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Патент USA US2137633

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Nov. 22, 1938.
A. c. sTocK‘ER
y
- 2,137,633
LOW FREQUENCY TONE CONTROL SYSTEM
Filed March 51, 193'?
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' FREQUENCY
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Gttorneg
2,137,633
Patented Nov. 22, 1938
UNITED STATES PATENT OFFICE
2,137,633
LOW FREQUENCY TONE CONTROL SYSTEM
Arthur C. Stocker, Haddon Heights, N. J., assign
or to Radio Corporation of America, a corpora
tion of Delaware
Application March 31, 1937, Serial No. 134,108
(Cl. 179-171)
'l Claims.
indicated at I2. The coupling capacitor for the
resistance coupling network is indicated at I3
and serves to convey signals to the grid circuit
I4 of the second stage 6, through a low frequency
. They present invention relates to a low fre
quency tone control system for an audio frequen
cy amplifier’ or signal transmission channel, and
has for its object to provide an improved tone
tone control network comprising a shunt circuit ,v
5 control system of that character wherein a min
imum- number of low cost circuit elements are
provided and which is not restricted to close tol
erances in the electrical values of said circuit
elements.
It is also a further object of the present inven
10
tion, to provide a low frequency tone control sys
connected across the audio frequency channel or
output circuit of the tube 5 through said cou
pling capacitor.
ometer control means, both attenuation and aug
The shunt circuit comprises two series resistors
I5 and I6 with a capacitive reactance in series
between them and provided by a capacitor I1.
A potentiometer device I8 is connected in par
allel with the capacitor I1 and the movable con
tact I8 thereof is connected to the grid circuit I4.
mentation of the low frequency end of the audio
frequency response range of the amplifier may
a grid supply filter comprising a series filter re
tem- for audiov frequency amplifiers and the like,
wherein, through- the medium of a single potenti
be provided.
Grid bias potential is applied to the grid through 15
‘
It is a still further object of the present in
vention, to provide a low frequency tone control
system which is adapted for use as a grid circuit
attenuator and as part of an interstage coupling
network» which includes a single control means
for attenuating and augmenting the low fre
quency portion of the response characteristic of
the amplifier.
The invention will, however, be better under
stood from the following description, when con
sidered in connection with the accompanying
drawing, and its scope will be pointed out in the
30 appended claims.
sistor I6. An audio frequency by-pass capacitor
23-is connected between the terminal 22 and chas
sis or ground-.24. The audio frequency circuit is
completed to cathode of the amplifier Ii through a
ground connection indicated at 25.
The .tone control network comprising the re
sistors I5, I6 andv I8 and the capacitor I1 is an
attenuator, the attenuation of which varies with
frequency, and the manner of this variation be
ing controllable by the resistor or potentiometer
I8. The values of the resistors I6 and I5 and
of the capacitor I'I determine the amount of low v _
In the drawing,
frequency correction and the highest frequency "
Figure l is a schematic circuit diagram of an
affected. r͑he control resistor or potentiometer
audio frequency amplifier having an interstage
coupling network embodying the invention,
35
sistor 20 connected between a bias supply lead
2| and the low potential terminal 22 of the re
Figure 2 is a graph or vector diagram illustrat
ing the amplitude relation between potentials
developed in the coupling network of Fig. 1,
I8 has no function other than that of control so
long as its total value is several times greater
than the reactance of the capacitor I‘I at the low
est 'frequency to be considered.
v
Assuming the resistances of the resistors I6, I8
Figure 3 is a graph showing curves illustrating
and I5 tobe R4, R5 and Re respectively and the
the operating range and tone control characteris
tics of the low frequency tone control network of
reactance of the capacitor I1 to be C3, the latter
Fig. 1, and
.
Figure 4 is a similar graph showing curves il
lustrating the low frequency response character
istic in percentage, for the limits of the control
range provided by the circuit of Fig. 1.
Referring to Fig. 1, 5 and 6 are first and second
stage audio frequency amplifier tubes provided
with an interstage coupling means which may be
of any suitable type and which, in the present
example, is of the resistance coupling type hav
-ing a plate resistor 'I in the output circuit 8 of
the first stage 5 and a plate supply filter com
prising a series resistor element 9 and shunt by
pass capacitor l0 to chassis or ground I I between
55 the plate resistor 1 and the anode supply lead,
is designed to be relatively small compared to the,
resistances RL; and Re when'the applied signal ’
frequency is above a predetermined high value,
that is,- above the low frequency tone control
ran/ge desired. Then the voltage
‘
evERrI-Re
approximately and is independent of the setting
-of R5, assuming that the alternating current
potential- applied to the tube 6 is indicated at e, .
and that the available signal. potential from the
first stage amplifier is indicated at E.
As the >frequency of the signals transmitted
through the amplifier is reduced, the voltages
across Rl; and~ Re drop' and that across Cs rises,
2
2,137,633
the vector sum always being equal to E. The dis
yond the range of operation normally utilized
tribution is substantially as shown in Fig. 2 where
in a and c represent the voltages across R4 and
in an audio frequency amplifier.
From the shape of the resulting curves in Figs.
3 and 4, it will be seen that the low frequency
response characteristic may be varied between
relatively wide limits to increase or decrease the
Re (R4 being somewhat larger than Re in this
case), and b` represents the voltage across C3.
The voltage e is then the vector sum of a and a
portion of b, the portion being determined by the
low frequency response continuously, by opera
setting of the contact I9 on R5.
The value of e may vary from a to e5 in Fig, 2,
as the potentiometer contact I9 is moved from
tion of the single contact I9.
In any circuit, the reactance of the capacity
C3 to signal frequencies above the range in which
low frequency tone control is desired, is made
relatively low with respect to the series resist
the lower potential end of the resistor I8 through
to the higher potential end thereof. With the
contact I9 at the lower potential end of the tone
control resistor I8, thereby including only the re
15 sistance R4 in the grid circuit, the voltage a will
be equal to the Voltage e and it is obvious that
the frequency characteristic of the output will
drop at the lower frequency end of the audio fre
quency range. The ratio of the voltage e to the
20 Voltage E is shown in Fig. 3 with respect to fre
quency and in this case
ances R4 and Re on either side of it in the shunt
circuit. As has been pointed out, the resistance
of the shunt potentiometer is preferably substan 15
tially greater than the reactance of the capacity
C3 at the lowest frequency in the range of fre
quencies to be controlled.
This system permits selection of either an at
tenuated, a fiat, or an augmented low frequency 20
response without recourse to resonant phenomena
or complicated circuits.
When the resistors R4 and Rs in the tone con
trol circuit are of the same order or lower than
When the contact I9 is moved to the upper or
high potential end of the tone control resistor
I8, it is obvious that the frequency characteristic
of the output will rise at the lower frequency end
of the audio frequency range. This is also shown
30 in the curve of Fig. 3 and the voltage ratio is
25
The low frequency limits in either case are
35 indicated in Fig. 3 by the lines 30 and 3l and the
shape of the response characteristic for attenuat
ing the low frequency end of the audio frequency
range isindicated at 32 while the augmentation
of low frequencies provided is indicated by the
40 curve 33. The normal high frequency response
or limit of response is indicated by the line 34.
If the contact I9 is moved to provide the vector
voltage e3 of Fig. 2, the voltage e will not bevaried,Í by the variation in frequency of an ap
45 plied signal. This may be seen by referring to
Fig. 2 wherein, at infinite frequency,
8
the output coupling resistor 1 in the preceding 25
stage, the latter is unloaded as the frequency of
the transmitted signals is lowered. This is for
the reason that the reactance of the series ca
pacity C3 rises, then by decreasing the shunt
load created by the circuit R4-C3-Re across the 30
resistor 1.
The effect of this is to cause E to rise and
thereby augment the low frequency response.
From the foregoing description, it will be
seen that a low frequency tone control network 35
may be provided as an interstage coupling means
and may be operated by a single control element
to attenuate or accentuate low frequency response
in a predetermined frequency range without ap
preciably affecting the high frequency- response. 40
Furthermore, as above pointed out, by the var
iable loading effect the low frequency response
may be increased automatically as the frequency
of the transmitted signals is lowered.
'
l claim as my invention:
45
l. The combination with an audio frequency
signal transmission circuit, of a low frequency
tone control network connected in shunt with
said circuit and comprising two resistance ele
ments of the order of the resistance of the 50
transmission circuit connected in series between
the high and low potential sides of said circuit,
means providing a capacity in series with and
connected between said resistance elements, the
capacitive reactance thereof being relatively low
with respect to the resistance of said resistance
50 and lies along the vector E. As the frequency is
reduced the junction of vectors a and b moves
to the right and down following a semi-circular
path to “0” at zero frequency. The junction of
the vectors b and c moves to E. The vector b
55 always crosses the vector E at the same place,
the Vector b swinging around this point and
the two ends of the vector b remaining always . elements in a higher frequency range above a
in the same ratio. If this ratio is that chosen predetermined upper limit of the low frequency
by the contact I9 on the resistance R5, e will tone control range, an output circuit, and means
including a potentiometer device directly in shunt
remain a constant portion of E regardless of fre
with said capacity means for variably including
quency.
The limits of response of the low frequency said capacity means in said last named circuit.
2. The combination with an audio frequency
control means thus provided is indicated in Fig.
e by the curves 35 and 36. It is not necessary to signal transmission circuit, of a low frequency
65 maintain the resistance of R5 higher than the tone control network connected. in shunt with
reactance of the tone control capacity C3 at all said circuit and comprising two resistance ele
frequencies, although in the present example ments of the order of the resistance of the trans
and as a preferred arrangement in the network mission circuit connected in series between the
shown, R4 and Rs are made equal to 10,000 ohms, high and low potential sides of said circuit,
70 and with a capacity at C3 of .1 mfd. the resistor means providing a capacity in series with and
R5 has a value of .5 megohm. 'I'he effect of using connected between said resistance elements, the
a lower resistance at R5 is to lessen the slope of capacitive reactance thereof being relatively low
the response characteristic at the low frequency with respect to the resistance ofA said resistance
end of the response range which gradually is re
elements in a frequency range above a predeter
75 duced to zero at some very low frequency be
mined upper limit of the low frequency tone con-
60
65
70
75
3
2,137,633
trol range, whereby the shunt load on the trans
mission circuit is reduced with decreasing fre
quency, thereby augmenting the low frequency
response.
3. The combination with an audio frequency
signal transmission circuit, of a low frequency
tone control network connected in shunt with
said circuit and comprising two resistance ele
ments of the order of the resistance of the trans
10 mission circuit connected in series between the
providing tone control means in said input cir~
cuit, said network including a coupling resistor
for applying audio frequency signals across said
last named circuit, a pair of resistance elements
having a resistance value not greater than said
coupling resistor and connected in series in said
last named circuit, a capacity element in series
high and low potential sides of said circuit,
with and connected between said resistance ele
ments, and a tone control potentiometer con
nected in shunt with said capacity element and 10
having a variable output contact connected with
means providing a capacity in series with and
said ampliñer tube to apply signals thereto.
connected between said resistance elements, the
capacitive reactance thereof being relatively low
15 with respect to the resistance of said resistance
elements in a frequency range above a predeter
mined upper limit of the low frequencytone con
trol range, a potentiometer resistor connected
in shunt with said capacity means having a re
20 sistance relatively high with respect to the re
actance of said capacity means at the lowest fre
quency in said tone control range, an output con
tact movable along with potentiometer resistor,
and a signal output circuit connected with said
25 contact and the low potential side of the signal
transmission circuit.
4. The combination with an audio frequency
signal transmission circuit, of a low frequency
tone control network connected in shunt with
30 said circuit and comprising two resist'ance ele
ments of the order of the resistance of the trans
mission circuit connected in series between the
high and low potential sides of said circuit,
means providing a capacity in series with and
35 connected between said resistance elements, the
capacitive reactance thereof being relatively low
with respect to the resistance of said resistance
elements in a frequency range above a predeter~
mined upper limit of the low frequency tone con
40 trol range, an output circuit, and means includ
ing a potentiometer device directly in shunt with
said capacity means for variably including said
capacity means in said last named circuit, so that
the output response characteristic at the low fre
45 quency end may be varied from a fraction of the
input voltage indicated by
6. In an audio frequency ampliñer, the com
bination with an amplifier tube having an input
grid circuit, of an interstage coupling network 15
providing tone control means in said input cir
cuit, said network including a coupling resisto-r
for applying audio frequency signals across said
last named circuit, a pair of resistance elements
having a resistance value not greater than said 20
coupling resistor and connected in series in said
last named circuit, a capacity element in series
with and connected between said resistance ele
ments providing reactance relatively low with
respect to the resistance of said resistance ele 25
ments in a frequency range above a predeter
mined low frequency, and a tone control poten
tiometer connected in shunt with said capacity
element and having a variable output contact
connected with said amplifier tube to apply sig 30
nals thereto, said potentiometer having a resist
ance relatively high with respect to the reactance
of said capacity element at the lowest frequency
to be controlled.
7. In an audio frequency amplifier, the com 35
bination with an amplifier tube having an input
grid circuit, of an interstage coupling network
providing tone control means in said input cir
cuit, said network including a coupling resistor
for applying audio frequency signals across said 40
last named circuit, a pair of resistance elements
having a resistance value not greater than said
coupling resistor connected in series in said last
named circuit, a capacity element in series with
and connected between said resistance elements 45
providing reactance relatively low with respect to
the resistance of said resistance elements in a
E_Ri-i-Rs-l-Rß
frequency range above a predetermined low fre
î
RVi-R5
nected in shunt with said capacity element hav 50
lng a variable output contact connected with said
E
R4+R5+Rß
to
50
,
where Eis the signal input voltage, e is the signal
output voltage, R4 and Re are the resistance of
the series connected resistance elements, and R5
is the resistance interposed across the capacitive
reactance.
5. In an audio frequency amplifier, the com
bination with an amplifier tube having an input
60 grid circuit, of an interstage coupling network
quency, and a tone control potentiometer con
ampliñer tube to apply signals thereto, said po~
tentiometer having a resistance relatively high
with respect to the reactance of said capacity
element at the lowest frequency to be controlled, 55
and means providing' a low impedance signal
path to ground each for the low potential end
of said coupling resistor and one of said series
connected resistors.
ARTHUR C. STOCKER.
60
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