Disabling the input monitoring of the IMG Stageline MX-2IO USB audio interface

Having just one more switch for what we are going to do would have been nice...

The front of the IMG Stageline MX-2IO

The back of the IMG Stageline MX-2IO

Since the IMG Stageline MX-2IO (or MX-21O or MX-210) doesn't allow the user to disable the input monitoring, I went ahead and found a somewhat easy solution that involves taking the audio interface apart and rerouting the headphone / monitor / PC speaker audio path by using two female to female jumper cables.

Be sure to have a screw driver with a good amount of different bits for it because this device uses several different types of screw heads.

Remove the four silver screws of the front, the four screws of the left and right side, two screws of the top rear edge and the two screws around the USB Type B port.

Once you've done that you can slide the casing towards its rear end, though it is a bit fiddly.

The inside of the IMG Stageline MX-2IO

Inside there is one mainboard and three daughter boards. The digital aspect of the device with its USB port resides on a single small daughter board and only offers a single stereo output and two mono inputs, the DACs and ADCs are integrated into the "HANMUS" chip, which identifies itself via USB as "USB AUDIO 24BIT" with a Vendor ID and Product ID of 0418:1418 (hex). Everything else is analogue. The potentiometer board receives audio signals, attenuates these with the volume knobs and then sends the audio back to the motherboard. The third daugher board provides the level meters but these work by themselves and are not controlled by the main audio chip. I found that the inputs do clip even before the clipping LED lights up, so these meters should be taken with a grain of salt. The motherboard contains dozens of OP amps of various manufacturers.

The signal path goes like that:

For each input, the 6.35mm jack input and XLR input are mixed together. Based on the pad function, each input may be attenuated by approximately 20 dB. The inputs then get sent off to the potentiometer board for attenuation. The level meters receive the inputs and will display the measurement. If the ST/M switch is flipped to "mono", both input one and two are mixed together. The auxiliary input from the front is mixed as is and not affected by the ST/M switch. Only then this goes to the USB daughter board (not joking). The system output of the USB board are mixed with the mono/stereo fiasco and are then again sent to the potentiometer board to attenuate that for the headphone and monitor / PC speaker outputs. The PC speaker output receives the mix as is, the volume for it can't be controlled but somehow still goes over the potentiometer board.

The inside of the IMG Stageline MX-2IO from another perspective

Since you've already unscrewed the USB board, you should be able to remove it from the mainboard. The potentiometer board has to be unscrewed too so that it can be removed. Watch as you do it, because reseating it back into its place is a bit fiddly because some of the pin grid arrays are colliding with the components of the mainboard.

A close up of the connection points we want to mess with

In order to get rid of the monitoring mix, we just bend two pins away by 90° for both the USB board and the potentiometer board and then connect both sides with each other as shown in the picture above. Thus whatever the USB board is outputting will be sent over directly to the potentiometer board as a audio source for all three outputs, bypassing the monitoring mix of the mainboard. Quick side note, the two test pads that go right in front of the two sys out pins are not connected to any audio path but instead are for power probing :)

Our mod from the left side

Reseat both boards and test if you got what you want. Especially check whether you got the left and right audio channels right. Once everything is fine, put everything back in reverse.

That's it.

Even though this audio interface has some slight annoyances here and there, it is surprisingly easy to work with.

And I probably overdid it a bit with the photos :D