TAS5707EVM: no output from amp

I am able to get signal output now from the amp!  Very strange behavior though.  I was trying to use the I2C memory tool and it was not reliably reading the register values for master volume/mute (0x07).  The clock control register (0x00) was returning the appropriate value stated in 5707 datasheet but when I was toggling the mute button in the GUI it was not reading the value correctly.  When GUI was muted, the I2C memory tool would read back something other than FF which should be mute.  Then I would unmute in the GUI and memory tool shows the same value, 31 or something, sometimes after clicking Read twice the value would change and no output still observed at the amp output terminals.  Not sure exactly what The master volume was set to at that time but it was definitely 0dB or more.

How do I convert the values read from I2C memory tool to dB?

After disconnecting the target and reconnecting a few times and observing the flaky memory tool readings, I adjusted the volume slider from 0 to 8db or something and all of a sudden there was a signal at the output!.  Have you seen this before?  

I might not have the best oscilloscope at the moment but am not too sure how to observe the I2C signals and PWM signals. To the best of my ability I was able to see a clock signal at the SCLK pin on the top of the J1 connector on the MC57xxPSIA board of about 2.5MHz.  I was not able to get any other reliable signals from the SCL or SDA pin.  Any guidance would be great.

Thanks

-Mike

Where can I probe to monitor the PWM signal on EVM?  GND pin on the J1 connector of MC57xxPSIA board and OUT_A at the L1 inductor?

Did some measurements on the TI 5707 amp and there seems to be a large HF roll off, about 9dB from 1k-20kHz.  Used 2Vrms analog input (with Jp2 & Jp3 not shorted) which gives an output of about 11Vrms at 1kHz.  This is with 24V supply and 8 Ohm load.  Is this expected?

What I am observing in the plot posted is a low-pass filter, filtering out high frequencies (1k-20kHz -9dB or 7Vrms).  I didnt think DC has an effect on High frequencies? 

Thanks for checking back.  Yes I am using TAS5707EVM. Is there a jumper that configs the LC filter in default setting for EVM?   I have set BQ to All Pass and set DRC to disable. 

I am connecting +/- of signal generator (Listen AmpConnect) to RCA analog input and output terminal A as +, B as - to 8 Ohm dummy load and that to analyzer input (Listen AmpConnect).  Anything wrong with my setup?

Thanks

Hi Michael,

There is no jumper for the LC filter setting. I mean the LC filter is still 15uH+0.68uF(there is no change on the EVM), right? I can't see anything wrong in your measurement setup. Please double-check the instrument setup, make sure there is no LPF added in the setting or the bandwidth of LPF is higher than audio band.

You could do a simple experiment: apply a 1kHz single-tone waveform, then measure the RMS value on the output. Repeat this with a 10kHz single-tone waveform. The result should be close between these two measurement. 

Best regards,

Shawn Zheng

To what I can tell, referencing the schematic on the EVM guide there is the 15uH inductor physically on the EVM and there is a small SMD capacitor labeled C27 (capacitor value difficult to tell on EVM). 

Again there is still a 4 Vrms difference between a 1kHz sin tone & 10kHz sin tone.  See attached xlsx sheet with amplitude sweep measurements.  Could you check this on a board you have in in your hands? 

TAS5707_ampSweeps_HF_attenuation.xlsx