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

[mightycicadalord]

MOTU support recommended me to file an issue to their techlink portal, so: "MTL169142 - Playback from the RCA outputs of M4 inverts the signals with 180-degrees (audio is out of phase)" got created.

I assume this was not resolved since they just asked me to demonstrate my issue on my ticket, oh well.

 

[trl]

"Issue Type
Other
TechLink Status
In Progress
Issue Date
Nov. 29, 2021, 11:23 p.m.
Products
M4"

No updates since then, so I followed up with them now.

 

[trl]

I assume this was not resolved since they just asked me to demonstrate my issue on my ticket, oh well.

They replied today saying that the issue cannot be reproduced. However, I re-explained them how to replicate it and nicely invited them to join this forum and take their customer support on the next level.

 

[mightycicadalord]

They got back to me with the same reply.

So can you recreate it? I'm going to assume my subs input phase was backwards, 0 was actually 180.

 

[trl]

QED: https://www.audiosciencereview.com/...d-few-in-house-measurements.17819/post-986235

 

[mightycicadalord]

I'm opening another ticket, but for a different issue. I'm not sure if anyone writes music here but for me, anything past 512 buffer is totally unusable. It makes no sense really. No matter that sample rate, 1024 and beyond causes massive amounts of underruns. I can have a nearly blank project open and still get issues with 1024 and up while 64 sample buffer works just fine? I am so confused. I'm exhibiting this behavior across two different computers with different DAW's.

 

[mightycicadalord]

So I updated my driver as it was out of date on my laptop, and now the same tracks that were working ok are completely unplayable. It's shocking how much worse it is. I'm no longer getting pops and clicks that you get with normal underruns, I'm getting complete silence that lasts several seconds between audio.

I have no idea what is was going on.

 

[mightycicadalord]

Sorry to make three posts in a row, but I narrowed my issue down to a bad plugin, which sucks because I use it a lot and it sounds great, Archtype Corey Wong. I will probably contact the devs of both FL and Archtype. I don't imagine this is relevant to most users here but hey. It's info on the web forever and might help someone.

 

[Hkat]

Hello.
I'm writing this message to ask for help from the forum members.

I got a MOTU M4 that is dead.
I have reworked some burnt DCDC control ICs and removed the short circuit on the power rail, but there is only one IC that is burnt and the marking is not readable.
It is a 6-pin IC, located near the USB TypeC connector.
Please give me information about the marking of this IC.
Also, if you know the model number, please let me know. Thank you very much for your help.

I am Japanese and do not speak English, so please forgive my poor English…

 

[Bamboszek]

My guess from layout that it would be some kind of USB high side switch IC (e.g. TPS2552) or integrated TVS diodes (e.g. IP4234CZ6)

 

[mightycicadalord]

I bet motu can tell you what it is if you contact them, but they're not going advise repair for liability reasons. do it anyway of course.

Your English is fine my friend.

 

[trl]

It's probably a power regulator os boost converter, maybe the SOT23-6 package. I am attaching a picture taken when I posted this review, so feel free to lookup after the marking code of...apparently S11. The part is the one from the left side, nearby the small inductor, which makes me think that we could be talking about a boost-converter after all.

http://www.smdmark.com/en-US/smd-code-S11.html has so many returns that makes me think that I might need to open up M4's case again and see if I can measure some In/Out voltages. Until I'll have time to do that, maybe others can post here their thoughts about this SMD 6-pin part.

 

[Hkat]

Thank you for your quick reply.
Based on your information, I found that this is most likely a high-side switch IC for USB power line.
I couldn't find the corresponding product in the S11 marking, but I thought so because the signal from the rocker switch reaches the pins of this IC.
However, the strange thing is that the differential signal from USB TypeC is connected to this IC.
The ferrite next to the IC seems to be a CMCC inserted in the USB differential signal line connecting the USB TypeC receptacle and the XMOS MCU.

Fortunately, I confirmed that the MOTU M4 works by shorting the two pins on the MCU side of the pattern of this IC. (The rocker switch does not work. but it starts immediately when the USB cable is connected.)
This is the operation to input 5V from USB to the DCDC converter power supply of the MCU.
My M4 has no audio output because the TPS65133, which generates the +-5V power supply for the internal op-amps, is burned out and I plan to replace it.
I will solder the new chip when it arrives.

The short circuit made the M4 work, but I'm still collecting information about the 6-pin IC marked S11, because I'm worried about the possibility of unexpected behavior.

Thank you guys !!

 

[trl]

Interesting findings, please do keep us updated.

However, how did you managed to burn so many chips from M4's board?

 

[Hkat]

It looks like the previous owner input the 12V to the Type C.
I don't understand how that happened...

It seems that the failure of the DCDC in short mode prevented the MCU from being damaged.

 

[spnc]

Anyone ever hear an update on the out of phase rca outputs?

Hi I would like to know about this too.

Someone commented on GS that the RCA out's is still phase inverted, some others are saying it's been fixed in the recent updates...

Who is right? Back in 2020 someone seemed to point out it was already fixed with 1.02 update.

Considering the potential M4 phase inverted issue, shall I connect my headphone amp to the RCA outs at the back or to the headphone amp?

I assume it will sound better/louder on the RCA outs (I'm not a big fan of the M4 headphone amp)? How do you guys use your headphone amp on the M4?

Also is the potential M4 phase inverted issue depending on whether I use a balanced versus unbalanced amp? Planning on getting the JDS atom lab.

Thank you.

 

[parenthetical]

I recently bought a M4, it is a new model, board revision 3.1 and rather different from this teardown.

for starters the board is blue not green and it doesn't say assembled in Austin any more.

DAC is now ES9026PRO, ADC is ES9840Q

opamps are still 1678 but they are SOIC8 not the square ones in the original.

headphone amp is still OPA1688 also now SOIC8

mic pres are still T6263

there's a large Atmel branded chip that seems to be a substitute for the Xmos one in the original

 

[Davide]

I recently bought a M4, it is a new model, board revision 3.1 and rather different from this teardown.

for starters the board is blue not green and it doesn't say assembled in Austin any more.

DAC is now ES9026PRO, ADC is ES9840Q

opamps are still 1678 but they are SOIC8 not the square ones in the original.

headphone amp is still OPA1688 also now SOIC8

mic pres are still T6263

there's a large Atmel branded chip that seems to be a substitute for the Xmos one in the original

View attachment 223100View attachment 223101View attachment 223102View attachment 223103View attachment 223104View attachment 223105View attachment 223106

Can you kindly post a picture of the whole pcb?
In first post I see rev 6... dont' understand this rev 3. Maybe we are speaking of different pcb layout?
However, all this difference is curious... maybe due to ic shortage.
Where did you buy it?

 

[MCH]

It seems the standard version 3:

Post in thread 'Motu M4 Audio Interface Review' https://audiosciencereview.com/foru...-m4-audio-interface-review.15757/post-1115478

 

[roykaandorp]

I also bought this interface, after testing I found the headphone output didn't work. After opening I saw there was a amateurish attempt to repair. The ferrite bead next to the headphone connector was missing and a failed bridge was made to the connector, you could also see the flux was still on the pcb. I bought it as new and it was sealed, because I opened it myself my warranty has been voided. I've mailed MOTU about it and I'm really wondering how they would handle this.
If I bridge the pads shall the noise be notable?