SSM2120/SSM2122

REV. C

–11–

FADER AUTOMATION

The SSM2120 can be used in fader automation systems to serve

two channels. The inverting control port is connected through

an attenuator to the VCA control voltage source. The noninverting

control port is connected to a control circuit (such as Figure 6)

which senses the input signal level to the VCA. Above the

threshold voltage, which can be set quite low (for example

–60 dBV), the VCA operates at its programmed gain. Below

this threshold the VCA will downward expand at a rate deter-

time constant in the 10 ms to 25 ms range, the modulation of

the VCA standing noise floor (–80 dB at unity-gain), can be

kept inaudibly low.

The SSM2300 8-channel multiplexed sample-and-hold IC

makes an excellent controller for VCAs in automation systems.

Figure 16 shows the basic connection for the SSM2122 operating

as a unity-gain VCA with its noninverting control ports grounded

and access to the inverting control ports. This is typical for fader

automation applications. Since this device is a pinout option of

the SSM2120, the VCAs will behave exactly as described

earlier in the VCA section.

The SSM2122 can also be used with two or more op amps to

implement complex voltage-controlled filter functions. Biquad

and state-variable two-pole filters offering low pass, bandpass

and high pass outputs can be realized. Higher order filters can

also be formed by connecting two or more such stages in series.

V–

2000pF

47

Ω

36k

Ω

36k

Ω

10pF

1/2

TL082

V+

10pF

0.1µF

+15V

200

Ω

1/2

TL082

8

1

2

3

4

7

6

5

14

13

12

11

16

15

10

9

SSM2122

200

Ω

220k

Ω

200

Ω

220k

Ω

200

Ω

50k

150k

Ω

V+

36k

Ω

V–

V+

50k

2000pF

47

Ω

36k

Ω

0.1µF

–15V

Figure 16. SSM2122 Basic Connection (Control Ports at 0 V)