The MDX-400 consists of three components; an in-dash 4 MD changer with fold-down detachable faceplate, a preamp/tuner unit, and a wired rotary remote control. It has no internal amplifiers. MSRP is US$1200; Sony factory outlet stores sell refurbished units for US$225. An optional wireless remote control (RM-X40) is available for approximately US$16.50, and is very useful.

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The tuner/preamp unit is 7.75 x 1 x 5.125 inches in size, and can be mounted anywhere in the car. It has the following connections:

If you have two antennas, the diversity tuning system will continuously sample each antenna and select the one with the best signal. The tuner is substantially better than the ones I've heard in other Sony car stereos.

The MD changer unit is mounted in the dash of the car. It has analog audio outputs, UniLink connector, and optical digital output (with XA-D210 optical adaptor). The supplied 4-disc magazine (XA-4) holds 4 MDs, and can be inserted or removed when the faceplate is folded down. The tuner works while the faceplate is folded down. I have had the MDX-400 for over 1 year, and it has never skipped. Disc changes take about four seconds. It reads the TOCs of all discs when the MD magazine is inserted. The entire optical assembly and motor are built on a rotating turntable, and they spin around to access each disc.

The detachable fold-down faceplate has a 2-line, 24 character backlit dot matrix LCD. It appears blueish, greenish or yellowish, depending on ambient lighting conditions. The buttons have a rubberized coating and selectable orange or green illumination. A diagram of the MD magazine is displayed on the LCD, showing which discs are present or playing. The display has an animated spinning MD or CD which appears in MD or CD mode, and a picture of an antenna with radio waves for tuner mode. MD titles can be scrolled using the "scroll" button on the wired remote control. The recording date of an MD can be displayed. In MD/CD mode, title information appears on the top line, and disc/track/time appears on the bottom line. In tuner mode, station name appears on the top line and preset/frequency appears on the bottom line. "List" function shows the titles of the four MDs loaded in the magazine, or the names of four radio stations or CDs. This function works well for the 4 MD changer, however with a 6 or 10 disc CD changer, only four titles can be seen at a time, in groups of discs 1-4, 5-8, and 9-10. So, if you are playing CD 3 and want to see the titles of discs 5 to 8, you will have to actually change to one of discs 5,6,7 or 8 before the titles of discs 5 to 8 will display in list-up mode. It is handy to leave the tuner in list mode all the time, since that way you can still see what station you're on (it's numbered in inverse video), and you can see what is on the surrounding preset buttons.

Not all functions are accessible via buttons on the in-dash unit (probably due to the large size of the LCD on the front panel). Instead, the wired or wireless remote controls must be used. The only important function which is missing from the faceplate is track +/- (tuning +/-). The wired remote is also required to set the clock, scroll the MD titles, set FM local/DX/mono and perform other minor functions. The MDX-400 does not have the "source tone memory" function found on most newer Sony car stereos.

An interesting feature of the MDX-400 is that the in-dash MD changer unit can be controlled by any Sony Unilink head unit (such as CD players or cassette decks), where it will act as an add-on MD changer. All data displayed on the main unit will also be displayed on the MDX-400's screen, and the MDX-400's buttons can be used to control functions on the main unit, such as volume, backlighting colour, etc. Therefore, if the MDX-400's tuner/preamp unit becomes broken for some reason, you could still use the in-dash MD changer portion with another Sony stereo.