Upgrade for Output Filter

[sudlud]

Output filters:

• recalculation of cutoff-frequency
  • measure intensity of alias-frequencies (signal path: anallog in --> dsp --> analog out)
  • based on different sampling-frequencies
• swap opamp
  • better opamp with single supply (ad8656, expensive)
  • better opamp with dual supply (ne5532, good & cheap)
• define phase-requirements

[basreflex]

prefer solution with 3rd order besseltype LPF. directpath output stage, no big caps, 3Vrms out @ 5V, 2V @ 3.3V vdd. still single supply. encl sim using gainof 2 headph amp signal centered around gnd.
ac and tran (5khz sq wave)

the actual tina noise sim failed due to errors in the noise model. ti confirmed that.. it was 3 orders of magn off...

update:
some measurements on the TPA6138 stage using a synthesised sine wave by the ADAU1701. THD at 0fsd (2V rms) -80dB harmonic 3rd and higher. at 1V rms only 3rd harmonic -80dB (looks like DAC distortion only). white noise density 400nV/rt hz, TPA amplifer only with dac muted 72nV/rthz. , (105dB unweigthed DNR)