicking noise. It also does not seem to enter power saving mode as other CS431xx devices do. Lastly, it does enter the dynamic range enhancement mode.

 

[ZolaIII]

I think it's a similar thing. "DRC" stands for Dynamic Range Correction or Compensation?

The "click noise" reported on the CS431xx may or may not be related to that feature. This Russian webpage describes that it is due to its power saving mode triggering its Class H mode. I do not know how this "power saving mode" is related to the dynamic range enhancement mode.

It's how you drive power rail and how fast it's able to switch (capacitors helped). It's not really about power saving it's adjusting optimal gain on the flight and trough the V rails (H mode).

 

[MC_RME]

The "click noise" reported on the CS431xx may or may not be related to that feature. This Russian webpage describes that it is due to its power saving mode triggering its Class H mode. I do not know how this "power saving mode" is related to the dynamic range enhancement mode.

'This russian website' confused me a lot by talking about 'clicks', a very clear and defined english word, that seems wrong for the content presented. I hear no 'clicks' in any of the sample files. What there is seems to be what is shown at the bottom in the zoomed waveform. The small dents in the sine are not audible, they are of very high frequency (see spectrogram, 90 kHz etc). Playing this at lower (normal) sample rates they would disappear completely.

The stated low frequency distortion (maybe caused by the < 9Hz clipping effect?) - it is very hard to hear a difference. It might be that the fade out of that deep drum bass rumble rerverb is a bit more grungy with CS. Or I just imagined that. But again. that would be a 'dull crumble' or 'dull crunch' or so, but in no way 'clicks'.

 

[jasonhanjk]

Crosstalk issue is expected if there's no 4th wire for ground noise feedback.
CS43131 have 2 pins that require this feedback.

 

[Eddie]

Is possible. See here, measured at the XLR outputs.

It even goes down to -150dB. Honestly, even with professional devices, I didn't know that this was possible with balanced outputs.

 

[markanini]

'This russian website' confused me a lot by talking about 'clicks', a very clear and defined english word, that seems wrong for the content presented. I hear no 'clicks' in any of the sample files. What there is seems to be what is shown at the bottom in the zoomed waveform. The small dents in the sine are not audible, they are of very high frequency (see spectrogram, 90 kHz etc). Playing this at lower (normal) sample rates they would disappear completely.

The stated low frequency distortion (maybe caused by the < 9Hz clipping effect?) - it is very hard to hear a difference. It might be that the fade out of that deep drum bass rumble rerverb is a bit more grungy with CS. Or I just imagined that. But again. that would be a 'dull crumble' or 'dull crunch' or so, but in no way 'clicks'.

Crunchy artifacts would describe it better than clicking IMO. Or perhaps crackling.

Otherwise, you would include subdued discontinuous waveform artifacts into the definition-this is not what most think of when talking about click sounds.

Thanks for raising the issue, misnomers stick sometimes and cause confusion: https://www.fender.com/articles/techniques/pitch-control-a-tremolo-primer