I have purchased a used Apogee Duet 2, and I am testing if everything's fine and I can close the deal. However, when I connect a headset to it, I hear a slight humming sound mostly on the left side.
About the noise :
- The noise is not the typical 50 hz, but at first it was slightly higher than a F#5, now, a C#4
- I thought at first it was only on the left channel, however there's the same humming sound on the right channel, but very very very dim
About the troubleshoot until now
- it does the noise (C#4), whatever the situation:
- when the interface is connected in USB only, or with the optional power supply in addition to usb
- when the mac is on battery, or plugged grounded (with the grounded cord between the power block and the outlet)
- Even when the interface is not plugged to the mac, but only powered by the interface's own power supply (which is not grounded)
- When I play a digital instrument (like an electric piano in garageband, or a software synth), the humming stops when there is sound, and it reappears after the end of the decay! Also, when the release is almost over, there is a sizzle preceding the humming. As if the digital-analog convreters behaved differently when loaded than when not... To me, this could be the symptom of overworked DAC, what do you think? I think such a high-end audio interface should not have this kind of humming.
Also, note that
- I tested with several headsets
- All were regular ones, 32 ohm impedence I guess
- (I purchased it to use with a high impedence headset which I don't have yet, but I guess it should still sound nice with regular headphones; and also it does it on only one side, so I think there's a problem)
- I tested with the headset left side on right ear, and right side on left ear.
- It's a rather dim sound (on the left), but I hear very slight sounds, like some USB chargers, USBC multi adapters, and so on. (I once heard a spider walking on the wall, 30cm from my head, in the middle of the night.) On the right side however it's not just dim, it's very, very, very ultra dim.
I read that for humming, it's possible that it's a grounding problem, however I think it's not that given the troubleshooting described above.
Before me, the interface has been used a lot of time mostly to listen to music (so much that the oled screen is overworked: it is dim and there is burn-in). This is not a problem as I knew it, but do you think the DAC inside can be overworked too, due to the long hours of service?
Or is there an option somewhere that I should set up correctly? (I guess not, because otherwise, it should sound the same on both sides.)
Sorry for long question. TLDR: read bold text only.
Edit: About the noise. I tried changing the sample rate: right now, when I change to any sample rate, the humming pitch is C#4, and after I play one note of a digital instrument, the humming pitch goes to A4. Then, if I change the sample rate, it the humming resets to C#4... And it's pretty systematic.