Simple decoupling circuit for DACs?

eVITAERC · 25th November 2005, 07:57 AM

(cross-posted form Power Supply Design, because nobody goes there)

Hi guys,

I'm planning an ultra-portable stereo designed to hook up to a laptop. The plan is to have the DAC (I'm using diyparadise's Monica 2) and a custom class-D amp run off the same 12V switching power supply that the laptop is using, while the laptop runs in power-saving mode operated by a remote.

The general circuit tests out, and everything can run without hitting current output limits on the SMPS. However the problem is that there is inavoidably a lot of noise in the PS, whether it's from the class-D or the laptop or the PSU itself. Is there a simple LC-decoupling/bypassing circuit that I can use to decouple the entire noise-sensitive DAC without lowering the supply voltage? What would be suitable values?

Thanks in advance

bocka · 25th November 2005, 10:16 AM

Have you made some measurements about the noise on the output of the class D amp or the DAC? Is the noise present at the DACs output first or on the class D amp? Did you use a star topology for grounding?

Although a SMPS creates (much) more noise than a standard linear regulator noise problems are most often grounding problems as the PSRR of the chips is high enough to supress power supply related noise.

25th November 2005, 07:57 AM	#1
eVITAERC diyAudio Member Join Date: Aug 2005	Simple decoupling circuit for DACs? (cross-posted form Power Supply Design, because nobody goes there) Hi guys, I'm planning an ultra-portable stereo designed to hook up to a laptop. The plan is to have the DAC (I'm using diyparadise's Monica 2) and a custom class-D amp run off the same 12V switching power supply that the laptop is using, while the laptop runs in power-saving mode operated by a remote. The general circuit tests out, and everything can run without hitting current output limits on the SMPS. However the problem is that there is inavoidably a lot of noise in the PS, whether it's from the class-D or the laptop or the PSU itself. Is there a simple LC-decoupling/bypassing circuit that I can use to decouple the entire noise-sensitive DAC without lowering the supply voltage? What would be suitable values? Thanks in advance

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25th November 2005, 10:16 AM	#2
bocka diyAudio Member Join Date: Jul 2003 Location: Hannover	Have you made some measurements about the noise on the output of the class D amp or the DAC? Is the noise present at the DACs output first or on the class D amp? Did you use a star topology for grounding? Although a SMPS creates (much) more noise than a standard linear regulator noise problems are most often grounding problems as the PSRR of the chips is high enough to supress power supply related noise.

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