Kenwood DP-M7750 (c. 1994)
A six-plus-one CD changer that shipped with a serial port and a Windows database - a computer peripheral disguised as a carousel.
Overview
The DP-M7750 is a 6+1 CD changer. Six discs preload into a removable magazine, and a single-disc drawer holds the one you want to hear right now. The odd part is a DB-25 RS-232C jack on the back panel. The archive's manual excerpt notes that the owner's manual barely mentions it, and the whole feature gets a callout on a back-panel line drawing. Kenwood's optional MoodMaker software, sold separately, turned the player into a computer-controlled jukebox. The magazine file system remembers eight-character titles and preferred track order for up to 42 magazines, and the internal memory registers names and programs for up to 255 CDs.
Audio (January 1995, p.90) put Edward J. Foster on the review, and he treated it as the first computer-controlled 6+1 changer to cross his bench. His verdict was measured: an average CD changer with wads of toys, not least of which is computerized operation. Computer hackers turned audiophiles should love it, he wrote; so would noncomputer audiophiles who like to spend leisure hours punching in their disc library character by character. Everyone else, he suggested, would probably want a more standard single-disc player.
The measured performance was a mixed bag. Frequency response came in within -0.04, +0.33 dB across the band. That beats Kenwood's own ±1 dB tolerance, though there was measurable high-end ripple and a modest treble boost. Channel balance was excellent at ±0.005 dB. THD+N ran 0.005% from 20 to about 200 Hz, then fell to 0.0025% at 1 kHz, half the published spec. After that it rose to 0.039% at 10 kHz and 0.48% at 20 kHz. Foster suspected the analog output stages rather than the converter. Linearity held down to -60 dB and showed the usual one-bit-era drift below that. The A-weighted S/N was a spectacular 128 dB referenced to a 0-dB recording, and channel separation cleared 92.5 dB at 1 kHz in either direction.
The published specs cover the rest. Frequency response is 4 Hz to 20 kHz, S/N is greater than 96 dB, dynamic range is greater than 94 dB, THD is less than 0.005% at 1 kHz, channel separation is greater than 90 dB at 1 kHz, and wow & flutter is listed as unmeasurable. Fixed output is 2.0 V into 3.3 kilohms. The headphone jack delivers 20 mW maximum into 16 ohms. Conversion is one-bit with eight-times oversampling. The unit draws 15 watts and measures 17⅜ inches wide by 5⅛ high by 14½ deep (44 x 12.8 x 36.8 cm), weighing 11.9 lbs (5.4 kg). Price was $399 at introduction, with MoodMaker software at $49.95.
Build quality is where the DP-M7750 takes its criticism. Foster found it rather noisy when loading or changing discs, which is typical of magazine changers built on a mostly plastic transport. The thin sheet-metal housing did little to suggest solidity. The skip and search buttons were less than positive. Sometimes a press had to be repeated, and sometimes a single tap produced a double skip. He suspected membrane switches or direct circuit-board contacts, the price of packing lots of features into a relatively inexpensive component.
The panel is a button farm. A jumbo power button sits upper left, with the phones level control and a gold-plated phones jack beneath it. Seven disc-select buttons sit beside the single-disc tray, one for the tray and six for the magazine. The function button handles naming and program storage. Characters are entered via the seven disc-select buttons and the first 19 numeric keys, which together cover the 26-character English alphabet, with typographical symbols on the track search and skip keys. The nine buttons above the transport controls have dual purposes, and Foster found some of them logically unrelated. The peak-search button for tape recording lives in the same cluster as the random-play button.
MoodMaker itself is a relational database organized in six-disc clusters. It catalogs by disc title, artist, composer, track title and artist, with notes and a 1-to-5 rating scale. Searching is case-sensitive, so ask for "Love" and you won't find "love." It can compile playlists of similar music from search criteria and send them to the player, and it displays cover art from .BMP or .DIB files. It needs an IBM-compatible running Windows 3.1 under MS-DOS 5.0 or higher, at least a 20-MHz 386SX with 4 MB of RAM, VGA or SVGA, and a free serial port. The software shipped on a 3½-inch floppy.
Listening impressions were honest but unflattering. Foster's one-bit reference player beat it on piano — tubby, indistinct bass, zingy tenor, brittle treble, wiry violins, shrill piccolos. On the plus side, the player was admirably quiet, especially on older undithered audiophile CDs. The DP-M7750 is a curio of the early home-computer era, when a CD changer could be sold partly on the promise of a Windows database. Collectors chasing one today should expect to hunt for the MoodMaker floppy and a period PC to use it, and should test every button on the panel before committing.
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