Motu M4 48V phantom noise

[fernandezjw]

Hi everyone, I hope you're all doing ok!

I'm a new Motu user and in some way, I feel really happy with my motu m4. But I have an issue with it and maybe you can help me:

Basic info:

Version
Firmware 2.02, driver 4.0.9.0087
OS
Windows 11 / 21H2
CPU
Intel(R) Core(TM) i7-10510U CPU @ 1.80GHz 2.30 GHz
RAM
16 Gb

Mics that I use:
Microphone AKG C414 XLS
Audio technica AT2020
behringer ecm8000

Issue:

Noise (listen to the file https://www.dropbox.com/s/t43xg1q566o8e ... e.wav?dl=0... noise with the akg, at sec 12 I turned 48V off but turned it back on sec 14. Turned the volume down slowly on sec 18 and turned it up again on sec 26).
The noise will dissapear even if I turn the 48V off, or if I turn the 2nd 48V power on with 2 plugged mics.

I got my unit back for replacement and motu did send a new unit. But is just the same situation. The interface has a problem on the circuit design?

Extra tests:

- Noise is there even on monitoring only or processed signal.

- It's not on specific mic but with any mic, the only difference is that higher impedance is related with more noise and different freq noise (higher freq noise on higher impedances).

- Noise is present even on monitors or earphones.

- Noise is present even with the lower input volume if the 48v phantom is on. But if I raise the volume, the noise becomes higher.

- Noise is the same even plugged into a pc or a direct USB adaptor.

- Noise is the same using a direct wall outlet or using 2 different furman power conditioners.

- Noise doesn't change with generic long XLR cable, or with a 3 ft mogami gold cable.


Thanks for reading, I´ll appreciate any comment.

[mikehalloran]

The noise will dissapear even if I turn the 48V off, or if I turn the 2nd 48V power on with 2 plugged mics.

Ok, this is weird.

Is the noise present with phantom on but no cables connected?

I know that the M4 is bus powered but how are you powering it exactly — from your PC or a powered hub?

Is your PC a desktop or laptop? If a laptop, does anything change if you switch to a different USB port? If you haven't tried this, do so—shouldn't be an issue with a desktop but try it anyway.

[fernandezjw]

Hello Mike, thank you so much for your answer.

Is the noise present with phantom on but no cables connected?

Something I haven't tried before: so with both monitors on for In 1L and 2R, both gains all the way up, input monitor all the way down to input monitor (no mix signal)... Actually there is a noise and changes the pitch with bot 48V on, but will not disappear. If I turn both 48V off, the noise goes away and just remains the floor noise.

Is your PC a desktop or laptop? If a laptop, does anything change if you switch to a different USB port? If you haven't tried this, do so—shouldn't be an issue with a desktop but try it anyway.

I did that test alredy... I have a laptop, but I also did the test but using a USB power adaptor (direct wall outlet and via furman power conditioner):

- Noise is the same even plugged into a pc or a direct USB adaptor.

[fernandezjw]

More info...


https://www.dropbox.com/s/d0e07k7mg945i ... 2.wav?dl=0

With mic on In 1 and a guitar on In 2, both gains all the way up

sec 0... none of the 48 V is on
sec 5.... In 1L 48 V is on until sec 14


2nd part

This has nothing plugged in, but both gains are all the way up

sec 20... only In 1L 48 V on
sec 23... In 2R 48 V is on (along with 1L)
sec 35... In 1L 48 V is off
sec 29... both 48V are off