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SSM2017S

Self-Contained Audio Preamplifier

Analog Devices 

SSM2017

G = V OUT

(+In) – (In)

=

10RkG⍀ +1

Basic Circuit Connections

GAIN

The SSM2017 only requires a single external resistor to set the

voltage gain. The voltage gain, G, is:

10 kΩ

G = RG +1

and

10 kΩ

RG = G –1

For convenience, Table I lists various values of RG for common

gain levels.

Table I. Values of RG for Various Gain Levels

AV

dB RG

1

0

NC

3.2

10 4.7k

10

20 1.1k

31.3 30 330

100 40 100

314 50 32

1000 60 10

The voltage gain can range from 1 to 3500. A gain set resistor is

not required for unity gain applications. Metal-film or wire-

wound resistors are recommended for best results.

The total gain accuracy of the SSM2017 is determined by the

tolerance of the external gain set resistor, RG, combined with the

gain equation accuracy of the SSM2017. Total gain drift com-

bines the mismatch of the external gain set resistor drift with

that of the internal resistors (20 ppm/°C typ).

Bandwidth of the SSM2017 is relatively independent of gain as

shown in Figure 21. For a voltage gain of 1000, the SSM2017

has a small-signal bandwidth of 200 kHz. At unity gain, the

bandwidth of the SSM2017 exceeds 4 MHz.

Figure 21. Bandwidth of the SSM2017 for Various Values

of Gain

NOISE PERFORMANCE

The SSM2017 is a very low noise audio preamplifier exhibiting

a typical voltage noise density of only 1 nV/√Hz at 1 kHz. The

exceptionally low noise characteristics of the SSM2017 are in

part achieved by operating the input transistors at high collector

currents since the voltage noise is inversely proportional to the

square root of the collector current. Current noise, however, is

directly proportional to the square root of the collector current.

As a result, the outstanding voltage noise performance of the

SSM2017 is obtained at the expense of current noise perfor-

mance. At low preamplifier gains, the effect of the SSM2017’s

voltage and current noise is insignificant.

The total noise of an audio preamplifier channel can be calcu-

late by:

En = en 2 +(inRS )2 + et 2

where:

En = total input referred noise

en = amplifier voltage noise

in = amplifier current noise

RS = source resistance

et = source resistance thermal noise.

For a microphone preamplifier, using a typical microphone im-

pedance of 150 Ω the total input referred noise is:

en = 1 nV/√Hz @ 1 kHz, SSM2017 en

in = 2 pA/√Hz @ 1 kHz, SSM2017 in

RS = 150 Ω, microphone source impedance

et = 1.6 nV/√Hz @ 1 kHz, microphone thermal noise

En =√(1 nV√Hz)2 + 2 (pA/√Hz × 150 Ω)2 + (1.6 nV/√Hz)2

= 1.93 nV/√Hz @ 1 kHz.

This total noise is extremely low and makes the SSM2017

virtually transparent to the user.

–6–

REV. C

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