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ADAU1701 with ext DAC stressed by EMI of Class-D AMP!?

Question asked by v!ta on Apr 23, 2018
Latest reply on May 31, 2018 by DaveThib
Branched to a new discussion



i run an adau1701 ("sure dsp board") with two external ADCs (PCM1802) and two DACs (PCM5102) via I2S. ADAU is the master feeding LR and Bit clocks to the four converters. MCLK comes from an external oszillator. at the beginning i had huge random spikes on the analog output signal, which vanished after i put buffers (SN74LVC2G34DBVR) in the LR and Bit clock lines as suggested somewhere here on ezanalog. so far everthing runs perfect.


i drive 2 classAB and 2 class-d amps, which are not in an extra case but somewhere near to the dsp as everything needs to be built in in the housing of the loudspeaker.


class-d is a IRS2092 based amp board in, i think, reference design. Its frequency is around 410kHz. ouput lowpass filter as in the reference design. (IRAUDAMP7S,  page 25). speaker are 8Ohms.

as long as i keep the volume moderate everything is fine, however when i increase the level there are "random" spikes, of course very audible.

i put the dsp/converters unit in a small steel box and put the class d amps further away (approx 40cm) and now the same problem still occurs however at higher levels.

i assume that it is caused by EMI ...!?

i suspect the problem being the line from ADAU to the DAC cause i also have the problem when i generate the testsignal out of the adau (via sigma studio)

so far the data line of the I2S is not buffered but goes directly from adau to dac, (on the dac board is a 33ohms resistor in series).

as i use the four gpios of the adau with some potis there are some wires, along with power wires and analog signal in and out which could work as antennas catching unwanted electromagentic waves generated from the AMPS ...?


any suggestions appreciated...