September 1969 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
As with restorers of vintage
radio equipment (as with Gary Steinhour's
Heathkit DX-60B project), there are
avid restorers of vintage computers (I'm working on retrofitting a Packard Bell
pizza box desktop), vintage televisions, vintage kitchen appliances, and vintage
tape recorders / players. In 1969 when this article appeared in Electronics
World, magnetic tape was a big deal. Reel-to-reel was the domain of true audio
aficionados - the most expensive type of equipment - while the rest of us settled
for cassette and 8-track tapes. Cassette tape people generally regarded 8-trackers
as audio Neanderthals, Philistines, bumpkins, non-sophisticates. I was - and still
am - an 8-track guy. In fact, not that long ago I did a minor restoration of the
Digest Model 800-XR stereo system that I bought originally in the mid 1970s
while in high school. I have an 8-track tape splice / repair kit that is used to tend
to my tapes as needed. Although 8-track tapes and players are larger than cassette
players, I always liked the feature that, because the songs were spilt among 4 parallel
tracks, you don't have to fast forward through as much of the tape to get to a specific
song. No matter what audiophiles tell you, I submit that most people cannot tell
the difference between a song recorded on a cassette tape or an 8-track tape...
and don't buy into the line that adjacent tracks bled over into each other since
only very poorly aligned heads will do that.
Cassette Tape Recorders - A New Breed
By Leonard P. Kubiak, Supervisor, Tape & TV Lab., Texas Dept. of Education
How do the new cassette recorders stack
up against reel-to-reel types? Here is a close look at one of the hottest items
to hit the audio market.
With its high degree of portability, simplicity of operation, and good over-all
performance, the new cassette tape recorder is one of the hottest items to hit the
home entertainment market in recent years. Most of these high-performing newcomers
are equally at home as car tape units; portable recorders for taping staff meetings,
conferences, and class lectures; or as compact tape decks to upgrade a home stereo
console to include the versatility of tape.
Development of the Cassette
Over five years ago, the Philips Company of Holland pioneered in the development
of a new concept in the recording field - a cartridge tape recorder as easy to load
as a film-cartridge camera, yet offering all of the features of a conventional open-reel
At the heart of this new recorder was a small tape cartridge containing two miniature
plastic reels wound with 1/8-inch (actually 150-mil) magnetic tape and completely
enclosed in a small plastic case - or cassette (Fig. 1). The tape operates at a
slow speed of 1 7/8 in/s.
Fig. 1. The cassette is a compact reel-to-reel cartridge using
special thin 1/8-in (actually 150-mill) tape. The tape is pulled from one of the
reels (acting as supply reel, past a tape-guide idler, then past pressure pad and
tape head. The tape then moves between the capstan and pinch roller on the tape
deck, around the other tape-guide idler, and then to the other reel (acting as take-up).
When the cassette is flipped over at the end of the tape, the capstan and pinch
roller are in the other openings and the function of the reels is reversed.
The first cassette recorder was marketed in the United States in 1964 under the
Norelco "Carry-Corder" label. A short time later, an unusual licensing agreement
was worked out to encourage other tape-recorder manufacturers to adopt the cassette
In view of the tremendous reception accorded the cassette recorder, a number
of companies rushed to obtain the right to market their own lines of cassette recorders.
This explains the similarity among early makes and models.
Today there are over 200 different models from more than fifty tape-recorder
manufacturers. Included in this growing list of cassette manufacturers are such
well-known names as Ampex, Norelco, Sony, Wollensak, Mercury, Panasonic, Aiwa, Crown,
RCA, Concord, and G-E.
Perhaps the most significant result of Philips' generous licensing agreement
was instant standardization. Today, all cassettes, both stereo and mono, are completely
interchangeable and can be played back on any make or model of cassette recorder.
The fact that both mono and stereo cassettes may be interchanged represents a
major breakthrough in recorder technology. Recall that conventional four-track stereo
tapes cannot be played on a mono recorder because of the location of the quarter-track
head gaps in relation to the tape tracks. Since the quarter-track stereo recorder
places two quarter tracks in the upper half of the tape, recorded in opposite directions,
a mono half-track head picks up both upper tracks which results in a garbled output.
The cassette quarter-track heads, on the other hand, record two tracks in the
upper half of the tape, but both are recorded in the same direction and may be picked
up equally well by either a cassette stereo or mono playback head (see Fig 2).
A disassembled tape cassette is shown here. Outside dimensions
of the cassette are 4 by 2 1/2 inches. Thickness is about 1/3 inch.
Cassette tape cartridge is compared here with an endless-loop
cartridge shown at left. The latter will operate in only one direction and it cannot
be operated at high speeds.
Cassette is compared with an ordinary 7-inch open reel of tape.
The portable cassette recorder shown at right is not very much larger than the 7-inch
reel of tape.
All cassette cartridges are equipped with a unique safety feature which serves
to prevent accidental erasure of a pre-recorded tape. This safety feature consists
of two plastic tabs located along the rear edge of the cassette. Removal of the
plastic tabs automatically activates a record safety interlock any time the cassette
is placed into a cassette recorder.
In order to re-record over a pre-recorded tape, simply place short lengths of
adhesive tape over each of the two spaces left by the missing tabs. The cassette
can then be erased and re-recorded just like an ordinary blank cassette.
Blank cassette tapes are available in three basic lengths: 300 feet, 450 feet,
and 600 feet. The 300-ft tape can record continuously for 30 minutes on each side
for a total of 60 minutes. Likewise, the 450-ft cassette provides for 45 minutes
of recording time per side, and the 600-ft cassette records up to two full hours
(one hour per side).
Since all cassettes are interchangeable, they all look alike. However, some brands
of tape cassettes employ a better system of internal lubrication, and a special
low-noise tape formulation provides for improved recording performance at 1 7/8
in/s, especially for the higher frequencies. Therefore, in order to obtain consistently
good-quality recordings, it is advisable to stick to one of the known brands of
cassette tapes and avoid the bargain counter offerings.
The four- and eight-track car-tape units are examples of endless-loop cartridges.
In comparison to the cassette, the endless-loop cartridge system should have slightly
better fidelity because of its higher tape speed (3 3/4 in/s compared to the cassette's
speed of 1 7/8 in/s). However, this endless-loop design has a major drawback. It
cannot be operated fast-forward or rewound but can only play in a forward direction
at normal speed.
The cassette, on the other hand, is constructed of two miniature reels which
operate in the very same manner as a conventional open-reel recorder. Therefore,
fast-forward and reverse are standard features on the cassette recorder.
Other recent developments in favor of the cassette have been the development
of better recording and playback heads along with the improvement in low-speed master-recording
techniques. Both the Dolby and the Ampex EX+ processes have been quite successful
in reducing surface and background noise for low-speed tape-recording systems. These
processes are responsible for new lines of relatively high-quality pre-recorded
musical tapes currently being marketed for the cassette recorder.
What About Fidelity?
The over-all acoustic response of most inexpensive portable cassette recorders
ranges from about 200 to 7000 Hz. This limited response is due, in part, to the
small speakers employed in the cassette's space-saving design. However, the full-size
stereo systems have a much broader acoustic response extending from approximately
80 to 10,000 Hz.
Even though the acoustic response of the portable line of cassette recorders
is somewhat limited, their preamp fidelity is quite good. What is more, some of
the new a.c.-operated stereo tape decks now available boast an electrical preamp
output signal (that may be applied to your stereo system) that is within 2 dB from
below 50 Hz to 12 kHz.
(Editor's Note: Also helping to maintain good high-frequency performance is the
use of a playback equalization curve that exhibits somewhat less bass boost and
a little less treble rolloff than is employed to play back tapes at higher speeds.
The playback curve is shown in Fig. 3. This curve is usually further modified with
some added treble boost to overcome high-frequency losses in the tape head.)
Although the cassette's response is below the 15,000 Hz normally considered essential
for high-fidelity reproduction of classical music, even a portable cassette machine
does surprisingly well in recording and playing back music.
To illustrate this point, the author recently arranged a tape demonstration involving
a professional reel-to-reel recorder and one of the good-quality portable cassette
recorders. A dub of the "1812 Overture" was made from the conventional recorder
to the cassette and then each of the recorder's pre-amp outputs was wired into a
professional-quality sound system by means of an audio switcher.
The two recorders were then carefully synchronized and playback levels matched.
At this point, a half-dozen music enthusiasts were invited to sit in on the demonstration
and attempt to determine which was the original tape being played on the conventional
recorder and which was the cassette dub. After a dozen runs, the scores of each
of the judges were tabulated. The fact that they scored less than 50% accuracy may
be viewed as a relative indication of the fidelity of the cassette recorder at a
preamp or tape-deck output level.
(Editor's Note: For a complete report on the lab performance of a number of these
new units, refer to the boxed copy at the end of this article.)
Some of the Problems
Fig. 2. The conventional quarter-track reel-to-reel recorder
uses tracks 1 and 3 for a stereo program while the cassette uses tracks 1 and 2.
This means that a mono cassette machine is compatible in that it picks up the upper
two similar tracks.
Fig. 3. The standard playback equalization curve for pre-recorded
cassettes (1 7/8 in/s) shows less bass boost and less treble roll-off than is used
at higher tape speeds. The characteristics of the curve are the same as would be
produced by RC circuits with a time constant of 1590 μs at the low frequencies
and 120 μs at the high frequencies.
Although the cassette design is relatively trouble-free, there are some problems
associated with the cassette recorder. Among these, especially with the less-expensive
portable models, are: inconsistent speed, excessive flutter and wow, poor frequency
response, noisy recordings, and broken or binding cassettes. Many of these problems
can be easily eliminated through the adoption of a good maintenance program.
Inconsistent tape speed, intermittent operation, and excessive flutter and wow,
may often be traced to low battery voltage. Most portable cassette recorders are
equipped with ordinary carbon-zinc batteries which have a usable battery life of
approximately 14 hours in this service. After that, the battery voltage is too low
to maintain proper tape speed. Also, a number of cassette recorders are damaged
by leak-proof carbon-zinc batteries that somehow manage to leak.
In order to obtain better battery performance, it is advisable to switch to alkaline
activated batteries or, whenever possible, use an a.c. adapter. The a.c. adapter
will rejuvenate the alkaline batteries a number of times, provided the batteries
are not allowed to discharge below half of their full-charge level. Alkaline batteries
cost up to twice as much as the carbon-zinc batteries but the alkaline batteries
last up to twice as long and deliver much better performance in the long run.
Another battery-saving tip is to stop the cassette recorder as soon as possible
after it reaches the end of the reel. Although the cassette recorder has a built-in
slip clutch to prevent the drive motor from stalling, the increased load on the
motor causes rapid battery drain, particularly if left in this condition for any
length of time.
Similarly, the use of a good-quality cassette tape can also increase battery
life by decreasing the drag on the drive motor.
Occasionally, a portable cassette recorder will develop intermittent operation
due to poor battery connections. Generally, good electrical contact can be restored
by rubbing the battery terminals with a pencil eraser.
There are three basic problems encountered in using cassette tapes: bunching
of tape near the capstan due to a loose or uneven tape wind, internal binding of
the reels due to poor lubrication, and end-of-the-reel leaders which come loose
from the reel.
To avoid these problems, use a known brand of cassette for those critical recordings.
Carefully check the smoothness of the tape wind as seen through the small window
on the front of the cassette. If necessary, rewind the tape before using it.
If the leader tape should happen to break loose from the end of the reel, simply
remove the screws holding the cassette together and reconnect the leader to the
reel by means of the special hold-down connector located near the hub of the reel.
In order to maintain the cassette's high-frequency response, signal-to-noise
ratio, and low percentage of flutter and wow, a good maintenance program similar
to that of a conventional reel-to-reel recorder should be employed. (See "Tape Recorder
Maintenance Program" in the October 1968 issue of this magazine.) For example, the
heads and transport unit should be cleaned often with a cotton swab and denatured
alcohol. In addition, the heads should be demagnetized any time the surface or background
noise becomes noticeable.
Prior to recording an important conference or speech, it's a good idea to check
the battery level, battery connections, and thoroughly clean the unit. In this manner
you can be assured of getting your best recording.
If head replacement is required, there is a line of replacement cassette heads
available equipped with pre-set integral tape guides for correct tracking without
the need for elaborate equipment. A mono head lists for approximately $16.00 and
the stereo version is available at approximately $22.00.
In the first generation of cassette recorders, most makes and models closely
resembled the original Norelco "Carry-Corder." However, today, most manufacturers
have modified the original design to include such features as push-button control,
automatic record-level control circuitry, tone controls, pop-up control for ease
in loading and unloading cassettes, hysteresis synchronous drive motors, etc.
Posted June 7, 2017