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TOPIC: Noise on outputs

Noise on outputs 2 years 3 months ago #32570

  • samoht
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Hi,
I have a 3 years old OpenDRC 2x2 with digital inputs and outputs. Recently i replaced the frontend by a SDIF / Toslink input and two analog outputs.
Now i can hear noise on both channels.
I measured a frequency of approx. 800 Hz with strong harmonics at 1.6 kHz and 3.2. kHz.
Has anyone an idea, where it comes from and what to do against?
I moved the internal cabling already, checked the Gnd, but without any success.

Best regards

Thomas
Last Edit: 2 years 3 months ago by samoht.
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Noise on outputs 2 years 3 months ago #32577

  • Richard
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3 years old - is it black case or silver aluminium case?
If it's ground noise / buzz - check if you have plastic or metal screws between the main boards and the case metal floor. They should be plastic - MiniDSP upgraded the design some years ago on suggestion of a forum member who tracked a noise problem down to that and solved it by swapping the conductive metal screw for plastic one. Do a forum search to read that thread.
If it's low level noise approx -124dBFS, you will always incur this due to the asynchronous sample rate converter built-in which cannot be bypassed even for clean native 48kHz digital input. Everything goes through ASRC and gets redithered.
If it's NOT occurring in your setup with a digital in> out configuration but swapping to the DA-FP board shows up the inherent noise floor of the analogue outputs plus also this particular 800Hz plus harmonics problem, then you're probably getting some local EMI interference noise from something like a fluorescent light tube in your house, or a lighting dimmer, or maybe a domestic appliance like fridge, microwave, television, computer or your other audio gear nearby. Try systematically turning all machines off and on to see if noise goes away.
The DA-FP board only costs $75 so it's design isn't really as well shielded against external EMI as some high end audiophile / pro DACs.
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Noise on outputs 2 years 3 months ago #32579

  • samoht
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Hi Richard,

Thank you very much fir your support. I will test it this evening.
I have a silver case unit and i recognized already, that the DSP board in the black case is mounted with plastic screws. The DSP board in the silver case is fixed by metallic screws. I will replace them and see.
I will report.

Best regards

Thomas
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Noise on outputs 2 years 3 months ago #32589

  • samoht
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Hi,

Metallic screws of the DSP board are replaced by plastic ones. Board turned by 90 degrees like in the new cases. This allows shortening of the connecting flat cable between DSP board and FP-DA board. Power supply cable now twisted. The result is noticable. The noise is significantly reduced, but still there. And unfortunately my second device shows the same nise level.
I have to say that the balanced output is switched to unbalanced by connecting pin 1 and pin 3. Maybe that has a negative impact on the noise level.
I will build an active balanced to unbalanced converter and hope that the noise will dissapear. But does anybody knows where the 800 Hz clock is coming from?

Best regards

Thomas
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Noise on outputs 1 year 10 months ago #34376

  • denstoff
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Hi Thomas! You could reduce the noise? Try to connect the Board DA-FP to a single power supply of 5 Volts. Noise will be less.

Denis.
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