How many of you have some old recordings on CD monophonic "vinyl" or on tape? If you've relegated to the bottom of the attic, it's time to go find them! The circuit that we propose in this paper is capable of converting any signal mono audio signal into a stereo.
course you can also listen to your old TV or audio from your microphone with excellent panoramic stereo!
FM radio stations can use this circuit to transmit all their old tapes in stereo and make their listeners an amazing surprise. Our converter
mono / stereo consists of only three integrated circuits and its manufacturing cost, widely available, is one more reason to try it.
The wiring diagram
For this project, we used operational amplifiers NE5532 from Philips as they provide a signal without noise and debit output enough current to power a stereo headset.
The first four amplifiers that appear on the diagram of Figure 4 (IC1/AB and IC2/AB) are used for 360 ° phase shift the signal applied to their input. The signal at the output of IC2-B is sent through the resistors R15 and R23, the respective inverting inputs of amplifiers IC3 IC3-A and-B.
On the same entries are also sent the signal collected by the inverter S1 input jack (see STEREO 1) or pin output of the amplifier IC1-A (see STEREO 2).
The amp IC3-A adds the phase signal to the input to produce the left channel of the stereo output.
The amp IC3-B subtracts the phase signal from that input to produce the right channel stereo output.
With the inverter three-position S1, we can choose between a normal stereo effect (STEREO 1), very pronounced (STEREO 2) or a mono signal (MONO).
The signal to be applied to the input of the converter must be provided by a preamplifier capable of controlling the tone and volume (see Figures 2 and 3).
The stereo signal at the output of the converter can be listened to with headphones or stereo inputs applied to a power amplifier through two shielded cables.
converter accepts a supply voltage between 9 V (minimum) and 30 V (maximum). It consumes a current of 20 mA and can be powered with two 9 V batteries connected in series to obtain a voltage of 18 V.
Figure 1: Photograph of the converter circuit mono / stereo mounted. 
Figure 2: The signal to be applied to the input of the mono / stereo should be provided by a preamplifier capable of controlling the tone and volume. 
Figure 3: If you are a musician, trying to listen to your performance using headphones or an amplifier Hi-Fi stereo (see Figure 8). You'll be thrilled! 
Figure 4: Diagram of converter mono / stereo. This circuit is powered with a voltage of between 9 and 30 volts.
Figure 5: View of connections NE5532 integrated circuit used in this project. Do not try to replace it with a TL082 as it provides a signal with low noise and sufficient current to power a stereo headset. 
Figure 6: The circuit can be mounted inside a plastic housing. In the kit, the holes are already made.
List components LX.1391
R1: R2
22 kW: 22 kW
R3: R4
22 kW: 22 kW
R5 R6
22 kW: 22 kW
A7: 22 kW
R8 : 22 kΩ
R9 : 22 kΩ
R10 : 22 kΩ
R11 : 22 kΩ
R12 : 22 kΩ
R13 : 10 kΩ
R14 : 10 kΩ
R15 : 22 kΩ
R16 : 22 kΩ
R17 : 22 kΩ
R18 : 22 kΩ
R19 : 100 Ω
R20 : 100 Ω
R21 : 22 kΩ
R22 : 22 kΩ
R23 : 22 kΩ
R24 : 22 kΩ
R25 : 10 kΩ
R26 : 10 kΩ
C1 : 1 μF polyester
C2 : 22 nF polyester
C3 : 470 nF polyester
C4 : 100 nF polyester
C5 : 22 nF polyester
C6 : 470nF polyester
C7 : 22nF polyester
C8 : 470nF polyester
C9 : 100nF polyester
C10: 22nF polyester
C11: 47 uF electrolytic
C12: 22 pF ceram.
C13: C14 220 uF electrolytic
: 220 uF electrolytic
C15: 22 pF ceram.
C16: C17 100nF polyester
: 220 uF electrolytic
C18: 47 uF electrolytic
DS1: Diode 1N4007 IC1
: integrated circuit IC2
NE5532: NE5532 integrated circuit IC3
: IC NE5532
S1: 3 position switch
Figure 7: Implementation plan components. The male headphone jack should be connected to the female jack on the right side of the circuit (OUTPUT STEREO).
Figure 7: Drawing of a printed circuit scale. 
Figure 8: To use a Hi-Fi stereo amp, draw the mono signal to a preamplifier capable of controlling the tone and volume. Connect the stereo output of the converter to the left and right power amp with two shielded cables. Practical realization
LX.1391 On the printed circuit board (see Figures 7 and 7a), you can start welding the mounting brackets for integrated circuits IC1 and IC2 IC3, resistors and LED DS1.
Insert all electrolytic capacitors, ceramic and polyester.
Now install the female jack for stereo headphones and if you intend to connect the converter to an amplifier, attach two RCA sockets (for BF) of the same type as that used for the input.
Once editing is complete, insert the ICs in their positioning notches-keyed towards the right (see Figure 7).
Attach the circuit board inside its plastic casing with four self tapping screws and place the inverter S1 at three positions on the front.
On the back of the casing, drill three small holes, one for audio input jack and two power cables.
To verify the proper functioning of the device, simply apply a mono signal to the audio input of the converter and listen to the signal output by the inverter switch S1 between its three positions.
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