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Maxim > Design Support > Technical Documents > Reference Schematics > Amplifiers > APP 161
Maxim > Design Support > Technical Documents > Reference Schematics > Audio Circuits > APP 161
Maxim > Design Support > Technical Documents > Reference Schematics > Digital Potentiometers > APP 161
Keywords: audio preamplifier, audio potentiometer, pushbutton digital potentiometer
REFERENCE SCHEMATIC 161
Using a DS1802 Pushbutton Digital Potentiometer to Create an
Audio Preamplifier with Attenuator
Jun 27, 2002
Abstract:
This application note discusses
how to best bias the AC signal to within the DC supply range and how to use digital
potentiometers in circuits designed for mechanical potentiometers. This understanding is crucial to effectively using the DS1802 in a
pushbutton-controlled audio preamplifier circuit.
Introduction to the DS1802 Dual Logarithmic Audio
Potentiometer
The DS1802 audio potentiometer contains two digitally controlled potentiometers and features a
logarithmic taper that produces a 1dB change per increment. The maximum attenuation is 63dB,
but the device also contains a mute function that attenuates a signal greater than 90dB.
Additionally, the DS1802 has four pushbutton inputs that can be used either as a
volume/balance controller for stereo applications or for independent position control of the two
potentiometers. The part also contains zero-crossing detectors, which, when used properly, can seamlessly change the volume to
create a professional-sounding audio system. The part is available in 20-pin DIP, SOIC, or TSSOP packages.
The DS1802 is ideal for applications where pushbutton-controllable resistance is desired. It also has a 3-wire interface that allows a
PC or microcontroller to control the potentiometers. This application note shows how to use the part, with a minimal amount of
hardware, to create a preamplifier circuit with a pushbutton-controllable volume for two stereo channels.
Single Power Supply Audio Circuits
The first step in using the DS1802 is understanding how to bias an AC signal to within the DC supply range. This is required because
the DS1802 will clip audio signals that attempt to go below GND or above V
CC
. The DS1802 can operate from a 3V or 5V supply, but
be aware that selecting the supply voltage will affect the maximum audio signal swing that the part can handle. Since audio signals
are generally symmetric, it is best to set the DC bias to V
CC
/2 to obtain the maximum audio signal swing.
The resistor-dividers, shown in Figure 1, can be used to set the DC bias of the input signal to V
CC
/2.
Figure 1. Resistors R1 and R2 add DC bias to an audio circuit.
This circuit allows an AC signal to be passed across the middle resistor (or potentiometer) with the same DC bias on both sides. This
is critical for a digital potentiometer because the zero-crossing detector switches the potentiometer's position when there is zero
voltage across the end-to-end resistance of the potentiometer. As a result, there is no voltage potential across the digital
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