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April 25, 1950
2,505,254
M. H. MESNER
TONE CONTROL CIRCUIT
Filed Sept. 7, 1944
70
Jb6P.C.
OF
7N
' I
ATTO R N EY
Patented Apr. 25, 1950
2,5105,254
T OFFICE
UNITED STA
2,565,254
TONE CONTROL CIRG
Max H. Mesner, Princeton, N. J., assignor tn Ptadio
Corporaition of America, a corporation of Delaware
Application September 7,1944, Serial No. 553,024
11 Claims. (Cl. 179-1111
My preseiit invention
1
2
conjunction wiili the adjustable element of
the tone control device.
generally. to freenGy discriminatory
and more parularly to a n improved audio fzequency tone
iri
nals in a wide range 01 frequencies. Furthermore, Lhe source of signals for the network may
cior output of a radio receiver, the
of apublic address system, the pickup
reproducing device, a n audio freC L E ~ C Y sipl?al distribution line or-even the video
signal transmission network of a -television r+
csiver. For $the.purpose-of the present application, however, it is assumed that the -source of
slgnd voltage is a n audio frequency voltage
source.
The nunzerai 1 designates an electron discharge
tube which is shown by way of illustration as
8 triode type. It is to.be clearly underof tube may be em20
e numeral 5 denotes the low potential or
ground lead of the input circuit. The cathode 6
of tube 1 is connected to ground th
usual grid bias network 7. The grid
sistor-8 is,connected from the output terminal of
folcondenser 3 to ground. The plate 9 of tube 1 is
30 comected to the +B terminal of a source of direct current (not shown) through the output load
resistor 10. Those skilled in the art of radio
communication are fully aware of ,the nature of
the direct current supply source -which may be
35 employed with a system of the type shown in
2j
connected to the g
tube whereby o
Fig. 1.
40
its input electrode or grid 12 connected to the
direct current blocking condenser 6 3. The input
terminal of the latter i s connected
best be
ead-of resistor I D . The cathode 14
connected to ground through the grid biasing
resistor 15, bypassed in suitable manner for alter60 naiing currents.
The direch current return resistor path for
grid 62 consists of resistor R1 and that portion
carried into effect.
of resistor R included between the grounded adIn the drawing
rejustable slider 16 and the lower end of resistor
55 R. The grid. return resistor path performs a
dotrhle function in my invention, and it is a n
my invention;
essential p a r t of the tone control device.
Fig. 2 shows various-respanse .curves secured
r end of resistor R is connected by
for various settfngs of thee
B ' P to the input ferminaltof condenses 13.
and
be seen, therefose, that adjustmept of
Fig. 3 iKlustra&s;a;diaI;mrh
45
2,605,254
4
3
slider or tap B Ei along resistor R varies concurcounterclockwise path of the potentiometer range,
higher audio frequencies are attenuated to a
rent$ the magnitlide 01 resi5tance in series with
greater or lesser degree depending 02 the amount
condenser 11 beheen the plate circuit of tube I
of resistance to ground that is placed in series
and ground, aiid also the magnitude of resistance
between the grid circuit of tube 1 1 and ground. 5 vJith condenser 17. For the higher audio frequencies the impedance of condenser C T plus the
The plate circuit of tube 1 t i s completed in the
resistance in series therewith becomes low encugh
usual manner. The signal voltage amplified by
tube 1 I is developed across load resistor 18. The
sufficiently to lower the plate load resistance 10.
amplified signal voltage transmitted to output
The impedance of condenser 17 at higher than
leads 19 will have its frequency response charac- !I? any chosen cut-off frequency should be nearly as
small as, or smaller than, the impedance of t i e
teristic dependent on the adjustment of slider 16.
The utilization means may be a loudspeaker, amload resistor 10. That is, of course, true f x
counterclockwise positions of slider $ 6 . This replifier or the like. By way 5f specific illustration,
the following values of the above-recited elements
duces the gain of tube I for the higher audio frehave been used in a successful embodiment of the ;i quencies.
The value of resistor R is chosen so that when
invention. My invention, however, is not limited
the slider 16 reaches the midpoint on R, the reto use of these particular values.
sistance in series with condenser 1’8 is sufficiently
Resistor IQ=33,000 ohms
high in comparison to the load resistance 1 i3 that
R1=lOO~OOO Ohms
y its shunting effect even a t higher audio 3cquenR = l megohm
cies becomes negligible. This midpoint on posiPlate resistance of tube B =8,000 ohms
tion 5 of indicatGr 20 is the “high fidelity” region,
‘Ondenser
1’1=0*025microfarad
where the tone control has no effect a t either the
‘Ondenser
L3=0*005 microfarad
high or low frequency end. This is best illusExplaining, now, the functions of the elements 2.5 trated in pig. 2 wherein the frequency response
curve corresponding to position 5 of indicator 20
of the tone control device, it is pdnted out that
the latter cons&tso; a simple potentiometer havPOSSeSSeS substantially uniform tranSmiSSiOII Of
audio freClUenCy currents above 100 cycles with
ing three terminals. atyo of these ternlinals a
arid b are connected
provide a variable attenuminimum attenuation of currents below 100
ation path for the higher audio frequency cur- 3!
If the slider 16 is moved closer to the lower end
rents. The thi1.d terminal c is connected to the
C Of the resistor R,that is clockwise, the resistlower end of the grid return resistor R ~ . The
ance from grid
to ground becomes less. For
values of coupling condenser 13, grid return rethe midpoint Position Of slider 16, the resistance
&tor R~ and the overall resistance R of the POtentiometer are SO chosen that the time constant ‘:? Of Ri PIUS half Of the resistance O f R is the factor
of the intertube coupling circuit is c:itically variwhich Controls the Value Of condenser 13. The
capacity Of condenser 13 is chosen so that the
able over half the range of the adjustable element 16.
time constant (i. e. the RC product) is great
enough t o J a S s low audio frequencies down to
The %tion of the tone control device
be
analyzed in the light of the experimental Curves !I) the lowest audio fRqUenCY required for high
fidelity. As the maximum clockwise position is
of Fig. 2 and the illustrative control dial of pig. 3.
reached the time constant b.ecomes less thereby
In Fig. 2 I have shown various frequency response
curves experimentally secured for various settings
causing the low frequency range to be curtai!ed.
At the extreme clockwke position of slider 16,
of the tone control adjustable element 16. “Response in decibels” is plotted against “Frequency J S that is Position 10 O f indicator 20 in Fig. 3, the
bass character is determined by the magnitude OP
.hcycles per second.”
CoUPling condenser 13 and resistor R1. The magIn Fig. 3 there is shown an illustrative dial that
may be used in conjunction wit11 the adjustable
nitude Of resistor RI is thus chosen to give the
maximum frequency range reduction required.
element 16. Let it be assumed that potentiomIt is Preferred to choose the magnitude O f Ri SO
eter slider 16 is rctated in an arc in sliding conthat it is COmparatiVelY large with relation to the
tact with the resistor R. In such case the indicator or pointer 25 would be mechanically coupled
load resistance 10. The reason for this relation
is that the tone control device will have a minit o element 16 for motion therewith. A t position
1 of slider 16 (extreme CQUnterclockwisepwition)
mum effecton the general Volume level. This can
the slider will be located at the upper end of re- Y’i best be accomplished by choosing the resistance
Of load 10 as low as the amplification require&tor R. At position 10 in Fig. 3 (extreme clockwise position) the slider is located at the terminal
ments W i l l allow. The impedance of condenser
c of resistor R. Position 5 of the indicator 20
13 at low audio frequencies should fie as great, or
greater than, that of Ri. Hence, at such frecorresponds approximately to the midway position of slider I 6 on resistor R. It will be noted 4’’ ~UenCiesthere will be a definite amount of voltage
that position 1 is the “Treble attenuation” point;
division a t the grid terminal.
position 5 is the “High fidelity” setting; setting
From the experimental curves of Fig. 2, it will
be seen that when slider f 6 is adjusted to posi10 is the ‘‘Bass attenuation” adjustment. Fig. 2
relates these three settings On the frequency retion 1 in Fig. 3 there will be maxiraum attenuasponse curves. Further, the response curves of ‘5 tion Of the higher audio irequencies, with no
Fig. 2 are numbered to correspond to the tone
effect on the lower audio frequencies. Adjustcontrol settings of Fig. 3.
ment to position 2 of Fig. 3 results in substanIt will be observed that when the slider 16 in
tially the same frequency response curve. SUCFig. 1 is adjusted to the upper end of resistor R,
cessive adjustments to positions 3 and 4 result
there will occur maximum bypassing of higher 70 in successive decrease of attenuation in higher
audio fFXlUenCieS. At the midpoint 5, as stated
audio frequency currents. In this position of the
before, there occurs optimum transmission over
slider the condenser 17 connects the plate circuit
of tube 1 directly to ground, and no portion of
the entire signal frequency range. Further adjustment of the slider to positions 8, 9 and 10
resistor R is included in circuit with the condenser. When the slider is adjusted in the 75 in succession results in increased attenuation of
’*
1
aftknuatibn of lower audio fIWUenpiing the plate end of said output load resistontrol device i0 ance to said control grid, a potentiometer havi ~ an
g adjustable contact connected to ground,
the median
setting.
a Second condenser of relatively low impedance
- to higher audio frequencies connected in series
from the plate end of said outDut load to one
16 end of saia potentiometer and through said cont
ground, a resistor OP fixed ma
‘C
d from ‘said control grid to th
e
aid potentlometer whereby said
gria is returned to ground through said fixed
magnitude resistor and a portion of said potenssion
tiometer, said fixed magnitude resistor befng
and
comparatively large relative to said output load
miresistance so that variation of said potentiome%er will have a minimum effect on the volume
and
and 25 level a t the output of the second amplifier tube.
output terminals being connected Go a common
5. In a system as defined in claim 2, said fist
etwork which in“condenser having an imQedance a t low audio fretor connected bewhich is ‘at least as great as the imof said resistor of fixed ma
tween said one input terminal and one end o i
system as defined in claim 2
a potentiometer having a n adjustable contact :so
ond condenser having a n impedance which, at
arm, and a fixed resistor connected betweelz said
higher than any chosen cut-off frequency, is a t
one output terminal and the other end of said
least as small as the impedance of said output
potentiometer, said contact arm being connected
load resistance.
to said common point.
7. I n combination with an audio frequency
2. In combination with an audio frequency 35
signal transmission network provided with a pair
signal amplifier tube provided with a n output
of input terminals and a pair of output termiload, a second amplifier tube provided with a t
nals and a coupling condenser connected beleast a cathode, a control grid and an output
tween one of said input and one of said output
electrode, a first condenser of low impedance to
high audio frequency currents coupling the 40 terminals, a n adjustable attenuation network
connected in shunt across the transmission netplate end of said output load to said control grid,
work, said attenuation network consisting of a
a potentiometer having an adjustable contact
compensating condenser having a relatively low
connected to ground, a second condenser of relaimpedance at the upper end of the audio fretively low impedance to higher audio frequencies
connected from the plate end of said output 4.5 quency range connected between said one input
terminal and one end of an adjustable potenload to one end of said potentiometer, and a retiometer resistor having a movable contact consistor of fixed magnitude connected from said
nected to the other input and output terminals,
control grid to the other end of said potentiomea second attenuation circuit including said couter whereby said control grid is returned to
ground through said fixed magnitude resistor 50 pling condenser, said coupling condenser having
a relatively low impedance to said high freand a portion of said potentiometer.
quency end of the signal frequency range, and a
3. In combination with an audio frequency
connection between said one output terminal
signaI amplifier tube provided with an output
and the other end of said potentiometer, the
load, a second amplifier tube provided with a t
least a cathode, a control grid and a n output 55 magnitude of the resistance included in said second attenuation circuit being directly dependent
electrode, a first condenser of low imoedance to
upon adjustment of said movable contact, and
high audio frequency currents coupling the plate
the impedance of said coupling condenser a t low
end of said output load to said control grid, a
audio frequencies being chosen to be nearly as
potentiometer having a n adjustable contact
60
great
as,or greater than that of the resistance inconnected to ground, a second condenser of relacluded in said second attenuation circuit a t any
tively low impedance to higher audio frequencies
,position of said movable contact.
connected in series from the plate end of said
8. In combination with an audio frequency
output load to one end of said potentiometer
signal amplifier tube provided with a n output reand through said contact to ground, a resistor 65 sistor, a second amplifier tube provided with at
of fixed magnitude connected from said control
least a cathode, a control grid and an output
grid to the other end of said potentiometer
electrode, a first condenser of low impedance t o
whereby said control grid is returned to ground
high audio frequency currents coupling the plate
through said fixed magnitude resistor and a porend of said output resistor to said control grid,
tion of said potentiometer, the overall resistance 70 a second condenser of relatively low impedance
value of said potentiometer between the ends
to higher audio frequencies connected in series
with a first variable portion of a potentiometer
thereof being very high compared to that of the
fixed resistor whereby the lower audio frequenresistor from the plate end of said output recies are not attenuated until after a substantial
sistor to ground, a resistor of fixed magnitude
portion of the resistance of said potentiometer is 75 connected from said control grid to said poten-
7
%,am,mrP
8
tiometer resistor whereby said control grid is re11. The combinaiton set forth in claim 1 In
turned to ground through said resistor of fixed
which the time constant of the resistance of said
magnitude and a second variable portion of said
fixed resistor plus one-half the resistance of said
Potentiometer with the capacitance of said COLIpotentiometer resistor, the overall resistance of
said ,potentiometer resistor being chosen very 5 pling capacitor is so related to the lowest frehigh compared to that of the fixed magnitude
quency of the signal frequency range that said
resistor whereby the lower audio frequencies are
lower frequency is passed through said network
not attenuated until after a substantial portion
substantially without attenuation.
of the resistance of said potentiometer resistor
MXX H. MESNER.
is included in series with the second condenser 10
REFERENCES CITED
to ground, said fixed magnitude resistor also being large compared to said output resistor.
The following references are of record in the
9. The combination set forth in claim 1 in
file of tihis patent:
which said compensating capacitor has a relaUNITED STATES PATEINTS
tively low impedance at the high frequency end 15
Number
Name
Date
of the signal frequency range and in which the
Aceves ____________ Dec. 18, 1934
1,984,450
overall resistance value of said potentiometer
is such that when said contact arm is centered
2,065,344
Newton ____________ Dec. 22, 1936
Dyksterhuis
Jan. 5, 1937
on said ootentiometer the resistance in series
2,066,676
Lansing ___________ Jan. 26, 1937
with said Compensating capacitor is sufficiently 20 2,068,685
2,113,332
Morse et al. ________ Apr. 5, 1938
high that the loading effect of said compensat2,121,150
Jarvis ____________ June 21, 1938
ing capacitor on said network is neligible.
2,264,715
Rohr _______________ Dec. 2, 1941
10. The combination set forth in claim 9 in
2,433,330
Atkinson __________ Dec. 30, 1947
which the time constant of the resistance of said
fixed resistor plus one-half the resistance of said 25
FOREIGN PATENTS
potentiometer with the capacitance of said couNumber
Country
Date
pling capacitor is so related to the lowest fre699,749
Dec. 16, 1930
France _____-______
quency of the signal frequency range that said
lowest frequency is passed through said network
substantially without attenuation.
30
________