Interesting link. I didn't realize the PT2399 uses a simple first-order delta modulator as an ADC. Neither does the person who wrote that website, but it is quite clear from the information on the site that that is what it is. I now understand what the comparator is for, it's the quantizer of the delta modulator.
See figure 2 of https://en.m.wikipedia.org/wiki/Delta_modulation The first-order low-pass filters (pin 9-pin 10 and pin 11-pin 12) are used as the integrators.
I built a doorbell with an equally simple first-order delta modulator when I was 17. It sounds awful at too low signal levels; it has no dithering, so you can get all sorts of limit cycles at low levels. At higher levels, it sounds quite reasonable, especially at high bit rates.
Regarding using the internal op-amps for the balanced in- and outputs that hobby_guy wants to have: I don't really see how you could do that, given that the op-amps are already needed for anti-aliasing and reconstruction filtering and that they all have one pin connected to the reference. On top of that, there is almost no information about them in the datasheets.
Regarding the capacitors between pin 10-pin 9 and pin 11-pin 12: as long as you use equal capacitor values for both, they should in principle not have any impact on the frequency response. That's because the first-order filter/integrator of the modulator is in its feedback path, and compensates for the first-order filter/integrator of the demodulator.
There is a compromise to be made, though. The larger the capacitors, the less quantization noise you get, but the easier you can drive the modulator into slew rate limiting with signals with a lot of treble.
There is a compromise to be made, though. The larger the capacitors, the less quantization noise you get, but the easier you can drive the modulator into slew rate limiting with signals with a lot of treble.
Not much; 31 nV/√Hz and only unity gain is supported. It's meant for balanced line level inputs rather than as a microphone preamplifier.
This is great, really enjoying following the technical discussions, as best I can. Thankfully, working with sound for live music is very forgiving, as quite a lot of distortion can be accepted and just labeled "sound coloration", or "effect" ;-)
This is for learning, and for personal use, so I'm really looking forward to getting my 9V prototype finished. I'll probably post an audio clip
This is for learning, and for personal use, so I'm really looking forward to getting my 9V prototype finished. I'll probably post an audio clip