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

jkim

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Introduction

Saaf1e4d8fd6243a89d564e08ae97878bz.jpg
PXL_20250407_190904741.jpg


Presented here is a review of the JCally JM20 Max based on detailed measurements. This DAC/headphone dongle has some features that piqued my curiosity:
  • It is a USB dongle that claims to provide relatively high unbalanced output power (195 mW @ 32 Ohm per channel), which is rare. Most dongles boasting high power measured at ASR, like the Fosi Audio DS1, DS2, and Tanchjim Luna, require balanced connection to headphones to access their maximum power.
  • Unlike the aforementioned devices with balanced outputs, it has a small, Apple-dongle-type form factor.
  • It is based on the Cirrus Logic CS43131---despite some undesirable behavior having been reported, it is a capable DAC chipset for this kind of application.
  • It uses a new Chinese-brand op-amp, SGM8262, as its headphone amp stage whose performance is not much known---some recently released Fiio portable DACs adopted it.
  • Relatively inexpensive (< $30).
In fact, Amir reviewed the standard JM20 which uses CS43131 with no additional headphone driver, and its measurements showed excellent performance. Can the JM20 Max be another value leader for those looking for a small yet powerful USB dongle that can be used with full-size headphones? Let's find out.

Measurement Setup
Results

First up is a 1 kHz sinusoid test under no load (10 kOhm):
JM20_1kHz_SINAD_LR_No_Load.png


This SINAD value essentially indicates that the additional headphone amp stage is very transparent, not adding much noise or distortion to the DAC chip's output. I also did the same test at its maximum volume:
JM20_1kHz_SINAD_No_Load_Max_Vol.png


Some incorrectly designed dongles clip with input of a 0 dbFS tone at the maximum volume, even if unloaded. That is not the case here. At its maximum output the SNR improves a little as expected, but harmonic products increase a little as well, resulting in 0.5 dB lower SINAD. But the distortion is still low, far below the audibility threshold.

Impressively, 32 Ohm loads do not lower the SINAD much:
JM20_1kHz_SINAD_LR_32Ohm.png


Performance of low-level 50 mV output is very nice, too:
JM20_1kHz_50mV_SINAD_LR_300Ohm.png


Its low-pass digital filter works great:
JM20_Filter_Right.png


Looking at its frequency / phase response, it seems that the default filter is the minimum-phase type:
JM20_FR_44p1_Right.png


Response at 96kHz sampling frequency:
JM20_FR_96kHz_Right.png


As expected the phase does not shift much in the audible band when the bandwidth is increased. If you're concerned about the phase shift, use a wide bandwidth setting.

Jitter suppression is great:
JM20_J-Test_24.png


Linearity (measured using 300 Ohm load) is great except for a tiny, 0.1 dB deviation for levels below -30 dB, just the same behavior as shown by the standard JM20:
JM20_MAX_Linearity.png


Multitone test:
JM20_Multitone.png


SMPTE IMD vs. output voltage under 300 Ohm load:
JM20_MAX_IMD_300_Ohm.png


Here we compare the JM20 Max to the E1DA 9039S---"the world's first dongle THD+N<-120db@12ohm." Indeed, the 9039S shows extremely low IMD levels especially at higher output voltages. But the results show that the JM20 Max's performance is no slouch.

How about IMD under 32 Ohm loads?
JM20_MAX_IMD_32_Ohm.png


Again, IMD levels are overall very low even under 32 Ohm.

THD+N vs. frequency is excellent, too:
JM20_MAX_THDN_vs_Frq.png


The above test was done using the 48 kHz bandwidth (i.e., 96 kHz sampling frequency) because any device based on CS43131 has somewhat elevated ultrasonic noise above 45 kHz due to noise shaping. See here:
JM20_MAX_FFT_Wide_BW.png

The most important tests for this dongle should be THD+N vs. output power:
JM20_Max_THD_vs_Power_300Ohm.png

JM20_Max_THD_vs_Power_32_Ohm.png

Note. (1) The E1DA 9039S was measured from its balanced output which is the only mode supported.
(2) All of the above THD+N vs. power tests were done with both channels driven.
(3) The bandwidth of 48 kHz was used.

This result easily makes it one of the top contenders in Amir's Portable DAC+Headphone Amp Power chart:
index.php


JM20 Max would be between Hidizs DH80s and Fosi Audio DS2, but it is the only device in the chart that can provide such high power from an unbalanced connection.

A chart of THD+N vs. output voltage (instead of power) is convenient for showing performance under various loads:
JM20_Max_THDN_vs_Volt.png


Its output impedance is close to zero at 0.57 to 0.58 ohm, measured using 100 Hz and 1 kHz sine tones for both channels. This is also indicated in the above chart showing the same noise levels under different impedance loads.

Lastly, some DACs based on CS43131 are known to exhibit abnormal 'clicking' behavior when the output level is in a certain range (see here for a detailed report). So, I performed a set of multitone tests by varying output levels:
JM20_R_Multitone_v_Lvl_dbFS.png


Just clean responses. Also performed were 10-tone tests, as suggested by the article linked above, at even more output levels as well as under 32 Ohm load. Check these out:
JM20_L_Multitone_v_Lvl.png JM20_L_Multitone_v_Lvl_32_Ohm.png

No issue was found.

Listening Test and Conclusion

Listening to music and other contents with Hifiman HE400SE (25 Ohm impedance) connected to the JM20 Max was very satisfying. I experienced no problem with its volume level for most music and online contents. Some classical music recorded at very low volume (to secure dynamic range) demanded more power. Otherwise, the JM20 Max provided sufficient, clean power in most cases.

Some USB DACs enter a 'power saving mode' after some seconds of no input. This seems to cause some weird volume ramp-up or fade-in/out issues. With the JM20 Max, I experienced no such problem. It appears to never enter such a mode! Not sure if this is a good thing. Perhaps that is the reason why it does not exhibit "clicking" behavior known to occur in CS43131-based DACs when the output level is in a certain range. In that respect it may be a good thing, but not good for battery life when used with a phone?

In sum, the JCally JM20 Max is a small yet versatile headphone dongle. The manufacturer is spot-on with their claimed output power: 195 mW @ 32 Ohm is exactly what I measured. Not only powerful but also very clean. It would serve as a very capable DAC, too---I have no problem using it with an external headphone amp if I need more power. This is a value leader in its class. But will it continue to be obtainable at a low price amid this ongoing trade war? We'll see.
 
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I just got one of these from AliExpress.

I can confirm, it sounds absolutely fine. :)
 
Yeah this combo of CS43131 + SGM8262 is definitely amazing, it's just concerns about the feasibility of such high power in such a small package and reliability concerns, a lot of people like me and others have had death and no audio issues with Fiio KA11, we will see if it's firmware or heat issues, hopefully JM20 Max doesn't exhibit such issues.
 
Just wow! And I don't mean the JM (ok, that one too) but your review! Thanks for all the details, really everything tested that we (I) would have liked to know.

Allow me a small comment, though:
>The most important tests for this dongle should be THD+N vs. output power:
In the first of the two pics there is no mention of the 9039s running/measured in balanced mode. That might confuse some. Maybe just add this info to the quoted text so you don't need to edit the pic.
 
I realize that negative prices aren't going to happen for these, but it's hard to believe a serious audio product could cost this little.
 
Allow me a small comment, though:
>The most important tests for this dongle should be THD+N vs. output power:
In the first of the two pics there is no mention of the 9039s running/measured in balanced mode. That might confuse some. Maybe just add this info to the quoted text so you don't need to edit the pic.
Alas, the time limit for editing has passed. In fact, the 9030S has only balanced outputs. I should've been clearer, though.
 
Notify the moderator, he can allow you more editing.
 
I found an interesting phenomenon about this device. I believe this occurs with any DAC built on CS43131 (and CS43198).

As discussed by @staticV3 and @amirm in the review of SMSL DL100 (see the thread from this post), CS43131 adopts a technique that increases dynamic range (DNR). Basically, it reduces analog gain when it meets with low-level signals and compensates for the decreased signal by applying digital gain. This way noise is reduced but the signal level is preserved. But information on precisely how it is implemented is not documented. Based on the data I observed for the JM20 Max---the only CS43131-based device that I own---, it seems that the way this DNR enhancement function is turned on is different from the way it is turned off.

Shown below are the rms noise level measurements from two separate 1 kHz sinusoid sweeps. The first sweep was from -120 dB to 0 dB, which is how this test is usually done, and the second swept from 0 dB to -120 dB (i.e., loud to soft levels):
JM20_MAX_Noise_Sweep.png


When the signal starts from a low level (-120 dB in this case), the DNR enhancement is turned on. Once it's on, the amount of noise reduction appears to be in its full state when the signal is lower than -40 dB, but above that level, noise reduction adapts to the signal, which seems to occur between -40 to -12 dB. In contrast, when the signal starts from a loud level, the function is turned off and responds to signal amplitude just like a brick wall. Noise reduction is turned on to its full state as soon as the signal reaches -51 dB.

More generally in music/audio playback, my guess is that whenever the signal goes below -50 dB in a certain time window, the DNR enhancement is turned on to its full state. But once it is turned on, going back to the off state does not occur by applying a single threshold, but rather signal-dependent, fine adjustment of analog/digital gain structure is made.

It has also been found that the DAC chip's digital compensation for analog gain reduction is not 100% accurate, which results in less than perfect linearity. See below for the measurements of linearity calculated from the above two sweeps:
JM20_Max_Linearity_Low_to_High.png

JM20_Max_Linearity_High_to_Low.png


Does this cause some unwanted audible effects? I doubt it. Just an interesting observation.
 
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Amazing review, great dongle. Congrats to both!
 
JM20 Max just arrived. Wow! That is exactly what I was looking for. Now I don't need the DS2 balanced anymore, this is far more comfortable, more than enough volume, power headroom and volume control reserve for my EU iPhone.

My first test was ramp-up issue on a Windows PC (as before with DS2) - none. I also did not hear any short noise on playback start (as reported for the non Max version). I used the already installed Bravo-HD ASIO drivers, but now I also see 'WASAPI headphone (CS43131+SGM826 HIFI Audio)' and that one works as well.

Will measure a bit on the weekend, but doubt it will be different to what is presented here already.
 
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Thanks for the review! Measurements look great! I just ordered one from Crinacle's website.
 
As discussed by @staticV3 and @amirm in the review of SMSL DL100 (see the thread from this post), CS43131 adopts a technique that increases dynamic range (DNR).
When the signal starts from a low level (-120 dB in this case), the DNR enhancement is turned on. Once it's on, the amount of noise reduction appears to be in its full state when the signal is lower than -40 dB, but above that level, noise reduction adapts to the signal, which seems to occur between -40 to -12 dB. In contrast, when the signal starts from a loud level, the function is turned off and responds to signal amplitude just like a brick wall. Noise reduction is turned on to its full state as soon as the signal reaches -51 dB.
Thank you! This is undisclosed information that has always circulated in scientifically oriented communities about the CS431xx DAC chips. DNR manipulation was confirmed, but the way it was implemented was unknown. Now with your measurements, everything is much clearer.
 
I'm using a JM20 Max dongle and there's noise when it's connected to a USB 3.2 port, but not with USB 2.0. Is this caused by interference or possibly overvoltage?
 
What noise? Laptop? Tried on battery?
 
What noise? Laptop? Tried on battery?
My setup is basically HD650 > JM20MAX > USB C to USB 3.0 > USB 3.2 PC Motherboard. When plugged into USB 3.2/3.0 there is hissing even when the music is playing also the driver still says USB 2.0 but it's fine when plugged into USB 2.0 no hissing. Do you think it's a driver/interface problem? Can someone replicate this to confirm?

I also have JCALLY JA3 CX31993 and it doesn't have that issue.
 
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I think it's a driver thing, when I plugged it back in via USB 3.0 for a while, the noise was still present, especially when playing music, but I realised the driver had not yet been installed until windows notified me the "CS43131+SGM8262 HIFI Audio is now ready" something similar, after which the noise is gone.
 
I would be curious to see crosstalk measurements for these dongles
Crosstalk is dictated from the quality of the ground connection from TRS female plug to internals of the USB-A connector. That value will change with cables plugged in, both by the basic design of the cable and the contact resistance of the TRS male jack. So whatever me or anyone else measures has no meaning for your personal setup.
 
Yeah this combo of CS43131 + SGM8262 is definitely amazing, it's just concerns about the feasibility of such high power in such a small package and reliability concerns, a lot of people like me and others have had death and no audio issues with Fiio KA11, we will see if it's firmware or heat issues, hopefully JM20 Max doesn't exhibit such issues.
I have washed mine twice in my laundry machine and use it daily. Months with zero problems. Do not worry too much.
 
maybe a stupid question but how does this compare to hidizs s9 pro? like that one but if this is comparable I might get it for even smaller dongle
 
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