Electrical Engineering Dictionary
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Stereo Amp

This is an example of a stereo amplifier circuit, dual channel. The circuit is shown with minimum components and can be used with op amps using a single or split voltage supply.

Op Amp Stereo Amplifier.

Single Supply Op Amp Speaker Driver Stereo Amplifier
Stereo Amplifier

A typical non-inverting Op Amp configuration.
Gain is defined by 1 +(Rf [100k] / Ri [2k]).
Of course the 100k potentiometers set the voltage level reaching the Op Amps. A dual ganged 100K-Ohm audio-taper potentiometer should be used over a linear taper or potentiometer. In some cases the component may be called a ganged stereo taper.

The schematic does not show pin numbers for the Op Amps because the circuit works for either a single or dual package Op Amp and of course a large number of different Op Amps. However to the right, some different pin numbering is shown.

Note that [although not shown well] the two potentiometers are ganged together, one knob changes both potentiometers at the same time. So although each channel uses a different potentiometer they both move up or down at the same time producing a volume control. A separate balance control could also be added to change the volume of one channel, while reducing the other. Or a separate potentiometer could be added into each channel so that each channel would be adjusted up or down, with regard to the other.

The amplifier could be constructed of either two individual Opamps or a package containing two Op Amps. The 741 is an example of a common Opamp having a single device within the package. Another common example would be a TL082 which is a component with two separate devices within the same package. The pin functions for both devices are shown the the right. Having two devices in the same package saves parts and and cost. However power dissipation is reduced by having two semiconductors operating in the same package, so a dual op-amp package may not be the way to go.

Regardless of the Op Amp used or the number of devices in a package, always bypass the power pin Vcc [Vs, V+] to ground using a .01uF capacitor [at a minimum]. Bypass capacitors are not shown in many of these schematic diagrams to make them less complicated to read. However it should be understood that by-pass capacitors are always used between all power pins and ground, and in some cases between differential power pins.

The 741 can also be compensated using the off-set null pins to center the output at zero volts [with no applied input].

Operation Amplifier Off-Set Null Compensation

Note that in some of these circuits the Op Amp has the inverting input at the top of the component diagram while in other cases the inverting input is below the non-inverting input. Its standard practice to rearrange the input or output pin locations in a schematic diagram to make the schematic easier to read or less complicated. Most CAD tools allow different versions of a part with different pin locations.

Speaker Drive;
When using a split power supply the output of the Op Amp may drive the speaker directly. Basically because the output of the Op Amp normally sits at zero volts, mid-way between to two supply rails. However a capacitor should be connected between the output of the Op Amp and the speaker when a single supply is used. The capacitor prevents any DC off-set developed by the Op Amp from reaching the speaker. A typical capacitor value may be 205uF.

Circuit Enhancements;
A Cross-over could be added to both the right and left channels so that additional speakers could be added. Even without separate speakers for base and treble, a single base control could be added to the circuit before the volume controls. In addition a treble control control could also be added. The circuit could be added after the volume control, but normally there are not separate controls per channel.
However to reduce complexity a tone control could be used instead of implementing both a base and treble control. A less complex loudness control might also be added to support the volume control instead of using a base control. Note a few of these circuits are represented as single channel, so they would have to be adapted to two channels.

PC motherboard

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