MANUFACTURER'S SPECIFICATIONS
Recorder, Frequency Response: 35-20,000 Hz ±2dB at 7 1/2 ips; 35-14,000 Hz ±2 dB at 3 3/4 ips; 35-10,000 Hz ± 3 dB at 1 7/8 ips.
Wow and Flutter: 0.12% at 7 1/2 ips; 0.20% at 3 3/4 ips; 0.30% at 1 7/8 ips.
Signal-to-Noise Ratio: 54 dB at 7 1/2 ips.
Speeds: 7 1/2, 3 3/4, and 1 7/8 ips.
Crosstalk: Greater than 50 dB.
Fixed Preamp Output: 1.0 V, each channel.
Controlled Preamp Output: 0 to 1 .3 V, each front channel.
Inputs: Microphone, Tuner, AUX, and Magnetic cartridge.
Amplifier, Frequency Response: 20-20,000 Hz ±1 dB through microphone, tuner, and AUX inputs.
Power Bandwidth: 18 to 22,000 Hz.
Tone Control Range: ±12 dB at 100 Hz; +7,-11 dB at 10,000 Hz.
Dimensions: 19 3/8 in. W. x 13 3/4 in. D. x 6 1/2 in. H
Weight: 24 lbs.
Price: $399.95.
The rapidly growing interest in four-channel tapes makes this recorder especially valuable to those who are planning for the system-of-the-future. Providing complete stereo recording and playback facilities for conventional use together with four-channel playback, the Wollensak 6364 is convenient to use and includes features which set it apart from the general run of tape recorders.
Electrically a three-head machine, the erase and record heads are of four-track, two-channel configuration and are combined in one unit physically. The play head is a four channel structure and feeds four separate preamps for quadraphonic operation.
The pressure pads and the pinch roller swing forward and down to permit easy threading, and they provide excellent access to the head faces for cleaning. The head structure is covered by a 5/16-in. thick clear plastic plate, allowing a view of the assembly even while operating. Two key-like controls toward the right of the front panel control the play and stop functions. A pause control integral with the play key holds the mechanism down until released to start the tape motion. Fast movement of the tape is controlled by a lever which moves to the right or left to produce fast forward or rewind motion respectively. Next to the left is the "Tape-Source" rocker switch which selects the feed to the monitor circuits. At the left end of the control panel are the two record-level controls, with microphone input jacks-standard phone type--between them. At the far right end of the control panel is the power switch, also a rocker type.
Along the left side of the top panel are the amplifier operating controls. Starting with the top, the first control adjusts the treble response of the "controlled preamp output" and the output from the built-in power amplifiers. The next control adjusts the bass to the same outputs. The balance control comes next, followed by the volume control. The input selector switch at the bottom of the panel selects between inputs from MICROPHONE, MAGNETIC PHONO CARTRIDGE, TUNER, and the ubiquitous AUX The two VU meters are just above the input level controls, and the three-position speed switch is located just above the head assembly. The four-digit counter is mounted between the two reel hubs. The reel spindles are of an unusual and interesting as well as effective design-each has a single spline to locate the reel, and a detent ball keeps the reel in place.
Along the left end of the walnut finished case is a panel which accommodates all the input connections except the microphone and headphone jacks, which are on the front panel. A pair of phono jacks for external speakers, also located on this left hand panel, provide sufficient power output for any conventional speaker system. Next is a pair of phono jacks labeled "controlled preamp output." This pair provides an output following the tone, volume, and balance controls and is useful when a higher level is desired than is available from the usual preamp outputs, which provide not-one or level-control facility. The controlled preamp output is actually taken from the speaker output circuit, scaled down by about 20 dB from the speaker terminals.
Next come the preamp outputs for tracks 1 and 3, the usual stereo configuration, followed by a bias switch which provides for normal or high bias, the latter being required for certain types of tape. The preamp outputs for tracks 2 and 4 are next on the panel, and then two jacks are labeled "mixing inputs." These jacks permit a variety of different recording techniques, such as recording a microphone with an already-recorded track in the usual sound-on-sound and sound-with-sound methods, or a pseudo-stereo mono recording, or a reverberant stereo, or a reverberant enhanced mono recording, as well as multiple mixing, using an external mixer to balance the several sources. Exceptionally clear instructions are given for the patching between the various inputs and outputs for these techniques.
The transport drive employs a heavy-duty induction-type motor for the capstan, with the usual three-step mechanism between the idler wheel and the heavy flywheel on the capstan shaft. Spooling employs a separate motor, a d.c. device enclosed in a shielded housing at the upper center of the unit, which drives the reel spindles through belts and also provides dynamic braking, thus eliminating the need for mechanical braking on the two spindles. The tape handling of the machine is smooth and was without any noticeable problem during the hours we operated it.
Fig. 1--Close-up of the head assembly as seen by the user.
Fig. 2--View of the 6364 with the top plate removed. The amplifier controls are shown in line at the left.
Fig. 3--Front view of the head assembly with the pinch roller and the pressure
pads partially closed. The roller retracts to the horizontal position, as
do the pressure pads, for easy threading.
Fig. 4--The input-output connector panel on the left end of the cabinet.
Bias level switch is seen at the center of the panel.
Circuit Description
Each of the four preamps employs two transistors in a feedback-pair configuration, with equalization being switched from the 7 1/2-ips speed to that required for the two lower speeds. The preamp outputs are tapped off at this point on tracks 1 and 3 (tracks 2 and 4 have no further amplification) and also fed to the volume control and thence to the tone control circuit, a Baxendall type. It is then further amplified by a two-transistor pair and fed to the three-stage power amplifier which terminates in a complementary-symmetry stage. The balance control is just ahead of the power amplifiers.
Each record amplifier employs a two-stage preamplifier which is flat for all but the magnetic phono input, and in that input it has the prescribed RIAA equalization, within ±2 dB. The record-level control is next, with the mixing input fed to the arm of this control, and this is followed by a two-stage amplifier equalized for the record characteristics of the three speeds. Its output is then fed direct to the VU meter network and to the recording head through the constant current resistor. The two levels of bias are selected by a switch which parallels a capacitor across the usual capacitor in series from the bias feed to the erase heads. All the circuitry is simple and straightforward. The bias/erase oscillator employs two transistors in a balanced circuit and provides a bias frequency of 98.7 kHz.
The power supply is conventional, with a bridge rectifier and adequate filtering to supply 50 volts for the output stages of the amplifier. The d.c. spooling motor gets the same in the fast mode and about 28 volts in the play mode. Progressively lower voltages are supplied to the earlier amplifier stages to provide better filtering of the low-level stages. A filament type pilot light indicates when power is on by illuminating the VU meters, and the record indicator light is fed from the d.c. supply to the bias oscillator. A pair of dynamic microphones and a supply of audio cables are supplied with the unit.
PERFORMANCE
We noted the speed to be exact at 120 volts, 1 percent slow at 100 volts, and 4.6 percent slow at 90 volts; similarly it was 1.5 percent fast at 135 volts. The frequency response curves for playback from a standard tape are shown in Fig. 5. Running the tape backward, we were able to measure responses from tracks 2 and 4, which are within 0.5 dB except at the top end where the difference rose to about 1.5 dB. Responses measured in the record/play mode are shown in Fig.6, and are reasonable for all three speeds. The effect of the tone controls is shown in Fig.7 for full and halfway positions of the controls. Hum-and-noise measured -43 dB in the playback mode, using a 15-kHz low-pass filter in the output circuit and a reference of an indicated +2 on the VU meters, at which point the distortion measured 3 percent. At zero indicated level, the distortion measured 2.5 per cent from 50 to 10,000 Hz. Fast-wind times measured 70 seconds for 1200 feet of tape, relatively fast for a "consumer" machine.
At maximum settings of the record-level controls, a signal of 0.4 mV was sufficient to provide a zero-dB indicated level, while 43 mV was required to reach the same level at the tuner and AUX inputs, all of which are within specifications.
From the amplifier alone, we measured an output of 11 watts per channel into 8 ohms at a distortion of 1.0 per cent from a signal which would indicate 0 level on the VU meters. Wow and flutter (rms) measured 0.06 percent at 1 7/8 ips in the band from 0.5 to 6 Hz; 0.12 percent in the band from 6 to 250 Hz, and 0.16 in the overall 0.5 to 250-Hz band. Similar measurements for 3 3/4 ips gave figures of 0.15, 0.16, and 0.25 percent, and at 1 7/8 ips we measured 0.18, 0.20, and 0.25 percent, respectively.
Fig. 5--Response from standard test tapes at the three indicated speeds.
Fig. 6--Record and playback response at the three indicated speeds.
Fig. 7--Tone-control curves taken at 7 1/2 ips. Solid lines indicate response
with controls at FULL positions; dashed lines show response with controls
at HALF positions.
Operation on Quadraphonics
In order to get the subjective feel of the 6364 with four channel tapes, we hooked up a pair of speakers to the speaker outputs for the normal stereo channels (tracks 1 and 3), and fed the rear-channel outputs (tracks 2 and 4) through our normal listening system. Thus our regular speaker systems became the rear speakers and the two additional units became the normal "left front" and "right front" speakers, so we simply had to turn around in the room to make everything come out right again. The two auxiliary speakers were not identical to the regular ones (who has four identical speakers this early in the quadraphonic game?) but they were of excellent quality-one was a Tannoy Orbitus, and the other a Fisher model of a few years ago, but still an excellent performer.
With the Vanguard test tape which accompanies the 6364, we finally got all four speakers carrying the program material they were supposed to according to the spoken announcements on the test tape and all equal in sound level as the announcer tells us. Then we went through the six selections on the demo tape--Handel's Jephtha, the inevitable Berlioz Requiem, two selections from Mahler's Symphony No. 3, two vocals from female pop singers, and a short bit of The Amazing Electronic Pop Sound of Jean Jacques Perry. Then we did it several more times, listening continually to the instrument and vocal placements and the overall effect. This was our first listening experience in our own familiar surroundings, and we must confess that "Surround Sound" is impressive and certainly a far cry from a system suggested 10 or 15 years ago by an enthusiast during one of the Los Angeles hi-fi shows.
This individual suggested four speakers, one in each corner of the room, with the (mono) sound being commutated from speaker to speaker continuously. (If you try to face the sound with this system, you either wind up with a twisted neck or sitting on a piano stool.) None of that, however, is real four-channel sound. Impressive it is, though not all rooms will easily accommodate four speakers. Most persons will like quadraphonic sound immensely of course, but some will not; this is up to the individual to decide.
Whatever your decision, you can be assured that the 6364 will give you a good performance of your four-channel recorded tapes and will still be a comfortable and effective machine to use for conventional two-channel stereo listening.
-C. G. McProud
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(Adapted from Audio magazine, Feb. 1972)
Also see:
Wollensak 4780 Cassette Tape Recorder (Aug. 1974)
Telex-Viking Quad/Sonic 2 + 2 quadraphonic tape deck (Equip. Profile, Jan. 1972)
TEAC 3340 Open-reel tape recorder (Equip. Profile, Mar. 1973)
Teac X-20R Open-Reel Recorder (Equip. Profile, Mar. 1982)
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