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Патент USA US2133816

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Oct. 1s, 1938.
Filed Dec. 2l, 1934
2 ShQeiî'S-Sheail l
m232.5 _
oct. 18, 193s.
P. F. G. HoLsT
2 sheets-sneek 2
Filed Deo. 21, 1954
‘ .Paul FG'. Holst
Patented Oct. 18, 1938~
APoul F. G. Holst, Audubon, N. J., assignor, by
mesne assignments, to Radio Corporation of
America, New ÍYork, N. Y., a corporation of
Application December-21, 1934, serial No. 758,602
7 Claims.
(Cl. Z50-20)
, The present invention relates to toner control
systems for radio receiving apparatus andthe
like, and has for its principal object to provide
an improved tone control` system havinga rela
tively sharp variable low frequency cut-01Tv char
It is a further object of the present invention
to provide an improved tone control system pro
viding high pass filter means >for an, audio >fre
10 quency signal circuit having a variable low fre
quency cut-oiT-characteristic.
It is also an object of the present invention to
provide, in radio receiving apparatus, an audio
grams of a portion of the circuit shown in
illustrating various connections :for diifering
conditions of operation thereof, and
Figs. 5 and G-are curve diagrams illustrating
certain frequency-response characteristics> of 5_
the circuits of Figs. 1 to4, inclusive.
Referring to Fig. 1, II is a radio receiver or
other source of signals having an audio fre
quency transmission channel or circuit, repre-y
sented by leads I3 and I5 forming the output
circuit in the present example, of a detector tube
I1 and being coupled through suitabletransf
frequency signal circuit having. variable low f-re
15 quency tone control means providing relatively
former coupling means I9 with .-a .plurality of
sharp low frequency lcut-off characteristic> and
pliiier indicated at 23 with an output device such
means responsive to a change in an` operating
condition of the apparatus, such as -wave band
change, for changing the range ofk control of said
control means.
f .
It is a still further object of the present in
Vention to provide, in an audio frequency signal
transmission circuit, combined tone‘and volume
control means providing variable low pass filterv
means and variable high pass ñlter means,
" whereby the frequency characteristic-- of said
system may be varied betweenA wide limits. ~ .
It is also a further object of the present in
vention to provide, in an audio frequencysignal
transmission circuit, low frequency tone control
means comprising high pass ñlter elements, one
of which is Variable, and high frequency tone
control means comprising ’low pass filter ele
ments, one of which is variable, in conjunction
35. with interstage coupling means'andvolume con
trol means for said signal transmission circuit.
It is also an >object of the present invention
to provide, in an audio frequency signal trans
mission circuit, a ñlter network having a varia
40. ble element providing low frequency tone con
audio frequency amplifier vtubes 2|. Y'I'he tubes
2|, in turn, are coupled through a `suitable am
as a loud speaker, indicated at 25.
The audio frequency transmission circuit
I3-I 5 is provided with shunt volume control po
tentiometer means comprising a resistor 21 con
nected in output
shunt across
tap 29.
the 'I‘he
and having
means is preferably compensated by suitable
shunt circuits indicated at 3| and 33 for control
ling the tone with volume, and for that reason
the receiver II is preferably provided with auto
matic volume control means as indicated bythe
'I‘he receiver II also, is preferablyiprovided
with sensitivity Vcontrol means indicated at 35.
and in present receiver Vconstruction may-also 30
embody a wave band selector means :indicated
at 31 whereby the receiver is selectively adjust
able for receiving signals over a plurality of dif
fering wave bands.
‘I'he detector anode circuit, indicated at 39, is
suitably coupled to the audio frequency trans->
mission circuit I3-I5 through an anode cou
pling resistor 4I and condenser 41. Anode po
tential is supplied through a ñltercomprisinga
variable element- providing high frequency tone- series resistor 43 and a shunt by-passvconden
trol means, a second ñlter network having a
control means, and volume control means in'
terposed in said circuit between said first and
Interposed in the audio frequency transmis
sion circuit, between the coupling condenser 41
and the volume control resistor or potentiometer 45
second named means whereby they are operable
in the same circuit.
21, is a ñlter network comprising a series con
The invention will, however, be better under- ' denser 49 of relatively lower capacity thanrthestood from the following description when con
sidered in connection with the accompanying coupling condenser 41 and two series connected
50 drawings, and its scope will be pointed out in the impedance elements arranged in shunt. across
the circuit between the coupling condenser 41 50
appended claims. In the drawings,
l _
Figure 1 is a schematic circuit` diagram'of a and the series condenser Y49 as indicated at 5I
and 53. The .element 5I is a resistorvof relative
radio receiver showing an embodiment of thein
ly high value arranged to provide .a potentiom
eter between a terminal indicated at A con
Figs. 2, 3, and 4 are fragmentary circuit dia~
nected with the transmission'circuit between
adjusted between the limits indicated by the
the two condensers and a terminal B connected
with one end of the element 53. The latter ele
ment is an audio frequency choke coil having
its opposite end connected as indicated at 55
curves A and B by adjustment of the contact 51
along the potentiometer resistor 5|.
It should be noted that in the position B shown
Fig. 3, the series condenser 49 is the controlling
with the lead I5 which is the low potential side
series element since it is relatively lower in ca
of the transmission circuit. In the present ex
pacity than the Ycoupling capacity 41„ while in the
ample the coupling elements comprise the con
position indicated in Fig. '2 the coupling condenser 41 which may have a value of substan
tially .25 mfd. While the series condenser 49 mayy denser 41 is the controlling series element and its 10
capacity determines the low frequency response
10 have a Value of .025 mfd. The resistor 5| mayv of the system.
have a resistance value of about 200,000 ohms
From the ‘foregoing description it will be seen
and the choke coil 53 may have a value of `ap
proximately 13 henries and about 1500 ohms that the .series circuit capacitor or condenser 49
.is short-.circuited-and a suiiicient resistance is put
D. C. resistance.
in series with the -inductance 53 to render its
elements 5I and 53 are connected in shunt with load across the circuit negligible, with the con
tact 51 at the terminal A, and that when
the audio frequency signal transmission circuit -the
'arm `51 is placed "in the position B, the re
across the input side of the series condenser 49, the
is placed across the condenser 49 and is
resistor element being connected adjacent tothe
suñiciently high to make the impedance of the
element `53’being connected Ladjacent to the low parallel combination ’5i -49 almost completely ca
pacita‘tive, lwith the impedance `of the choke coil
potential side or lead I5. The resistor 5I is pro
53 `shunted across_the volume control resistor '21
vided with a _movable ycontact indicated at ‘51, or
acrossïthe audio ireq-uency ‘transmission circuit,
which i's connected "with the -'output side of the
-a high -pass filter --variable be
series `condenser` s`49 and ‘with 'the high potential
side or lead I3jas -indicated at 59. _
tween relatively wide limits and having ~a rela
tively sharp low `frequency »cut-«o'if characteristic
With -'this arrangement, the'conta‘ct 51 fis ~mov
able between ‘the -terminals A and B vto variably
short circuit 'the condenser «49 as «it is moved
in the minimum low frequency response position.
-`On ‘the Aoutput ‘side »oi 'the volume control means
21-’29 a low A-p'ass filter 'arrangement is provided
30 toward the terminal A 'and'to place 'the choke coil
53 effectively across ‘the output side of the con
having a variable element providing l'iigh'jire
quency'tone control lmeans. ‘This is `provided by
a `choke coilï63 ‘in fs‘er-ies l:wi'tli'the p'rimaryf65 Iofthe
transformer îI9 Aand =a -shunt'lc‘ondenser 51 con
nec'tedïacross the secondary> 69 -of the transformer
denser v4'9 lwhen the -contact 'is moved toward 'and
to ,the Vterminal 2B. '
-The effect Áof this control means on 'the trans
mission xcircuit 'will’ïbe seen by reference «to Figs.v
2 and ‘3 along ‘with Fig. l, like parts _in said figures
through ia variable high lresistance ".I I .
bearing the same reference numerals as in Fig. 1.
Fig. '2 represents the Vcondition oi -the circuit
when the contact '51 Vis -moved to ïth'e position A,
short-circuiting the i'condenser 4 9, as ’indicated’by
the’bridgïing lead "`6'Iv inFig. '2, fand ì placing the 're
sis'tor 5I Tully ‘in "series with :the ¿choke ‘coil >53,
thereby rendering ’the latter 'as well 'as ‘the -vcon
quency characteristic oi »the ytransmission circuit
and l‘giving’maximum lo'w frequency 'transmission
eñiciency. " The transmission e'iiiciency, -further
more, is indicated in Fig. 5 by the curve A plotted
between 'the 'coordinates indicated and taken with
' a given 'input potential >at vthe detector ‘measured
50 across 'the ’terminals of the volume 'control po
te'n’tiome'ter '21.
When the conta'ct251'is 'moved to the'posîtion B,
the circuit ’then fassumes ‘the connections indi
cated in Fig. 3 wherein the choke lc'oil 53 is moved
55 to the loutputside of 'the series’condens'er 49 fdi
rec‘tiy inshunt :across the :signal transmission-'cir
cuit, and fthe »series :condenserf49 is shunted by‘a
relatively> high resistance provided "by ‘the re
60 sistance element Í5‘ïI whichl ¿is ‘substantially Einei‘f ec
tive "to 'change'the leffect -of ’the condenser in the
shunt with' thefsecondary.
"Iiheihigh 'frequency response peak "is 'indicated
at L "in Fig. l`6 Ion ‘fthe 'curve '71, and is desirable in
denser substantially ineiïect'ive tocontrol 'the fre
capacity >.may be provided `îby fa -'sh-unt >condenser
indicated 'at T13. The arrangement is 4such that
the coil is‘resonated Yat-'a high 'frequency peak-and
this may be reduced byrdecreaïsfing îthe resistance
of ~:the ‘resistor ‘1'I to place fthe _condenser ‘61 "in
The result is such that the low frequency
signals ¿through the transmission circuit are not
only fattenua'tedïby ëthe series element 49,'but are
'further Lattenuated'by the shunt `velement "53 which
in conjunction 'with the series condenser l49 pro
Vides a’highlpass filter, the ‘frequency character
istic'of which is indicatedfbythecurve B in "Fig. 5.
'It will -be noted that “a llarge percentage ‘of the
70 low frequency response y*of the _circuit lis'cut ofi
and thatv the 'slope of the'jcurveB is ‘relatively
sharp, asis desirable. Thisis for the reason that
the circuit is then arranged substantially as .a
high pass iilter in the audio frequency trans
75 mission circuit. The 'effect oi the ñlter may be
the audio lfrequency transmission 7chara‘cter'istic
ofthe system to'compensa'te îor‘îthe attenuation yoi
the high rrequencyfend 'of the range inthe 'radio
circuits. ’The `iow ifrequency ypeak caused bythe
loud -"speaker is aiso'indicated atîS Y'on the curve 11.
‘The four-ve T.1 ’represents »a :condition o'f `maxi
mum high :and low ¿frequency response through
the audio »'-irequency transmission circuit, `with
the low> îirequency iton'e lcontrol means 51 vad
justed fin the position A land 'the 'resistance ‘TI
Wholly'in I‘circuit 'infserïies with 'the condenser YB1.
The effect-of »reducing the'low'i-re'quency :response
by operation fof ‘the »contact ‘5W ‘tothe position B
is shown 'by îthe dash and »double dot line curve
19 while the effect lupon the Joverall response of
reducing ¿the resistance 'o'f 'the resistor ‘-1`I lto ‘zero
is shown -'by 'the dash Iline curve 8l.
>The effect of reducing ‘both 'the high and low
.frequency controls for minimum ‘low Aand high
frequency response `Iis indicated by the >dash and
dot ‘line’curve ¿83. l*It will‘thus ‘be >seen that com
plete control of the audio frequencycharacteris
tic Eoi ¿the "transmission system may 'be lobtained
'by 'the two iilter'networ‘ks 'interposed in the cir
cuit'on opposite'sides-oif‘the volume control means .
S21-*29. 'Separate control means, 'as indicated by
the control knobs ‘85, >'81',and’89, -are provided ¿for
varying tone controls and Volume. The choke
coil B3 in series'with the‘primary ofthe coupling
transformer I9, together with the Variable .re
sisitor vand ’series `condenser 1'1-61 provided
2,133,8 1 6
across'y the secondary ‘of 1 the 'said ’ transformer;
provides a low pass filter with a variable- :high
frequency cut-off, characteristic- on the output
side of the volume :control -means for .the 'audio'
frequency transmission circuit. Signals of- sub
stantially constant average amplitude are sup
plied to the detector from the receiver having
automatic volumek control means andthe volume
and frequency characteristic thereof may be ad
10 justed by the low and high frequency tone con
trol means and the» interposed volume‘control
In connection with ajmulti-wave receivenit
has been found 'that it is desirable to limit the
control range of the low frequency tone control
means or ñlter network when receiving signals in
certain ofthe higher frequency bands; It has
further been found that the range> of 'low fre-à
quency tone control may be reduced by maintain
20 ing the high pass filter- in the circuit as a perma
nent part thereof and permittingonly the series
condenser element to be varied.-~ This is provided
in the circuit of the present example by provid
range may be .reduced with? increase kkin ‘the frequency response of therec'eiven'the waveband
selector 31 may be connected by suitable means
indicated -by the dottedline '95, ‘with the switch >
93»to 'be operable therewith or thereby.-
kIn the present example, the switch 'is provided
with five contacts 91 corresponding to ñve dif
ferent vwave. bands, the wave bands'over which
compensation vfor Vthe low frequency response is
desired being connected in circuit by the arm 99 10
of the switch, with the choke coil and contact 51
through leads ~|.0|‘. The switch 93 thus provides
' selector means for connecting lthe contact 51 with
terminal B, thereby changing the low -frequency
cut-off point of the high pass filter and vlimiting 15
the low `frequency tone control range for certain
of the receivedwave bands. By connecting the
switch with the wave band-selector, the low fre
quency tone control >range is automatically -ad- ,
J'usted with the wave band.
In the foregoing description it will be seen-that
.in an audio frequency transmission system a low
frequency tone 'control filter may be provided
comparatively few changes inthe> circuit and
necting the _contact 51 with the terminal 13r of
the'series resistor 5| whereby the choke coil 253 . that likewise the high frequency tone control
filter may be added and thaty it isparticularly
is permanently connectedacross the `audio fre
adapted-to a transmission circuit having therein ~
quency transmission circuit onthe output side of »
ing suitable means such as a switch Y93 for, con
the series condenser 49. l Adjustment of the con
30 tact 51 along the resistor 5|
vthen serves to vary
the relative series effect in the circuit of the
_ series condenser 49 with respect tothe coupling
a,shunt1vo1ume control means, the one filter be
ing `connected on one side thereof and the other
on theopposite side of said volume control means
whereby all three controls are operable in the
same circuit independently of each` other.
condenser 41, the latter being eifectiveto control
In the present example a series coupling con
the circuit when the resistor 5| is substantiallyv
n denser of relatively largevalue _is followed by a'
out of circuit, the contact 51 being in the posi
tion A and the choke coil 53 remainingin shunt, series condenser of relativelylower-value ina
variable high pass filter arrangement comprising
across the volume control resistor 21 or across
theaudio frequency transmission circuit on the
output side of the series condenser 49.
It will be noted that with the contact 51 in the
position B and with the switch 93 closed, the same
condition exists in Fig. 4 as exists in Fig. 3 for a
minimum low frequency response, and the system
is adjusted to operate in accordance with the
curve B of Fig. 5, or the curve 19 of Fig. 6,
measurements being taken at the loud speaker
for the latter curve instead of at the volume con
trol terminals. However, as the resistor 5| is
short-circuited gradually across the condenser 49
50 the low frequency response is increased because
of a reduction in the series impedance in the cir
cuit presented by the condenser 49 and the re
sponse characteristic of the system reached that
indicated by the curve C of Fig. 5 showing that
the low frequency tone control has been reduced
from the limits A-B to the limits C_B.l In
other words, the low frequency response of the
system is reduced to a new and higher low fre
control means comprises a series choke vcoil in
the primary of an audio frequency coupling
transformer lto reduce the high frequency re
sponse peak tol a value within the desired audio
frequency range and a shunt condenser provided
with series variable control r>means across the
transformer secondary.
While my invention has been illustrated and
described in connection with an audio frequencyY 50
signal circuit for a radio receiver, it is not limited
thereto but may be applied to any audio frequency
signal circuit requiring either or both, high and
low frequency tone control, in conjunction with
the loud speaker, and limitation of the low fre
quency tone control range for certain conditions
quency limit, and this has been found to be de
sirable to prevent howl, that is, acoustical feed
back, and low frequency cabinet resonance in
high frequency all-wave receivers. The acous
of operation. To this end the control means 93
may be actuated manually or by any other suit
able means.
tical feedback may result, as is Well known,
through vibration of the various parts of the re
1. In a multi-wave radio receiver, the combina
- ceiver by sounds from the loud speaker.
disturbances and beat notes at low frequencies
are also reduced by this means.
The effect upon the overall response of the
receiver of the adjustment C of Fig. 5 is shown
in Fig. 6 by the curve |93. It will be noted that
while the loud speaker response peak is pre
dominant, it is materially reduced to a relatively
low level, as indicated at S', in comparison to the
high frequency response peak L.
a resistor and a choke coil vin series across the
transmission circuit on'the input side of the lcon
denser between the high potential and the low
potential sides of the circuit. The contact on fi()
the resistor is connected with the output side of
the series condenser, and the high frequency tone
I claim as my invention: '
tion with an audio frequency signal transmission
circuit, of a condenser in series and a choke coil
in shunt with said circuit providing a high pass
filter means therein, and variable control means
connected with said condenser and choke 'coilî
for gradually rendering said condenser effective ,
in said circuit as a series impedance element and
said choke coil as a shunt impedance element on
the signal output side of said condenser, means
for limiting the range of control of said last
named means, wave band selector means, and
In order that the low audio frequency response ,
means providing a connection between said last
named meansfand saidvlimiting‘meansfor simul~
taneousoperation therewith.
H2. 'I‘he `combination With 'a radio receiver, of
signal waveband selector means, variable low
frequencytone control meanshaving a predeter
mined‘tone control range of variation for one
Wave band, and means simultaneously operable
with and bysaid Wave band selector means vfor
limiting the effective ’frequency range of. control
10 provided by variation of said tone control means
for another Wave band.
3. In a radio receiver, the 'combination with
signal Wave band changing means, of manually
variable electrical circuit means'for varying the
15 low frequency response lcharacteristic of said re
ceiver within a predetermined frequency range
for one Wave band, and means connected with
and operable by said wave band changing means
for limiting the effective frequency range of con
20; trol provided by variation of said second named
means for another wave band.
4. In a radio receiver, the combination with
Wave band changing means, of means for vary
ing the low frequency response characteristic of
25,. said'receiver, said means lcomprising an audio
frequency transmission circuit, of a condenser in
series and 'a choke coilconnected in shunt with
said circuit providing a high ‘pass filter means
therein, variable control means connectedwith
30 said condenser and choke coil for gradually ren'
dering said >condenser effective in >said circuit as
a series impedance element and said choke coil
as a shunt impedance element on the'signal out
put side of said condenser, and -means connected
35 withV and' operable by-said Wave band changing
means 'for limiting the range of variation of said
second named> means. ~
~ 5. The combination with a receiver adjustable
to receive signals over a plurality of> frequency
bands, "of means for varying the low audio fre
quency Ytone'charac'teristic of said receiver, and
means for limiting the low yfrequency end of said
variation range when said receiver is adjusted to
respond to signals >in certain of said frequency
6. 'I'he combination with a receiver adjustable
to receive signals over a plurality of frequency
bands, of means for varying the low audio fre
quency tone characteristic of said receiver, means 10
for limiting the low frequency end of said varia
tion range when said receiver is adjusted to re
spond to certain of said frequency bands, sepa
rate means for manually controlling the volume
of said receiver associated in circuit with said
first named means, and separate means for con
trolling the high frequency tone characteristic of
_ '7. The combination with a receiver adjustable
to receive signals 'over a plurality of frequency 20
bands, of means for varying the low audio fre
quency tone "characteristic of said receiver, and
meansforlimiting the low frequency end of said
variation range when said receiver is adjusted
to respond‘to certain of said frequency bands, ß
said first named means including an audio fre
quency circuit, an audio frequency choke coil
connected in shunt relation to said circuit, a series
capacitor in said 'circuit and a variable resistance
device for jointly controlling the effect of said f'
capacitor and choke coil in said circuit, and said
last named means comprising a frequency band
changing device and switch contacts connected
therewith for connecting said ,audio frequency
choke coil across said audio frequency circuit in
dependently of the operation of said Variable
resistance device.
' Y POUL F. G. HOLS'I‘.`
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