The power supply
The supply voltage must be a symmetrical, two batteries of 4.5 V or 9V battery is enough. You can also use a single supply of between 9 V and 24 V, associated with a symmetrizer power such as that seen in the following diagram:

Notes :

• Wire R3 as close to U1: A, R4 and R5 and the closest to U1: B
• If you see a parasitic oscillation when the gain is maximum, add a capacitor of 22 pF to 100 pF in parallel with the resistor R5.
• Minimize the cable length between the input connector and the input assembly.
• The output of the TL072 has a current limiting resistor integrated, which makes it inappropriate to attack large cable lengths. There are specific integrated circuits dedicated to this task such as drivers or DRV134 SSM2142 balanced line (sample application). Remember that this preamp is simple, and can not bring the qualifier professional!

The post Low Cost Pre-amplifier Circuit based TL072 appeared first on Amplifier Circuit Design.

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

The post Asymetric Pre-amp with Dual Supply Voltage appeared first on Amplifier Circuit Design.

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.

The post Asymmetric Pre-amplifier Circuit appeared first on Amplifier Circuit Design.

The post Single Chip Audio Preamplifier LM 358 appeared first on Amplifier Circuit Design.