XLR to RCA Balanced to Unbalanced

Pre-amplifier Headphone Amp Low Distortion LG139 Board

Circuit principle:

The distortion and noise of this circuit are much lower than ordinary circuits, so the circuit looks less simple and more complicated, and the purpose is low distortion and low noise. Generally speaking, to convert a balanced signal into an unbalanced (single-ended) output signal, you can use 1/2 NE5532 plus 4 10K resistors, which can be realized according to the IC2A connection in the figure. At this time, R5~R8 are all 10K in the figure, and a pair of balanced signals are input from the left end of R5 and R6, and a single-ended output signal can be obtained from the right end of R9. This differential amplifier circuit is quite simple. The output noise is also low, roughly reaching -104dBu (0dBu=775mV), but the noise is still large. For this reason, the so-called double-balanced stage is used, that is, two differential amplifier stages composed of IC2A and IC2B, which are simultaneously received and balanced. After the input signals are added together, the uncorrelated noise can be partially cancelled, so as to obtain a noise reduction of 3dB, and also improve the circuit common-mode rejection ratio (CMRR).

A further improvement is to add a voltage follower IC1A and IC1B before IC2A and IC2B. This not only increases the input impedance, but also reduces the resistance of the 8 resistors R5, R6, R7, R8, R13, R14, R15, R16 from the original 10K to 820 ohms, which greatly reduces the thermal noise of the resistors. Finally, the noise of this stage is reduced by -112dBu, which is 8dB better than the above-mentioned traditional single difference amplifier circuit.

One board is mono, and two boards form stereo.

Exquisite FR4 double-sided glass fiber board, high-quality PCB board (77×37mm), board thickness 2mm, and arc wiring is grounded at one point. Imported high-quality RC components are assembled. Japan KOA 1/4W high-precision five-color ring metal film resistor, Nissan's famous electrolytic, gold-plated IC socket (convenient to upgrade), 2 US-made NE5532 dual op amps, connect to ±5V～±15V stable voltage to work.

Working mode: This circuit board is used for the balanced XLR signal output of the CD player and converted to the single-ended RCA output to the next stage (pre-stage or power amplifier) through this circuit.

Input balanced signal and output unbalanced signal. It is suitable for sound system with balanced output of sound source and unbalanced input only for subsequent equipment.

Especially for those who use professional equipment as their homes, the professional audio source is XLR balanced output. This board can convert your signal source to the single-ended RCA signal required by a general power amplifier.

This circuit board can be replaced with a better operational amplifier, such as AD826, AD827, OPA2134, OPA2604, OPA2111 and other high-end operational amplifiers, the effect will be better.

Note: 
When using, pay special attention to the power supply voltage not exceeding ±18V, and the three wires of the balanced XLR signal cannot be connected incorrectly. The NE5532 integrated block on the circuit board is a genuine second-hand disassembled machine. Because the components on the board are different due to different assembly batches, the brands, models, and specifications of some capacitors will be slightly different. The components and parameters on the received board shall prevail!

Packing List:

1pcs Balanced to Unbalanced XLR to RCA Pre-amplifier Headphone Amp Low Distortion