SSM2165-2S-REEL7 Analog Devices Inc, SSM2165-2S-REEL7 Datasheet - Page 8

• Manufacturer Part Number: SSM2165-2S-REEL7
• Description: IC PREAMP AUDIO MONO AB 8SOIC
• Manufacturer: Analog Devices Inc
• Type: Class ABr

Specifications of SSM2165-2S-REEL7

• Rohs Status: RoHS non-compliant
• Output Type: 1-Channel (Mono)
• Voltage - Supply: 4.5 V ~ 5.5 V
• Features: Microphone
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Max Output Power X Channels @ Load: -

SSM2165
Compression Adjustment—A Practical Example
To illustrate how to set the compression ratio of the SSM2165,
we will take a practical example. The SSM2165 will be used
interface an electret-type microphone to a post-amplifier, as
shown in Figure 8. The signal from the microphone was mea-
sured under actual conditions to vary from 2 mV to 30 mV.
The post-amplifier requires no more than 350 mV at its input.
We will, therefore, choose the SSM2165-1, whose “rotation”
point is 40 mV and whose VCA fixed gain is 18 dB ( 8), thus
giving 320 mV at limiting. From prior listening experience, we
will use a 2:1 compression ratio. The noise gate threshold of the
SSM2165-1 will operate when the input signal falls below 500 V.
These objectives are summarized in Table II. The transfer charac-
teristic we will implement is illustrated in Figure 10.
Test Equipment Setup
The recommended equipment and configuration is shown in
Figure 9. A low noise audio generator with a smooth output
adjustment range of 100 V to 25 mV is a suitable signal
source. The output voltmeter should go up to 2 V. The oscillo-
scope is used to verify that the output is sinusoidal, that no
clipping is occurring in the buffer, and to observe the limiting
and noise gating “knees.”
Breadboard Considerations
When building a breadboard, keep the leads to Pins 2 and 3 as
short as possible. Use a central analog ground and decouple
power supply connections adequately.
Table II. Objective Specification of Example
Input Range
Output Range
Limiting Level
Compression
Gain
Noise Gate
GENERATOR
VOLTMETER
2k
AND AC
+2V
+
MICROPHONE
(ELECTRET)
0.1 F
2 mV–30 mV
To 350 mV
320 mV
2:1
18 dB
500 V
C1
SSM2165-1
+5V
V+
+1
GND
BUFFER
BUF
DETECTOR
LEVEL
OUT
AVG CAP
10 F
22 F
C2
C3
+
+
VCA
STEP 1. Initialize Potentiometer
With power off, preset R1—Compression Ratio potentiometer
to zero ohms.
STEP 2. Check Setup
With power on, adjust the generator for an input level of
50 mV (–24 dBu), 1 kHz. The output meter should indicate
approximately 350 mV (–6.9 dBu). If not, check the setup.
STEP 3. Find the Rotation Point
Set the input level to 50 mV (–24 dBu), and observe the output
on the oscilloscope. The output will be in the limiting range of
operation. Slowly reduce the input signal level until the output
level just begins to stop limiting and follows the input down.
Increase the input so that the output is 320 mV (–7.7 dBu).
This is the knee of the rotation point.
STEP 4. Adjust the Compression Ratio
With the input set as in Step 3, note the exact value of the input
signal level just below the knee (around 40 mV (–26 dBu)). Next,
reduce the input to 1/4 the value noted, (around 10 mV (–38
dBu)), for a change of –12 dB. Next, increase the R
ometer resistance so the output is 160 mV (–13.7 dBu) for an
output change of –6 dB. You have now set the compression,
which is the ratio of input change to output change, in dB, to 2:1.
STEP 5. Confirm the Noise Gate Threshold
Set the input to 1 mV, and observe the output on the oscillo-
scope. A 20 dB pad between generator and input may facilitate
this measurement. Reduce the input gradually until the output
falls off more rapidly. This point is the noise gate threshold, and
should be approximately 500 V (–64 dBu). The noise gate
threshold on the SSM2165 is fixed at 500 V, a practical value
for many microphones. Should a different noise gate threshold
be required, consider using the SSM2166.
200k
IN
CONTROL
VCA
CW
GENERATOR
VOLTMETER
SIGNAL
1:1
R1 – COMPRESSION
15:1 RATIO SET
AC
AC VOLTMETER
AND OSCILLOSCOPE
HEADPHONES
SSM2165-1
OSCILLOSCOPE
VOLTMETER
AC
COMP
potenti-