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PCM4204: low-frequency noise

Part Number: PCM4204


I've been noticing a fair amount of low frequency noise coming from this chip, which is in the A/D section of a presonus audio interface I recently overhauled. In the image below, there's that spike that looks to be near-DC, around 5Hz—all eight channels are doing this (there are two PCM4204s in this circuit), the peak of this spikes randomly fluctuating between -90dB and -60dB. This is not in the audible range, obviously, but it seems to suggest some problem with PSU stability, or de-coupling. One of the things I modified was the de-coupling capacitors in the converter section, which were largely undersized (10uF tantalum). I replaced with 560uF organic poylmer caps, which I had to solder directly to the SMD pads.

Thanks for your guidance!

  • Hi Ryan,

    I would guess that this is 1/f noise on the front end that you are seeing plus the dc offset if you are not using a high-pass filter in this measurement. The supply decoupling isn't likely to influence this because low frequency supply noise is going to be rejected quite well by the PSRR of the chip and generally stability issues will manifest at much higher frequencies. If you look at the datasheet FFT plots you can also see that low frequency noise increases with higher sampling rates. If you're running at 192kHz, this may also be contributing to the behavior you are seeing.