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The Optimus CD-6100 com pact disc changer, distributed through Radio Shack stores, is designed to play as many as five discs automatically. Unlike most early CD changers, whose separate magazines had to be loaded with discs before playing, the CD-6100 has a built-in front-loading “carousel” mechanism that accepts either 5- or 3- inch discs.
Loading it is similar to loading a single-disc player. At a touch of the open/close button, the carousel plat form moves forward to expose three of its disc wells to view, although only one at a time is accessible for loading or removing a disc. The DISC SKIP button rotates the platform for access to any of the other disc positions. After the discs are loaded, pressing the open/close button moves the platform into the cabinet, with Disc 1 positioned over the playing spindle. The DISC SKIP button can be used to move any of the other discs into the playing position.
Operation of the player is straight forward and conventional for the most part. The other front-panel buttons include play/pause, stop, and a pair of track-skipping controls labeled ASMS (for Automatic Search Music System). Other buttons are used to program a sequence of as many as fifty tracks in any order from any or all of the loaded discs and to initiate shuffle play, which selects a random sequence of tracks or discs.
The pushbutton power switch is at the upper left of the panel. A timer switch at the lower left allows unattended, straight-through (unprogrammed) playback when the unit is powered through an external timer. There is a front-panel headphone jack with level knob, and the rear apron contains standard analog line-output jacks.
The display window along the bottom edge of the panel has symbols showing the player’s operating status (pause and play), a row of numerals from 1 to 5 (the number of the playing disc is circled), and larger numerals for the track number and elapsed playing time. A small TIME button above the disc carousel toggles the display to show the remaining time on the track or the disc (when a disc is first loaded, the display shows its total number of tracks and total playing time).
The specifications for the CD-6100 indicate that it uses quadruple-over- sampling (at 176.4 kHz) and digital filtering as well as dual digital-to-analog (D/A) converters. Its frequency response is rated as 20 to 20,000 Hz ±1 dB, its dynamic range as more than 90 dB, and its signal-to-noise ratio (s/N) as more than 100 dB. At 1,000 Hz, the rated total harmonic distortion (THD) is less than 0.05 percent, and the stereo channel separation is rated at more than 95 dB.
The CD-6100 is supplied with a com pact wireless remote control that also augments the front-panel control functions. In addition to the standard disc- transport controls, it has a FADER button, which smoothly increases or decreases the volume over a 5-second period. Other buttons provide direct access to any of the discs and duplicate the DISC SKIP function. The remote control also has a fast-forward/reverse scan mode with sound and a repeat function that is effective in all modes, including programmed operation.
The Optimus CD-6100 is a compact unit, measuring 14 inches wide, 15 1/4 inches deep, and 4¼ inches high. It weighs only 11 pounds, 5 ounces. Price: $250 [ca. late 1990]. Radio Shack, Dept. SR, 700 One Tandy Center, Fort Worth, TX 76102.
The Optimus CD-6100 delivered 2.1 volts output at 1,000 Hz from a 0-dB (maximum-level) test recording. Its frequency response was flat within +0.02, —0.3 du from 20 to 20,000 Hz, and the channel levels were matched to better than 0.01 dB. The separate D/A converters for the left and right channels kept the phase shift between channels to less than 0.06 degree over the full audio range. De-emphasis response error was less than 0.15 dB from 100 to 16,000 Hz.
The channel separation (slightly different for left and right channels) was 90 to 96 dB at 100 HZ, 86 to 90 dB at 1,000 Hz, and 62 to 68 dB at 20,000Hz.
The 1,000-HZ distortion (THD plus noise) was 0.074 percent from -60 to -20 dB, increasing to about 0.08 percent at 0 dB. At a constant 0-dB signal level, the distortion measured between 0.09 and 0.05 percent from 20 to 1,000 Hz, and it increased to 0.22 percent at 10,000 Hz and 0.8 percent at 20,000Hz.
The low-level linearity of the D/A converters was exceptional, especially for conventional ladder-type converters. From -60 to -90 dB the amplitude error rarely exceeded 0.5 dB, and the levels of the two channels were closely matched. A spectrum analysis of the noise and hum in the player’s output showed 60- and 180-HZ levels of -119 and -113 dB, respectively, with the random noise level decreasing from -115 dB at 10,000Hz to -140 dB at 20 Hz. The A-weighted noise in the audio range was -107.2 dB. The player’s dynamic range (EIAJ) was about 90 dB, and quantization noise was at -80 dB. The play back speed error measured -0.00 13 percent.
Although the CD-6100 is not a heavy player, it proved to be relatively impervious to physical shock. It was difficult to cause mistracking by fist blows to the sides of the cabinet, and a firm slap or blow on the top was needed to impair the laser tracking audibly. The slew rate of the laser servo was average; it required 2.5 seconds to go from Track 1 to Track 15 of the Philips TS4 test disc. When disc changes were involved, the elapsed time between the selected tracks was typically 7 to 8 seconds.
The error-correction system of the CD-6100 was good, requiring a defect size of 1,250 micrometers to cause audible mistracking. The headphone volume, with medium-impedance (AKG 340) phones, was adequate though never really loud.
The Optimus CD-6100 proved to be a very satisfactory CD player, even for conventional use with a single disc loaded. It is no more difficult to use in the single-play mode than other CD players (in fact, it’s simpler), and its performance was at least as good as that of most competitively priced models. And, where extended pro grams are required, its five-disc capacity will provide up to 5 or 6 hours of uninterrupted music.
Although the instruction booklet is quite specific concerning how to pro gram a playback sequence, the procedure is unlike that of most single-play units. We needed some experimentation to get the hang of it, but after a little hands-on experience the process was easy. In all, at $250 the Optimus CD-6 100 changer represents exceptional value.
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Maximum output level: 2.1 volts
Total harmonic distortion at 1,000 Hz: 0.09% at 0 dB, 0.075% from —20 to —60dB
Signal-to-noise ratio (A-weighted): 107.2 dB
Dynamic range: 90.8 dB
Channel separation 93 dB at 100 Hz, 88 dB at 1,000 Hz, 65 dB at 20,000 Hz
Maximum interchannel phase shift 0.6 degree at 13,000 Hz
Frequency response: + 0.02, —0.3 dB from 20 to 20,000 Hz
Low-level linearity error (average of both channels): + 0.6 dB at —60 dB, —0.22 dB at —70dB, +0.6dB at —80dB, +0.75 dB at —90dB
Speed error: —0.00 13%
Slewing time: 2.5 seconds (7 to 8 seconds between discs)
Cueing accuracy: A
Impact resistance: top B; sides A
Defect tracking: tracked 1,000-micrometer defects on Pierre Verany #2 test disc
Source: Stereo Review (Jan. 1991) Julian Hirsch, Hirsch-Houck Laboratories