Got the UcD modulator daughter board assembled. It’s the UcD on the right with the DIP comparator. It works quite well and played the first time, something I have found with UcD all the times I have tried this kind of modulator .. it’s just so easy to get to oscillate.
With the chosen components it has a little ess gain than the SODA implementation. It also seems that noise level is a bit les, but this might just be because of the lesser gain ….
Have made some first measurements on distortion (without any special filter as you really should use measuring switching amps … ) and it seems that the SODA version have a little less distortion. But this is only the first trials, so I will not be that supprised if it turns out otherwise!
For the SODA I measured the first harmonic at some 0.16% for the UcD it was 0.23%. With a filter this would probably be a lot less, on the other hand it was measured at 100 Hz