Amplification calculation of an differential amplifier, when one input is grounded

[u/MarBar_SK]

Hello

I'm using DAC121S101CIMK (via SPI) in combination with PAM8302AADCR to get somewhat decent audio out of Arduino. Now, the output of the DAC is a signal with a voltage between 0 and 5V. Since the DAC does not produce differential signal, I grounded Vin-, and connected attenuated signal to Vin+ from the DAC. The amplification of the PAM is given by equation 10^(2×log⏨(160k/(Rinpreminent+10k))). Amplification is also equal to Vout/Vin. I have calculated using Thiele-small speaker parameters that I need an output signal of the amplifier to be 4,4V in amplitude. I have set Rinpreminent to be equal to 75k, in order for the amplifier to accept input signal with 1,25V amplitude (half of the DACs output) via DC de-biasing capacitor (180nF). Now the thing is that the whole PAM is differential two-stage BLT amplifier -- it has differential signal internally inbetween the stages. The equation for amplification is based on the ratio of Rf (80k) and total input impedance (Rinpreminent+10k). However, I'm not sure how valid is that equation, when I've grounded Vin-. I'm concerned about Rin=10k plausibly being against Vdd/2, not between Vin+ and Vin-. If that were to be the case whole equation would be out of whack, since the Rin equation now has 2 paths to GND (internal resistor divider and my Vin- grounding via Rin).

Please tell me if I need to recalculate the input signal parameters, and if so, how? Or should I just somehow create differential input to skip this whole situation when I'm unsure of the A= 20×log⏨(160k/(Rinpreminent+10k)))?

Thanks a lot

DAC datasheet

PAM datasheet

Speaker datasheet

[u/SkipSingle]

I’m not sure how the PAM works because i don’t have the data sheet at hand. But as i se it, you provide an input signal below zero due to the one blocking cap on the positive input. So the negatieve halve of the signal goes below zero. Perhaps set In- at halve the voltage and apply without blocking or apply accordingly to the data sheet with a second blocking cap.

But that’s my first guess. I would use accordingly to the typical application.

Edit: Now i see your data sheet as well👍😃