SSM2166

Data Sheet

Rev. E | Page 16 of 20

SETUP SUMMARY

The transfer condition of Figure 2 has been implemented. For

inputs below the 100 μV noise gate threshold, circuit and back-

ground noise is minimized. Above it, the output increases at a

rate of 1 dB for each 2 dB input increase until the 500 mV rotation

point is reached at an input of approximately 15 mV. For higher

inputs that drive the output beyond 500 mV, limiting occurs

and there is little further increase. The SSM2166 processes the

output of the buffer, which in the previous example is 20 dB, or

10× the input level. Use the oscilloscope to ensure that the

buffer is not being driven into clipping with the highest expected

input peaks. Always take the minimum gain in the buffer consis-

tent with the average source level and crest factor (ratio of peak

to rms). The wide program range of the SSM2166 makes it

useful in many applications other than microphone signal

conditioning.

Table 6. Initial Potentiometer Settings

Function

Potentiometer

Range

Initial Position

Initial Resistance

Effect of Change

Gain Adjust (VCA)

R10

0 kΩ to 20 kΩ

CCW

0 Ω

0 dB; CW to increase VCA gain

Rotation Point

R3

0 kΩ to 50 kΩ

CCW

0 Ω

1 V; CW to reduce rotation point

Compression Point

R6

0 kΩ to 100 kΩ

CCW

0 Ω

1:1; CW to increase compression

Noise Gate

R7

0 kΩ to 1 MΩ

CW

1 MΩ

300 µV; CCW to increase threshold

Table 7. Demonstration Board Parts List

Component

Value

Description

R1

10 kΩ resistor

Feedback

R2

10 kΩ resistor

Input

R3

50 kΩ potentiometer

Rotation point, adjust

R4

500 Ω resistor

Rotation point, fixed

R5

0 Ω resistor

Compression ratio, fixed

R6

100 kΩ potentiometer

Compression ratio, adjust

R7

1 MΩ potentiometer

Noise gate, adjust

R8

500 Ω resistor

Noise gate, fixed

R9

1 kΩ resistor

Gain adjust, fixed

R10

20 kΩ potentiometer

Gain adjust

R11

330 Ω resistor

Mute

R12

100 kΩ resistor

Power-down, pull-up

C1

0.1 µF capacitor

Input dc block

C2

1 µF capacitor

Buffer low F, G = 1

C3

0.1 µF capacitor

+V bypass

C4

2.2 µF to 22 µF capacitor

Average capacitor

C5

0.01 µF capacitor

Mute click suppress

C6

10 µF capacitor

Coupling

C7

10 µF capacitor

VCA noise/dc balance

IC1

SSM2166

MIC preamp

IC2

OP113, IC

Operational amplifier, output buffer

S1

SPST, Switch

Mute

J1

1/8-inch mini phone plug jumper

MIC input

J2

RCA female jumper

Output jack