PHONOGRAPH RECORDS -- A PERSPECTIVE
The compact disc has taken away the phonograph record for most people. Here are a few comments about the
properties of this still quite viable recording system:
- How many grooves are on the average LP record? Over a thousand? Nope! There are only two: One
on each side. The groove spirals in from the edge to the center.
- On the subject of sides, how many ways of sequencing record sides have been used for multi-disc
albums? The answer is four:
- The simplest, the manual sequence, requires turning each record over before
going to the next record. A few record changers were made that turn the records over. The side couplings of a
four record set are:
|FRONT SIDE|| 1|| 3|| 5|| 7|
|BACK SIDE|| 2 || 4 || 6
|| 8 |
- Since most record changers do not turn over the records, the other two sequences were designed
for record changer use. The drop sequence is designed for record changers that drop records one by
one to the turntable. These do not reverse the order of the stack of records as they go through it, so the side
couplings must reverse when the entire stack of records is turned over:
|FRONT SIDE|| 1|| 2|| 3|| 4|
|BACK SIDE|| 8 || 7 || 6
|| 5 |
- The third sequence is for record changers that reverse the order of the record stack as they go
through it. Examples are the early RCA changers that, after playing each record, took it off the stack on the
turntable and placed it to the side, Capehart turnover changers, and the Thorens TD-224 changer with the record
carrying arm. With one exception, the only records ever made in this sequence were 78 rpm albums. Since these
changers reverse the stack, the side couplings must not be reversed in the slide sequence after the
stack of records has been turned over:
|FRONT SIDE|| 1|| 2|| 3|| 4|
|BACK SIDE|| 5 || 6
|| 7 || 8 |
- A fourth set of couplings has been used for cassette albums for dual cassette players, and for
DJs. The relay sequence works like the slide sequence for each group of two tapes. If there
is an odd number of tapes, the last tape contains the last two sides. But this sequence was never used for records,
with a few exceptions for use by DJs.
|FRONT SIDE|| 1|| 2|| 5|| 6|
|BACK SIDE|| 3 || 4 || 7
|| 8 |
- On the subject of record changers, several methods have been used to detect the end of a record:
- The position trip starts the change cycle when the arm gets to a certain place on the record.
It does not work well with all records.
- The eccentric trip uses the backward motion of the arm in the eccentric groove found at the
end of most electrically recorded 78s and early LPs. It is not very reliable, and does not work with modern
- The velocity trip detects the speed up of the arm when it enters the runout groove on most
records. It is the most reliable, and was used on most record changers made after 1955.
- The progress trip was used by only one company. It detects that the pickup arm has stopped
moving forward. It takes some time to trip the changer at the end of the record. It also trips after about 30
seconds if the record gets stuck.
- Some changers have both the position and eccentric trip.
- Some changers have both the position and velocity trip.
- How is sound recorded on a record? The groove wiggles back and forth in the surface of the record.
These wiggles correspond to the waveform of the recorded sound. As the playback stylus follows these wiggles, it
vibrates with them, producing the audio signal.
- The earliest records, and all cylinders, used an up and down motion. The sound waves made the groove deeper
- Most monaural records have the wiggles going from side-to-side (toward and away from the spindle).
- A few early records, and all Edison records, used up-and-down motion.
- When stereo came along, they wisely decided to use 45 degree diagonal motions to record the left and right
channels. The diagonal slanting down toward the spindle is the left channel, and the diagonal slanting up toward
the spindle has the right channel.
- A mono record plays with equal volume and phase in both stereo speakers.
- When Dolby Surround is put on a record, the left and right channels are the same as above, the dialog
channel uses the side-to-side motion, and the surround channel uses the up-and-down motion.
- How does the record changer separate one record from the stack to drop it? There are two methods:
Some record changers required that a plastic insert (a spider) be put in the large hole to make the record fit
the standard .25" spindle.
- Most changers push the record to be dropped to one side. A key in the spindle keeps the
second record from moving sideways. When the record falls off the ledge in the spindle, it drops to the
- An overarm keeps the records level. A lever in the spindle pushes the record.
- A shelf holds the edge of the stack. A lever in the spindle pushes the record.
- An overarm keeps the records level. The cap of the spindle moves to one side to push all but the bottom
record, then a shelf retracts in the spindle to release the bottom record.
- A shelf holds the edge of the stack. A lever in the shelf pushes the record.
- A shelf holds the edge of the stack. It nods toward the spindle to push the record.
- A shelf holds the edge of the stack. The spindle nods toward the shelf.
- Another method grips the second record to keep it from falling:
- Grippers in the spindle hold up the second record. Three fingers retract to drop the bottom record.
- Two shelves hold up the stack. Slicer blades knife between the bottom two records, then the shelves
retract to drop the record. This tended to break records.
- Large hole 45 rpm records are dropped by retracting shelves, after knives slice into the space between
them to hold up the rest of the stack (This is why the very center of the 45 rpm record is thinner than most
of the label is).
- Why are there four speeds?
- Originally, 78.26 rpm was a compromise among several record companies to standardize on one speed. (They
used 70, 75, 76, and 80 rpm) It was necessary with shellac records to turn them this fast to get good sound.
And radio stations demanded a standard speed.
- With the development of vinyl records, a slower speed was possible, extending recording time. Columbia
used 33.33 rpm, a speed used for radio voice recordings for years.
- RCA decided that 45 rpm would deliver more fidelity than 33.33, but their design of the 45 record retained
the short playing time of 78 records. The speed 45 rpm seems to have come from a record lathe design originally
commissioned by guitarist Les Paul for use in pitch-changing effects.
- Each found a place in the market.
- 16.67 rpm was used only for Audio Books, until their speed was later changed to 8.33 rpm, and a special
player or adaptor was needed.
- Other speeds were used in the early days. Pathe used 90 and 120 rpm. Several other manufacturers used
speeds between 80 and 90 rpm.
- Why did RCA make the spindle hole larger in the 45 rpm record? They did it to make a record
changer with all of the record-dropping parts in the spindle. No reliable way of doing it with the .25" hole had
been made at the time, so RCA used a 1.5" hole. It was also a ploy, so that you had to buy their player to play
their records. But just before the 45 was released, the .25" center push spindle was perfected, and the problem
was solved (but the large hole remained). Also, Farnsworth produced a working umbrella spindle which needs no
side shelf or overarm just before the 45 was introduced.
- Why are there three sizes of records?
- Small nonstandard sizes abounded in the first few years of the disc record.
- The 10-inch record was the first standard size. It was standardized to make automatic record players possible.
- The record companies added 12-inch for classical music, to provide fewer side changes in the middle of the work.
- When RCA designed the 45 rpm record, it used 7-inch to make the records handier.
- Actually, there are several other sizes.
- Pathe made 14-inch and 20-inch records.
- 16-inch was the standard size for radio transcriptions during the entire time records were made.
- Germany used 8-inch records for a while. Polkas were too long for 7-inch records.
- Many record companies made 6-inch children's records.
- In the late 1960s, Hip Pocket records were made with a 4-inch diameter.
- A Collaro record changer that was made between 1954 and 1967 could play all sizes between 12-inch and 6-inch
- How do record changers handle the different sizes?
See my page on the subject.
- How do record changers know when to shut themselves off?
- Early cheap ones repeat the last record over and over.
- Late cheap changers have a knob so the user tells the changer how many records are on it.
- The RCA changers that placed the records to the side simply set the arm down beside the turntable edge (where
a record would be) when there were no records left on the turntable.
- Most changers with a balancing arm use the fallen balancing arm to trigger automatic shutoff on the next
- Most changers that do not have balancing arms check for the weight of a record on the spindle, dropping
fingers, or the side shelf.
- Some changers with a pusher in the spindle move the pusher backwards to test for the presence of a record
- Some changers use a feeler arm or the pickup arm to feel the edge of the stack (or a lowering record) for
size. They shut off when they do not detect a record when scanning for size.
- Capehart turnover changers repeat the entire stack over and over. Some of them have a dial to set the number
- How does the compact disc measure up to the LP?
- You can't vary the speed of a CD to tune it to an instrument.
- The CD has only one side, but over twice the maximum playing time of an LP side. It was designed to hold
Beethoven's 9th Symphony.
- Since there is only one side on a CD, there is only one side-coupling order for multi-disc sets.
- It is harder to damage a CD.
- CDs have no surface noise.
- The CD changer is much larger than the disc, where the LP changer was usually not much bigger across than
the record itself.
- CD players can vary the order of the tunes, most LP players can not.
- Record changers usually turn off their power. CD changers stay on after finishing their supply of CDs.
- LP records are not generally made anymore.
- The phase of harmonics in the upper two octaves is not accurate on a CD.