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My setup consists of a DSP board with the ADAU1701 chip on it. Signals will come from my phone through an AUX-cable to the DSP. After processing the signals with the DSP they will be converted through 4 PCM5102 DACs into analog signals. The analog signals will then be transmitted through a cable to 25 PAM8403 amplifiers.

First I connected all the electronic (DSP, DAC, PAM8403) to one cheap 5V powersupply but when I turned up to ~15% of volume everything sounded like crackling and clipped noise. Below that everything was somehow okay.

Then I got myself a DC DC isolator (Gaptec 3S4A_1UP) and connected only the DSP and the DAC with output of the DC DC isolator. The input of the DC DC isolator is connected to the same cheap powersupply like all the PAM8403 amplifiers are.

The problem with the volume was gone completely but in all stages of volume I could clearly hear a sharp random crackling (every 0.5-1 second.)

After I connected the DAC and DSP to a seperate USB powersupply and the PAM8403 amplifiers to the cheap power supply there were no more problems anymore.

My questions are:

  1. Why doesn't the DC DC isolator deliver clean power or why does it produce noise into the system?
  2. What are the sharp crackling noises?
  3. What other options do I have to prevent them?
  4. Why did everything clip at low volume when connected together to one powersupply?

Edit: Here are some usefull Hyperlinks:

Recorded example of crackeling noises, PAM8403 Amplifier Datasheet, The amplifier module I use, PCM5102 DAC Datasheet, The PCM5102 module I use, ADAU1701 Datasheet,DSP board I use, The DC DC Converter Datasheet,

I am looking forward to every answer.

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    \$\begingroup\$ Do you have a recording if the noises? One person's "sharp crackling" may be some one else's "buzz." \$\endgroup\$ – JRE Aug 28 '20 at 10:29
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    \$\begingroup\$ A diagram of your setup would probably help us as well. \$\endgroup\$ – JRE Aug 28 '20 at 10:30
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    \$\begingroup\$ And hyperlink to the datasheets of the devices please. \$\endgroup\$ – Andy aka Aug 28 '20 at 10:30
  • \$\begingroup\$ @JRE now I added a record of the noise \$\endgroup\$ – Severin Getzner Aug 28 '20 at 11:21
  • \$\begingroup\$ @Andy now I provided datasheets aswell as the Modules I used \$\endgroup\$ – Severin Getzner Aug 28 '20 at 11:21

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