Now using the modified ATI line amps to buffer and make the extra copies of the program and advance signals used by The Lathe. Had been using y-cables with resistive dummy loads on the two unused legs of the six of eight snake, but that wasn't really working well with just resistors - I'd need to simulate the reactance of the audio inputs on the disk computer or else the responses of the channels would not be identical at all frequencies, even if there was compensation for nominal gain (at 1 kHz, e.g.). Now, with the modified ATI line amp (faster chips (Burr-Brown SoundPlus series) and Wima polypropylene capacitors), the signals sound pure, are robust, discrete, and buffered, tracking identically, resulting in uniform groove packing with nestled sine waves: Program Left and Program Right to cutter amps; Advance Left and Right, plus another Advance RIght (all, 1-rev look-ahead), and a copy of Program Left, go to the LS-76 disk computer's signle-ended inputs (which have male (!) XLR input connectors for which pin 3 is Hi and pin 2 is Ground (pin 1 floating). I can now make milliVolt adjustments to each channel, using the new 12-turn trimpots and a tweaker with the Fluke 179 looking at 1 kHz and lower.
Although the tape mastering room gear is calibrated to 0 VU = -14 dBFSD = 0.775 VRMS, I have calibrated the disk cutting room gear to +1.228 VRMS = -14 dBFSD = 0 VU = 5.0 cm/sec/channel, diagonal peak velocity at 1 kHz (i.e., 7 cm/sec/lateral peak velocity at 1 khz, i.e. 3.54 cm/sec/channel, diagonal RMS velocity at 1 kHz...), so that the DACs are at the same output level as the MCI tape machine, since that's eventually coming on line at Dingbat L. S. D., as well. Heads sent to JRF for inspection and possible relapping... Fingers crossed they are still decent...
(follow up: 1/2" 2-track heads' profiles and head gaps at 600x were fine, so they just got polished 1/4" 2-track were replaced, with NOS, and aligned, at JRF 1/4-track originals were fine, also; preamp electronics in sliding drawers at front of console sent to Mara Machines and returned, rebuilt and tested √)