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Патент USA US3077533

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Feb. 12, 1963
J. H. RlGGs _ETAL
3,077,519
STEREOPHONIC PHONOGRAPH
Filed NOV. 17, 1959
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4 Sheets-Sheet :l
Feb. 12, 1963
J. H. Rises ETAL
STEREOPHONIC PHONOGRAPH
Filed Nov. 17, 1959
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3,077,519
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-Feb. 12, 1963
3,077,519
v J. H. RlGGs ETAL
sTEREoPHoNIc PHONOGRAPH
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Filed Nov. 1T, 1959
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Feb- 12, 1963
J. H. RIGGs ETAL
3,077,519
STEREOPHONIC PHONOGRAPH
Filed Nov. 17, 1959
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3,077,519
Patented Feb. 12, 1963
2
A further object is to provide a new and improved
3,077,519
multiple channel audio sound system which twill simultan
John H. Riggs, Kenmore, and Robert D. Barry, Lockport,
N.Y., assignors to The Wurlitzer Company, Chicago,
ent electrical sound signals in a manner which automati
cally compensates for the over-al1 volume or loudness level
of the sound signals, While at the same time preserving the
STEREGPHÜNIC PHONOGRAPH
Ill., a corporation of Ghia
Filed Nov. 17, 1959, Ser. No. 853,511
9 Claims. (Cl. 179-1001)
eously and independently amplify a plurality of independ
mutual independence yof the signals.
A further object is to provide a new and improved
stereophonic phonograph which transforms stereophonic
The present invention relates to automatic coin oper
electrical sound signals into stereophonic sound without
ated phonographs or -recording playing machines, and is 10 distortion
and with undiminished stereophonic acoustical
concerned particularly with problems involved in the con
effectiveness, While at the same time automatically com
trol of such machines which are designed to play stereo
pensating for the degree of inherent loudness Iof the record
phonic records.
being played through the use of relatively simple and
Automatic coin operated machines of this character are
electrical amplifying and control means.
commonly installe-d in public yor semi-public places to play 15 dependable
Other objects and advantages will appear from the tol
a selection of records in any selected order. lt is eX
lowing description of the exemplary embodiment of the
tremely desirable that the volume or loudness of the sonic
invention illustrated in the drawings, in which:
or acoustical output of an automatic phonograph of thisv
character be maintained within an optimum range which
is most acceptable in the environment in which the ma 20
chine is installed. On one hand, a machine must have a
sonic output which is suñiciently loud to permit all patrons
of the machine to enjoy the music. On the other hand,
the output should not be so loud as to be offensive or irri
tating to others ‘who may be present. Since such machines 25
operate unattended, a problem arises in maintaining the
acoustical output of individual machines within the opti
FIGURE l is a diagrammatic illustration of a stereo
phonic phonograph embodying the invention;
FlG. 2 is a diagrammatic illustration of a portion of
the electronic circuit used in the phonograph of FIG. l;
FlG. 2A is a continuation of the circuit diagram of
FIG. 2 which adjoins the right-hand edge of FIG. 2; and
FIG. 2B is a further continuation of the circuit diagram
of FIG. 2. and adjoins the right-hand edge of FIG. 2A.
Having reference to the drawings in greater detail, the
stereophonic phonograph forming the exemplary em
mum range of loudness for each specilic installation.
bodiment of the invention is illustrated schematically in
This problem arises from the fact that individua-l rec
ords played -on such machines have different degrees of 30 FlG. l and identified by the number l0. As depicted
schematically in IFIG. l, the phonograph 10 comprises a
inherent loudness. Thus, one record when played in an
turntable 12 which supports and rotates a stereophonic
record 14 in engagement with a stereophonic pickup 16.
The machine is equipped with conventional automatic
record changing devices and conventional coin controls
35
inherent loudness of individual records may exceed the
well known in the art and requiring no specific description
optimum range of loudness for a machine in any speciiic
here. _It is suñicient to note that the machine operates to
location.
play a selection of records in any selected order, the suc
To maintain the sound level of such automatic ma
cessive records being automatically placed on the turn
chines within the optimum limits desired, it has been the
practice to equip the machines with means which auto 40 table 12, or the equivalent, and rotated in engagement
with the pickup 16 for playing.
matically compensates for dilîerent degrees in the inherent
lt will be understood that stereophonic records are cut
loudness of the records played. ln general, the compen
to have in eilect two sound tracks or sound recording sur
sating means used for this purpose attenuates the output
faces which physically recorld two sound signals which
of the machines to a degree which is inversely propor
tional t-o the inherent loudness of the individual records. 45 are independent of each other. The pickup 16 itself is
of a conventional construction and engages the two sound
In this manner, relatively quiet or soft records are played
recording surfaces of a record 14 simultaneously, and
with suiiicient ampliñcation to be heard and enjoyed while
produces two separate and independent electrical sound
the ampliiication of the playing of inherently louder rec
ords is reduced to remain within the acceptable sound 50 signals at two separate outputs 2i), 22 of the pickup.
The electrical sound signals supplied to the pickup out»
range.
puts 20, 22 during playing of a record 1‘4 are amplified
The expedients previously used for this purpose have
independently of each other through two separate elec
been acceptable in record playing machines designed to
tronic amplifying channels illustrated diagrammatically
play monaural records. Here, the matter of compensating
for different degrees of inherent loudness in successive 55 in FIG. l, and identiñed respectively with the legends
“Channel A” and “Channel B.” The outputs of the chan
records is simplified by the fact that only one sound signal
nels
“A” and “B” are connected respectively to stereo
is produced and ampliñed through a single amplification
phonic speakers 24, 26 which are normally spaced from
channel.
each other to produce the desired stereophonic sound ef
As will be presently explained in greater detail, the con
trol means used for compensating for different degrees of 60 fects.
Stereophonic records, like monaural records, dilîer
record loudness in machines designed play monaural rec
from each other with regard to the degree of inherent
ords is inadequate for handling the problems of volume
loudness in the inidividual records. Hence, it is desirable
or loudness control in machines designed to play stereo
that the eiiective output volume or `acoustical loudness of
phonic records, in which two sound signals are produced
phonograph 10 be controlled to compen-sate for the
and separately amplified through separate amplification 65 the
degree of inherent loudness of the stereophonic records
channels that energize a stereophonic speaker system.
being played to maintain the output volume of the instru
One object lof the invention is to provide a new and
ment within the loptimum range desired in the environ
improved stereophonic phonograph which will automatic
-ment in which the instrument is installed. Since such
ally compensate for the degree of inherent loudness in
phonographs operate unattended any means used to com
individual records played, while at the same time providing
pensate for the inherent loudness of successive records
uncompensated machine may produce a sonic output
volume greatly exceeding that of another record played
under similar conditions. Moreover, the difference in the
a fully eiîective stereophonic reproduction of the recorded
sounds.
should be automatic in its operation.
3
3,077,519
The matter of providing in a stereophonic phonograph
automatic -compensation for the inherent loudness of in
dividual records is immensely complicated by the neces~
sity for maintaining the full stereophonic effectiveness of
the sound reproducing system.
In a stereoplionic phonograph of the character de
scribed, -the volumetric level or effective loudness of both
sound signals, which are independent and separ-ately am
plified, are affected by the inherent loudness of .the record
4
serving .the full stereophonic effectiveness of the acoustical
reproduction of lthe stereophonic sound signals.
Thus, with reference to the exemplary embodiment of
the invention depicted in the drawings, the pickup 16,
yFIGS. l »and 2, is connected >through a plug 28 and a
socket 30 with the independent pickup output terminals
20, 22. As previously explained, the pickup 16 supplies
two independent electrical sound signals or voltages to the
respective terminals 20, 22.
being played.
To maintain the over-all loudnes-s or in
The pickup terminals 20, 22 are connected through
teiisi-tyV of the sound being produced within the desired l0 jacks 32, 34 with two independent volt-age amplifiers 36,
optimum range, it is desirable to compensate for differ
ences in the strength of the two sound signals from the
pickup 1'6 due to diiîerent degrees of loudness of succes
38 in the respective 'amplifying channels “A” and “B.”
The voltage amplifiers 36, 38 include, respectively, two
triodes 40, 42, together with suitable coacting resistors and
sive records being played.
capacitors interconnected with the tubes, as illustrated in
Yet in providing compensation for different degrees of 15 FIG. 2. Plate voltage is supplied to the tubes 40, 42
strength of the two signals from the pickup 16 due to
through a conductor 44 leading from a power supply plug
the inherent loudness of different records, it is necessary
46, FIG. 2B.
to take into account that the electrical sound signals pro
The previously mentioned voltage amplifiers 36, 38
duced at the two pickup terminals 20, 22 not only vary 20 function as first stage amplifiers in the respective channels
in relation to each other, but it is essential to the achieve
“A” and “B,” as intimated. The output of the amplifier
ment of the stereophonic sound effect desired that these
36 is connected through a fixed lresistance 48 with the in
signals at the two terminals vary independently of each
put of a second stage amplifier 50 in the channel “A.”
other. Otherwise, the effectiveness of the stereophonic
The resistance 4S is made up of a plurality of resistors 52
reproduction of the recorded sound would be greatly _ha Ol connected together as shown in FIG. 2.
diminished or destroyed.
Similarly, the output of the first stage amplifier 38 in
Thus, ‘the use of independent loudness compensating
the channel “B” is connected through a fixed resistance
means -in each of the sound `channels “A” and “B” to com
54, formed by a plurality of interconnected resistors 56
pensate Íor the .strength or -volume of the electric sound
with the input of a second stage amplifier 58 in chan
signals in ‘the respective channels would greatly diminish
nel “B.”
the desired stereophonic acoustical effect. For example, 30 As will presently appear, the resistaiices 48 and 54 con
at a particular period in the playing of a stereophonic
nected in series between the first and second amplification
record 14 a relatively strong -signal may be supplied at the
» stages in the respective channels “A” and “B” are used in
pickup terminal 20 and amplified through the channel
automatically controlling the out-put volume of the re
“A” while only a much weaker signal is supplied at the 35 spective channels.
pickup terminal 22 and amplified through the channel
“B.” The result is to produce a relatively high inten
Amplification is accomplished in the respective second
stage amplifiers 50, 58 by cathode following triodes
sity of sound from the speaker 24 with a much lower_1ntensity of sound coming from the speaker 26. This is pre
60, 62.
The cathode of the tube 60 in the amplifier 50 is con»
40 nected through a conductor 64, FIG. 2, and a socket 66
However, with automatic volume compensation
with a loudness control 68 which is adjusted by a manual
cisely the efiect desired inv stereophonic reproduction'of
sound.
being independently applied to each of the channels “A”
control 70. The output of the loudness control 68 is
connected back through the socket 66 with a conductor
, the stronger signal applied -to the channel “A” would be
72 leading to the input of a third stage amplifier 74 in
suppressed in relation to the amplification of the weaker 45 channel “A.” The amplifier 74 includes a triode 76.
signal supplied through the channelf‘B” with a conse
In a similar manner, the output of .the cathode follower
quent loss in stereophonic effectiveness.
amplifier 58 is connected through a conductor 78, the
As a practical matter, it is not feasible to compensate
socket 66, a loudness control 80 ganged with the loudness
the overall volumetric acoustical output from `both speak
control 68, the socket 66, and a conductor 82 with the
ers 24, 26 in accordance with the composite strength of 50 input of a third stage amplifier 84 in channel “B.” The
both of the two signals being amplified. This expedient
amplifier 84 comprises a .triode 86.
and “B” in the manner described, the amplification of
tends to destroy the independent operation of the _two
Output conductors 88, 90 from the third stage ampli
lamplifying channels “A” and “B” with cross modulation,
fiers 74, 84 in the respective channels “A” and “B” are
distortion `or other interference with independent opera
connected through tone control circuits 92, 94 of a gen
tion of the two amplifying channels.
55 erally conventional character, FIG. 2A, with conductors
Y The matter of controlling the output volume of both
sound channels of a stereophonic phonograph in accord
ance with the strength of the signals in one of the channels
96, 98 leading to separate phase inverters 100, 1-02 in
the respective channels “A” and “B,” which drive inde
pendent push-pull power amplifiers 104, 106 in the re
is complicated by inherent characteristics of stereophonic
spective channels, see FIG. 2B.
recordings. Thus, in a recording .of an orchestration, for 60
The power amplifier 104 in channel “A” is coupled
example, -there may be protracted periods in which `a very
through a transformer 108 with a loud speaker 24 which
strong signal is supplied to one channel when only a very
generates sound corresponding to the signals supplied at
weak signal is supplied to the other ch-annel. Assuming
the pickup terminal 20.
the volumetric output of bot-h channels were compensated
In like manner, the output of the amplifier 106 is
in Vaccordance with the signal. supplied «to the channel
65 coupled through a transformer 112 to the loud speaker
which, in the assumed example, is supplied over a pro
26 which produces sound corresponding to the signals
tracted period with the weaker signal, the stronger signal
supplied by the. pickup 16 to the terminal 22.
supplied to the channel not used as a control would be
The operating power for the phase inverters 100, v102
Y excessively amplified to produce excessive loudness in the
playing'of the recording.
In accordance with the invention, the improved stereo
phonic phonograph is automatically controlled through
and for the push-pull amplifiers 104, 106 is supplied from
70 the previously mentioned power plug `46 through power
distributing conductors 114, FIG. 2B.
The overall output volume of the two speakers 24, 26
the use of relatively simple and dependable means to com
is automatically controlled to compensate for the degree
pensate .for different degrees of inherent loudness in dif
of inherent loudness of the record 14 being played, in a
ferent records being’played, while ‘at the same time pre 75 manner which preserves the independent operation of the
¿077,519
5
two channels “A” and “B,” while at the same time main
taining the full stereophonic effect of the reproduction
ofthe stereophonically recorded sound.
' The two electric sound signals amplified in the re
spective electronic amplifying channels “A” and “B” are
attenuated independently of each other by the controlled
introduction of voltage drops across the resistances 48
and 56 interposed in the respective amplifying channels,
as described.
For this purpose the output sides of the resistances
48, 56 are connected to ground through variable resistance
triodes 11-6 and 118, as shown in FIG. 2. The admittance
of the two tubes 116, 11S is controlled by a control volt
age applied to the grids of both tubes through a conductor
120 leading from a time delay, averaging or integrating
circuit 122, which is designed to produce an output volt
age corresponding to the inherent loudness of the record
being played.
to a maximum value of the order of ten seconds While
supplied with a very strong sound signal without sig
niiicantly reducing the volumetric output of either chan
nel. Hence, either channel “A” or channel “B” is free
to amplify a strong signal over a ten second period while
the other channel is amplifying a much weaker signal
without interference with the record loudness control
circuit. In the playing of stereophonic records which
utilize both channels to obtain the desired stereophonic
effect the duration of any period during which the sig
nal supplied to one channel greatly and continuously ex
ceeds the strength of the signal supplied to the other
channel will not exceed ten seconds, the period in which
the circuit 122 allows the channel “B” to amplify weak
signals without increasing the ampliñcation in channel
“AI”
Having reference to the drawings, it will be noted with
reference to FIG. 2 that the record loudness compensat
ing circuit 122 comprises an input amplifier formed by a
The two variable resistance tubes 116, 113 shunt the
124V the grid of which is connected through a block
respective- resistances 48, ‘54 to ground and draw current 20 triode
ing capacitor 126 with the output of the iirst stage arn
through the resistances, and hence induce voltage drops
plifier 38 in channel “B.” Plate voltage is supplied to the
across the respective resistances which are proportional
tube 124 through a conductor 128 leading from the power
to the admittances of the respective tubes 116, 118.
supply plug 46.
As will presently appear, the effect of this is to at
The output of the amplifying tube 124 is connected
tenuate the electric -sound signals at the outputs of the 25 through
a blocking capacitor 130 with a rectifying tube
respective lirst stage ampliiiers 36, 38 to a degree propor
132. The output side of the capacitor 130 and the input
tional to the admittances of the compensating discharge
Side of the tube 132 are grounded through a resistor 134.
tubes 116, 118.
The output side of the rectifying tube 132 is connected
The previously mentioned circuit 122 used to supply
through
a resistor 136 with the conductor 120 which
30
an admittance controlling voltage to the compensating
supplies a control voltage to the volume compensating
tubes 116, 118 is designed to avoid diminution of the
tubes 116, 118. Operate ends of the resistor 136 are
stereophonic sound reproducing capabilities of the instru
grounded through two capacitors 138, 140.
ment, while at the same time providing a volume corn
pensating control voltage which conforms to the inherent
loudness of the record being played.
The resistor 136 and the capacitors 138, 140 have
35 values which operate this circuit to provide an output
- To avoid interference with the operation of the channels
with each other, the circuit 122 is connected to sense the
volumetric or loudness level of the electric sound signals
voltage on the conductor 120 which corresponds to an
averaging of the signal voltage supplied to the circuit
122 from the channel “B” over a time interval which
is of sufficient extent to avoid more than an unnoticeable
Moreover, the circuit is designed to re 40 change in the voltage on the conductor 120 due to a sub
passing through only one of the channels, in this instance
channel “B.”
spond to the inherent loudness of the record being played
stantial change in the signal voltage supplied to the circuit
stereophonic recordings.
The circuitry used in implementing the invention in
the manner described is relatively simple and inexpensive
122 over a ten second period. By Way of example, the
while at the same time avoiding interference with the de
resistor 136 can have a resistance of 1.5 megohms when
sired ability of the two amplifying channels to operate
the capacitors 138 and 140 have capacities of one and two
over substantial periods of time at radically dilierent
sound or loudness levels in order to properly reproduce 45 microfarads, respectively.
' Thus, in accordance with the invention the volumetric
output of both channels “A” and “B” is automatically
compensated in accordance with the average or continu
and provides great dependability in operation.
It will be appreciated that the invention is not neces
ing general loudness or volumetric level of the signals
supplied to channel “B” during the playing of an individ
ual record. The volumetric level of the signals supplied
sarily limited to the specilic construction illustrated but
includes variants and alternatives within the scope of the
not only produces an output voltage which corresponds
to the average strength of the sound signals in the channel
“B” over an extended period of time, and hence to the
inherent loudness of the record being played, but at the 60
pliiiers, an electrical pick-up unit having two separate
invention as deiined by the claims.
The invention is claimed as follows:
to either channel, in this instance channel “B,” when aver
l. In a phonograph for playing stereophonic records
aged over an extended period of time is an accurate
measure of the true loudness level of the recording in 55 and automatically compensating for the inherent loudness
of individual records, the combination of two signal arn
each of the channels of a typical record. The circuit 12.2
same time allows the channel “A” to amplify a strong
signal to the optimum degree `desired over a rather ex
electrical outputs connected to said respective amplifiers
to control the latter, two signal attenuating resistors
coupled to the outputs of said respective amplifiers, an
averaging circuit coupled to the output of only one of
said signal »amplifiers ahead of the coacting resistor, said
averaging circuit including circuit means for producing an
tensive period of time While the channel “B” is supplied
instantaneous electrical output which is a function of the
with only a much weaker signal. Similarly, the circuit
«122 provides proper ampliñcation of a weak signal sup 65 average signal voltage of said one signal ampliñer over an
extended period of time, two electronic discharge valves
plied to channel “A” while a much stronger signal is being
amplified over a rather extensive period of time in channel
“B,”.thus maintaining the full stereophonic capability of
connected to the outputs of said respective signal arn
pliiiers through said respective resistors, two power am~
pliiiers having inputs coupled through said respective
the instrument unaiiected by the operation of the means
70 resistors with said respective signal amplifiers, electrical
used to control record loudness.
sound producing means connected to said respective power
As will be described in greater detail, the record loud
amplifiers and means coupling the output of said averag
lness compensating circuit 122 operates to respond to the
ing circuit to both of said discharge valves to control the
Joverall average value of the sound signals supplied to
admittances of both valves at once in accordance with
the channel “B” while at the same time allowing the
the
output of said averaging circuit to produce a con
75
'channel “B” to operate continuously through -a period up
3,077,519
7
tinuous modulation of the signal attenuating effect of
both of said resistors simultaneously to compensate for
prolonged changes in the average output of said one
signal amplifier.
2. In a multiple channel sound system, the combina
tion of multiple electronic amplifying channels, multiple
sources of electric sound signals connected to the inputs
of said respective channels, sound generating means con
nected to the outputs of said respective channels, an at
tenuator connected into each of said channels to modify
the output thereof, an averaging circuit coupled to only
one of said channels ahead of said attenuator therein, said
averagingcircuit including means for producing an elec
trical output which is a function of the average strength
of the Isignals applied to the input of the averaging circuit
over an extended period of time, and means coupling
the output of said averaging circuit to both of said at
tenuators to control the output levels of both of said
channels to compensate in the outputs of Aboth channels
8
compensate in the outputs of both channels for prolonged
changes in the average strength of signals in said one
channel ahead of said resistor therein.
5. In a volume compensated, multiple channel audio
sound system, the combination of two electronic amplify
ing channels, two sources of electric sound signals con
nected to the inputs of said respective channels, two elec
tric sound generators connected to the outputs of said
respective channels, electric volume control means coupled
to each of said channels to modify the output thereof, an
averaging circuit coupled to only one of said channels
ahead of the volume control means coacting therewith,
means coupling the output of said averaging circuit to
`both said volume control means to control both of said
control means to modulate at once the output levels of
both of said channels to compensate in the outputs of
both channels for prolonged changes in the average
strength of sound signals in said one channel ahead of the
coacting
control means, said averaging circuit
simultaneously for prolonged changes in the average 20 including volume
a series resistor and two capacitors connecting
strength of the sound signals from the'sound signal source
opposite ends of said resistor to ground, and said resistor
connected to said one channel.
and said capacitors having electrical values which pro
3. In a stereophonic -sound system, the combination of
duce at the output end of said resistor an electrical output
two electronic amplifying channels, two sources of electric
which is a function of the average electrical signal applied
sound signals connected to the inputs of said respective
to the input of the averaging circuit over an extended
amplifying channels, sound producing means connected
period of approximately ten seconds duration.
to lthe outputs of said respective channels, a resistor
6. A phonograph for playing stereophonic records un
coupled into each of said amplifying channels in series
attended with automatic compensation for differences in
therewith, a time delay integrating circuit coupled to one
the inherent loudness level of different records, compris
of said channels ahead of said resistor therein, said time 30 ing, in combination, a stereophonic pickup unit, means
delay integrating circuit including means for integrating
for moving a stereophonic recording in association with
»the signal voltage Vin said one channel ahead of said resis
said pickup unit to activate the latter, two separate am
tor therein over an extended period of time to produce an
plifying
channels connected to said stereophonic pickup
electrical output which is a function of the average of said
unit to be controlled by the latter, two loudspeakers ener
signal voltage over said extended period of time, two elec
gized by said respective amplifying channels, two inde
tronic discharge valvesV connected to the output `side of
pendent volurne control circuits coupled with said respec
said respect-ive resistors in said respective channels, and
tive amplifying channels to control the outputs of the
means connecting the output of’said time delay integrating
latter, a volume compensating circuit having an output
circuit to both said discharge valves to control the admit
tance of both valves simultaneously in accordance with 40 connected in controlling relation to both said volume con
trol circuits to impose volume control on both said chan
the output of said time delay integrating circuit to produce
nels, means coupling said volume compensating circuit
, in said resistors »in both channels simultaneous signal
to one of said amplifying channels ahead of said volume
modulating elïects which compensate in the outputs of
control circuit coacting therewith, and said volume com
said sound producing means of both channels for pro
longed changes in average strength of sound signals in 45 pensating circuit including electrical integrating means for
integrating over an extended period of time electrical
said one channel ahead of said vresistor therein.
signals supplied to said compensating circuit and provid
. in an electronic amplifying system for amplifying
ing an electrical output as applied to said volume control
stereophonic sound signals, the combination of two
circuits which is a function of the average intensity over
electronic amplifying channels, two sources of electric
an extended period of time of the electrical signals sup
sound signals connected to the inputs of said respective
plied to the input of said volume compensating circuit and
amplifying channels, each amplifying channel includ
which
serves through control of both of said control cir
ing a voltage amplifier and a power amplifier coupled
cuits at once by said volume compensating circuit to com
in series through an attenuating resistor electrically in
pensate in the loudness level of the loudspeakers of both
terposed therebetween, a pair of variable admittance dis
charge devices connected to said respective channels -be 55 channels for changes over said extended period of time
in the average strength of sound signals in said one chan
tween the attenuating resistor and power amplifier in
. nel ahead of said control circuit therefor.
each channel, volume control circuit means coupled `to
7. A stereophonic recording player for playing stereo
only one of said channels between the voltage amplifier
and the attenuating resistor therein, -said volume control
circuit means including means'for continuously accumu
lating'an yelectrical charge in accordance with the signal
voltage at-the »output-of the voltage amplifier in said one
phonic recordings with automatic volume compensation
for different degrees of inherent loudness of different re
60 cordings, said player comprising, in combination, a stereo
phonic pickup having two outputs for two electrical sound
signals, meansV for moving a stereophonic recording in
channel, said» volume control circuit means including
association with said pickup to activate the latter to pro
means for dissipating the charge from said charge ac
cumulating means, said charge accumulating means and 65 duce stereophonic sound signals at the outputs thereof, two
voltage amplifiers connected to the respective outputs of
said charge'dissipating means being related to each other
said pickup, two attenuating resistors connected to the
to provide a charge in said charge accumultaing means
outputs of said respective voltage amplifiers, two elec
which is a function of the lsignal voltage at the output
tronic discharge valves connecting said respective resistors
of said one channel voltage amplifier over an extended
period of time, and means connecting said volume con 70 to ground, a volume control amplifier having an input
trol circuit -to both said Velectronic discharge devices to
connected to the outputof one of said voltage amplifiers
control the admittance of both devices in accordance with
ahead of the coacting one of said resistors, a rectifier con
the instantaneous charge accumulated in said charge
nected to the output of said volume control ampliñer, a
accumulating'means to produce in said -resistors in both
volume control resistor connected between the output of
channels simultaneous signal attenuating ‘effects which 75 said rectitier and both of said discharge valves to control
3,077,519
the admittances of both valves simultaneously in accord
ance with the voltage supplied from said volume control
resistor, two volume control capacitors connected between
opposite ends of said volume control resistor and ground,
said volume control resistor and said volume control ca
pacitors having effective values related to each other to
provide an integrated volume control Voltage which corre
sponds to an integrated averaging of the voltage output
of said volume control amplifier over an extended period
10
the output of both said channels at once in accordance with
the volume control voltage at the output end of said re~
of time of approximately ten seconds, two power am
pliñers having inputs connected to respond to the outputs
of said respective voltage amplifiers as modified by the
flow of current through the attenuating resistors asso
ciated therewith so that the output levels of both power
amplifiers are modulated simultaneously in accordance
with said integrated volume control voltage to compen
sate for prolonged changes in the average strength of
sound signals from the pickup output connected to said
one voltage amplifier, and two loudspeakers energized by
sistor to effect compensations in the output volumes of
both said channels for prolonged changes in the average
strength of sound signals supplied to said one channel from
the corresponding pickup outlet, and two loudspeakers
energized by the outputs of said respective amplifying
channels.
9. A recording player for playing stereophonic record
ings With automatic compensation for different degrees of
inherent loudness of the recordings played, said player
comprising, in combination, a stereophonic pickup, means
for moving a stereophonic recording in association with
said pickup to activate the latter, means forming two sepa
rate amplifying channels connected to said pickup to be
controlled by the latter, two loudspeakers energized by
said respective amplifying channels, two signals attenua
tors coupled with said respective amplifying channels to
control the outputs of the latter, a volume compensating
20 circuit having an output coupled to both said attenuators
the outputs of said respective power amplifiers.
in controlling relation thereto to impose volume control
8. A stereophonic recording player for playing stereo
on both of said channels simultaneously means coupling
phonic recordings with automatic compensation for dif
said volume compensating circuit to one of said amplifying
ferent degrees of inherent loudness of recordings played,
channels, and said volume compensating circuit including
said player comprising, in combination, a stereophonic
electrical integrating means for integrating over an ex
pickup unit having two outputs for two electrical sound 25 tended period of time electrical signals supplied to said
signals, means for moving a stereophonic recording in
compensating circuit and providing in controlling relation
association with said pickup to activate the latter to pro
duce stereophonìc sound signals at said outputs thereof,
to both of said attenuators an electrical output which is a
function of the average intensity over an extended period
means forming two separate amplifying channels con
of time of the electrical signals moving through said one
nected to the respective outputs of said pickup unit, two 30 channel and which serves through control of both said
signal attenuators coupled to said respective amplifying
attenuators to effect in the output levels of both said
channels, a volume compensating amplifier having an
channels automatic compensation for prolonged changes
input coupled to one of said channels, a rectiiier connected
in the average strength for sound signals supplied to said
to the output of said volume compensating amplifier, a
one amplifying channel from said pickup.
35
resistor connected to the output of said rectifier, two ca
pacitors connected between opposite ends of said resistor
and ground, said resistor and said capacitors having effec
tive values related to each other to provide an integrated
volume control voltage at the output end of said resistor 40
which corresponds to an integrated averaging of the level
of the input signal to said one amplifying channel over
an extended period of time, electrical control means cou
pling said resistor in controlling relation to both said
attenuators to operate the latter in unison for modifying
References Cited in the tile of this patent
UNITED STATES PATENTS
1,993,859
2,098,561
2,126,929
Roberts ______________ _.. Mar. 12, 1935
Beers ________________ _.. Nov. 9, 1937
Snow ________________ __ Aug. 16, 19,38
2,822,429
Watson __________ _,__,_.._.. Feb, 4, 19,58
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