I got as far as testing audio output from the master bus and testing simple audio recording from both a test tone fed to the master out bypassing the mixer section, and also the regular bus.
All fails.
I didn't have any test point on the preamp cards so I couldn't even probe signals there.
My main suspect was the polarity switches, the footprint is so small that it's impossible to know what's going on.
In any case I'm using this opportunity to do things more properly.
I'm ditching the analog summing and analog polarity switching, and attempting to make this a 5 channel recorder, summing / polarity itb.
The major changes now are going with a differential input adc driver. I looked at Birt, the Cirrus recommended driver,TI driver, and AK. AK is simplest topology (appeals to me), Cirrus I have some questions about, TI uses a FDA - have a few questions about that, and I modelled the Birt circuit a few days ago trying to understand the gain.
I think if Wayne can help out I can just go with the Birt and not try to waste time with the other approaches.
Found another design error/ question. My power rails are +-5v for the That chips and the Cirrus CS5366. Reading the datasheet more carefully, these will swing to +-.3v beyond the rails. So my 5V supply won't cut it. I either run everything at 6.5v-7v or add in a boost dc-dc somewhere for the driver. Do I even want to push that limit and feed the adc right up to those +-.3v levels or just keep the adc at 5V peak to peak.
Questions on the Birt driver as shown in the 5263 datasheet figure 12...
First, what is the proper way to define full scale? Up till now I was thinking with 5v rails, the That1580 sheet says it swings to +-4v. So everything following I was thinking max swing is 8v p/p.
Do I need ac coupling - C11 and C12, or does the servo on the 5171 eliminate enough dc at the output of the 1580? Figure 12 does not show any caps.
https://statics.cirrus.com/pubs/appNote/an241-1.pdf
I don't know how relevant Cirrus's buffer recommendations are, or whether I should try to incorporate them into the Birt circuit.
- they use a high pass filter with the ac coupling cap.
- I have also seen people add a low pass with corner ~220khz
I think C17 in the 5263 datasheet is a miller compensation cap? Over my paygrade. Should I stay with the 2n2 value or is there bench experimentation needed.
R12 changes to 91r as per the Cirrus circuit.
Gain is set with R11/R9 (and R13/R10)? I thought that R12 and R15 are in the FB loop but running the sim showed just R11/R9 set gain.