Technics SH-400 CD-4 Demodulator
A demodulator that made the finicky CD-4 process bearable — and its built-in meter is the reason why.
Overview
The SH-400 is a CD-4 demodulator — the box that decodes the discrete four-channel signal carried on CD-4 quadraphonic records — and it arrived as Technics' follow-up to the earlier SE-405-H demodulator. Audio (July 1975, p.49) noted the SH-400 is "decidedly bigger than its earlier equivalent," the SE-405-H, and (with some amusement at the Japanese habit of numbering backwards) suggested the newer model number was a step down numerically while the hardware itself had grown. High Fidelity (November 1976, p.75) identified the demodulator as one of the first places the Tate circuit appeared in integrated-circuit form, noting the chip was used in the SH-400 as well as several Technics quadraphonic receivers, and that a kit from Southwest Technical Products had also adopted it.
The headline feature for anyone who actually lived with CD-4 is the calibration routine. CD-4 demodulation depends on precise cartridge and channel setup, and the old method used a mandatory 7-inch 45-rpm test disc and a series of warble tones that had to be listened to. Audio (July 1975, p.49) was blunt about how miserable that was — the reviewer described the warble tones as nearly driving him out of his mind and said he couldn't hear a second of warble without an incipient migraine. The SH-400 replaces that with six pushbutton level sets and a built-in meter: the whole adjustment is done by sight, reading the meter, and takes seconds. The same review noted the reviewer redid the procedure every few days just to be sure.
The SH-400 also carries a CCC — crosstalk compensation circuit — which Audio (July 1975, p.49) credited with doing "a memorable job" straightening out the problems still dogging the cartridge's supersonic response. The review described it as a feedback cancellation arrangement that adds "a new security" to CD-4 demodulation, which it noted is "inherently close to margin and ever so easily thrown off tolerance." There's also a Hi Blend option, which lets the listener derive most of the CD-4 signal and separation from otherwise noisy or distorted CD-4 discs — useful especially for old and used records.
One practical touch separates it from its predecessor: an instant Direct switch. Audio (July 1975, p.49) noted the SH-400, unlike the earlier model, has a cartridge feed-through that turns you over to the matrix side of things in a quarter of a second with no reconnections. That's a small thing on paper and a large thing in use.
Collectors should note that the SH-400 is a CD-4 demodulator, not a matrix decoder, and it does its job only when fed a CD-4 record and a CD-4-capable cartridge. Buyers should expect to verify the meter and the six level-set buttons, since those are the parts that make the SH-400 worth having.
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