Balanced Audio Line Driver (Unbalance to Balance Audio Signal Converter) Using DRV135/SSM2142

The Mini board converts unbalance Audio signal into balance audio signal, the project is based on SSM2142 or DRV135 IC which are differential output amplifier that converts a single ended audio signal input to a balanced output pair. This balanced audio driver consists of high-performance op-amps with on-chip precision resistors. They are fully specified for high-performance audio applications and have excellent ac specifications, including low distortion (0.0005% at 1 kHz) and high slew rate (15 V/µs).

The on-chip resistors are laser-trimmed for accurate gain and optimum output common-mode rejection. Wide output voltage swing and high output drive capability allow use in a wide variety of demanding applications. They easily drive the large capacitive loads associated with long audio cables. Used in combination with the INA134 or INA137 differential receivers, they offer a complete solution for transmitting analogue audio signals without degradation.

Note: SSM2142 and DRV135 pin to pin compatible, any of this IC can be used.


  • Supply Dual 15V DC (+/-15V DC)
  • Balanced Output
  • Low Distortion: 0.0005% at f = 1 kHz
  • Wide Output Swing: 17Vrms into 600 Ω
  • High Capacitive Load Drive
  • High Slew Rate: 15 V/µs
  • Low Quiescent Current: ±5.2 mA IC
  • Companion to Audio Differential Line Receivers
  • Header Connector Provided for Audio Signal Input
  • Header Connector for Supply Input
  • Audio Output from XLR Connector
  • Input Aux Audio Signal
  • On-Board Power LED


  • Audio Differential Line Drivers
  • Audio Mix Consoles
  • Distribution Amplifiers
  • Graphic Equalizers
  • Dynamic Range Processors
  • Digital Effects Processors
  • Hi-Fi Audio Equipment’s


  1. Capacitor C5, C10, C7 Non-Polar Capacitors
  2. All Resistors SMD 0805 5%
  3. LED SMD 0805
  4. C1,C3,C7 Electrolytic Capacitors SMD
  5. Output XLR Male Connector
  6. ETH Chassis Ground

Design Requirement

Consider a design with the goal of deferentially transmitting a single ended signal of up to 22.2 dBu through 500 ft of cable with no load at the receiving side. The signal at the end of the cable should have no more than 0.002 per cent of total harmonic distortion plus noise (THD+N) at 10 kHz and less than 0.0005 percent of THD+N for frequencies between 20 Hz and 1 kHz.

The system is required to put out a single-ended signal 0 dB with respect to the input signal and accommodate inputs with a peak to RMS ratios of up to 1.5 for the maximum 22.2 dBu range established above.

The DRV134 and DRV135 were designed for enhanced ac performance. Very low distortion, low noise, and wide bandwidth provide superior performance in high-quality audio applications. Laser-trimmed matched resistors provide optimum output common-mode rejection (typically 68dB), especially when compared to circuits implemented with op-amps and discrete precision resistors. In addition, high slew rate (15 V/μs) and fast settling time (2.5 μs to 0.01%) ensure an excellent dynamic response. The DRV134 and DRV135 have excellent distortion characteristics. As shown in the distortion data provided in

the Typical Characteristics section, THD+Noise is below 0.003% throughout the audio frequency range under various output conditions. Both differential and single-ended modes of operation are shown. In addition, the optional 10μF blocking capacitors used to minimize VOCM errors have virtually no effect on performance. Measurements were taken with an Audio Precision System One (with the internal 80 kHz noise filter

Example Circuit With Balanced Line Receiver



Design Description

This design inverts the input signal, Vi, and applies a signal gain of –2V/V. The input signal typically comes from a low-impedance source because the input impedance of this circuit is determined by the input resistor, R3. The common-mode voltage of an inverting amplifier is equal to the voltage connected to the non-inverting node, which is ground in this design. D1 indicates the power, all connection can be done using CN1 header connector, Capacitors, Resistors, LEDs are SMD components size 0805. Op-Amp TLV170 from Texas Instruments.

D1=Power LED, CN1= 6 Pin male header connector

ViMIN=-7V, ViNMAX=7V, VoMIN=–14V, VoMAX=14V, F=3KHZ, V+=15V, V-=-15V

Design Notes

  1. Use the op amp in a linear operating region. Linear output swing is usually specified under the AOL test conditions. The common-mode voltage in this circuit does not vary with input voltage.
  1. The input impedance is determined by the input resistor. Make sure this value is large when compared to the source’s output impedance.
  1. Using high value resistors can degrade the phase margin of the circuit and introduce additional noise in the circuit.
  1. Avoid placing capacitive loads directly on the output of the amplifier to minimize stability issues.
  2. Small-signal bandwidth is determined by the noise gain (or non-inverting gain) and op amp gainbandwidth product (GBP). Additional filtering can be accomplished by adding a capacitor in parallel to R1. Adding a capacitor in parallel with R1 will also improve stability of the circuit if high value resistors are used.
  1. Large signal performance may be limited by slew rate. Therefore, check the maximum output swing versus frequency plot in the data sheet to minimize slew-induced distortion.
  1. For more information on op amp linear operating region, stability, slew-induced distortion, capacitive load drive, driving ADCs, and bandwidth please see the Design References section.




Application Courtesy of Texas Instruments





Pro Audio Microphone Pre-Amplifier Using INA217 and OPA2137

Its simple Tiny Pro-microphone Pre-Amplifier using INA217 instruments amplifier and OPA2137 op-amp. Circuit has been designed using SMD components, 3 Pin female XLR connector has been used for direct micro-phone input.

The board has been design around INA217 low distortion, low noise instrumentation amplifier. The INA217 is ideal for low-level audio signals such as balanced low-impedance microphones. Many industrial, instrumentation, and medical applications also benefit from its low noise and wide bandwidth. Unique distortion cancellation circuitry reduces distortion to extremely low levels, even in high gain. The INA217 provides near-theoretical noise performance for 200Ω source impedance. The INA217 features differential input, low noise, and low distortion that provides superior performance in professional microphone amplifier applications. An OPA2137 op-amp used as a feedback to eliminate the offset voltage. Phantom power is not part of the circuit its just for reference. 


  • Supply Dual +/-15V DC
  • Output Unbalance Single Ended
  • PR1 Gain Adjust G=1+10000/Rg PR1









Power Supply for Hi-Fi Audio Amplifier – Symmetrical Output Including +/-15V DC Output

The power supply has been designed to use for audio power amplifiers. This power supply uses a transformer, a bridge rectifier, various rail capacitors, fuse for protection, also supply has separate dual regulators for +/-15 V DC output.  Maximum output for main audio amplifier +/-42V DC, high voltage output possible by altering bus capacitor voltage. The power supply also provides +/-15 V DC to power up pre-amplifier or other support circuit required symmetrical low regulated voltage. Replace LM7815/LM7915 IC with LM7812/LM7912 if need +/-12V regulated output. NTC used for inrush current at power on. All inputs and outputs provided with Screw terminals for easy connections. Project can provide Load current up to 10Amps for amplifier and +/-15V 500mA for pre-amplifier. R2 and R3 resistor used to discharge the capacitor at power off.

Note 1 : Default Bus capacitor value used for 30-0-30V AC Transformer, For higher voltage output use appropriate capacitor voltage. 

Note 2 : Short the EMI transformer T1 terminal using jumper wire as shown in circuit  (Transformer not required for Audio amplifier)

Note 3 : Advisable to use Chassis earth connection, Tie ETH terminal to amplifier chassis


  • AC Input 30-0-30V AC 10Amps Center Tape Transformer
  • AC Input 12-0-12V 500mA
  • +/-42V, 10Amps DC Output ( Unregulated)
  • +/-15V , 500mA DC Output ( Regulated) for Pre-Amplifier and Biasing Circuit












This is easy to construct microphone pre-amplifier project using compact electret condenser microphone. The pre-amplifier is important building block of many audio communication systems. Circuit has been built around Op-Amp LM358.


  •  Power supply : 5 to 12 VDC @ 10 mA
  •  Output: Gain Approx. 100
  •  On-Board electret condenser microphone 
  •  Header connector for connecting of power supply input and audio output
  •  Power-On LED indicator







3.1W Stereo-SE Audio Power Amplifier with DC Volume Control LM4952

The LM4952 is a dual audio power amplifier primarily designed for demanding applications in flat panel monitors and TV’s. It is capable of delivering 3.1 watts per channel to a 4Ω single-ended load with less than 1% THD+N when powered by a 12VDC power supply. Eliminating external feedback resistors, an internal, DC controlled, volume control allows easy and variable gain adjustment. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4952 does not require bootstrap capacitors or snubber circuits. Therefore, it is ideally suited for display applications requiring high power and minimal size. The LM4952 features a low-power consumption active-low shutdown mode. Additionally, the LM4952 features an internal thermal shutdown protection mechanism along with short circuit protection. The LM4952 contains advanced pop & click circuitry that eliminates noises which would otherwise occur during turn-on and turn-off transitions.

Key Specifications

  • Supply 12V DC
  • Quiescent Power Supply Current 18mA (typ)
  • VDD = 12V, RL = 4Ω, 10% THD+N 3.8W (typ)
  • Shutdown current 55μA (typ)
  • Volume Control : 0 To 3.3V DC


  • Pop & click circuitry eliminates noise during turn-on and turn-off transitions
  • Low current, active-low shutdown mode
  • Low quiescent current
  • Stereo 3.8W output, RL = 4Ω
  • DC-Controlled volume control
  • Short circuit protection

Download Data Sheet LM4952



  • Flat Panel Monitors
  • Flat panel TV’s
  • Computer Sound Cards





68W High Performance Stereo Audio Amplifier Using LM3886

The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4Ω load and 38W into 8Ω with 0.1% THD+N from 20Hz–20kHz.

The performance of the LM3886, utilizing its Self Peak Instantaneous Temperature (°Ke) (SPiKe) protection circuitry, puts it in a class above discrete and hybrid amplifiers by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe protection means that these parts are completely safeguarded at the output against overvoltage, under voltage, overloads, including shorts to the supplies, thermal runaway, and instantaneous temperature peaks.

The LM3886 maintains an excellent signal-to-noise ratio of greater than 92dB with a typical low noise floor of 2.0µV. It exhibits extremely low THD+N values of 0.03% at the rated output into the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE) typical rating of 0.004%.

Note : Amplifier Required Large Size Heat sink


  • 68W Cont. Avg. Output Power into 4Ω at VCC = ±28V
  • 38W Cont. Avg. Output Power into 8Ω at VCC = ±28V
  • 50W Cont. Avg. Output Power into 8Ω at VCC = ±35V
  • 135W Instantaneous Peak Output Power Capability
  • Signal-to-Noise Ratio ≥ 92dB
  • An Input Mute Function ( J1 & J2 Jumper)
  • Output Protection from a Short to Ground or to the Supplies via Internal Current Limiting Circuitry
  • Output Over-Voltage Protection against Transients from Inductive Loads
  • Supply Under-Voltage Protection, not Allowing Internal Biasing to Occur when |VEE| + |VCC| ≤ 12V, thus Eliminating Turn-On and Turn-Off Transients
  • Input Slandered Audio Line signal







3W Stereo Audio Amplifier Using TDA7266

Tiny stereo audio amplifier board has been designed around SMD TDA7266D IC from ST. The TDA7266D is a dual bridge amplifier specially designed for Portable Audio, for LCD TV/Monitor, PC Motherboard, and TV applications. This circuit provides high quality audio output of 3W approx.  on each channel with standard audio signal input.  The circuit works with 3.5V to 5V. Due to low supply input this amplifier suitable for small size audio gadgets and portable audio applications like MP3 player, Voice messaging system, Warning signals, Annunciator.

Key Features

  • SUPPLY VOLTAGE RANGE 3.5 to 5V (Maximum supply 5V due to small PCB and   small thermal Area)
  •  OUTPUT POWER 3+3W @THD = 10%, RL = 8Ω, VCC = 3.7V (3W Approx.)
  • MUTE FUNCTIONS (Jumper Closer)

Download Data Sheet TDA7266








Digital Potentiometer Using Optical Rotary Encoder & LS7184

The primary application of the project is to replace the mechanical potentiometer with optical encoder which is long life, accurate, smooth in operation. The simple project has been designed around LS7184 quadrature clock converter IC from LSI semiconductor, AD5220-10 Digital potentiometer from Analog Devices, and optical encoder from Burns.

Quadrature clocks derived from optical encoder, when applied to the A and B inputs of the LS7184, are converted to strings of Clock and an Up/down direction control. These outputs interfaced directly to AD5220-10 Digital potentiometer IC.

The AD5220-10 contains a single channel, 128 positions, and digitally-controlled 10K ohms variable resistor (VR) device. This device performs the same electronic adjustment function as a potentiometer.

Jumper J1 provided for scale of the 3-state input to select resolution x1, x2 or x4. The input quadrature clock rate is multiplied by factors of 1, 2 and 4 in x1, x2 and x4 mode, respectively, in producing the output UP/DN clocks. x1, x2 and x4 modes selected by the MODE input logic.

levels are as follows:

Mode = 0 : x1 selected

Mode = 1 : x2 selected

Mode = Float : x4 selected


  •     Supply 5V DC
  •     J1 Encoder pulse multiplication ( Jumper JL Close =1X, Jumper JH Close = X2, J1 Open = X4)
  •     Header Connector for Supply and Output
  •     Potentiometer Resistance 10K Ohms
  •     R5 Resistor For Programmable output pulse width (200ns to 140μs) – Read Data Sheet
  •     X1 , X2 and X4 mode selection
  •     Excellent regulation of output pulse width
  •     On-chip filtering of inputs for optical or magnetic encoder applications.
  •     TTL compatible I/Os

Note : Input for external component connection. A Resistor (R5) connected between this input and VSS adjusts the output clock pulse width (Tow). Refer to graph for appropriate bias resistor value.
















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