I am mostly done moving to the new apartment. DSL is up. The kitchen is still a disaster. I'm on page 650 of 900 reading Harry Potter and the Order of the Phoenix aloud with a friend in the evening. It's slow going, but more fun that way. Work on the PPA continues.
Kurt's measurements indicate there is no benefit to adding more buffers to the ground channel but not the left and right channels. So, for example, we could not detect any difference between 2-4-2 and 2-2-2. In order from best to worst, here is our ranking of buffer configurations:
4-4-4 > 3-4-3, 3-3-3 > 2-4-2, 2-3-2, 2-2-2
More buffers mean lower output impedance, tighter bass, and less distortion. As a result, we have no plans to eliminate the 4 buffer per channel configuration in favor of lesser configurations, a possibility which was discussed previously.
We could not tell the difference between 2000uF and 8000uF of filter capacitance, nor between Elna Cerafine and Panasonic FC. Using 8 220uF Cerafine or 2 1000uF FC should be fine.
There was almost no difference between using a cheap unregulated wallwart, a regulated Elpac WM080 wallwart, and an LM317 based regulated supply. Despite these results we have not given up on the capacitive multiplier power supply yet, as it may come in handy for powering the battery board or other amps, and it should please the uberanal.
Using a single set of FET isolated power rails to power all 3 opamps instead of 3 sets of rails, one per opamp, Kurt and I were unable to either measure a difference using RMAA or hear any difference after about 30 minutes of listening. While we acknowledge your ears may be better than ours, we will include jumpers so that the PPA can optionally be wired for a single set of opamp rails. If nothing else, it will be interesting to see if anyone else (besides PPL) can hear a difference.
We are currently working on resolving some battery board and power flow integration issues. A new layout and updated documentation will follow.
