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Overall Length: 12.33 in. (31.3 cm).
Pivot-Stylus Distance: 9.33 in. (23.7 cm).
Bearing Type: Ball.
Tracking Forge Range: 0-1.5 gms.
ZLM Phono Cartridge
Frequency Response: 10 Hz to 20 kHz, ± -1 dB.
Channel Separation: 30 dB at 1 kHz.
Stylus Assembly: Nude "Aliptic" with tapered cantilever.
During the long and, I must say, tedious process of preparing methods to test and evaluate phono cartridges and arms in combination, it became apparent that, if correlations were to be made between objective technical measurements and subjective impressions gathered during listening sessions, some new approaches needed to be tried. Many different approaches were investigated including even generating a new test record which would allow tests which are not possible with existing records. It was decided, however, that at least for the present certain available test records could be used to present data in new formats which seem to correlate well with subjective listening impressions. These subjective evaluations were made by a listening panel. This panel auditioned passages from recordings of various types of music. A reference system was used to allow comparative comments to be made. The technical measurements had previously been completed in order that the setup of the phono carridge-arm combination could be optimized. The data gathered during these technical measurements were inspected later to see if correlations existed between the data and subjective comments made by panel members during the listening tests regarding various characteristics of sound quality.
Rather than separate the objective technical measurements from the subjective impressions of the listening panel, both aspects of the report are presented concurrently. Since this report deals with a specific phono cartridge and arm corn hin anon s, comments pertaining to the mechanical parameters of the arm which would affect its use with other cartridges are presented later.
ADC ZLM Phono Cartridge
Serial No. 7A4147
Dynamic Tracking Force, B&K 2010, grams (Gms x 980 = dynes)
Dist., %, Left | Dist., %, Right
Band 3,+8 dB
Band 4,+6 dB
Band 5, +4 dB
Band 6, +2 dB
Band 7, +0 dB
Tracking vs. Radius, HFS-75, grams
Outer grooves 1.3
Middle grooves 1.3
Inner grooves 1.3
Cartridge Mass: 5.55 gms.
Hum Rejection: Good
High Frequency Resonance: 28.6 kHz.
Rise Time: 24 pS. Low Frequency Resonance: 10 Hz.
Low Frequency Resonance Q: 3.3.
Recommended Load Resistance: 47 kilo
Recommended Load Capacitance: 275 p F.
Recommended Tracking Force: 1.6 gms hms.
ADC LMF-2 Tonearm:
Pivot-to-spindle Distance: 8.75 in. (22.23 cm). Pivot-to-stylus Distance: 9.33 in. (23.7 cm). Pivot-to-rear of arm Distance: 3.0 in. (7.62 cm). Spindle-to-rear of arm Distance: 11.688 in. (29.69 cm). Overall Height Adjustment: 1.5-3.2 in. (3.8-8.3 cm). Tracking Force Adjustment Range: 1.7 gms with calibrated scale; more with separate gauge.
Tracking Force Calibration: 0.5 to 1.7 gms.
Tracking Force Accuracy: -0.1 gm at 0.8, 1.0, 1.3 and 1.5 gms settings, but -0.2 at 1.7 gms.
Cartridge Weight Range: 3 to 11 gms.
Counterweights: 15.0 (14.9 actual), 30.0 (30.5), and 45 (44.9) gms.
Counterweight Mounting: Two "O" rings; rubber main rod isolation.
Sidethrust Correction: Marked for 0 to 2 gms, with excellent uniformity.
Lifting Device: Finger lift on headshell and delayed-action damped lever.
Headshell Weight: 4.05 gms.
Headshell Offset: 24 degrees vs. 20 degrees specified.
Overhang Adjustment: Sliding screw mounts in headshell, with template.
Bearing Alignment: Good in both planes.
Bearing Friction: Less than 50 mG in both planes; too low to measure accurately.
Lead Torque: Very little effect.
Arm Lead Capacity: 20 pF internal, 255 pF external, 275 total.
Arm Lead Resistance: 0.89 ohms internal, 0.23 ohms external, 1.12 ohms total.
Lead Length: 48.5 in. (123 cm).
Structural Resonances: Very dead, tight "clack" when tapped.
Base Mounting: Single hole, nut on pillar.
General Comments: Effective mass specified as 8 gms.; good fit between head shell and arm with no play; good cueing level with short delay before starting cycle; recommend CD-4 lead wires and added external capacitance as needed.
It should be noted that the reference system consists of an excellent moving-coil phono cartridge, a Swiss-made arm, and a highly regarded turntable. This reference system was used to allow comparisons to be made during the subjective evaluations by the listening panel. The two systems were designated "A" and "B." Comments were elicited from panel members regarding the sound reproducing qualities of each system and comparative comments were made. This format seemed to allow panel members to crystallize their feelings regarding different aspects of the reproduction quality and therefore to make statements which could be correlated to measured technical data. The panel members did not have prior access to the technical data so their comments were based solely upon the listening tests. Two listening formats were utilized. In one format, rapid A vs. B comparisons were made by synchronizing the two turntables, playing copies of the same record, with a delay of about 4 to 5 seconds between them. In a second format, the same record was played with system A and then system B, with relatively long spans for each selection, about 2 to 4 minutes. Both formats were deemed valuable by the members of the listening panel.
This synopsis of the background of the new format adopted for reporting on photo cartridges and arms is intended as a guide for this first review. It is necessarily limited but it is hoped that a more comprehensive article will be forthcoming. We feel very strongly that this new format will be very helpful in correlating at least a few important subjective impressions with specific technical measurements. (Editor's Note: We would like to emphasize that many of these measurement techniques are new and, though carefully done, somewhat experimental in the sense that we are not yet certain as to the strength of the correlation between subjective observation and technical measurement.
We suggest, therefore, that readers do not fully judge the techniques or the cartridge and arm on the basis of this single review but rather evaluate them as part of a continuing series of reviews. E.P.)
The ZLM phono cartridge is the top of the extensive ADC line. It employs a transduction technique originated by Peter Pritchard, who founded ADC. A small permeable sleeve is fitted to the rear of the stylus cantilever. This causes the magnetic field of a rather large, fixed magnet to be vaned by the motion of the stylus. This type of cartridge design was first introduced in 1964 in the ADC Point Four phono cartridge. Many refinements have been made since then.
The ZLM was mounted in the ADC LMF-2 phono arm which features an interchangeable headshell. ADC also makes the LMF-1 without this feature but offering slightly lower effective mass.
The arm was mounted on the Pioneer PLC-590 turntable which is the top of their line and provides an excellent test platform. It has quartz-referenced speed control and excellent isolation from mechanical and acoustical feedback. The 3/4-in. thick, interchangeable arm-mounting blocks are a boon to arm-o-philes and reviewers because arms can be changed in about one minute. The instant stop feature was also a great advantage when cueing different bands of the test records and changing from one record to another.
Figures 1a and 1b show the left (upper) and right (lower) channel outputs to the 300 Hz tone on CBS test record STR112. This format is followed for all other photos. Figure la represents the output when reproducing band 4 which is +15 dB referenced to an amplitude of 11.2 pM. This is a very high modulation level, and the clean waveform shown is heard as a very pure tone.
Figure 1b is the waveform of the signal from each channel, when attempting to reproduce the even higher level on band 5 on STR-112. The modulation level of this band is +18 dB re: 11.2 pM. Most cartridges have great difficulty trying to reproduce this band. The reproduced tone is not very clean. The symmetry of the mistracking indicates that adjustment of the side thrust correction, also known as bias correction or anti skating, is quite good. Even though Fig. lb indicates mistracking at 300 Hz for +18 dB, no comments which could be directly related to mistracking were made by the listening panel when playing musical recordings.
Figure 2a is a graph of the output vs. frequency and inter channel output, commonly referred to as crosstalk. The balance between the main channel outputs is off by about 1.5 dB which could easily be corrected by adjusting the balance control of the amplifier or receiver. This channel imbalance is corroborated by the unequal measured resistance and impedance of the cartridge coils (see table). It would seem that the channel to channel balance of a top of the line cartridge such as the ZLM, should be quality controlled to be much closer than our sample. We therefore requested two more samples from the firm, and output for both channels of all three are shown in Fig. 2b.
Note the increase above about 1.5 kHz. Some and perhaps most of this distortion is probably due to the test record.
During the listening tests, one panel member commented on the quality of certain piano notes as being a type of resonant coloration. A correlation to the particular timbre of this coloration was found by looking at the crosstalk data in Fig. 2a. The output in the 1/3-octave band centered at 315 Hz is greater than the general trend, as in the output from the 250 and 400 Hz filters. Barely noticeable in the main output of each channel is a discontinuity at about 250 Hz. These measurements are made with such a slow sweep speed, that for practical purposes, they may be considered to be steady state. Under groove excitation due to the rapid, transient nature of the piano notes, this resonant-produced coloration is more audible than might be supposed. Figure 2 does correlate with listening quality to at least the extent of providing clues to the cause of this perceived effect. The dip at 18 kHz in the main output curves shown in Fig. 2 is documented by B&K as being an anomaly present in all pressings of their test record 2009.
Another aspect of the quality mentioned by all panel members was the bright, forward sound which at the same time lacked the extreme highs of the reference system. It is an interesting point that the ZLM exhibits to a greater degree the very quality for which some moving-coil cartridges are highly praised. It has a more forward quality than usually associated with cartridges of this design type. Part of this quality can be explained by the very tiny amount of droop in output above 2 kHz. This drop in output of only 0.5 dB centered around 5 kHz is less than that exhibited by some cartridges of similar design type. It is felt that the other part of the explanation is found by correlating this forward, bright quality to the rise in distortion, especially third harmonic distortion in the 3 to 10 kHz range. This is shown in Figure 3. No absolute distortion data is available for the B&K 2009 test record, so only relative information can be extrapolated. The disc cutting system used to make these recordings has a resonance at about 2 kHz. Above this frequency, the feedback in the system decreases to avoid instability at high frequencies.
It would seem reasonable to assume that the distortion inherent in the B&K 2009 test record would increase in the range above 2 kHz because of the decreasing amount of feedback, but part of the distortion may also be due to the response of the cartridge. Since most commercial records are also cut using this or another similar feedback cutting system, which exhibits a resonance at about 1 kHz, most, if not all, commercial records will exhibit similar distortion characteristics. Further research is being carried out in this area to isolate the distortion inherent in the test records.
During the listening tests another aspect of performance drew comments, which had to be carefully sorted out since two phenomena seemed to be occurring simultaneously. The program material during which these effects were noted was complex, with many instruments playing from various positions in the stereo image. The comments alluded to some lack of precision in positional accuracy and in timbre during these complex musical passages. During less complex passages, the stereo positional accuracy of various sources, heard individually, was quite good. The timbre of each instrument was also good except as previously described. The interchannel crosstalk data shown in Fig. 2 correlates well with the aural impression that the cartridge is excellent in this respect during relatively noncomplex musical passages which approach steady-state measurements. Figures 4 through 7 show essentially the same information as that of Fig. 2 but in a different form. Each figure is divided into a) which shows the amplitude vs. time response of both channels of the cartridge to steady-state sinusoidal signal, and b) which represents the left vs. the right channel. The b) part of each figure could be called the interchannel phase response. The frequency represented by each figure is 3, 5, 10, and 20 kHz, respectively. The slight bowing in the phase response is due to nonlinear distortion components as previously shown in Fig. 3. An absolutely coherent or zero degree phase relationship between the channels would be indicated by a straight line at about a 45° angle. The cursor lines shown are not meant to indicate x-y axes. They are related to the position of the cursor lines in the appropriate "a" part of each figure. The data in Figs. 4 through 7 correlate well with the data of Fig. 2 and also with regard to the image stability and excellent separation provided by the cartridge when reproducing simpler program material.
Figures 8a, b, and c provide the technical data necessary to correlate to the image and timbre quality perceived during complex passages. It should be pointed out that the waveforms shown in all the photos are taken from the screen of a digital storage device, which means that parts a, b, or c of each of the figures are directly related to each other. They are presented in a different format by utilizing computer manipulation. This is important if only because other insights may be drawn from this data, at a later date, which are beyond our capabilities at present. Figure 8a indicates that response to the 1-kHz square wave signal provided by CBS record STR112 is very good but that each channel is slightly different.
Since the square wave represents a complex signal composed of odd-order (i.e. 3rd, 5th, 7th, etc.) harmonics, each with a specific amplitude and phase relationship, it would appear to be a good test signal for determining performance during at least one type of comliJex signal conditions. Figure 8b which is the same as Fig 8a, but, expanded to show the leading edge, indicates the high frequency resonance due to the equivalent tip mass of the stylus and record material compliance. This resonance is at 28.6 kHz with this particular record material.
It should be pointed out that this frequency will change according to the stiffness (the reciprocal of compliance) of any given record. The stiffer the material, the higher the frequency. There is no ringing in the groove modulation of the STR112 test record, which was examined with a microscope. This high frequency resonance is so well damped that it is not easily determined from amplitude vs. frequency response data taken using a record which provides signals up to 45 or 50 kHz. This will be seen later. Figure 8c shows the same 1 kHz test signal in the left vs. right channel (x vs. y) format. A perfect correlation between the signals in each channel would result in only two bright dots. As can be seen, while there are two bright areas, they are a bit fuzzy and there are intermediate points scattered on an ellipse. The major ellipse indicates some interchannel phase misalignment between certain frequency components in each channel.
This technical information correlates with the perceived spatial smearing or broadening of individual musical instruments during complex passages. The minor ellipses near each bright spot indicate a shift in the relationships between the individual frequencies of the square wave. Such a shift could affect the timbre of instruments when they are producing complex transient musical tones.
Figure 9 shows the effect upon the high frequency response of the cartridge caused by changing the resistive component of the load impedance from the recommended 47 kilohms to 100 kilohms. Only the left channel is shown for the sake of clarity since the effect is the same for the right channel. The capacitive component of the loading was al= ready slightly greater than the maximum recommended which is 275 pF. The capacitance of the leads inside the arm was measured as being 20 pF and the cable supplied which connects the arm to the input of the preamp had a measured capacitance of 255 pF. To this total of 275 pF must be added the input capacitance of the preamp and test switching system which is 60 pF. Thus the total capacitance during our measurements was 60 pF over the value recommended by ADC or 335 pF. Since any preamp will have some value of input capacitance, it would seem that the recommended value of 275 pF will always be exceeded, since the capacitance of the arm and cable supplied total 275 pF. ADC does supply another low capacitance cable, designated CD4W, as an accessory to the arm. Unfortunately we did not have this cable at our disposal during the tests. It is listed as having a capacitance of only 100 pF. We would have liked to have been able to run curves showing the effects of lower capacity upon the output, but it appears that the ADC recommended value of 275 pF is correct. During the listening tests we were able to reduce the capacitance by about 40 pF to a total of 295 pF, since the switching system used for the interchannel tests was eliminated.
During the listening session, a passage with very deep bass was auditioned. The general consensus of the panel was that the ZLM/LMF-2 combination provided a less tight bass than the reference system but that the bass output was also slightly more pronounced. Figure 10 shows the low frequency resonance due to the combination of stylus compliance and effective tone arm mass. The Q of this resonance is about 3.3.
It is very probable that low frequency bass passage in the recording caused this resonance to be excited, a small amount of which could cause the "blubbery effect" in the bass notes commented on by one panel member. The modulation effects produced by this low frequency resonance have lately come under investigation by a number of researchers. We are investigating the effect of some of the external damping devices which are being offered to reduce the high Q of this low frequency resonance, which is found in all cartridge-arm combinations. The frequency of this resonance with the ZLM/LMF-2 combination is 10 Hz, which, at the present time, has become the generally accepted magic number. Thus, from the standpoint of this criterion, the ZLM/LMF-2 is a very compatible combination.
Figure 11 shown the scanning loss of the ZLM at the inner diameter of a record (3.75 in. or 9.53 cm) vs. the outer diameter 5.625 in. or 14.29 cm) for the left channel. The right channel exhibited a similar characteristic. This scanning loss is a general characteristic of all cartridges. It is a function of the inter-relationship between the dimensions and shape of the stylus and the groove modulation. Since scanning loss data may be new to many, it must be said that the scanning loss of the ZLM is neither worse nor better than most cartridges. No specific tests were devised during the listening session to elicit comments from the panel members regarding this effect.
Figure 12 shows data regarding another situation which is also related to the scanning effect. In this case, a wider frequency test record, the B&K 2010, was used. The change in output is a function of tracking force. When the tracking force is reduced from 1.6 to 1.4 grams, the output at high frequencies increases! Actually, this increase in output is due to the addition of distortion products. Once an optimum tracking force is found, no further increase in force causes a change in output during this test, however it should be noted that ADC recommends 1.25 grams, while we found that 1.6 grams gave the best results in our tests.
Since we were very aware of the deleterious effect of acoustical and mechanical feedback upon the audible quality of a turntable-arm-cartridge combination, great pains were taken to secure maximum isolation. Figure 13 shows the effect upon left channel output and crosstalk with and without an external sound field. The sound pressure level (SPL) measured at the cartridge was between 94 and 100 dB from 30 Hz to 200 Hz. This is a very severe test. The effect upon the main output is all but invisible, however the crosstalk does exhibit a change between the sound field being on or off. The sound field was produced by an oscillator which was tracking the chart recorder and was therefore a slowly swept sine wave of the same frequency as being reproduced by the cartridge from the test record. The change in crosstalk at 50 Hz, where the sound field measured 98 dB, was from 23 dB to 20 dB or only 3 dB. During the listening sessions the maximum SPL at the turntable was, at the most, 15 dB lower than during this severe test.
We are trying to develop a standard method for determining the hum rejection which will give a repeatable result which can be given in the form of a number. At this point we can only say that the ZLM/LMF-2 has excellent hum rejection. The microphonic effect of the ZLM/LMF-2 is also very low, so coloration due to this phenomenon should be very small.
Further investigations of the ZLM/LMF-2 combination, using the square wave on CBS STR-112, yielded some interesting information about the relationship between the reproduction of lateral (mono) and vertical (stereo) modulation.
The vertical modulation seems to exhibit a time delay vs. frequency which gradually increases at a greater rate than that of the lateral modulation. This could possibly cause an extra sense of spatiality from that actually present in the record grooves. It would seem that more research in this area is warranted.
Figure 14 shows the response of the left and right channels of the ZLM/LMF-2 combination to the 10.7 kHz filtered tone burst of Shure TTR-103 test record. This interesting test signal has more merit than meets the eye and you will see more of it in the future. We have included it in this report for reference so that you may compare it with future reports.
The LMF-2 arm is very easy to use, especially while making adjustments during tests. The mounting of the arm to the turntable is not difficult compared to some other arms. The main problem will be in using the template supplied to find the proper location of the hole which must be drilled for the arm. Because the template is of cardboard and must be held above the spot on the mounting board to be marked, an error might occur so care is advised during this operation.
Because the same template is used to determine the proper stylus overhang, the locating hole in the template is as large as the tone arm pillar which is about 11/16 in. (1.746 cm) in diameter. This is a very nice way to assure correct overhang but it makes locating the exact center of the tonearm pillar hole a bit more difficult. Perhaps later production might include two templates with different size center holes for each operation.
The mechanical aspects of the arm are generally quite good. The lateral and vertical bearing frictions are so low that they defy accurate measurements. Three counterweights of 15, 30, and 45 grams are provided to allow the use of cartridges weighing from 3 to 11 grams. It is always best to use the largest counterweight possible so that the weight may be located close to the arm pivot, rather than further out on the back of the arm. This will reduce the moment of inertia, which is very desirable. The sidethrust correction is not only very effective (see the even results obtained on the outside, middle and inner bands of test record HFS-75), but can be adjusted while playing a record. This is a great feature to have during the optimization of the arm-cartridge system.
The tracking force, which is calibrated in 0.1-gram increments, is off calibration by about 0.1 gram in the middle of the range. At the maximum indicated setting of 1.7 grams, the actual value was 1.5 grams. This error on the low side might possibly cause people who tend to set the tracking force as low as possible to have some tracking and scanning problems (see Fig. 12). A second person was asked to adjust the arm as a check and he came up with a slightly greater error. It can be presumed that most persons who purchase ADC's top of the line ZLM cartridge and LMF-2 arm are doing so with the expectation of achieving super performance. To help achieve this, we recommend that, unless a person has access to an accurate gram gauge, he should have the turntable, arm, cartridge combination set up and adjusted by someone who has such a gauge or set the tracking force just slightly on the high side.
We have listed other measurement data in tabular form for convenience. This is not because they are less important than some of the data we have mentioned. We have listed some items, such as the headshell offset, without comment and although the risetime of the cartridge was measured as being 24 pSec, we reserve comment to such data can be correlated to the perceived aural impressions of listeners. Listing such data does allow determinations to be made at a later date when we are all a little smarter and that includes yours truly.
In conclusion, we are pleased to be able to present some correlation between the subjective comments made by the listening panel and the objective technical measurements performed in the laboratory. The fact that the combination of the ADC ZLM cartridge and LMF-2 arm is of such high quality, makes such correlation appear even more impressive. We are continuing to explore other test procedures which will provide better correlations to subjective impressions of performance.
--Edward M. Long
(Source: Audio magazine, Jan. 1979)
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