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Motu M4 - Tear down, bit of internals analysis and few in-house measurements

AllanDavidson

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The Analogue to Digital conversion is done by the 4-channel AKM AK554VN chip that is able to provide a THD+N of -106 dB, pretty close to the -104 dB Amir measured on the Line-In 3/4 inputs here:

Just a minor correction, its AKM AK5554VN, and as the final number implies, it provide the 4-channel ADC to the Motu M4. The Motu M2 uses the 2-channel AKM AK5552VN instead.

What I don't understand, is that this is a high quality ADC capable of delivering 768 KHz @ 32bits and clean frequency vs THD, and yet it have some weird stuff happening on Amir's review. ¯\_(ツ)_/¯


Analogue inputs from the front panel are buffered by couple of OPA1678 op amps and the gain is adjusted by the dedicated THS4522 and THAT6263 chips. I am guessing that the first one acts as an input buffer and is having a fixed gain, while the second is changing the gain in 3dB, per manufacturer datasheet, although in real-life M4 mic inputs are fine adjusted by 1dB and not by 3dB. Perhaps someone else could jump in here with some thoughts about how the above two chips might be used inside the M2 & M4.

Well, both these preamps are stereo, and the M4 have 4 inputs to power, which can mean:

1) The inputs on the back share the preamps with the front inputs
2) The inputs on the back are not amplified, on the inputs on the front
3) The THS4522 operates on the back inputs, THAT6263 operates on frontal inputs.

Looking at the PCB, the XLR combos have identical circuitry, with the THAT6263 between them.

Also, the Headphone Monitor knob is a digital step controller that act on 1db steps. IIRC, the Input Monitors act in 0.05db steps instead.


_________

EDIT: A video of said step controller on the unit, plus an additional pot on the signal chain.

https://panther.kapsi.fi/site/files/motu_m4_potentiometer.mp4
 
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trl

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There should probably be an input stage opamp with a gain higher than 1. Or maybe the two THS4522 and THAT6263 chips are serialized somehow...not sure what to say. Here Motu engineers need to step up and reply. :)
 

AnalogSteph

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It would not surprise me if they were "filling in the gaps" and providing extra gain in the digital domain, which is a fairly trivial exercise these days. By the time you are providing +34 dB of analog gain, a -127 dBu EIN gets amplified to -93 dBu, equating to an SNR of 101 dB relative to 2 Vrms (+8 dBu). A 115 dB ADC will degrade this to 100.8 dB. So you'll have a whopping 0.2 dB more noise if you're only providing digital gain from this point on.
3) The THS4522 operates on the back inputs, THAT6263 operates on frontal inputs.
This seems a reasonable assumption. THAT6263 is basically a "microphone input frontend in a box", and the THS4522 would likely be used to form a fully differential line receiver stage.

Together with the +12.5 dBu (~9.2 Vpp) maximum headphone out, this makes me think that the entire unit runs on no higher than +/-5V analog supplies (the THS452x even is +5V only). So even the power supply section can remain appealingly minimal - they'll need some filtering for the incoming USB power (maybe an LDO tops) and an inverter to generate -5V, that's it.

I am not surprised that this approach resulted in a still rather inexpensive, yet comparatively well-performing interface. Having IC manufacturers do a lot of the heavy lifting for you definitely helps, and while picking more modern parts tends to drive up parts cost, it did permit reducing complexity.
 

AllanDavidson

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The reason why I got a M4 instead of every other recent budget interface out there, it's because it is a complete package for musicians, including MIDI ports, a frontal display for easy metering, very low latency, and very low headphone out impedance. All this in a mobile, USB-C powered compact metal enclosure.

I'm thinking about getting an Audient EVO 4 to use on my laptop when I'm traveling, it may be handy in the future.
 
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Together with the +12.5 dBu (~9.2 Vpp) maximum headphone out, this makes me think that the entire unit runs on no higher than +/-5V analog supplies (the THS452x even is +5V only). So even the power supply section can remain appealingly minimal - they'll need some filtering for the incoming USB power (maybe an LDO tops) and an inverter to generate -5V, that's it.
There is indeed 10V RMS on the opamp pins. :) There are some LDOs on the bord, in my previous post.
 

AllanDavidson

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Together with the +12.5 dBu (~9.2 Vpp) maximum headphone out, this makes me think that the entire unit runs on no higher than +/-5V analog supplies (the THS452x even is +5V only). So even the power supply section can remain appealingly minimal - they'll need some filtering for the incoming USB power (maybe an LDO tops) and an inverter to generate -5V, that's it.

Just a quick reminder that USB-C (if Power Delivery is used) can deliver a lot of power.

https://www.electronics-lab.com/usb-c-pd-module-provides-9v-12v-15v-20v-sells-1e/
 
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Motu M4 works with high-speed USB 2 ports, although it is plug-compatible with the USB 3 standard too. USB-C is just the plug on the interface side, but internally it works at high-speed USB 2. I'm not aware of a studio interface that works specifically with the new USB 3.0 standard and doesn't works under USB 2 computers, I'm sure there are, just not aware of any and I'm not sure if there will ever be an advantage of running under USB 3.0 protocols vs. USB 2.

However, the USB 3 socket and the cable will benefit of the 15 W power from a USB 3 compatible computer, like Clarett 2Pre USB does (although data transmission is still USB 2), but there is not the case of the Motu M4, because it will not benefit of the extra power of a USB 3 socket (my tests were done on a USB 3 blue port on a desktop computer).
 

AllanDavidson

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USB 2.0 can deliver up to theoretical 480 Mbps, this is enough to handle +64x [email protected] (6Mbps) in parallel, even if we account for losses and overhead, so data is not an issue, but power is.
 

Danny_K

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Is there a way that a hobbiest level solderer (such as myself) could modify the M2 and add coax spdif In / out?
Maybe with something like this or similar: https://www.minidsp.com/images/documents/Product Brief-MCHStreamer.pdf

My PC has a PCI-E audio interface with coax spdif in / out.
I’m thinking with an iOS audio interface with spdif in / out, I could use my iPad Pro as a virtual external effects rack via Auria or AUM.

My M2 is perfect for my music hobby workflow, except for ability to digitally connect to my PC while being connected to the iPad Pro.
There are a few iOS interfaces I’ve seen that offer coax spdif in / out, but nothing less than ~$500.
 
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Can't you record the virtual effects from your tablet and use them later in post processing while the M2 is connected to your computer via USB?

You might try to purchase some SPDIF to Analogue external adapter, most likely SPDIF to RCA, then you will need an RCA to XLR converter.

I also have a Clarett, I'm using the optical input from the TV to my active monitors, so you might swap the M4 with an audio interface that has optical input. I guess having an audio interface that can accept both optical and USB inputs might be more helpful.
 

umbral

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After @amirm published Motu M4's measurements review, several ASR members became interested in this audio interface, me included. I was able to get this from Thomann, after I almost decided to cancel my order due to manufacturer delay, but in the end I was able to get it after few weeks of waiting.

Details and specs about the M4 interface could be found on the manufacturer website: https://cdn-data.motu.com/manuals/usb-c-audio/M_Series_User_Guide.pdf.

The M4 was assembled in the U.S., it is actually written on the board VIRTEX - Austin, TX: https://www.virtex.us/. However, “Assembled in” is different than “Made in”, based on https://www.themadeinamericamovement.com/made-in-usa-certified/difference-between-assembled-made-in-usa/#:~:text=The product is assembled in,of Columbia, and U.S. territories., so I guess the board and soldering, but also the assembly of the parts are all done in the U.S. Probably the case and most of the electronic components are still manufactured in ASIA, perhaps in China, but not sure this matters much given that the final product is really good.


View attachment 95455
Motu M4 board from top

View attachment 95456
Motu M4 board from top

Soldering looks good to me, the board is clean on top and also on the bottom, just a bit of flux residue around the output plugs. Board is multi-layer and with a huge visible ground plane on top and bottom layers to minimize noise and interferences. Plugs are soldered very well and seem sturdy and not moving when I try to bend or pull them. Also, the RCA plugs from back are kept in place with a couple of dedicated screws, so it's very unlikely these plugs to move or become loose with time due to plugging/unplugging the cables.

All knobs, but all of them, even the small one from the headphones amplifier volume, are made of aluminum, not regular plastic like most interfaces in this price range. The black anodized aluminum case is not easy to get scratched, it seems robust and should last long.

The front display is fancy and eye catchy, a very good tool to get an idea about the input/output levels, although the OLED VU-meters are kind of slow, much slower than regular analogue lights from, let’s say, Scarlett interfaces. They’re displaying more of a top-averaging of the SPL of the sound, instead of rapid peaks, but if clipping occurs then the red light stays lit on top of the display for few seconds, so there should be no problem in getting a good recording after all.

I tend to press the 48V buttons when I unplug the XLR mic plugs with my fingers, so unbalanced dynamic mics might get destroyed by this (https://www.shure.com/es-CO/desempeno-y-produccion/louder/top-8-microphone-myths-exposed) or the phantom power itself might get damaged, depends. Some say (https://royerlabs.com/ribbon-mics-and-phantom-power/#:~:text=The ribbon elements in some,stretched or completely blown ribbon) that older ribbon mics could also get damaged by the 48V too, so take good care when unplugging such mics from the M2/M4 or simply power it off before doing this, as it is also recommended, due to the inherent noise that pops into the speakers anyway. However, I'm using balanced dynamic and condenser mics, so I don't are much about this.


View attachment 95458
OPA1678 operational amplifiers buffers DAC outputs

Six OPA1678 (https://www.ti.com/lit/ds/symlink/opa1678.pdf), marked as TI 02 1AW7, are used as output buffers for the four TRS and RCA outputs from the backside of the case. These are connected between the DAC-outputs and the interface balanced output plugs, so the TRS and RCA outputs are direct-coupled, without any capacitors in between.


View attachment 95461
OPA1678 THD+N from TI datasheet

One OPA1688 is the driver for the headphones. This is a dedicated op amp for use as output buffer for headphones output and is able to deliver 50mA @32Ohms with a very low distortion and noise. Despite it’s relatively low output power, I was able to listen to comfortable levels to headphones like AKG K701 (62 Ohms and relatively hard to drive) and LCD2-F. However, when switching to Hifiman HE-560 the OPA1688 powered by the 10V rails was not able to deliver enough power to put the joy on my face, so for hard to drive cans an external headamp might be required. When headphones volume knob passes 3 o’clock, with 0dB recorded music, distortions become clearly audible, but this output volume is too much anyway for most studio monitoring headphones, so keeping the volume below 3 o’clock seems reasonable enough.

View attachment 95462
OPA1688 THD+N from TI datasheet


View attachment 95473
OPA1688 headphones output buffer

The USB interfacing is handled by the XMOS XU216-256-TQ128-C20 microcontroller chip. Nearby there is a SO8 chip that might be ST922 op amp (https://www.st.com/resource/en/datasheet/ts922.pdf); given it’s 0.005% THD+N and its location I’m sure it was not placed in the audio signal path, so it’s probably there for a different reason (comparator?, protection?). A flash memory (http://www.issi.com/WW/pdf/25LP-WP080D-040D-020D.pdf) was probably used to store the firmware, so future upgrades can be easily done through the dedicated MOTU application.



To combat ripple and noise MOTU installed eight aluminum polymer surface-mount capacitors on the board. Initially I thought that these capacitors were Nichicon CS-series, but on a closer look I find them more likely to be the ones manufactured by a Chinese brand named YTF, more details could be found here: https://www.ytfcapacitor.com/smd-capacitor/Hot-Offer-SMD-470uF-SMD-Electrolytic-Capacitors.html. Also, JB seems that used to manufacture similar looking caps as well: https://www.jbcapacitors.hk/post/2010_7.html. If I am right about the YTF manufacturer, then these caps are rated with a “load life” between 3000-5000 hours, although no datasheet could be found to be downloaded. We could probably press the “wirte us” button from their webpage to ask them about more details about these caps. However, their video presentation
shows us a decent manufactory, so I guess the caps are pretty decent, but time will tell. There are also several smaller capacitors on the boards as well, but unable to tell the manufacturer.

We can also spot seven Panasonic FK-series polymer capacitors, probably used for decoupling purposes.

The device is powered via the USB-C plug, so the 5V coming from computer's USB is split into +/-5V by the 250mA dual converter TPS65133 chip (TI 87I C1NC marking on the board). Inside the chip there is a boost converter that generates the +5V and an inverting buck-boost converter that generates -5V; this way the internal op amps and other active components from M4’s board will be powered by a total of 10V, the headphones driver too.


View attachment 95466
TPS65133 dual converter responsible for getting the +/-5V rails

On the board there are several LDO regulators like: https://www.ti.com/lit/ds/symlink/lp5907.pdf, https://www.ti.com/lit/ds/symlink/lp5912-q1.pdf etc.

The MIDI input, being a serial transmission protocol, is using a H11L1M optocoupler for protection, more details to https://hackaday.com/2018/05/09/opt...microcontroller-midi-and-a-hot-tip-for-speed/ and to https://learn.sparkfun.com/tutorials/midi-tutorial/hardware--electronic-implementation. Per Wikipedia (https://en.wikipedia.org/wiki/MIDI): “Opto-isolators keep MIDI devices electrically separated from their connectors, which prevents the occurrence of ground loops[75]:63 and protects equipment from voltage spikes”.



Digital to Analog Conversion is done by the -110 dB THD+N ESS ES9016S 8-channel chip. Four channels are used for the four outputs from the backside (two for Monitor Out and two for Line Out), while two seem to be used for driving the headphones, via the two 4580R (https://www.ti.com/lit/ds/slos412d/slos412d.pdf) operational amplifiers and the OPA1688 buffer. The other two channels from the ES9016S DAC chip don't seem to be connected to the board.



View attachment 95488
4580R operational amplifiers, placed between DAC and output buffer

Worth mentioning that Headphones-Out is mirroring the 1/2 Monitor outputs only, so when using the 3/4 Line outputs with an external amplifier, pre-amp or mixer you will not be able to use the built-in headphones amplifier. Also, to listen to both 1/2 and 3/4 outputs you will need an application that knows how to work with both outputs at the same time, like a 4-channels player, otherwise the operating system will see the two output as two distinct playback devices and choose only one of them as being primary.

The Analogue to Digital conversion is done by the 4-channel AKM AK554VN chip that is able to provide a THD+N of -106 dB, pretty close to the -104 dB Amir measured on the Line-In 3/4 inputs here: https://www.audiosciencereview.com/forum/index.php?threads/motu-m4-audio-interface-review.15757/.


View attachment 95469
AKM AK554VN ADC chip

Internal 40MHz quartz clock from around the AKM4554 ADC chip is an American brand: ILSI; not sure these are entirely manufactured in US, but based on https://abracon.com/about they do have headquarter and facilities in Spicewood, TX. I was able to find couple of datasheets too, just not the exact match type for the TCXO installed inside the M4: https://abracon.com/datasheets/ILSI/I533.pdf and https://www.tme.com/Document/5876ac880aecd10660839d4d7584f0de/I547_I747_Series.pdf. Probably the 24MHz TCXO from nearby the XMOS microcontroller is made by ILSI too.​


View attachment 95471
ILSI TCXO nearby the ESS DAC and AKM ADC chips

Analogue inputs from the front panel are buffered by couple of OPA1678 op amps and the gain is adjusted by the dedicated THS4522 and THAT6263 chips. I am guessing that the first one acts as an input buffer and is having a fixed gain, while the second is changing the gain in 3dB, per manufacturer datasheet, although in real-life M4 mic inputs are fine adjusted by 1dB and not by 3dB. Perhaps someone else could jump in here with some thoughts about how the above two chips might be used inside the M2 & M4.


View attachment 95472
THAT6263 dedicated microphone pre-amplifier

Motu M4 is a good looking USB audio interface with a very low latency (<5ms is using 128Kbs buffer) and drivers and control interface are robust under Windows and work flawless, although under MacOS I wasn’t able to find any control panel to do some more settings to the M4. I’m probably spoiled by the Focusrite control panel where several mixing and audio rerouting can be done with ease, but Motu comes in handy with its “loopback audio recording” so everyone can record the audio track that is playing at the same moment (e.g.: recording audio track while playing Tidal or while having a Whatsup call with a friend etc.).

The backside 3/4 balanced Line In TRS plugs are bypassing the input gain controls and can be used for audio measurements with a THD+N of -106 dB, per Amirm’s measurements. However, if you’re not comfortable with the fixed input level where 0 dBFS is a bit over 6 V RMS, then you could do your audio measurements on the 1/2 gain adjustable inputs, but increasing the gain will increase the noise a bit, making the M4 more or less an option for sensitive audio measurements, depending on your needs.

Despite all the THD measurements done to audio interfaces, home microphone recordings done with different modern audio interfaces will usually measure and sound very similar, because today audio interfaces are very capable, while most microphones are having a THD up to 1% @94 dB-SPL. Basically, regarding the THD of the final track, I consider the limiting factor being the microphone itself and not the actual audio interface, due to the transducer (https://www.shure.com/es-CL/desempeno-y-produccion/louder/mic-basics-transducers) and the diaphragm inside. So switching from one interface to another might be considered an upgrade if the EIN of the interface is lower (that means lower noise preamps), more inputs or the internal gain is higher, to better accommodate low sensitivity mics, without worrying much about the THD of the audio interface, which usually is way above the capabilities of the microphone itself. A great reading would be: https://www.neumann.com/homestudio/en/will-a-better-preamp-give-you-lower-noise.


View attachment 95477
SE X1S connected to Motu M4 @60Hz sinewave

View attachment 95478
SE X1S connected to Focusrite Solo Gen3 @60Hz sinewave

View attachment 95480
ECM999 mic connected to M4 - THD sweep

View attachment 95482
ECM999 mic connected to Solo Gen3 - THD sweep
As we can se from the above two screenshots, using the same microphone to two different audio interfaces, made by different manufacturers too, didn't changed much the harmonic profile nor the final THD+N, although track's recorded background noise might be different in the final mix, depending on the EIN of each interface.

Motu M4 has a EIN of -129 dBu at maximum gain, measured with a 150Ω resistor, A-weighted . Testing the M4 on my high impedance 600 Ohms and rather low sensitivity AKG D5 S dynamic mic (2.6 mV/Pa or -51.7 dBV/94 dB-SPL) proved a low noise recording and the +60 dB of internal gain was pretty much OK, even for low talk during the night.

Moving on the SE X1S condenser mic, which is a very sensitive one (30 mV/Pa or -30.5 dBV/94 dB-SPL), I didn’t noticed any significant background noise and even the tiniest move of the lips was clearly recorded on the track.

In case you’re wondering if the 150 Ohms 1.12 mV (-59 dBV/94 dB-SPL) sensitivity SHURE SM7B dynamic mic will be a good match for the +60 dB of gain from the M4, I don’t have one SM7B to test it right now, but if you’re a low talker then you will probably be needing an interface having at least +65 dB of gain or add an in-line or an external pre-amp to gain few more extra dB. However, in this thread https://www.audiosciencereview.com/forum/index.php?threads/which-preamp-for-sm7b.14028/#post-427838 there’s lot of talking about the SM7B/M4 compatibility and seems that under normal conditions the match between the SM7B and M4 should be a decent one.

Worth mentioning that with 1V or 2V analogue signals the M4 will have a THD+N worse than the one measured by Amir at Full Scale on both DAC-out and ADC-in.

View attachment 95484
Solo Gen3 outputting 1V RMS into M4

View attachment 95485
M4 outputting 1V RMS into M4

We can easily spot the added noise shape when lowering the DAC volume on the Motu M4. Seems that the analogue volume control in Solo Gen3 handles better this noise. Basically, M4 has this issue only when volume knob is between 10:30 and 1:30 o'clock, otherwise the noise gets lower.

Overall, I find the Motu M4 being a great interface, it has a good amount of gain, a proved low noise when fed with both dynamic and condenser mics and is capable of a clean audio recording and playback.

What will happen when the 3000-5000 hour capacitors die like the specifications say ?
If you keep the device on the capacitors work all the time. It will die after that ?

What is the normal lifespan of Motu in your opinion, taking into account the components it uses ?
 
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trl

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What will happen when the 3000-5000 hour capacitors die like the specifications say ?
Well, what usually happens in all electronic devices, TVs included. :)

However, those 3000 hours are counted at 80C, not at 40C, so in real life and with 6-8h/day usage I expect at least 4-5 years of operation. Also, only those caps that are dealing with lot of ripple might have troubles, not the others.
 

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When using monitor out, my copy can achieve the best THD + N at around 3 o'clock. Also a home made u-pad (-30dB) performs slightly better (around 2dB better) than software volume control and main knob volume control. Overall, very satisfied with this purchase.
 
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You are using TRS - Monitor instead of TRS - Line Out? By 'home made u-pad" are you referring to an external analogue volume knob?

Thanks!
 

lizhuoyin

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You are using TRS - Monitor instead of TRS - Line Out? By 'home made u-pad" are you referring to an external analogue volume knob?

Thanks!
Yes, I am using TRS - Monitor Out because I want to compare performances among software/M4 main knob/attenuator.
The home made u-pad is an -30dB balanced attenuator cable I made.
 

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After @amirm published Motu M4's measurements review, several ASR members became interested in this audio interface, me included. I was able to get this from Thomann, after I almost decided to cancel my order due to manufacturer delay, but in the end I was able to get it after few weeks of waiting.

Details and specs about the M4 interface could be found on the manufacturer website: https://cdn-data.motu.com/manuals/usb-c-audio/M_Series_User_Guide.pdf.

The M4 was assembled in the U.S., it is actually written on the board VIRTEX - Austin, TX: https://www.virtex.us/. However, “Assembled in” is different than “Made in”, based on https://www.themadeinamericamovement.com/made-in-usa-certified/difference-between-assembled-made-in-usa/#:~:text=The product is assembled in,of Columbia, and U.S. territories., so I guess the board and soldering, but also the assembly of the parts are all done in the U.S. Probably the case and most of the electronic components are still manufactured in ASIA, perhaps in China, but not sure this matters much given that the final product is really good.


View attachment 95455
Motu M4 board from top

View attachment 95456
Motu M4 board from top

Soldering looks good to me, the board is clean on top and also on the bottom, just a bit of flux residue around the output plugs. Board is multi-layer and with a huge visible ground plane on top and bottom layers to minimize noise and interferences. Plugs are soldered very well and seem sturdy and not moving when I try to bend or pull them. Also, the RCA plugs from back are kept in place with a couple of dedicated screws, so it's very unlikely these plugs to move or become loose with time due to plugging/unplugging the cables.

All knobs, but all of them, even the small one from the headphones amplifier volume, are made of aluminum, not regular plastic like most interfaces in this price range. The black anodized aluminum case is not easy to get scratched, it seems robust and should last long.

The front display is fancy and eye catchy, a very good tool to get an idea about the input/output levels, although the OLED VU-meters are kind of slow, much slower than regular analogue lights from, let’s say, Scarlett interfaces. They’re displaying more of a top-averaging of the SPL of the sound, instead of rapid peaks, but if clipping occurs then the red light stays lit on top of the display for few seconds, so there should be no problem in getting a good recording after all.

I tend to press the 48V buttons when I unplug the XLR mic plugs with my fingers, so unbalanced dynamic mics might get destroyed by this (https://www.shure.com/es-CO/desempeno-y-produccion/louder/top-8-microphone-myths-exposed) or the phantom power itself might get damaged, depends. Some say (https://royerlabs.com/ribbon-mics-and-phantom-power/#:~:text=The ribbon elements in some,stretched or completely blown ribbon) that older ribbon mics could also get damaged by the 48V too, so take good care when unplugging such mics from the M2/M4 or simply power it off before doing this, as it is also recommended, due to the inherent noise that pops into the speakers anyway. However, I'm using balanced dynamic and condenser mics, so I don't are much about this.


View attachment 95458
OPA1678 operational amplifiers buffers DAC outputs

Six OPA1678 (https://www.ti.com/lit/ds/symlink/opa1678.pdf), marked as TI 02 1AW7, are used as output buffers for the four TRS and RCA outputs from the backside of the case. These are connected between the DAC-outputs and the interface balanced output plugs, so the TRS and RCA outputs are direct-coupled, without any capacitors in between.


View attachment 95461
OPA1678 THD+N from TI datasheet

One OPA1688 is the driver for the headphones. This is a dedicated op amp for use as output buffer for headphones output and is able to deliver 50mA @32Ohms with a very low distortion and noise. Despite it’s relatively low output power, I was able to listen to comfortable levels to headphones like AKG K701 (62 Ohms and relatively hard to drive) and LCD2-F. However, when switching to Hifiman HE-560 the OPA1688 powered by the 10V rails was not able to deliver enough power to put the joy on my face, so for hard to drive cans an external headamp might be required. When headphones volume knob passes 3 o’clock, with 0dB recorded music, distortions become clearly audible, but this output volume is too much anyway for most studio monitoring headphones, so keeping the volume below 3 o’clock seems reasonable enough.

View attachment 95462
OPA1688 THD+N from TI datasheet


View attachment 95473
OPA1688 headphones output buffer

The USB interfacing is handled by the XMOS XU216-256-TQ128-C20 microcontroller chip. Nearby there is a SO8 chip that might be ST922 op amp (https://www.st.com/resource/en/datasheet/ts922.pdf); given it’s 0.005% THD+N and its location I’m sure it was not placed in the audio signal path, so it’s probably there for a different reason (comparator?, protection?). A flash memory (http://www.issi.com/WW/pdf/25LP-WP080D-040D-020D.pdf) was probably used to store the firmware, so future upgrades can be easily done through the dedicated MOTU application.



To combat ripple and noise MOTU installed eight aluminum polymer surface-mount capacitors on the board. Initially I thought that these capacitors were Nichicon CS-series, but on a closer look I find them more likely to be the ones manufactured by a Chinese brand named YTF, more details could be found here: https://www.ytfcapacitor.com/smd-capacitor/Hot-Offer-SMD-470uF-SMD-Electrolytic-Capacitors.html. Also, JB seems that used to manufacture similar looking caps as well: https://www.jbcapacitors.hk/post/2010_7.html. If I am right about the YTF manufacturer, then these caps are rated with a “load life” between 3000-5000 hours, although no datasheet could be found to be downloaded. We could probably press the “wirte us” button from their webpage to ask them about more details about these caps. However, their video presentation
shows us a decent manufactory, so I guess the caps are pretty decent, but time will tell. There are also several smaller capacitors on the boards as well, but unable to tell the manufacturer.

We can also spot seven Panasonic FK-series polymer capacitors, probably used for decoupling purposes.

The device is powered via the USB-C plug, so the 5V coming from computer's USB is split into +/-5V by the 250mA dual converter TPS65133 chip (TI 87I C1NC marking on the board). Inside the chip there is a boost converter that generates the +5V and an inverting buck-boost converter that generates -5V; this way the internal op amps and other active components from M4’s board will be powered by a total of 10V, the headphones driver too.


View attachment 95466
TPS65133 dual converter responsible for getting the +/-5V rails

On the board there are several LDO regulators like: https://www.ti.com/lit/ds/symlink/lp5907.pdf, https://www.ti.com/lit/ds/symlink/lp5912-q1.pdf etc.

The MIDI input, being a serial transmission protocol, is using a H11L1M optocoupler for protection, more details to https://hackaday.com/2018/05/09/opt...microcontroller-midi-and-a-hot-tip-for-speed/ and to https://learn.sparkfun.com/tutorials/midi-tutorial/hardware--electronic-implementation. Per Wikipedia (https://en.wikipedia.org/wiki/MIDI): “Opto-isolators keep MIDI devices electrically separated from their connectors, which prevents the occurrence of ground loops[75]:63 and protects equipment from voltage spikes”.



Digital to Analog Conversion is done by the -110 dB THD+N ESS ES9016S 8-channel chip. Four channels are used for the four outputs from the backside (two for Monitor Out and two for Line Out), while two seem to be used for driving the headphones, via the two 4580R (https://www.ti.com/lit/ds/slos412d/slos412d.pdf) operational amplifiers and the OPA1688 buffer. The other two channels from the ES9016S DAC chip don't seem to be connected to the board.



View attachment 95488
4580R operational amplifiers, placed between DAC and output buffer

Worth mentioning that Headphones-Out is mirroring the 1/2 Monitor outputs only, so when using the 3/4 Line outputs with an external amplifier, pre-amp or mixer you will not be able to use the built-in headphones amplifier. Also, to listen to both 1/2 and 3/4 outputs you will need an application that knows how to work with both outputs at the same time, like a 4-channels player, otherwise the operating system will see the two output as two distinct playback devices and choose only one of them as being primary.

The Analogue to Digital conversion is done by the 4-channel AKM AK554VN chip that is able to provide a THD+N of -106 dB, pretty close to the -104 dB Amir measured on the Line-In 3/4 inputs here: https://www.audiosciencereview.com/forum/index.php?threads/motu-m4-audio-interface-review.15757/.


View attachment 95469
AKM AK554VN ADC chip

Internal 40MHz quartz clock from around the AKM4554 ADC chip is an American brand: ILSI; not sure these are entirely manufactured in US, but based on https://abracon.com/about they do have headquarter and facilities in Spicewood, TX. I was able to find couple of datasheets too, just not the exact match type for the TCXO installed inside the M4: https://abracon.com/datasheets/ILSI/I533.pdf and https://www.tme.com/Document/5876ac880aecd10660839d4d7584f0de/I547_I747_Series.pdf. Probably the 24MHz TCXO from nearby the XMOS microcontroller is made by ILSI too.​


View attachment 95471
ILSI TCXO nearby the ESS DAC and AKM ADC chips

Analogue inputs from the front panel are buffered by couple of OPA1678 op amps and the gain is adjusted by the dedicated THS4522 and THAT6263 chips. I am guessing that the first one acts as an input buffer and is having a fixed gain, while the second is changing the gain in 3dB, per manufacturer datasheet, although in real-life M4 mic inputs are fine adjusted by 1dB and not by 3dB. Perhaps someone else could jump in here with some thoughts about how the above two chips might be used inside the M2 & M4.


View attachment 95472
THAT6263 dedicated microphone pre-amplifier

Motu M4 is a good looking USB audio interface with a very low latency (<5ms is using 128Kbs buffer) and drivers and control interface are robust under Windows and work flawless, although under MacOS I wasn’t able to find any control panel to do some more settings to the M4. I’m probably spoiled by the Focusrite control panel where several mixing and audio rerouting can be done with ease, but Motu comes in handy with its “loopback audio recording” so everyone can record the audio track that is playing at the same moment (e.g.: recording audio track while playing Tidal or while having a Whatsup call with a friend etc.).

The backside 3/4 balanced Line In TRS plugs are bypassing the input gain controls and can be used for audio measurements with a THD+N of -106 dB, per Amirm’s measurements. However, if you’re not comfortable with the fixed input level where 0 dBFS is a bit over 6 V RMS, then you could do your audio measurements on the 1/2 gain adjustable inputs, but increasing the gain will increase the noise a bit, making the M4 more or less an option for sensitive audio measurements, depending on your needs.

Despite all the THD measurements done to audio interfaces, home microphone recordings done with different modern audio interfaces will usually measure and sound very similar, because today audio interfaces are very capable, while most microphones are having a THD up to 1% @94 dB-SPL. Basically, regarding the THD of the final track, I consider the limiting factor being the microphone itself and not the actual audio interface, due to the transducer (https://www.shure.com/es-CL/desempeno-y-produccion/louder/mic-basics-transducers) and the diaphragm inside. So switching from one interface to another might be considered an upgrade if the EIN of the interface is lower (that means lower noise preamps), more inputs or the internal gain is higher, to better accommodate low sensitivity mics, without worrying much about the THD of the audio interface, which usually is way above the capabilities of the microphone itself. A great reading would be: https://www.neumann.com/homestudio/en/will-a-better-preamp-give-you-lower-noise.


View attachment 95477
SE X1S connected to Motu M4 @60Hz sinewave

View attachment 95478
SE X1S connected to Focusrite Solo Gen3 @60Hz sinewave

View attachment 95480
ECM999 mic connected to M4 - THD sweep

View attachment 95482
ECM999 mic connected to Solo Gen3 - THD sweep
As we can se from the above two screenshots, using the same microphone to two different audio interfaces, made by different manufacturers too, didn't changed much the harmonic profile nor the final THD+N, although track's recorded background noise might be different in the final mix, depending on the EIN of each interface.

Motu M4 has a EIN of -129 dBu at maximum gain, measured with a 150Ω resistor, A-weighted . Testing the M4 on my high impedance 600 Ohms and rather low sensitivity AKG D5 S dynamic mic (2.6 mV/Pa or -51.7 dBV/94 dB-SPL) proved a low noise recording and the +60 dB of internal gain was pretty much OK, even for low talk during the night.

Moving on the SE X1S condenser mic, which is a very sensitive one (30 mV/Pa or -30.5 dBV/94 dB-SPL), I didn’t noticed any significant background noise and even the tiniest move of the lips was clearly recorded on the track.

In case you’re wondering if the 150 Ohms 1.12 mV (-59 dBV/94 dB-SPL) sensitivity SHURE SM7B dynamic mic will be a good match for the +60 dB of gain from the M4, I don’t have one SM7B to test it right now, but if you’re a low talker then you will probably be needing an interface having at least +65 dB of gain or add an in-line or an external pre-amp to gain few more extra dB. However, in this thread https://www.audiosciencereview.com/forum/index.php?threads/which-preamp-for-sm7b.14028/#post-427838 there’s lot of talking about the SM7B/M4 compatibility and seems that under normal conditions the match between the SM7B and M4 should be a decent one.

Worth mentioning that with 1V or 2V analogue signals the M4 will have a THD+N worse than the one measured by Amir at Full Scale on both DAC-out and ADC-in.

View attachment 95484
Solo Gen3 outputting 1V RMS into M4

View attachment 95485
M4 outputting 1V RMS into M4

We can easily spot the added noise shape when lowering the DAC volume on the Motu M4. Seems that the analogue volume control in Solo Gen3 handles better this noise. Basically, M4 has this issue only when volume knob is between 10:30 and 1:30 o'clock, otherwise the noise gets lower.

Overall, I find the Motu M4 being a great interface, it has a good amount of gain, a proved low noise when fed with both dynamic and condenser mics and is capable of a clean audio recording and playback.
Wow thanks for the insight including cross references to other ASR threads!! This kind of dedicated articles makes the name Motu which I didn't knew to one I will follow closely. Thanks!!!!
 

lizhuoyin

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More tests with my MOTU M4.
Connected a TRS to XLR balanced cable from Monitor OUT 1 to MIC IN 1;
Feeded -5.00 dBFS 1K sine wave in REW;
The main knob range best for THD+N (-99 dBFS to -100 dBFS) is around 3 o'clock. The main knob range is corresponding REW input RMS between -12.24 dBFS and -4.74 dBFS.
 

umbral

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Well, what usually happens in all electronic devices, TVs included. :)

However, those 3000 hours are counted at 80C, not at 40C, so in real life and with 6-8h/day usage I expect at least 4-5 years of operation. Also, only those caps that are dealing with lot of ripple might have troubles, not the others.

Thank you.
Does Focusrite Clarett has has worse capacitors comapred to M2/M4 ? Rated at ~2000 or less ?

https://www.audiosciencereview.com/...analysis-and-few-in-house-measurements.18605/
 
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