TESTED THIS MONTH by Hirsch-Houck Laboratories:
Harman/Kardon 900+ Receiver
JBL L100 Speaker System
Pilot 211 AM/Stereo FM Tuner
Pioneer RT-1020L Tape Deck
by JULIAN D HIRSCH
---------
Harman/Kardon 900+ AM/FM Four-Channel Receiver
The 900+ is Harman/Kardon's finest AM/FM four-channel receiver. It features a built-in CD-4 demodulator, two SQ-matrix characteristics, and an "enhanced-stereo" mode for deriving rear-channel signals from a conventional stereo program. The FM tuner section employs H/K's "quieting meter," which indicates the relative signal-to-noise ratio of a received signal. The audio amplifiers, rated at 35 watts per channel in the four-channel mode, can be switched to a two-channel stereo mode to provide in creased power output per channel.
When the tuner functions are in use, the "blackout" dial area becomes a multi-colored display of AM and FM dial scales. Indicator lights below the dial scales identify the receiver's operating mode. A numeral--1 or 2-corresponds to mono or stereo operation. In any of the matrix-decoding modes, a " 4-2-4" legend signifies that the four output channels have been decoded from a two-channel form. In ENHANCED STEREO mode, the legend reads "2-4," and in a discrete (or CD-4) mode it is "4-4." Playing a CD-4 record also causes a red "CD-4" to appear on the panel. Also in the tuning-dial area are the red STEREO indicator for FM, and a yellow IN TUNE indicator that becomes visible only when an FM station is tuned correctly. For AM tuning, the large FM quieting meter becomes a conventional relative-signal-strength meter.
Below the dial there are front- and rear-channel headphone jacks, an illuminated POWER pushbutton switch, and a group of ten pushbutton controls. Four of them activate the MAIN and REMOTE front and rear speakers. Two are for tape monitoring-the 900+ can accommodate a four-channel recorder plus a two-channel recorder (actually, two four-channel recorders, but with off-the-tape monitoring capability for only one). The two-channel tape inputs and outputs are also usable for an external Dolby noise-reduction unit. The other buttons control the high- and low-cut filters, loudness compensation, and FM muting.
The MODE Mitch selects MONO, STEREO, SQ MATRIX 1 and 2, ENHANCED STEREO, and CD-4/DISCRETE operation, simultaneously lighting the appropriate numbers under the dial scale. The SQ 1 position provides the "original" SQ matrix, with full left-right separation but very limited front-rear separation. In SQ 2, there is some blending of left and right channels, along with a substantial improvement in front-rear separation.
The Harman/Kardon 900+ has three tone controls-bass, mid-range, and treble. Each has two concentric sections for independent adjustment of front and rear channels. The FUNCTION switch selects the input source: PHONO 1, PHONO 2, STEREO FM (with automatic switching to mono), FM (mono only), DISCRETE FM/AUX 1, AUX 2, and AM. The DISCRETE FM/AUX 1 input is a four-channel input which could be used with an external four-channel discrete FM de coder should such a system be approved and hardware become available. The last knob on the panel is the master volume control, and the right end of the panel is occupied by a "joystick" four-channel balance control.
On the rear apron, beside the expected inputs and outputs, are two knurled control shafts for the CD-4 separation adjustments. These are used with the special test record provided to optimize the left and right front-to-rear separation for the particular phono cartridge used.
There are terminals for 75- and 300-ohm FM antennas and an external AM antenna, as well as a pivoted AM ferrite-rod antenna. A 4-cH FM OUT jack is provided for that hypothetical four-channel converter, and a control shaft adjusts the FM interstation-noise muting threshold.
There is a slide switch to convert the audio outputs from four-channel operation to "bridged" two-channel operation.
Each speaker output. as well as the power line, is fused. One of the two a.c. outlets is switched.
The Harman/Kardon 900+ , in its handsomely styled walnut cabinet, is 20 1/8 inches wide, 61 1/4 inches high, and 17 inches deep; it weighs about 40 pounds.
Price: $749.95, including a 12-inch CD-4 test/demonstration record.
Laboratory Measurements. With all channels driven with a 1,000-Hz test signal into 8-ohm loads, the output waveform clipped at 41.3 watts per channel. With only the two front channels driven, the power at clipping was 71.5 watts per channel into 4 ohms. 47.5 watts into 8 ohms, and 27.6 watts into 16
------------
-----------Rear panel of the HK 900+. The "strapping- switch (with locking tab) that pairs up the four amplifiers for two-channel use is at bottom center. All four of the power amplifiers are fused.
--------- In the graph of FM performance, the levels of both random noise and noise plus distortion are compared with the audio-output level as signal strength increases. Both mono and stereo are shown.
-------------
ohms. In the "bridged" mode, the output into 8 ohms was 120 watts per channel.
The remaining tests were made in the four-channel mode, with only the two front channels driven.
At 1,000 Hz, the total harmonic distortion (THD) was below the noise level up to a I-watt output (where it measured 0.052 per cent), and decreased to just over 0.01 per cent between 10 and 40 watts output before rising to 0.1 per cent at about 48 watts. The intermodulation (IM) distortion did not exceed 0.07 per cent at any power output from 40 milli-watts to above 40 watts. Using 40 watts per channel as a reference full-power output, the THD was under 0.1 per cent from 20 to 20,000 Hz (typically 0.02 percent). At half power and one-tenth power, the distortion was less than 0.03 per cent at most frequencies.
The CD-4 separation adjustments also vary phono sensitivity, as is the case with most receivers with built-in CD-4 capability. With the factory settings, an input of 1.4 millivolts (mV) produced a 10-watt output, and the input overloaded at 40 mV. At the maximum setting, the sensitivity was 0.25 mV, with a 9-mV overload point. The installation instructions are specific with regard to using a low setting of these controls for stereo cartridges. Since the settings with CD-4 cartridges are in inverse proportion to the cartridge output, the system is essentially self-regulating insofar as overload is concerned. The Aux-input sensitivity was 95 mV, with overload occurring at a 3.5-volt input. We noted that phono overload caused a gentle rounding of the waveform (which produced mostly low order harmonics) rather than the more objectionable hard clipping frequently encountered. The audio signal-to-noise ratios were 73.5 dB (Aux) and 72 dB (Phono)- both very good.
The bass and treble tone controls had conventional characteristics, with a sliding bass-inflection point and a hinged treble response. The mid-range control action centered at 1,200 Hz; partial control settings had only a slight effect, but at the extremes the result was a boost or cut of 10 dB, with all its effect confined between 700 and 2,000 Hz. The loud ness control boosted only low frequencies (to a maximum of 8.5 dB), thereby avoiding the unduly heavy sound of most such systems. The filter curves, with 6 dB-per-octave slopes, were down 3 dB at 150 and 3,000 Hz.
The RIAA equalization was exact, with less than 0.25 dB variation from 100 to 13,000 Hz, falling to -2 dB at 30 and 15,500 Hz. The response cuts off sharply above 15,000 Hz because of the CD-4 low-pass filter which is always in the phono circuits. A positive byproduct of the CD-4 circuit configuration was the isolation of the RI AA equalizer from the cartridge inductance. As a result, the cartridge had a negligible effect on the phono input's high-frequency response (about 1 dB, in the worst case). Since most preamplifier sections show a 2- to 6-dB high-frequency loss from this effect, the 900+ should have a phono high-frequency performance that is as good as, or better than, most units, de spite the cutoff at 15,000 Hz.
The FM tuner had an IHF sensitivity (in mono) of 1.9 microvolts (µV), reaching 50 dB of quieting at 2.5 µV with 0.85 percent distortion. The stereo muting threshold was about 30 µV, and 50 dB of quieting was reached in stereo at 35 µV, with 1.6 per cent THD. The ultimate quieting (at 1,000 µV) was 70 dB in mono and 62.5 dB in stereo, and distortion at those points was 0.11 per cent in mono and 0.8 per cent in stereo. The capture ratio (0.8 dB at 1,000 µV, 1.8 dB at 10 µV), AM rejection (64 dB), and image rejection (92 dB) were well above average. The alternate-channel selectivity was a good 58 dB. FM interstation noise muting occurred between 2.5 and 4 µV with the factory settings; the control in the rear provided a range from 2/3.6 µV to 38/48 µV (the two figures represent the turn-off and turn-on signal levels for the muting circuits).
The stereo FM frequency response was almost perfectly flat from 30 to 10,000 Hz, rising to +0.7 dB at 15,000 Hz. In spite of the lack of any rolloff at the high end, the 19-kHz pilot-carrier rejection was an excellent 69 dB. The stereo channel separation was very uniform across the frequency range-about 28 dB at low and middle frequencies, and still 20 dB at 15,000 Hz. The AM frequency response was also better than we are accustomed to seeing--within ± 1 dB from 200 to 3,800 Hz, rising to +4 dB at 100 Hz, and down 6 dB at 48 and 5,500 Hz.
Comment. The overall excellence of the Harman/Kardon 900+ FM tuner is complemented by its highly effective tuning indicator and muting system. The IN TUNE light comes on only when the station is tuned "on the nose." Since it is much easier to see than the pointer of the quieting meter, the latter is useful chiefly for orienting a directional antenna. The interstation muting is positive and thump-free. The rather high stereo-threshold level (of our sample, at least) may prevent reception in stereo of some otherwise usable signals, but it is a guarantee that any station heard in stereo will be heard properly, with low noise and distortion.
The FM dial scale, with its linear distribution of frequencies, is numbered only at 2-MHz intervals. The calibration is quite accurate, permitting station frequencies to be estimated with relative ease, but we would have preferred closer calibration intervals on a tuner of this quality. AM radio listeners will find the sound of the 900+ to be far above the norm, with none of the muffled, constricted quality typical of most AM tuner sections.
The power and low distortion of the audio amplifiers speak for themselves.
The CD-4 demodulator requires no carrier-level adjustment, unlike most we have used. The separation adjustments require only a few seconds, using the record supplied with the receiver. Having the adjustments in the rear, yet accessible, seems to be an ideal arrangement, since there is little likelihood of their settings being disturbed once set.
We were concerned about the possibility of phono overload because of the somewhat limited "headroom" of the phono preamplifier. By comparing the outputs of the CD-4 cartridge and the preamplifier output on an oscilloscope, we determined that even the highest velocities on our test records (30 cm/sec) did not cause any clipping. Any other CD-4 cartridge should be equally safe, but the manufacturer's instructions for setting phono gain with conventional stereo cartridges should be followed carefully. In listening tests with CD-4 records and cartridges, the sound was as good as we have heard from other similarly equipped receivers, or even from separate demodulators.
Although the SQ matrix is without logic assistance, the ability to optimize separation either for the left-right or front-back directions does help to get the best possible results from any given record (short of that obtainable with logic, of course). No RM matrix is provided.
Unlike most "derived" back-channel systems, which use the stereo "difference" (L--R) signal for that purpose, in the ENHANCED-STEREO mode the 900+ shifts the phase of each stereo channel, in opposite directions, by 90 degrees to derive the back channels. This is not only very effective with stereo programs, but it works well even with mono pro gram material.
+++++++++++
JBL L100 Speaker System
THE JBL L100 Century speaker sys tem has enjoyed great popularity, both here and abroad, since its introduction several years ago, and we have recently tested a late model of the same unit.
The JBL L100 is an 8-ohm, three-way system using a 12-inch woofer in a ported cabinet. There is a crossover at 1,500 Hz to a 5-inch cone mid-range driver and at 6,000 Hz to a 1.4-inch cone tweeter.
The walnut enclosure is 23 1/2 x 14 1/4 x 13 5/8 inches, and the system weighs about 45 pounds. The acoustically trans parent sculptured-foam grille snaps off to reveal the drivers and two level controls.
Marked PRESENCE and BRILLIANCE, each control has an indicated "flat" set ting with a control range of up to ±3 dB around that level. The speaker terminals, recessed into the back of the cabinet, are insulated spring clips. The price of the JBL L100 is $273. The grille is avail able in a choice of orange, blue, or brown.
Laboratory Measurements. The integrated frequency response of the JBL L100 (with its controls set at "0") was unusually smooth and flat, within ±3 dB from 55 to almost 17,000 Hz. The bass response fell off smoothly below 60 Hz, but was still effective down to about 45 Hz. The low-frequency distortion of the L100 was quite low, under 1 per cent down to 50 Hz at a 1-watt drive level, and increasing to 6 per cent at 40 Hz and 10 per cent at 36 Hz. The speaker is quite efficient, so that 1 watt of drive produces a decidedly loud acoustic out put-a sound-pressure level (SPL) of about 96 dB in the mid-range. When we increased the drive to 10 watts, the increase in distortion was not significant.
It should be noted that most of the energy below 40 Hz is radiated by the port, thus making it difficult to compare the bass-distortion figures with those of a non-ported system. Suffice it to say that the bass is as clean as one could desire, and although we have measured stronger low bass from some acoustic-suspension speakers, the L100 is still a fine performer in this area. On the other hand, the L100 is at least 6 dB more efficient than an equivalent acoustic-suspension system, requiring only 0.25 watt of amplifier power in the mid-range to produce a 90-dB SPL at a distance of 1 meter.
The tone-burst response was very good, as is illustrated by the photos. In
--------------
-----The fine tone-burst performance of the L100 is shown by the two oscilloscope photographs above, taken at 8,000 (left) and 200 Hz. The input signal appears below the output of the speaker in both.
------- The L-100's foam grille is easily removable to give access to the mid- and high frequency level controls.
----------------
each case, the lower waveform is the output of the amplifier driving the speaker, and the upper is the output of the pickup microphone (the lateral displacement represents the time required for the sound to travel to the microphone). The impedance of the L100 remained be tween 4 and 8 ohms over most of the 20-to 20,000-Hz range, except for the resonant rise to 40 ohms at 68 Hz. When driving more than one speaker per channel, it might be advisable to consider the L100 as a 4-ohm system.
Comment. When we first listened to the JBL L100 (before making any tests), we recognized that it was some thing out of the ordinary. The smooth ness and lack of coloration were unmistakable. The overall sound was open and airy-some might call it "bright," but there was not a trace of stridency or shrillness. Its high efficiency permits it to be used with relatively low-powered amplifiers, although we doubt that most users would team up a speaker such as this with any but the highest-quality amplifiers. The L100 can take power lots of power-without damage or distortion. We drove the test units with an amplifier that delivered 400 watts on peaks with no damage to the speakers or to our sonic sensibilities.
Our simulated live-vs.-recorded test (which is, in effect, a test for flat response from 200 Hz on up) was a real ear opener. Most of the time, we were unable to detect the change-over from the "original" sound to its reproduction through the L100. In this important, though not definitive, test the JBL L100 ranks with the most accurate speakers we have tested-certainly no other has been better. Undoubtedly this was aided by the fact that our reference speaker (which supplies the "live" sound) is also a three-way direct-radiating system whose dispersion pattern is similar to that of the L100. The fact remains, however, that the L100 is an extraordinarily fine speaker for home hi fi service, whether your taste runs to the classics or to rock.
++++++++++++++
Pilot 211 AM/Stereo FM Tuner
THE Pilot 211 AM/stereo FM tuner features a blackout dial scale with linear FM calibrations and an illuminated dial pointer whose color changes from white to red when a station is tuned correctly.
Separate AM and FM tuning meters are provided (the latter a zero-center type), and only the appropriate meter is illuminated. The AM/FM selector switch has a third position for FM/AFC. The MODE switch offers a choice of MONO, automatic MONO/STEREO, or STEREO ONLY reception (in which case the tuner output is muted until a stereo station is received).
A stereo light below the dial scale indicates stereo reception. Pushbuttons switch in the FM MPX filter (which blends the channels at high frequencies to re duce noise on weak stereo signals), the FM MUTE system, and the POWER to the tuner. The audio-output level is con trolled by a front-panel knob that affects both channels. A front-panel TAPE-OUT jack can supply signals (at a 10,000-ohm impedance level) tapped off ahead of the tuner's volume control.
On the rear apron of the Pilot 211 are the antenna terminals (for 300- and 75-ohm FM antennas, plus a wire AM antenna), a pivoting AM ferrite-rod antenna, and two a.c. outlets, one of which is switched. The audio outputs are in duplicate. A DET-OUT jack supplies an audio output, ahead of the de-emphasis and multiplex circuits, for possible use with a yet-to-be-developed four-channel discrete FM broadcasting system. A slide switch next to this jack disconnects it for normal stereo listening. The Pilot 211 tuner is supplied complete with a wood en walnut-finish cabinet 15 inches wide, 11 1/2 inches deep, and 5 1/8 inches high. Price: $199.90.
Laboratory Measurements. The Pilot 211 surpassed all its published specifications by a comfortable margin. The I HF usable sensitivity was a very good 1.6 microvolts (µV) in mono and 5µV in stereo. Quieting of 50 dB was achieved at 4.5 µV in mono and 33 I.LV in stereo.
The ultimate signal-to-noise ratio (at 1,000µV) was 69 dB in mono (rated 65 dB) and 66 dB in stereo. The capture ratio of 0.8 dB was not only considerably better than the rated 1.5 dB, but it ranked with the best we have measured.
The Pilot 211 has a rather elaborately equipped rear panel. There are two sets of audio outputs, plus an FM DET jack (in anticipation of four-channel FM), and two a.c.-line convenience sockets.
In the graph of FM performance, the levels of both random noise and noise plus distortion are compared with the audio-output level as signal strength increases. Both mono and stereo are shown.
The AM rejection was a good 62 dB, and the image rejection of 86 dB surpassed the rated 80 dB handily. The alternate-channel selectivity measured 82.5 dB and 63 dB above and below the signal frequency, averaging 73 dB. This is well beyond the rated 65 dB selectivity. The 19-kHz pilot carrier was sup pressed by 72 dB in the audio outputs.
Muting occurred gradually between signal levels of 1.1 and 11 µV, but it occasionally injected loud bursts of noise as we tuned past a station. The automatic stereo switching threshold was between 2 and 3.5µV. There was no tendency for the tuner to drift, nor was it at all critical to tune for minimum distortion and noise. We therefore did not use the AFC, which in any case was rather mild.
The FM frequency response was an excellent ±1 dB from 30 to 15,000 Hz.
Stereo channel separation exceeded 27.5 dB from 250 to 15,000 Hz (about 35 dB in the mid-range), falling smoothly at lower frequencies to 12.5 dB at 30 Hz.
The FM distortion was also much lower than the published ratings; we measured it as 0.17 per cent in mono and 0.32 per cent in stereo. The maximum audio out put level was about 2 volts. Performance on AM was satisfactory, with the frequency response down 6 dB at 3,000 Hz, but exceptionally flat down to the lower frequencies.
Comment. The tuning dial was reasonably accurate and the tuning-indicator pointer worked very well, providing a clearly visible indication (even from across the room) that a station was tuned correctly. However, because of the 2 MHz calibration intervals and a pointer whose width was equivalent to about 150 kHz, it was not easy to identify stations from the dial settings alone.
The Pilot 211 is an honestly--even conservatively--rated tuner, with note worthy quality and overall performance for a unit of its price. In A-B listening comparisons between this tuner and other fine tuners and receivers, we were not able to hear any differences-which is as it should be. Overall we find the Pilot 211 to be a basically handsome and high-performance tuner selling for a comparatively modest price.
+++++++++++++++++
Pioneer RT-1020L Tape Deck
PIONEER'S deluxe Model RT-1020L open-reel tape deck is a three-head, three-motor machine with a four-gap playback head and four playback amplifiers. This makes it possible to play four-channel tapes as well as to record and play back in the conventional open-reel four-track stereo format. The four-gap head also permits playback of half-track stereo tapes if appropriate rear-panel connections are made.
The RT-1020L can accommodate 10 1/2-inch small- and large-hub (NAB) reels as well as 7-inch or smaller reels.
The capstan is driven by a two-speed hysteresis synchronous motor, with pushbutton selection of the 71/2- or 33/4 ips tape speeds (the equalization is simultaneously changed). The reels are driven by six-pole induction motors with differential band-brakes to bring the tape to a swift stop under controlled tension.
A pushbutton sets the optimum tape tension for 7- or 10 1/2-inch reels, and another button controls the power to the recorder. The machine can be set to operate with common line voltages from 110 to 240 volts and at either 50 or 60 Hz.
The tape-transport mechanism is constructed on a heavy diecast frame and chassis plate. The tape-threading path includes a guide roller and a tape-tension arm that shuts off the motors when the tape runs out or breaks. The PAUSE switch on the transport panel stops and starts the tape without disengaging the recording interlock circuits. There is a four-digit index counter.
The lower portion of the panel contains the electronic section and the tape-transport control buttons. The latter, though they operate solenoids, are also mechanically latched. This permits the RT-1020L to be set up for recording with no power applied. An external timer switch controlling the power line can then turn it on at some selected time to make a recording in the absence of an operator. When the timer turns off (or the tape runs out), the transport shuts off and disengages completely.
The five buttons (REC, REWIND, STOP, PLAY, FAST FORWARD) can be operated with one hand, but are so designed that the REC and PLAY buttons won't be simultaneously pushed accidentally. A convenience, when adding new material to a portion of a recorded tape, is the ability to go from play to record while the tape is in motion. This requires pressing the REC and PLAY buttons simultaneously; touching the REC button alone shuts off the recorder. The transport functions are interlocked, with appropriate delays to prevent damage to the tape, while retaining the ability to go from any mode to any other without first pressing the STOP button.
Below the transport-control buttons are six small lever switches. Two of them activate the left and right recording circuits; by operating them singly, one can make four-track mono recordings or create sound-on-sound effects (external patch cables are required for the latter).
Tape monitor switches are provided for each of the two recording channels. One of the remaining switches selects two- or four-channel playback, and the other connects the two level meters and the headphone jack to monitor either the front or rear channels in the four-channel mode.
Below these switches is the head phone jack, designed for 8-ohm phones.
Two small concentric knobs adjust play back output levels separately for front and rear channels. Two small rotary switches optimize the recording bias and equalization for the tape in use. The BIAS switch has three positions: for STD (standard), LH 1 , and LH 2 tapes. The last two provide successively higher bias levels for various low-noise/high-output tapes. The EQ (equalization) switch has STD and LH positions which provide different amounts of high-frequency recording boost. The instruction manual lists recommended settings of the bias and equalization switches for most standard-brand tapes.
Two large illuminated meters read both recording and playback levels; in playback they indicate the actual line output, and they are affected by the play back level controls. Below the meters are two 1/4-inch phone jacks for micro phones, which may have any impedance from 600 to 50,000 ohms. Above the meters are two red light-emitting diodes that indicate the recording status of each channel. To their left are the recording-level control knobs. One concentric pair adjusts the microphone-input gains, and a similar pair controls the line inputs.
The two signal sources can be mixed.
In the rear of the recorder are the two line inputs and four outputs, plus a DIN connector whose signal is routed through the microphone input circuits.
The Pioneer RT-1020L is supplied with a walnut wooden case, a 10 1/2-inch metal reel, two NAB hub adapters for large reels, and other accessories such as connecting cables, splicing tape, and a head-cleaning kit. The deck can be operated horizontally or vertically; upright, it measures about 17 3/8 inches wide, 17 inches high, and 9 inches deep. It weighs 46-lbs. An alternate version, the Model RT-1020H, operates at 7 1/2 and 15 ips.
Price: $649.95 for either model.
Laboratory Measurements. We made our tests with 3M 207 tape, using Pioneer's recommended settings of STD bias and LH equalization. The playback frequency response, over the range of the Ampex quarter-track test tapes, was ±0.6 dB from 50 to 15,000 Hz at 7 1/2 ips and ±0.5 dB from 50 to 7,500 Hz at 3 3/4 ips. All playback channels did equally well. The overall record-playback frequency response at 3 3/4 ips showed a gentle rolloff of the high frequencies, but it met the Pioneer specification of ±-3 dB from 40 to 12,000 Hz (it was actually within ±3 dB from 20 to 12,000 Hz). At 7 1/2 ips, the frequency response was exceptional. Although rated at ±3 dB from 40 to 20,000 Hz, we measured the 1020L as ±3 dB from 20 to 30,000 Hz, and within ±-2 dB from 20 to 20,000 Hz.
Furthermore, response variations stayed within ±3.5 dB over the full audio range for recording levels as high as 0 VU, which is exceptional. The response with Maxell UD-35 tape was similar, but with somewhat more high-frequency energy, varying less than ±-0.5 dB from 1,000 to 20,000 Hz. We also tried 3M 1 1 1 (a "standard" tape), using STD bias and equalization, and measured a very creditable ±3 dB from 25 to 25,500 Hz. Low-frequency response with all speeds and tapes was unusually smooth and extended.
ated horizontally or vertically; upright, it measures about 17 3/8 inches wide, 17 inches high, and 9 inches deep. It weighs 46-lbs. An alternate version, the Model RT-1020H, operates at 71/2 and 15 ips. Price: $649.95 for either model.
Laboratory Measurements. We made our tests with 3M 207 tape, using Pioneer's recommended settings of STD bias and LH equalization. The playback frequency response, over the range of the Ampex quarter-track test tapes, was ±0.6 dB from 50 to 15,000 Hz at 7 1/2 ips and ±0.5 dB from 50 to 7,500 Hz at 3 3/4 ips. All playback channels did equally well. The overall record-playback frequency response at 3 3/4 ips showed a gentle rolloff of the high frequencies, but it met the Pioneer specification of-±-3 dB from 40 to 12,000 Hz (it was actually within ±3 dB from 20 to 12,000 Hz). At 7 1/2 ips, the frequency response was exceptional. Although rated at ±3 dB from 40 to 20,000 Hz, we measured the 1020L as ±3 dB from 20 to 30,000 Hz, and within ±-2 dB from 20 to 20,000 Hz.
Furthermore, response variations stayed within ±3.5 dB over the full audio range for recording levels as high as 0 VU, which is exceptional. The response with Maxell UD-35 tape was similar, but with somewhat more high-frequency energy, varying less than ±-0.5 dB from 1,000 to 20,000 Hz. We also tried 3M 1 1 1 (a "standard" tape), using STD bias and equalization, and measured a very creditable ±3 dB from 25 to 25,500 Hz.
Low-frequency response with all speeds and tapes was unusually smooth and extended.
Measurements of the effects of the bias and equalization switches, using the 3M 207 tape, showed that a change of 3 to 5 dB could be expected in the 10,000-to 20,000-Hz octave over the range of bias adjustment. The EQ switch was more dramatic in its effect, with 10 dB more recording boost (and correspondingly less "headroom" before overload) at 20,000 Hz with STD equalization.
A line input of 44 millivolts, or 0.19 millivolt at the microphone inputs, pro vided a 0-VU recording level on the meters. The line output from this input (in the SOURCE position of the selector) was 325 millivolts; switching to the TAPE/PLAY position dropped the output to about 300 millivolts. The available headphone volume, even with 200-ohm phones, was considerably greater than we have encountered with most tape recorders.
For a 1,000-Hz test signal recorded at a 0-VU level, the total harmonic distortion in playback was a low 0.7 per cent (rated less than 1 per cent) at 7 1/2 ips,
------------
FREQUENCY IN Hz (CYCLES PER SECOND)
Pioneer RT-1020L Tape Deck ...
and 1.2 per cent at 3 3/4 ips. The 3 per cent standard-reference level of distortion required an input of +12 dB at the higher speed and +11 dB at the lower speed. The unweighted signal-to-noise ratios, referred to 0 VU, were respectively 47 and 48 dB at the two speeds.
When referred to the 3 per cent distortion level, the signal-to-noise ratio of the RT-1020L was 59 dB at either speed (rated better than 55 dB). The micro phone preamplifiers were unusually quiet, increasing the noise by only 3 dB at their maximum gain.
The wow was negligible-in effect, it was at the test-tape residual of less than 0.02 per cent. The unweighted flutter (rms) was 0.1 percent at 7 1/2 ips and 0.13 per cent at 3 3/4 ips, exactly as rated. The operating speeds of our test sample were slightly fast: we estimate they would cause a timing error of 6 to 10 seconds in 30 minutes. In fast forward or rewind, 1,800 feet of tape was handled in 82 seconds. When the RT-1020L is in fast forward or rewind, pressing the PLAY button brings the tape to a stop in about 0.5 second. After a pause of 4 to 5 seconds, it goes to the selected playing speed. The recording-level meters responded more slowly than standard VU meters, reaching 70 per cent of a steady state reading with a 0.3-second tone burst (as compared with 99 per cent for a VU meter).
Comment. The Pioneer RT-1020L operated with impressive smoothness and silence. It had an aura of precision manufacture that was consistent with its performance. We did find a minor human-engineering annoyance: when threading the tape (especially hurriedly) through the guide-roller assembly we tended to engage the pause lever inadvertently. We have been informed by Pioneer that current models of the RT 1020L have a guide-roller arm that locks out of the way when pushed counter clockwise, and this change should help the situation.
Although, at 3 3/4 ips, there was some loss of the higher frequencies that was occasionally audible on FM broadcast material, the RT-1020L at 7 1/2 ips was simply superb. At that speed, even FM interstation hiss could be recorded and played back without audible change. The exceptional recording "headroom" of the RT-1020L, especially with LH equalization, makes it practical to record with average maximum program levels of 0 dB with little chance of tape saturation on peaks.
+++++++++++++++++
----------
Also see:
TECHNICAL TALK--What Is Noise?
WILLIAM SCHUMAN The fortunes of an American composer, educator, and administrator. SHEILA KEATS