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

[capslock]

Apologies if this has been covered before, but how do you go about dismantling the unit? I got some B-stock, but it appears someone (unsucessfully?) opened the unit. It came sans the screws of the front and back plates, and the knobs looked like someone had tried to yank them off with tweezers.

What is the correct way?
- remove rubber feet including screws?
- slide PCB with front and back plate still attached out?

 

[capslock]

Nobody?

 

[trl]

Sorry mate, but I can't remember the exact steps I did to remove the cover. However, by looking at the screws, it doesn't looks very complicated, so do give it a try by removing the bottom screws forst and see what's happening after.

 

[trl]

Apologies if this has been covered before, but how do you go about dismantling the unit? I got some B-stock, but it appears someone (unsucessfully?) opened the unit. It came sans the screws of the front and back plates, and the knobs looked like someone had tried to yank them off with tweezers.

What is the correct way?
- remove rubber feet including screws?
- slide PCB with front and back plate still attached out?

Hello and Happy New Year!

Hope you already managed to open it up in the end, but if not then see below.

Remove the four screws from the bottom

Close-up with two of the four screws from the bottom

Remove the five screws from the backside

Slowly take off the backside with or without removing the wires from the power knob​

The above operations should be done carefully and with the USB-C power adapter removed.

Sorry I couldn't post this earlier, due to the winter Hollidays I was streched a bit with my free time.

Good luck with your M4 and looking forward for some inside pics from yours, so we can see if the previous owner messed something inside or not.

 

[capslock]

Thanks. Unfortunately, the previous owner must have been a complete idiot. He put front panel screws meant to bite into the plastic sockets on the bottom plate where machine screws belong. So they have ruined the threads in the standoffs have become fused to these screws, turning with them and with no chance to remove.

 

[trl]

I see, so he was mixing plastic screws with metal screws with different threads pitch, sorry to hear that. However, functionality of the device will not get affected by this, but if you're not feeling comfy you can probably return it and get a new one. What's more important is warranty (if still exists) to not be voided by the affected screws holes.

If the device have no more warranty, you could probably use a soldering iron to heat the screws a bit, but not much, just enough to partially melt plastic standoffs, so you can easier remove the screws. Or maybe you could use a plier to remove the screws by pulling them anti-clockwise with the plier?

L.E.: Plastic standoffs are only the two ones form the RCA plugs, all others are metallics.

 

[Pancreas]

Does it make speakers pop when thrning on and off?

 

[MCH]

Does it make speakers pop when thrning on and off?

I cannot tell when turning on because my amp has audio sense but when turning off mine makes a weak click, nothing that bothers me too much but it is there.

But more significant than that, after i turn it off and while the amp is still on (it takes 10 minutes for the auto off to get triggered) i can hear a hum from the speakers. Note that the hum is not there when the Motu is on and note as well that there are two subs connected to the motu as well (via RCA). I am curious if other owners experience the same. My M4 is version 3

 

[umbral]

Does it make speakers pop when thrning on and off?

I cannot tell when turning on because my amp has audio sense but when turning off mine makes a weak click, nothing that bothers me too much but it is there.

But more significant than that, after i turn it off and while the amp is still on (it takes 10 minutes for the auto off to get triggered) i can hear a hum from the speakers. Note that the hum is not there when the Motu is on and note as well that there are two subs connected to the motu as well (via RCA). I am curious if other owners experience the same. My M4 is version 3

Bad speakers

 

[Pancreas]

I cannot tell when turning on because my amp has audio sense but when turning off mine makes a weak click, nothing that bothers me too much but it is there.

But more significant than that, after i turn it off and while the amp is still on (it takes 10 minutes for the auto off to get triggered) i can hear a hum from the speakers. Note that the hum is not there when the Motu is on and note as well that there are two subs connected to the motu as well (via RCA). I am curious if other owners experience the same. My M4 is version 3

I was told and read review saying they don't pop and maybe Motu added something a capacitor to block the pops, but I don't know how to confirm this

usually these pops are prevented with a delay or dc blocking capacitor

 

[trl]

Does it make speakers pop when thrning on and off?

Not in my case. My M4 gets into Mackie sub, then into Mackie speakers. I had tested few minutes ago with my M4 fed by a MacBook via USB-C to USB-A and no audible pop on both On and Off.

 

[Atanasi]

Not in my case. My M4 gets into Mackie sub, then into Mackie speakers. I had tested few minutes ago with my M4 fed by a MacBook via USB-C to USB-A and no audible pop on both On and Off.

M4 has a physical on/off switch in the back. There is an audible thump when switching that. I didn't check if connecting or disconnecting USB has an impact.

 

[trl]

I was refering to that switch, of course. During powering On & Off my M4 was connected to the MacBook. If an audio interface is or not connected to a laptop or PC is something that matters while performing suchs tests.

P.S.: No thumps an be heard im my setup while switching my M4 On or Off. Perhaps newer M4 versions might be prone to that or maybe something else in the setup.

 

[Atanasi]

P.S.: No thumps an be heard im my setup while switching my M4 On or Off. Perhaps newer M4 versions might be prone to that or maybe something else in the setup.

I have probably the first version.

 

[trl]

Me the same, check the first post of this thread.

 

[trl]

Here's an interesting sound recording I just got today, listen to the attached file and you'll notice:
- there is absolutely no thumps noise while powering the M4 On or Off
- there's static noise when M4 gets powered Off.

Well, the same static can be heard if the USB-C cable is plugged in Clarett 2Pre USB or in any other device (audio or no audio), but the "culprit" is generated by the MacBook Pro 16" (i9, not M1) connected to a Lenovo USB-C to USB-A mini-dock! In any other configuration or with any other lapotp or desktop tested I get zero static noise and, of course, absolute zero thump noise while powering On or Off.

So, in case someone is getting any static with the M4 or with another studio interface, I would suggest to check if there's some USB adapter or dock attached or, why not, test with another laptop or desktop and see if the noise is still there.

Best!

L.E.: Just realised now that the file attached earlier was not actually published here due to being .mp3 instead of image file, hence reattaching the sound file again, as a .zip file this time.

 

[frankcifuentes]

I'm super happy with my M4. I recently had a problem with the output 1. One of the TRS plugs got stuck, more likely cause it was smashed. Now the TRS jack seems to be bad. Do you know if repairing it is a "simple" thing? I guess I would have to replace the whole 2xTRS jack. Or should I send it to repair? Thanks

 

[trl]

It's a plug, so if the PCB is not destroyed it can just be simply replaced. If you have a local service/store that can do that for you might be even better. Maybe it's just simple pin from the plug that needs resoldered, you should be able to tell that after you'll open up the case.

 

[frankcifuentes]

Thank you for your response. The solder is good. The problem in fact was the plug was hit and the jack was damaged

 

[richlooker]

Thank for a great, thorough review! Based on this, I bought a Motu M4 for audio measurement&analysis purposes.

I have one issue; the input gain pots. I need to have a calibrated level, eg. I need to know that 0.775V RMS input measures -6dB. I can calibrate that in my measurement software (AudioTester), but just the slightest touch at the gain pot srews the calibration, and when I need higher or lower gain, I have to calibrate with a reference signal again.

I am thinking it should be possible to replace the pots with SP4T subminiature rotary switches, and use suitable precision resistors to get 0dB (full gain), -10dB, -20dB and -30dB. The best candidate switch I have found is a C&K one: https://no.mouser.com/ProductDetail/CK/RM104772BCB?qs=367PjNmvCmm6FSOFBATF3Q==

How challenging a task do you think this is?