Motu M4 Buzzing

[usrockband]

Hi all, I posted a little while ago about an issue with a Topping A90 and received a lot of very helpful tips and info. I’m hoping to get some assistance with a new issue.

After doing some research, I recently picked up a Motu M4 to use as a DAC for some headphone amps, as well as for ADC. However, I’m having some confusing buzzing issues which I can’t really understand.

For extra context, the setup I'm trying to use involves running the MOTU into my THX 887 via RCA so that I can connect another SE amp into the SE passthrough on the 887. I’m using RCA outputs 3+4 since they run at line level.

The interface seems to have a buzz at higher gain levels when connected to my amps solely via RCA. However, I can get rid of this noise in the RCA outputs completely by adding a single TRS-XLR cable between the M4 and the 887. HOWEVER, I have to plug this cable into either output 1 or 2 on the MOTU, otherwise I can hear bad distortion in the signal coming out of RCAs 3+4.

So… what is going on here? Does this sound normal, or is there something wrong with my interface / amp?

Really appreciate any insight I can get on this. Thank you in advance.

 

[somebodyelse]

Hum, buzz or 'computer noises' usually point to a grounding issue. Jensen Transformers' application notes cover the technical details and include a step by step process to trace and fix such problems. You don't need to use their products to do it. AN007 covers almost everything in a single place, but may be a bit much if all you want it the process.

 

[usrockband]

This was more of a distortion or overload in the audio signal than a hum or buzz. I ended up just exchanging the unit for another which doesn’t seem to have this issue under the same connections and conditions. Maybe some sort of EF shielding issue with the first unit? Not sure.

On another somewhat related note - are these units known for having shaky QC? The unit I exchanged this one for arrived to me with a bad USB connector which would lose connection at the slightest movements of the cable. Third unit seems to be good on all fronts, but bit surprising to have such bad luck..