Hello Quadaphiles,
surroundophile, The best turntable is one that mimics the original cutting lathe. This would be the linear tracking turntable. The reason is that there is no tangential tracking error as in turntables with arms. There is one caveat however. In some modern recordings there is tangential error pre-distortion used in cutting the original disk. This would create a virtual tangential error in the linear turntable. Using a high compliance phono cartridge reduces to some extent this problem in both types of turntables.
Quadzilla, Low capacitance cables are still recommended because the load impedance of typical phono pre-amplifiers is 50,000 Ohms. At this impedance, it does not take much capacitance to affect the high frequency response of the cartridge.
Rolv-Karsten, The frequency response of the CD-4 system is not as much a compromise as you may think. Modern LP records have little if any energy much above 14 to 15 KHz. The standard stereo cutting system is capable for short time of doing this, but when mastering an album of 20 to 30 minutes a side at real time, it is very easy to overheat and damage the cutting head with much energy above 15KHz. Half speed cutting can improve this with the exception that the modified playback reel to reel tape machine has much difficulty reproducing at 15KHz and above with stable amplitude and phase. During the half speed-real time cutting controversy, RCA did an energy density average of 5000 commercially available LP disks. These disks were divided into 2 groups, real time mastered and half speed mastered. The half speed group was much smaller(173 disks), while the real time was the rest (4827 disks). The result was that 98.3% of the energy density was between 25Hz and 13.5KHz, 1.6% energy density between 13.5KHz and 15KHz and .2% above 15KHz. The energy density measurement range was from 0dBm(5 cm/sec) to -45dBm over the frequency range of 20Hz to 20 KHz. A little personal history about this subject. In 1966, I was fortunate to be taught disk mastering by one of the best mastering engineers in the industry, Mel Tanner, at Coast Recorders in San Francisco California. At that time 45 RPM mono singles and stereo 33 1/3 LP records were the most requested masters and dubs. It should be noted that phono cartridges had very poor (stiff) compliance(7*10-6cm/dyne) at that time. This made it very hard for good high frequency performance much above 10 KHz. I was taught that in most real time stereo masters, to roll off frequencies above 13 KHz. This has remained pretty much a standard. This allowed very cheap low compliance cartridges to work without being thrown out of high frequency groove undulations. Variable pitch and variable depth techniques can extend this another 1.5 KHz higher. All this to say that the 15KHz high frequency response of CD-4 is about the same as standard stereo records with few exceptions that have pushed the cutting envelope. The half speed and real time CD-4 mastering systems would helium cool the cutting head to prevent over heating and head burnout.
bad robot, Power supply is built in!
justforthesounofit, The direct preamp outputs have no 15KHz lpf, the main outputs do.
Quadro-Action,
Dietrich, The answer is simple business. No record company wanted to have dual inventories. Without compatibility, there would have to be a stereo disk and a quad disk. CD-4 allows a single inventory and the stereo listener can buy the CD-4 record and still get great stereo playback.
Quadfather, The filter in the main channel really serves 3 purposes. It matches the frequency response of the sub-channel. It matches the delay of the sub-channel and it eliminates any carrier ultrasonic signals from reaching the matrix, which could create birdies(unwanted tone noise) in the outputs. Matching filter parameters is very easy these days!
That is it for this post, see you all next time,
Lou Dorren
With a name that long though, it will HAVE to be in a 19" rack mount case to get all the lettering on it. 
