Stereo 3.7W Class D Audio Amplifier

Stereo 3.7W Class D Audio Amplifier
Stereo 3.7W Class D Audio Amplifier
Created by Bill Earl
Last updated on 2016-10-06 02:39:50 PM UTC
Guide Contents
Guide Contents
Overview
2
3
Specifications:
What is a Class D Amplifier?
3
4
Other Audio amps available at Adafruit
Assembly
4
6
Solder the header:
For breadboard use:
For use with connectors:
And Solder!
Add Gain Selection and Speaker Terminals
7
7
7
8
8
Connections and Settings
Inputs:
Outputs:
Gain:
Power:
9
9
10
11
Build a Portable Sound System
Materials:
Mount The Speakers
Mount the Controls
Wire it up!
Mount the Amplifier
Add some stuffing
Plug And Play!
Downloads
Files
Schematic
PCB Fabrication Print
© Adafruit Industries
9
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Overview
This incredibly small stereo amplifier is surprisingly powerful - able to deliver 2 x 3.7W
channels into 3 ohm impedance speakers. Inside the miniature chip is a class D controller,
able to run from 2.7V-5.5VDC. Since the amp is a class D, its incredibly efficient (over 90%
efficient when driving an 8Ω speaker at over a Watt).
This amplifier is perfect for portable and battery-powered projects. It has built in thermal and
over-current protection, but you really have to drive it hard before it even gets warm! This
board is a welcome upgrade to basic "LM386" amps!
Specifications:
Output Power: 3.7W at 3Ω, 10% THD, 1.7W at 8Ω, 10% THD, with 5V Supply
Passes EMI limit unfiltered with up to 12 inches (30 cm) of speaker cable
High 83dB PSRR at 217Hz
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Page 3 of 18
Spread-Spectrum Modulation and Active Emissions Limiting
Differential Inputs
Five pin-selectable gains: 6dB, 9dB, 12dB, 15dB and 18dB. Select with a jumper or by
setting the G and G' breakout pins (see schematic for breakout board showing gain
pin settings (http://adafru.it/aWT) for details)
Excellent click-and-pop suppression
Thermal and short-circuit/over-current protection
Low current draw: 2mA quiescent and 10uA in shutdown mode
What is a Class D Amplifier?
A Class D Amplifier uses PWM to generate high-frequency square waves with a duty-cycle
proportional to the voltage level of the input audio signal. By minimizing the transition time
between fully on and fully off, the MOSFET drivers are able to operate at a very high
efficiency. Class D amplifiers such as this one typically operate at over 90% efficiency,
compared to efficiencies of 50% or less for typical class AB amplifiers.
The high frequency square-wave component of the output signal is filtered by the
inductance of the speaker voice coil, leaving only the amplified audio signal.
Other Audio amps available at Adafruit
We have a few choices of audio amplifiers, here's how you can compare them
MAX98306 (http://adafru.it/987) - This class D audio amplifier has selectable gains of
6dB, 9dB, 12dB, 15dB and 18dB that you can choose with a jumper. It can do up to
3.7W into 3Ω, 2.8W into 4Ω and 1.7W into 8Ω. However, you cannot shut down each
speaker separately. Its a good choice where you don't mind setting the gain with a
jumper and if you do not need to ever turn off only one audio channel and you do not
need more than 18dB. Its an excellent amplifier that can driver down to 3Ω speakers
Like the TS2012, it has differential inputs, bridge tied outputs, and can run from 2.7V
to 5.5V
TS2012 (http://adafru.it/1552) - This class D audio amplifier has selectable gains of
6dB, 12dB, 18dB and 24dB that you can choose with a jumper (the MAX98306 goes
up to 18dB only). It can do up to 2.8W into 4Ω and 1.7W into 8Ω. It cannot drive 3Ω.
© Adafruit Industries
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Page 4 of 18
You can shut down each channel separately. Setting the gain is easy on the onboard
DIP switches. Its a good choice where you don't need to drive 3Ω speakers or if you
ever want to turn off only one audio channel. If you need 24dB gain this amp can do it.
Like the MAX98306, it has differential inputs, bridge tied outputs, and can run from
2.7V to 5.5V
Available from Adafruit! (http://adafru.it/987)
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Page 5 of 18
Assembly
The amplifier breakout board is fully assembled and tested. To easily integrate the amplifier
into your project, we include the following:
A 9-pin header for use with breadboard or connectors
3.5mm screw-terminal blocks for your speakers
A 2x4 header + jumper for setting the gain
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Page 6 of 18
Solder the header:
Cut the header to size (9 pins)
and insert it into a breadboard
(long pins down!) to hold it
steady.
For breadboard use:
Place the amplifier module faceup over the headers. Prop the
back-edge up with the leftover
header strip to align it.
For use with
connectors:
If you are going to build this into
a project and want to connect
from the front side, place the
amplifier module face down for
soldering.
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Page 7 of 18
And Solder!
For tips on soldering, see our
Adafruit Guide to Excellent
Soldering. (http://adafru.it/aTk)
Add Gain Selection
and Speaker
Terminals
Solder the 2x4 pin header for
gain selection to the top of the
board as shown. Also solder in
the 3.5mm screw terminals for
the speakers.
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Page 8 of 18
Connections and Settings
Inputs:
The amplifier inputs are coupled
via 1.0uF capacitors so they can
handle single ended or
differential signals.
For Single Ended signals (shown
on left), connect:
R+ to R+
GND to RL+ to L+
GND to LFor differential signals, connect:
R+ to R+
R- to RL+ to L+
L- to LFor volume control, a dual 50K
audio taper pot can be wired in
series with the inputs as shown.
Outputs:
This amplifier is designed to
drive moving coil loudpeakers
only. Speaker impedence must
be 3ohms or more. The output
signal is a 360KHz PWM square
wave with a duty cycle
proportional to the audio signal.
The inductance of the speaker
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Page 9 of 18
coil serves as a low-pass filter to
average out the high-frequency
components. Do not try to use
this as a pre-amplifier.
The outputs of each channel are
"Bridge-Tied" with no connection
to ground. This means that for
each of the two channels, the +
and - alternate polarity to create
a single channel amplifier with
twice the available power.
However, that means you
cannot bridge R and L
together, so don't try to connect
ROUT to LOUT, it will damage
the amp! If you only need one
speaker, just connect to either
ROUT or LOUT and leave the
other output set alone
Connect your speakers using the
3.5mm screw-terminal blocks.
Gain:
Gain is configurable for 9, 12, 15
or 18 dB. For higher level outputs
such as from a WaveShield, you
will want to select a lower gain.
For low-level outputs such as
from an iPod or MP3 player, a
higher gain setting works best.
To set the gain, install the jumper
in one of the 4 marked positions
on the 4x2 header.
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Page 10 of 18
Power:
The amplifier can be powered by
2.7 to 5.5v DC. Good power
sources are:
5v 2A power
supply (http://adafru.it/276)
3xAA (4.5v) battery
holder (http://adafru.it/771)
Connect the negative wire to
GND and the positive wire to
VDD.
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Page 11 of 18
Build a Portable Sound System
Materials:
To build a portable sound system, you will need:
1 Adafruit Stereo Class-D Amplifier (http://adafru.it/987)
2 speakers (3 ohm minimum. 3" to 4" is a good size)
1 3xAA Battery Pack (http://adafru.it/771)
1 Power Switch (http://adafru.it/482)
1 Phono Jack (We used a 1/4" here)
1 50kOhm Stereo Audio-taper pot
1 knob
Jumper wires (http://adafru.it/266)
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Page 12 of 18
1 Box (We used the case from a power tool. But any lunch-box sized enclosure will
work as well)
2 Speaker Grilles (We used some 4" fan grilles here)
Screws & nuts to mount the speakers.
Polyester batting or pillow stuffing
Mount The Speakers
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Page 13 of 18
Cut holes in the box to fit your
speakers and mount them in the
box with screws. Here we used
4" speakers with 4" fan grilles
and mounted them with 3/4" 6-32
machine screws and nuts.
Mount the Controls
Drill holes to fit your power
switch, volume pot and phono
jack in a convenient location and
mount the controls.
Here we used a 1/4" phono jack.
Smaller plugs can be
accomodated via adapters. Our
volume pot has a Spinal-Tap
compliant volume scale that
"goes to eleven".
Wire it up!
Make all connections as shown
on the diagram to the left. We
used these pre-terminated
jumper wires (http://adafru.it/266)
to simplify connections to the
amplifier.
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Page 14 of 18
Mount the Amplifier
Some double-sided foam tape
will hold it securely inside the
box.
Add some stuffing
Loosely stuff the back of the box
with some polyester batting or
pillow stuffing for a less 'hollow'
sound.
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Page 15 of 18
Plug And Play!
For an iPod or similar player, you
will want to use the highest gain
setting.
© Adafruit Industries
https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier
Page 16 of 18
Downloads
Files
MAX98306 Datasheet (http://adafru.it/e7o)
Fritzing object in Adafruit Fritzing library (http://adafru.it/aP3)
EagleCAD PCB files on GitHub (http://adafru.it/rJc)
Schematic
PCB Fabrication Print
Dimensions in inches
© Adafruit Industries
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Page 17 of 18
© Adafruit Industries
Last Updated: 2016-10-06 02:39:49 PM UTC
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