Concatenation of the two previous schemes Asymmetric Pre amp and Asymetric pre amp with dual supply voltage.

Power supply
As already stated, a single or dual power supply is required to power this circuit. You can do with a single +15 V power supply as described on page single supply, or a dual power supply as described on page Asymetric pre amp with dual supply voltage.

But any other single power supply delivers a regulated DC voltage value between 12 V and 24 V appropriate very well (max 30 V). If symmetrical power supply, do not exceed + /-15V (absolute maximum of + /-18V). If you absolutely want to use a power higher value, then you should choose a double op amp that is able to handle this voltage. If you want to integrate this set into a AF amp and use existing power to the amp.

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Virtual ground
With power of symmetrical type, we do not need the virtual ground, and components that were working for this function have no purpose.

Output coupling capacitors?
A priori, we should not need coupling capacitors in the signal AF output of the preamplifier, since the resting voltage (no audio signal at the input) is close to 0V continuously. However, I leave to you to decide whether or not to implement them, knowing that the value of the voltage may be present output depends on the op amp used.

Asymetric pre amp scheme for single or dual power supply

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Single power supply and virtual ground
The use of a single power supply requires the presence of a voltage equal to the voltage divided by two. This half-voltage is created by the resistors R9 and R10 connected in voltage divider bridge. This half-voltage, which is a virtual ground, is stabilized by capacitor C8 and is brought on the non-inverting input of the op amp by the resistors R5 and R6 to the input signals are superimposed BF

Amplification
The capacitors C3 and C4 are used to limit the DC gain, since a capacitor acts like an open switch for DC voltages The gain is indeed defined by the resistors R1 and R2 for the left channel, and the resistors R3 and R4 for the right way. If the capacitors C3 and C4 do not “lead” not continuous, as if the resistors R1 and R3 were a very high value, as they are “disconnected” For more gain (AC, ie signals with BF), increase the value of resistors R2 and R4. For less gain, decrease in value. With the values ​​adopted here, the gain is about 15 dB (gain of about 5, 12 dB corresponds to a Gainde 4, and 20 dB corresponding to a gain of 10).

Asymmetric Pre amp Output
The AF output is made through coupling capacitors, to avoid passing the half-voltage output of this op amp. The resistors R7 and R9 determine the potential of the negative output capacitors C5 and C6, to a zero potential, so it has no “cloc” when connecting or disconnecting the output preamp, and allow at the same time reduce distortion if the equipment following features input coupling capacitors that are not referenced to ground.

Asymetric pre amp for dual supply voltage scheme.

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This Simple preamplifier circuit provides sufficient gain to weak audio signals from the microphone. This circuit can also be supplied from the voltage baterry 3 to 9 volts if necessary. Take a note that the microphone used in this pre-amp circuit is electret type.

If you are using high fidelity sound system, the this mic pre-amp will not become a good choice, you should be find other circuits.

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