analog output from EVAL-ADAU1701MINIZ is not passing

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why not to use the analog output(J6)?

I want to measure it with a oscilloscope and I need an amplification so I try the speagker output with the class D amp

but I get instead of analog sine I get something else...

How can I measure the analog amplified output without phase shift?

Best

The Class-D amplifier's output is very difficult to scope since each channel is a pulse-width modulated (PWM), full-bridge driven output. Below shows the left channel's + and - outputs:

The speaker load wired between the two output pins sees the differential signal -- and its voice coil inductance filters the digital pulses into the correct output waveform. I simulated this effect by connecting a transformer across the left channel output, then viewing its secondary winding with the scope. We see how the transformer -- hence the speaker -- sees a true sine wave:

Best regards,

Bob

thanks a lot bob!!

what about the J6 output+a power amplifier?will it be ok?

Hello,

Absolutely. This output can drive most sorts of audio amplifiers, including amplified computer speakers, powered studio monitors, packaged amplifiers such as those from Stellar Labs, and most IC or hybrid amplifiers in suitable circuits.

Best regards,

Bob

Awesome answer Bob,

Hello Net Eyal,

One other thing I want to add to this discussion is that if you want to measure the output of a class D amplifier with test equipment like an Audio Precision, you will need to filter the out of band energy from the waveform. This energy will throw off any measurements for distortion and noise floor etc. Audio Precision makes a class D filter set and I assume there are others available from other test gear manufacturers. This noise is not a problem when presented to a speaker because it is too high for the speaker to reproduce it but test equipment will happily measure it and throw off the measurements.

Dave T

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