The PGA2311 Stereo Audio Volume Control: A High-Performance Digital Volume Board

Featuring 0.0004% THD+N and a 120 dB dynamic range, this design drives 600 Ω loads directly via a 3-wire serial interface. Zero-crossing detection ensures click-free level steps.

Project November 04, 2026 by Rajkumar Sharma, All About Circuits

The Stereo Audio Volume Control is a compact board built around the Texas Instruments PGA2311, a precision digital volume control IC with an integrated, high-performance operational amplifier. The device delivers very low noise and distortion, making it suitable for professional and high-end consumer audio systems. The board breaks the PGA2311 out to pin headers and four 3.5 mm stereo sockets (Figure 1).

Figure 1. The assembled Stereo Audio Volume Control board.

The PGA2311 can drive loads as low as 600 Ω directly, with no additional buffering. A host controller sets the volume over a 3-wire serial interface, so the module connects easily to a wide range of microcontrollers. Multiple PGA2311 devices can also be daisy-chained for multi-channel applications.

The board runs from a dual ±5 V analog supply and a +5 V digital supply. Ferrite beads and decoupling capacitors filter the supply rails.

Specs and Features

Analog power supply: ±5 V DC (dual supply)
Digital power supply: +5 V DC
Two independent audio channels (left and right)
3-wire serial control interface
Gain range: +31.5 dB to –95.5 dB in 0.5 dB steps
Dynamic range: 120 dB, with 0.0004% THD+N at 1 kHz
Zero-crossing detection for click-free, noise-free level changes
Hardware and software mute
Low inter-channel crosstalk
Drives loads as low as 600 Ω
PCB dimensions: 55.39 × 42.66 mm
Four 3 mm PCB mounting holes

How It Works

The PGA2311 has two independent channels, left and right. As the block diagram in Figure 2 shows, a serial control port loads an 8-bit gain value for each channel and sets the gain of that channel's amplifier stage.

Figure 2. Block diagram of the PGA2311. Image used courtesy of TexasInstruments.

Figure 2. Block diagram of the PGA2311. Image used courtesy of Texas Instruments.

Analog Inputs and Outputs

Each channel has its own input and output pin. The inputs are VINL (pin 16) and VINR (pin 9), and the outputs are VOUTL (pin 14) and VOUTR (pin 11). All signals are unbalanced and referenced to analog ground (AGNDL and AGNDR).

The input and output swing must stay within 1.25 V of the analog supply rails. With ±5 V supplies, the maximum signal swing is approximately 7.5 V peak-to-peak. A low source impedance gives the best performance. A source impedance of 600 Ω or less is ideal, and up to 2 kΩ causes minimal THD+N degradation.

Gain Settings

An 8-bit register sets the gain of each channel: L[7:0] for the left channel and R[7:0] for the right. A value of N = 0 mutes the channel by connecting its input to analog ground. For N = 1 to 255, the gain is:

Gain (dB) = 31.5 – [0.5 × (255 – N)]

The gain changes in precise 0.5 dB steps.

Zero-Crossing Detection and Mute

The zero-crossing feature gives smooth, click-free volume changes. It is enabled when ZCEN (pin 1) is high and disabled when ZCEN is low. When enabled, a gain change takes effect only when the input signal crosses zero or after a 16 ms timeout. This minimizes audible clicks and pops.

Muting works in two ways:

Hardware mute: Pulling the MUTE pin low disconnects the output buffers, and the outputs are internally terminated with 10 kΩ resistors to ground. The mute engages at a zero crossing or after a 16 ms timeout. It also performs an internal offset calibration.
Software mute: Loading all zeroes into the gain register sets the internal amplifier to unity gain and connects the input to analog ground.

Serial Interface and Daisy-Chaining

The PGA2311 uses a simple 3-wire serial interface, plus a serial data output for chaining devices:

CS (pin 2): Chip select, active low.
SDI (pin 3): Serial data input, which receives the 16-bit control word.
SCLK (pin 6): Serial clock. Data is latched on the rising edge.
SDO (pin 7): Serial data output, used for daisy-chaining. It is tri-state and goes high-impedance when CS is high.

The 16-bit control word holds 8 bits of gain data for the left channel and 8 bits for the right channel. The data is sent MSB first in straight binary coding. Figure 3 shows the typical connection between a host controller and the PGA2311.

Figure 3. Typical connection diagram for the PGA2311 and a host
controller. Image used courtesy of Texas Instruments.

Figure 3. Typical connection diagram for the PGA2311 and a host controller. Image used courtesy of Texas Instruments.

Multiple devices can share the same CS and SCLK lines and be controlled through one SDI line. As Figure 4 shows, the SDO pin of each device feeds the SDI pin of the next. This reduces the number of control lines needed and suits multi-channel audio systems.

Figure 4. Daisy-chaining multiple PGA2311 devices. Image used courtesyof Texas Instruments.

Figure 4. Daisy-chaining multiple PGA2311 devices. Image used courtesy of Texas Instruments.

Schematic and Bill of Materials

The schematic is shown in Figure 5. Each audio input and output passes through a 1 Ω series resistor (R2 to R5). Optional 2-pin headers (CN3, CN4, CN6, and CN7) provide an alternative to the stereo sockets.

Figure 5. Schematic of the Stereo Audio Volume Control board.

The bill of materials is shown in Table 1.

Table 1. BOM for Stereo Audio Volume Control PGA2311.

REF	DESCRIPTION	QTY	MFG	SUPPLIER	PART NO.
CN1	6-pin male header, 2.54 mm pitch	1	WURTH	DigiKey	732-5319-ND
CN2	7-pin male header, 2.54 mm pitch	1	WURTH	DigiKey	732-5320-ND
CN3, CN4, CN6, CN7	Optional (DNP)	4		DigiKey
CN5	3-pin male header, 2.54 mm pitch	1	WURTH	DigiKey	732-5316-ND
C1, C3	100 nF/50 V ceramic, SMD 0805	2	YAGEO/MURATA	DigiKey
C2, C4	10 µF/16 V tantalum, SMD 1210	2	KEMET	DigiKey
C6	100 nF/50 V ceramic, SMD 0805	1	YAGEO/MURATA	DigiKey
D1	LED, red, SMD 0805	1	OSRAM	DigiKey	475-1278-1-ND
L1, L2, L3, L4	Ferrite bead, 600 Ω	4	LAIRD	DigiKey	240-2394-1-ND
R1	2 kΩ, 5%, SMD 0805	1	YAGEO/MURATA	DigiKey
R2, R3, R4, R5	1 Ω, 5%, SMD 1206	4	YAGEO/MURATA	DigiKey
U1	PGA2311	1	TI	DigiKey	296-48643-1-ND
CN8, CN9, CN10, CN11	3.5 mm stereo female socket	4	CUI AUDIO	DigiKey	CP1-3525N-ND
C5	10 µF/25 V ceramic, SMD 0805	1	YAGEO/MURATA	DigiKey