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Crackling/static noise with Aeon2 Noire + SMSL SP400

sgb

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Feb 13, 2020
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So about 2 weeks ago I finally got my first-ever headphone system set-up with I guesstimate around less than 8 hours of total listening:
  • DCA Aeon2 Noire
  • SMSL SP400
The source is a network streaming DAC that I have previously use (and still does) with my speaker set-up that is connected as follow:
DAC->transformer passive preamp-> speaker amplifier or SP400-> speakers or Aeon 2 Noire.

Balanced connections from all the way from DAC to the headphones.

With the preamp turned all the way up, it gives 0 attenuation- so basically just a pass-through.

I encountered 2 noise problems:
  1. There is a hum coming through the headphone that is easily audible when the volume of the SP400 turned to 80 above @ 2V output from the DAC; and SP400 volume to 60 above @ 6V output from the DAC. With no music playing and "grounds" lifted at the preamp. If I left the "ground" on, hum can be more easily audible at lower volume levels.
  2. With music playing: there is crackling/static noise accompanying high notes e.g. Sarah McLachlan's Adia & George Winston's February Sea. However, I do not hear the same noise on mid tone downwards. These are the 2 pieces of music that is most readily hear such crackling/static noise. Oddly, if I played the recording from Lincoln Center Jazz Orchestra's Bli Blip (album: Live in Swing City - Swingin' with Duke) does not exhibit such noise problem.
I have ruled-out my headphones cos I played the same songs using the THX Onyx dongle via the iPad. Although the DAC was only used in the speaker set up before, I never have heard either of the noise before.

Do I have a defective SP400 or DAC? Thanks in advance.
 

Snoopy

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Did U try going from a laptop or phone directly into the DAC (fixed volume) and from there into the amp?

The crackling could be from the USB input or be introduced by the passive pre-amp.
 
OP
S

sgb

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Did U try going from a laptop or phone directly into the DAC (fixed volume) and from there into the amp?

The crackling could be from the USB input or be introduced by the passive pre-amp.

The DAC is only using a network (cable) input and is running fixed volume (max.)

The passive preamp is non-powered ie. only audio cables in and out. I do have single-ended (RCA) going from the preamp to the speaker amp but the speaker amp is not powered on when I have the SP400 on.
 

Snoopy

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The DAC is only using a network (cable) input and is running fixed volume (max.)

The passive preamp is non-powered ie. only audio cables in and out. I do have single-ended (RCA) going from the preamp to the speaker amp but the speaker amp is not powered on when I have the SP400 on.
That did not answer my question.

Try source (phone, laptop, tablet ) with the DAC straight into the amp.
If that's working fine introduce the passive pre-amp. If that's still fine add the streamer.

After that the speaker amp.

Could be static, DC offset, groundloop..
 
OP
S

sgb

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That did not answer my question.

Try source (phone, laptop, tablet ) with the DAC straight into the amp.
If that's working fine introduce the passive pre-amp. If that's still fine add the streamer.

After that the speaker amp.

Could be static, DC offset, groundloop..
Thanks for the suggestion! Will try the going with the DAC straight into the SP400 first and report back later.

I’ve tried disconnecting the RCA going into the speaker amp (from the passive preamp) before to see if I could break the hum but that didn’t work..
 
OP
S

sgb

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Thanks @Snoopy for the tip and after some de-spaghetti-ing of the cables behind the system, I finally found the real problem!

It was a faulty left channel coming out of the balanced output of the DAC. I nailed this down by connecting directly from the DAC to the SP400.

Unbalanced output (RCA) of the DAC was fine with both direct connection and via the passive preamp even with the “ground-on”.

Thanks again!
 
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