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This treatise was not intended to evaluate cartridges solely for their ability to reproduce discrete four channel records, but since there has been considerable speculation about cartridges usable for reproducing them, we will try to clarify some of the requirements. To that end, all of the cartridges reported on in this profile were tested out to 50,000 Hz, although only one made any claims to CD-4 readiness.
In making the frequency-response measurements, a Bruel & Kjaer frequency-sweep record, QR-2009, with a range from 20 to 20,000 Hz, was used, and with the response recorded automatically on Justi-Meter III, the graphic audio recorder designed by this reviewer. To cover the range from 1,000 to 50,000 Hz, a newly available record from JVC was used. Not much can be told about this record, since the information on the jacket was in Japanese, a language with which this reviewer is only slightly familiar, such knowledge including such words as arigato and sayonara, both learned from movies. However, the information on the record label tells us that it is a "High Frequency Response Test Sweep, No. TRS-1005," of JVC's Technical Record Series, and that there is a spot or reference tone, of 1000 Hz, followed by a period of no modulation, then a sweep starting at 1000 Hz and continuing up to 50,000, with nine pairs of left and right sweeps on each side. The time of the sweep is such that it matches the B & K QR-2009, assuming that the 1000-Hz reference tone is started at the 50-Hz mark on the chart. The reference tone continues for a few seconds, then stops (which starts the chart motor), and then the sweep commences at the 100-Hz line on the chart, so that the plotting is just 10 times the indicated frequency.
The response from 20 to 20,000 Hz was recorded for both left and right channels from both outputs from the cartridge, to give both frequency response and separation. Only the left channel was recorded for the range from 1000 to 50,000 on the JVC record. Output was measured from the left-channel cut on CBS STR-100 at a stylus velocity of 3.54 cm/sec, and corrected mathematically to indicate the output (in mV) per centimeter/ sec of stylus velocity. Square wave photos were made using CBS STR111 for the source, again using only the left-channel cut since both were nearly identical in all cases. In two cases-the Decca models-both the vertical and lateral sweeps of the QR2009 were measured just out of curiosity, and were found to be quite close over the range-enough so that their responses are not included. The Decca cartridges are, of course, built with vertical and lateral transducers, with the matrixing done internally, presumably, so that the outputs are left and right, and thus compatible with most other cartridges in which the signals are developed directly from the 45/45 aspects of the grooves.
It should be noted in advance that these cartridges represent the latest outputs of the various manufacturers, and that most are not specifically intended for CD-4 reproduction. The only exception to the "latest output" designation is the Stanton 681EE, which is about two years old, but still a creditable cartridge.
High-Frequency Measurement Problems
We have long noted the variations in response caused by different capacitances in the leads from the cartridge to the measuring instrument. In some cases, the manufacturer specifies the recommended value of capacitance, and unless used with that much capacitance, response is likely to show a peak somewhere around 19,000 Hz, and a broad droop in the 6000 to 9000 range. With proper load capacitance, the droop is flattened out, and the peak is reduced, so that response is flatter over the entire range. Measurements of a number of turntables with their supplied connecting leads indicates that an average value of capacitance is around 300 pF. Consequently, responses were measured at this value, and also with added capacitances of 100 and 200 pF, so that where is a significant difference in response between 300, 400, and 500 pF, it is noted.
In all cases, the high-frequency ranges were measured with lead capacitances of 105 pF. In trying to duplicate the published responses of the Audio-Technica AT 15S cartridge, it was found necessary to reduce the lead capacitance appreciably. In fact, the load resistance in the CD-4 demodulator unit is said to be 100k ohms instead of the usual 47,000 in phono inputs of conventional receivers and amplifiers. Furthermore, it seems that the leads from the cartridge to the demodulator are described as "large, fat cables." Since it was found that there was a great difference in response with a standard 300-pF connecting cable, another cable was made up using two 3-foot lengths of RG-58/ U, resulting in a total capacitance of 105 pF from the stereo plug to the cartridge clips. (Input to the recorder is by means of a standard stereo jack.) With this pair of leads, it was possible to come within 2 dB of the published response of the cartridge at 50,000 Hz.
What we are trying to tell you in all this dissertation is that if you plan to convert to CD-4, don't expect to get good results with the cables supplied with your turntable-replace them with leads made from cables with lower capacitances in the vicinity of 40 pF/ ft, and that's not counting the small leads, also shielded, within the turntable itself. It is suggested that you make a new set of leads-not RG58/U, since that is with a solid conductor, but with a good 75-ohm video cable, flexible, such as Belden 8279, with 21 pF/ft., or Dearborn 195/U, with 15.2 pF/ft. RG58/U has a capacitance of 17 pF/ft., but with its solid conductor is difficult to handle. It is likely that with the decoder you would get new leads, but don't forget the extra capacitance within the turntable itself.
Next to the top of the line (the top is AT-20S) is this model which is claimed to be usable for CD-4 reproduction. From the standpoint of frequency response it certainly could, since it is down only 3 dB at 50 kHz.
In this company's line, two separate magnets are mounted on the stylus "arm" near the fulcrum. These magnets are less than half a millimeter in diameter and only about two millimeters in length, and are mounted at right angles to the stylus "bar," which is actually a conical tube of minute dimensions. The stylus is a nude diamond mounted directly onto the end of the tube, and it has the Shibata shape, which is designed to contact a larger area of the groove, thus reducing stylus pressure at the same stylus force, which is recommended at 1.5 to 2 grams.
Resistance measured 485 ohms per coil, and inductance 410 mH. Output measured 1.02 mV/cm/sec.
Slightly lower in performance, and somewhat lower in price is the AT 13E, which is fitted with an elliptical stylus. Coil resistance is higher, measuring 1240 ohms per coil, and inductance is also higher, at 870 mH per coil. Output measured 1.10 mV/cm/ sec. This unit is similar in construction, but with higher resistance and inductance has a less extended range, being within ± 2 dB from 20 to 20,000 Hz, and dropping off rapidly after that. Separation still excellent, ranging about 20 dB up to 20 kHz.
This is the lowest in price of the Audio-Technica line, and performance is satisfactory by 1973 standards, with response within ± 3 dB from 20 to 20,000 Hz and very rapidly dropping off after that. Separation was 15 dB clear out to 15,000 Hz, dropping to 10 dB at 20 kHz. This model had coil resistances of 1200 ohms and inductances of 850 mH, and with its conical stylus with a radius of 0.7 mils could hardly be expected to have an extended response. However, its output--1.72 mV/cm/sec--might prove an advantage where the additional 5 dB was needed.
Decca London Export
To our knowledge, Decca is the only current manufacturer whose products operate on the vertical and lateral principle. That is, there is one coil which translates the vertical motion of the stylus, and another which translates the lateral motion. Actually, what was probably the first such pickup was the famous Western Electric 9A, which used two coils to move with the stylus motion. When connected in series opposition, they reproduced only the lateral motion; connected in series aiding, they reproduced only the vertical motion. The two coils came out to the terminals separately, and one was reversed by means of an external switch. In its patent application, the idea of matrixing these coils was described for the possibility of stereo reproduction of 45/45 records--and this was in the early '30's. It was a great pickup in its day, but massive. It followed the D-spec vertical 'hill and dale' cartridge, and was long used in broadcast stations until about the middle '40's when better cartridges--probably first was the Pickering--came onto the scene.
Decca claims some special advantages in its construction, and while we have little "inside" information about it, it is likely that the matrixing is done internally. The unit is small--11/16" wide and 15/16" long--and light (4 grams). It fits onto a plastic bracket which is mounted in the head and provides the terminals for external connections. Only three terminals are provided, within the common terminal serving for both right and left channels.
The stylus proper is mounted on the tip of a tiny "arm" which is shaped to transmit the motion to the two coils' pole pieces. What appears to be the stylus arm is actually a nylon tie-back cord to hold the stylus in place. The stylus is not replaceable by the user, a disadvantage in the amount of time it would be out of service while sent back for replacement, but an advantage in that its placement is factory-perfect, and when so replaced it is in effect a new cartridge.
Resistance of each channel measured 4320 ohms, and inductance was 75 mH. Output was 1.16 mV/cm/sec, and there was no noticeable difference in the response with the three values of capacitance over the 20-20,000 Hz range. Note that response is within 3 dB from 20 to 30,000 Hz, unusually good for normal stereo use. Reproduction excellent, with particularly smooth highs, apparently limited only by the records themselves.
Identical in appearance to the London Export (except for the body color, which is light gray in the Export and blue in the London). Also identical in construction, although the Export is said to be made of slightly better materials and undergoes additional quality control checks. Performance differences are slight-output of the London is 2.51 mV/cm/sec, and the response curve is much more peaked at about 18 kHz, while above that it is erratic. Separation is somewhat less, as noted on the response curve.
It would seem desirable for the critical user to have a London Export for his principal cartridge, with a London as a spare he could use if the Export were sent off for stylus replacement. The difference in prices would make that a reasonable suggestion. Recommended tracking force on both models is three grams.
Ortofon M15E Super
This is a more conventional cartridge than previous models of this company's product line. The stylus is interchangeable, with a slip-in plastic structure which is exceptionally well guided by the plastic, not depending on the stylus housing for location. The unit is slightly longer than usual, and weighs 5 grams. Recommended tracking force is one gram, which demands a high-quality turntable. Resistance per coil is 1205 ohms, and inductance is 980 mH. Output is 1.30 mV/cm/sec.
Absolutely no effect was noted with load capacitances from 300 to 500 pF. Response is within ± 1.5 dB from 20 to 21,000 Hz, and separation is approximately 20 dB to 12 kHz, decreasing above that to 10 dB at 20 kHz. Unit is packed in a neat plastic covered metal box, with a tiny stylus brush.
Pickering XV 15 / 1 200E
The top-quality model of this long established line, the XV 15/ 1200E does what would be expected--frequency response exceptionally flat to about 27,000 Hz and with no peaks whatever.
Separation is over 20 dB throughout most of the range, decreasing above 11,000 Hz to about 5 dB at 20,000 Hz.
Among the features of this cartridge are the snap-in mounts-a group of four plastic moldings which can be fitted to the tonearms of four popular turntables to permit the instant change of cartridges without the tedious fitting of screws. You will have to attach the leads, however. A wide variety of interchangeable styli is available, but with the elliptical stylus with which this model is equipped, tracking force is specified as 0.75 grams +0.5, -0.25--that is, from 1/2 gram to1 1/4 grams. That is possible only with the highest quality turntables and/or arms, of course.
Resistance per coil was measured as 1240 ohms, with inductances of 810 mH per coil. Output measured at 0.93 mV/cm/sec, which is about average.
Shure V-15 Type III
Nothing ever stands still. The V-15 Type II Improved was better than the V-15 Type II, which was better than the original V-15. Any one of these was excellent in its time, but improved materials and improved designs permit continual improvements in the ultimate product-in most any category. Basically, Shure engineers have developed a laminated core structure and have decreased effective stylus mass by 25 per cent. These improvements have made possible better trackability at still lower stylus forces.
The V-15 Type III has a resistance of 1450 ohms per coil and inductance of 500 mH per coil. For whatever reason, no noticeable difference was found with the three capacitance load values of 300, 400, and 500 pF, although Shure recommends between 400 and 500 pF, as they also did for the V-15 Type II, but in the latter case there was a considerable difference in frequency responses. Output measured 1.27 mV/cm/sec. In appearance, the Type III is almost identical with the Type II, with one noticeable improvement in the molding of the housing which provides a "hole" rather that a "slot" into which the mounting screws fit, thereby making it much easier to mount.
Frequency response was within ± 1.5 dB from 20 to about 26,000 Hz, and separation was close to 25 dB up to 10 kHz, decreasing above that.
Stanton 681 EE
This cartridge is some two years old, and has long been used by this reviewer as a measuring standard. It is not, therefore, representative of the latest output of this manufacturer. Resistance, 1430 ohms/coil; inductance 800 mH/coil; output, 1.16 mV/cm/sec. Response is within ± 1.0 dB from 20 to 25,000 Hz, and separation is 24 dB at midrange, 19 at 20 Hz, and decreases starting at 3500 Hz to a minimum of about 5 dB at 10 to 20 kHz. Not bad for an old cartridge, which was simply included for comparison purposes.
With the exception of the two AT models, there would be very little to choose from in this group of top-quality cartridges. A wide variety of records was listened to extensively, including the latest version of Shure's "Audio Obstacle Course," the "era III." This observer would be satisfied with any one of the group excluding the Decca London and the last two Audio-Technicas--AT-13E and AT-10. Any of the others seemed to be comparable to the best, and it would be difficult-nay, impossible-to say which was really the "best."
-C. G. McProud
(Adapted from: Audio magazine, Aug. 1973)
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