14

Tone Control Circuits

High slew rate, wide bandwidth, high output voltage

capability and high input impedance are all characteristics

required of tone control amplifiers. Two tone control circuits

that exploit these characteristics of the CA3140 are shown in

Figures 19 and 20.

The first circuit, shown in Figure 20, is the Baxandall tone

control circuit which provides unity gain at midband and

uses standard linear potentiometers. The high input

impedance of the CA3140 makes possible the use of low-

cost, low-value, small size capacitors, as well as reduced

load of the driving stage.

Bass treble boost and cut are

±15dB at 100Hz and 10kHz,

respectively. Full peak-to-peak output is available up to at

least 20kHz due to the high slew rate of the CA3140. The

amplifier gain is 3dB down from its “flat” position at 70kHz.

Figure 19 shows another tone control circuit with similar

boost and cut specifications. The wideband gain of this

circuit is equal to the ultimate boost or cut plus one, which in

this case is a gain of eleven. For 20dB boost and cut, the

input loading of this circuit is essentially equal to the value of

the resistance from Terminal No. 3 to ground. A detailed

analysis of this circuit is given in “An IC Operational

Transconductance Amplifier (OTA) With Power Capability” by

L. Kaplan and H. Wittlinger, IEEE Transactions on Broadcast

and Television Receivers, Vol. BTR-18, No. 3, August, 1972.

FIGURE 19. TONE CONTROL CIRCUIT USING CA3130 SERIES (20dB MIDBAND GAIN)

FIGURE 20. BAXANDALL TONE CONTROL CIRCUIT USING CA3140 SERIES

4

7

+

CA3140

-

+30V

3

2

0.1

µF

6

0.005

µF

0.1

µF

2.2M

Ω

2.2M

Ω

5.1

M

Ω

0.012

µF

0.001

µF

0.022

µF

2

µF

18k

Ω

0.0022

µF

200k

Ω

(LINEAR)

100

pF

100pF

BOOST

TREBLE

CUT

BOOST

BASS

CUT

10k

Ω

1M

Ω

CCW (LOG)

100k

Ω

TONE CONTROL NETWORK

FOR SINGLE SUPPLY

+15V

3

0.1

µF

0.005

µF

5.1M

Ω

0.1

µF

-15V

2

6

7

4

+

CA3140

-

TONE CONTROL NETWORK

FOR DUAL SUPPLIES

NOTES:

5. 20dB Flat Position Gain.

6.

±15dB Bass and Treble Boost and Cut

at 100Hz and 10kHz, respectively.

8. -3dB at 24kHz from 1kHz reference.

4

7

+

CA3140

-

+32V

3

0.1

2.2M

Ω

2.2

M

Ω

FOR SINGLE SUPPLY

µF

6

2

0.1

µF

20pF

750

pF

750

pF

2.2M

Ω

0.047

µF

BOOST TREBLE

CUT

51k

Ω

5M

Ω

(LINEAR)

51k

Ω

TONE CONTROL NETWORK

BOOST

BASS

CUT

240k

Ω

5M

Ω

(LINEAR)

240k

Ω

+15V

3

0.1

µF

0.047

µF

0.1

µF

-15V

2

6

7

4

+

CA3140

-

FOR DUAL SUPPLIES

NOTES:

9.

±15dB Bass and Treble Boost and Cut at 100Hz and 10kHz, Respectively.

11. -3dB at 70kHz from 1kHz Reference.

12. 0dB Flat Position Gain.

TONE CONTROL

NETWORK

CA3140, CA3140A