MANUFACTURER'S SPECIFICATIONS
Stylus: 0.0002 x 0.007 in. elliptical diamond.
Frequency Response: 5 Hz to 20 kHz ± 2 dB.
Tracking Force Range: 0.9 to 1.1 grams.
Channel Separation: Nominally 30 dB at 1 kHz, nominally 20 dB at 10 kHz.
Output Voltage: 3 mV at 5cm/sec. peak recorded velocity.
Load Recommendation: 47 kOhms.
Price: $110.00.
Also available as QDC-Ie for CD-4, $120.00, and QDC-Is with spherical stylus, $100.00. Although the electret principle is considered by many to be of recent vintage, it actually is about 50 years old. The electret principle, which in reality is dielectric absorption, was developed by the Japanese scientist, Eguchi, in 1925.
Eguchi permitted melted mixtures of wax to harden in a strong electric field and found that he had obtained dielectric absorption which remained relatively undiminished over a period of years. Thus, the electret is a permanently polarized solid dielectric and the electrostatic analog of a permanent magnet. Its application in audio did not come until about 35 years later when scientists at Western Electric improved the electret to the point that it would hold its polarized charge indefinitely, thus forming the basis for its first audio application--the electret microphone.
The Micro-Acoustics QDC-Ie electret transducer is an almost perfect device for transforming mechanical vibrations into analogous electrical signals (without the use of an external voltage source), whereby the output voltage is the exact analog of the mechanical vibrations. These vibrations are coupled from the record groove by the stylus bar and resolver (the resolver is a mechanical device used to separate the complex vibrations of the stylus into the left and right components). The resolver, in turn, is in direct mechanical contact with the left- and right-channel electret transducers, where varying pressure on the transducers generates electrical signals which are transmitted to the internal resistive network at the cartridge output terminals. The resistive network converts the cartridge from an amplitude to a velocity responding cartridge. Like all stereo cartridges, it operates into the usual 47 kOhm load present at the phono inputs of most preamplifiers. However, it will operate equally well across any load resistance, e.g., 100 kOhms. Any standard audio cables may be used between the cartridge and phono input of the preamplifier inasmuch as the frequency response of the Micro-Acoustics QDC-le is not affected by the usual cable capacitance. The electret self-resonance (mechanical) is above 40 kHz, well above the audio spectrum, and is damped by the special damping blocks inside the cartridge. There is no electrical resonance present in an electret cartridge.
Measurements
As is our practice, measurements are made on both channels, but only the left is reported. During the test period, temperature was 70' F ± 1' and the relative humidity 60-64 percent.
Before any measurements are made, the optimum tracking force is determined and ordinarily used throughout evaluation. However, this was not the case with the Micro-Acoustics QDC-Ie cartridge. The optimum tracking force was found to be 800 mg (0.8 g), but to track the very high levels of the Shure TTR-103 or the AEL-100 test records cleanly, the tracking force had to be increased to 1.5 g. This situation appears to be due to the fact that the QDC-Ie is a direct-coupled device requiring a small amount of mechanical bias to effect contact between the resolver mechanism and the electrets and to cause an incremental deflection of the electrets. Therefore, the 1.5 g tracking force is the total of 1.1 g needed for actual tracking plus the additional 400 mg (0.4 g) required to couple the stylus bar to the electrets.
We suggest that the tracking force be set at 1.5 g unless using a tone arm with minimal friction, e.g., the Audio-technica AT-1009 or the SME 3009, in which case a tracking force of 1.25 g may be used.
Frequency response is flat within ± 2.5 dB from 35 Hz to 11 kHz,-3 dB at 20 Hz, +4 dB at 15 kHz, and 0 dB at 20 kHz.
Separation is 23 dB at the mid-range, 20 dB at 10 kHz, and 18 dB at 20 kHz. Channel balance is within 0.5 dB, and the trackability is good. Using the AEL-100 test record, which contains tracking velocities from 7 cm/sec to 70 cm/sec at 1 kHz, lateral cut, peak velocity, the QDC-le tracked the 35 cm/sec band. The 300-Hz test bands on the German Hi-Fi Institute "Listening and Measurement" Record No. 2 were tracked up to 70 microns (.007 cm) lateral and 50 microns (.005 cm) vertical, which is average for the better cartridges.
Cartridge and tone-arm resonance, with Audio-technica AT-1009, appears to be just below 10 Hz. Compliance measured as 7.2 x 10-s lateral and 6.3 x 10-s vertical. Signal output was 1.09 my/1-cm/sec. Other measurements were: Wt. 7.18 g; tracking force 1.5 g; anti-skating 1.25 g; output 1.09 mV/1-cm/sec; IM dist. (4:1) +9 dB lateral, 200/4000:1.8%, +6 dB vertical, 200/4000:2.6%; crosstalk -23 dB; ch. bal. 0.5 dB; trackability: high freq. (10.8 kHz pulsed) 30 cm/sec; mid-freq. (1000 + 1500 Hz, lat. cut) 31.5 cm/sec; low freq. (400 + 4000 Hz lat. cut) 24 cm/sec; passed all bands of the Shure Audio Obstacle Course, Era III test record.
Test records used in the evaluation were the AEL-100; Shure TTR-107, TTR-103, and TTR-100; Columbia STR-100, STR-112, SQT-1100; Stereo Review SR-12; B&K QR-2009; German Hi Fi No. 2, and Ovation OVQS/4000.
Fig. 1--Frequency response and separation of Micro-Acoustics QDC-Ie phono
cartridge.
Fig. 2-1--kHz square-wave response of the Micro-Acoustics QDC-Ie using CBS
Lab's STR-112 test record.
Listening Evaluation
Although laboratory measurements of a cartridge's parameters are of great importance, obviously one cannot listen to measurements. However, our listening evaluation bore out what the measurements generally indicated, that this is one of the better stereo phono cartridges on the market.
The Micro-Acoustics QDC-le was used with the following equipment in the listening evaluation: Technics SP-10 turntable, Audio-technica AT-1009 tone arm, two Phase Linear 4000 preamplifiers, two Crown D-150 amplifiers, four Micro-Acoustics FRM-1 speakers, and the Janis Audio Associates W-1 subwoofer along with the Crown VFX-2 crossover network in a common mode configuration. The matrix quadraphonic decoders used were the Lafayette SQ-W, the Sansui X-2, and the SQ and QS positions of the Denon UDA100. As is our practice, a rigorous listening evaluation of the QDC-Ie was conducted, exceeding 40 hours of use. All the stereo and matrix quadraphonic records listed in the report on the Supex SD-900/E published in Audio, September 1975, p. 61, and the following additional records were used in the listening evaluation of the QDC-le cartridge.
Stereo Lincoln Mayorga & Distinguished Colleagues-Sheffield, Lab. 1, Volume III The Missing Link-Sheffield, S10, Volume II Von Suppé Overtures-London, SCP 21069 Khachaturian: Symphony No. 3; Rimsky-Korsakoff: Russian Easter Overture-RCA LSC-3067 Rossini: The Siege of Corinth-Angel SCLX-3819 QS Synergy: Electronic Realizations for Rock Orchestra-Passport Records PPSD-98009 Fireballet: Night on Bald Mountain-Passport Records PPSD-98010 SQ Boulez Conducts Ravel-Columbia MQ 32838 E. Power Biggs Plays Scott Joplin on the Pedal Harpsichord-Columbia MQ 33205 Handel: Water Music (Boulez Cond.)-Columbia MQ 33436 Massenet: La Navarraise-Columbia MQ 33506 Weather Report: Tale Spinnin'-Columbia PCQ 33417 Chicago VII (2 discs)-Columbia C2Q 32810 The QDC-le cartridge reproduced all types of recorded music exceptionally well, particularly in the high frequencies, without any noticeable coloration. It is particularly good in voice reproduction, as evinced by the Rossini: The Siege of Corinth and the Massenet: La Navarraise recordings. Organ music is reproduced quite faithfully, especially the organ pedal notes. The pedal harpsichord, a difficult instrument to both record and reproduce, comes across surprisingly well in the Scott Joplin rendition by Biggs. Some exceptionally well-reproduced records are Weather Report's Tale Spinnin', and the superb QS recordings, Synergy and Fireballet. The Synergy recording is the best electronically synthesized (Mini-Moog) music we have ever heard-particularly the Slaughter on Tenth Avenue rendition. The recording sounds exceptionally good in the QS Vario-matrix mode and almost as good in stereo. The bass in the Synergy recording is clean and clearly defined. Transient response is exceptionally good.
Micro-Acoustics claims that the QDC-le cartridge makes a recording sound indistinguishable from its master tape in a direct "A-B" test. Obviously, since few audiophiles would be able to acquire such master tapes in order to verify these claims, most will have to reserve judgment on this. However, in spite of the difficulty in verifying such claims, our measurements and subsequent listening evaluation are strong evidence that such may, indeed, be justified.
We have lived with the Micro-Acoustics QDC-le cartridge for some time, playing the gamut of monophonic, stereo, and matrix quadraphonic recorded music from our record library. Based upon our laboratory measurements and listening evaluation, we can recommend the QDC-Ie without hesitation to the discerning audiophile who desires a top quality cartridge.
-B. V. Pisha
(Audio magazine, Jan. 1976)
Also see:
Micro Acoustics 630 Phono Cartridge (Mar. 1984)
Pickering XSV/3000 Stereo Cartridge (Equip. Profile, June 1977)
Phono Equalization Kits--various models (Mar. 1979)
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