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Intermittent noise with ADAU1446 application

Question asked by stuartmc on Jun 27, 2017
Latest reply on Aug 11, 2017 by mmmike


We're a speaker company and have a new power amplifier application that's using ADAU1446 DSP with AD1939 CODEC. The amp has 4 x analogue inputs, 4 x Class D power amplifier outputs and 2 x line level outputs. We've just reached pre-production phase and have started using Sigma Studio to work out some signal routing and EQ profiles to use with our speakers. In doing that we've discovered that the noise floor of all amplifier channels will intermittently increase when cold-booted or when the DSP is reset (in our topology this causes a profile to be loaded from an EPROM). In normal operation the terminal noise of the amplifier is around 600uV, but can be as much as 4-5mV when re-booted with some profiles. If we upload any profile live to the DSP or change any parameters while the amp is running we never see this problem. Would appreciate any help you can give as we are not DSP engineers, just using Sigma Studio to get the profiles we need for our speakers.

Schematic for DSP and CODEC is attached.