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Apogee duet noise issue resolved Audio Interfaces
Old 1st May 2015
  #1
Here for the gear
Apogee duet noise issue resolved

Hi all. Recently was asked by a pal to look at his Duet, which he is very fond of.
I found a number of past questions on GS regarding a common increasing noise problem in the Apogee Duet while researching online.

I thought it might be good news for some Duet owners to know that there is a fix for this problem, but unfortunately it is a mechanical fault related to long term degradation. Also, this is an issue built into the original design and will inevitably happen to all of them. Kind of a bummer to anyone who has had this happen on a replacement!

It took a few weeks of my spare time.. But, I've mapped out the schematic from many hours of beeping a multimeter and have come up with a bug fix. This also avoids the problem happening again in future.
I've also bought a broken second-hand Duet to verify the fix and now I have a fully functional one myself!

If anyone is interested in having theirs refurbished, please get in touch. I'm in New Zealand but the postage system here is adequate.

Cheers,
Lee
Old 1st May 2015
  #2
Lives for gear
 

Quote:
Originally Posted by sprucemoose View Post
Hi all. Recently was asked by a pal to look at his Duet, which he is very fond of.
I found a number of past questions on GS regarding a common increasing noise problem in the Apogee Duet while researching online.

I thought it might be good news for some Duet owners to know that there is a fix for this problem, but unfortunately it is a mechanical fault related to long term degradation. Also, this is an issue built into the original design and will inevitably happen to all of them. Kind of a bummer to anyone who has had this happen on a replacement!

It took a few weeks of my spare time.. But, I've mapped out the schematic from many hours of beeping a multimeter and have come up with a bug fix. This also avoids the problem happening again in future.
I've also bought a broken second-hand Duet to verify the fix and now I have a fully functional one myself!

If anyone is interested in having theirs refurbished, please get in touch. I'm in New Zealand but the postage system here is adequate.

Cheers,
Lee
Hey Sprucemoose, thanks for posting. There were a few different noise problems associated with the duet. The first was the loud earthing issue with all the computer noise which you are obviously not referring to. My own issue was a very soft (but none the less annoying) hiss on monitors that disappeared when swapping to headphones (it was assumed this was related to an impedance issue) ... thirdly the hiss was reduced when swapping sampling rates (no one ever really got to the bottom of this one). Is this the version of the "noise" for which you have found the root cause? If so, I'm all ears
Old 2nd May 2015
  #3
Here for the gear
I believe that any noise that is present on tracks recorded through the XLR inputs are related and that that the problem is not due to grounding. Possibly misinformation from Apogee for any number of reasons.
Improving the grounding will certainly help but won't get around the fact that there's internal circuit damage on the board that will cause the main XLR inputs to act as antennas for any minor circuit noise.
This is not a fix for the headphone output, which is a bit hissy, and i have noticed that one of the Duets still has a decent amount of noise on it's instrument lines, which I'm on the road to figuring out.
Old 2nd May 2015
  #4
Here for the gear
It turns out the instrument inputs are actually fine. I've been testing the device with inputs floating. Under load it's not there. At maximum gain there was a buzz and a squeal, but that disappeared when I turned the guitar volume down, which left a small amount of white noise. Doh! Poorly shielded cables..

Quote:
Originally Posted by dr_Jezz View Post
the hiss was reduced when swapping sampling rates (no one ever really got to the bottom of this one).
Do you know if increasing the sample rate reduced or increased?

I might be wrong, but my understanding is that changing sample rates when there is pre-existing noise going through the opamp is likely just to interact with the problem resulting in the difference in what you hear.

On the ones I've fixed there is no audibly discernible change to the noise floor between sample rates, with or without 48V.

Update: fixed a third unit this evening. Seems the fault has a few different symptoms, but is related to the same f*#k up in several places on the board.
Old 3rd May 2015
  #5
Lives for gear
 

Quote:
Originally Posted by sprucemoose View Post
It turns out the instrument inputs are actually fine. I've been testing the device with inputs floating. Under load it's not there. At maximum gain there was a buzz and a squeal, but that disappeared when I turned the guitar volume down, which left a small amount of white noise. Doh! Poorly shielded cables..



Do you know if increasing the sample rate reduced or increased?

I might be wrong, but my understanding is that changing sample rates when there is pre-existing noise going through the opamp is likely just to interact with the problem resulting in the difference in what you hear.

On the ones I've fixed there is no audibly discernible change to the noise floor between sample rates, with or without 48V.

Update: fixed a third unit this evening. Seems the fault has a few different symptoms, but is related to the same f*#k up in several places on the board.
Hey SM, my main monitors won't be back here until Tuesday, but I'll check the sample rates then - as far as I was aware the problem wasn't on the inputs, just the outputs as it seems you've confirmed. Good work on figuring this out, Apogee weren't any help.
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