Over the last few weeks I've assembled two more ProtoDACs (now 4 total). I got four of the Soviet K77-1 0.68 polycarbonate caps previously discussed to use for I/V output. I had used K75 hybrid caps very successfully in passive crossovers, so was positively inclined. I used the Panasonic
EEU-FR1A102LB electrolytics on both dacs. The sole difference is vishay bulk Z-foils (purchased from @
hifinet early in this adventure) and vishay dale rn55d mil-spec 1/8 watt resistors in the I/V positions. I was curious to hear a compariaon.
The second ProtoDAC I built is essentially a copy of the 'poster' dac with the PCP polycarb caps and bulk Z-foils. Comparing that dac (#2) with the bulk Z-foil K77-1 led me to slightly prefer the K77-1. All three dacs were burned in for 100 hrs+. In this first comparison, with identical resistors, the K77-1 version was a tiny bit more musical/richer.
Comparing the other rn55d K77-1 with the Z-foil K77-1 was a bit of a surprise. I heard more air/transparency perhaps 2.5 khz up with the Z-foils, but a richer, better integrated sound from 1.5 khz or so downward. I'm 77 and have very mild tinnitus, so I'm sensitive to bad recordings with too much HF or HF distortion. I'm sure this plays into this result through my ears. I am not saying one is better than the other. The difference is small, and the majority of listeners are likely to prefer the Z-foil in the build configuration. The resistor comparison seems consistent comparing either of the Z-foil dacs to the rn55d one.
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On another subject, I have and have been using an Allo Shanti power supply for several months now (purchased in 2021). It has two separate linear supplies, a higher current one for the RPi, and a 1 amp or so for the hat if the hat GPIO power connection can be cut one way or another. I've only used the single high current section connected to the RPi 4B thus far, but will be using a pin extender with pins 1, 2, and four cut to use both sections of the Shanti.
In other discussions wrt RPi's and hats, and also usb situations. People have mentioned noise on the RPi grounds. Is there a simple way minimize this (potential) problem?
