Monday, October 12, 2009

1 W Home Stereo Amplifier Project

Introduction To Home Stereo Amplifer
This is a 1 watt home stereo amplifier module project using the KA2209 IC from Samsung, which is equivalent to the TDA2822. It operates from 3-12V DC and will work from a battery since the quiescent current drain is low. It requires no heat sink for normal use. The input and output are both ground referenced. Maximum output will be obtained with a 12V power supply and 8 ohm speaker, however it is particularly suitable for driving headphones from a supply as low as 3V.

The Specifications of the home stereo amplifier are:

D.C. input : 3 – 12 V at 200 – 500 mA max
Idle current : approx. 10 mA
Power output : > 1 Watt max. 4-8 ohms, 12V DC
Freq. Resp. : approx. 40 Hz to 200 kHz, 8 ohm, G=10
THD : <> 80 dB, G = 20 dB
Sensitivity : < g =" 20">
Home Stereo Amplifier Description

Home Stereo Amplifier Parts List

The gain is adjustable from 10 to 100, i.e. 20 to 40 dB. Start with feedback resistors R1 and R3 of 1k ohm, this will give a gain of 10 which should be adequate for most applications. If you require more gain, you can remove resistors R1 and R3. This will give a gain of approximately 100, or 40 dB.The input attenuation can be adjusted via the potentiometer which can be used as a volume control. The IC gain should be kept as low as necessary to achieve full output, with the input potentiometer and your signal source at maximum.

This will keep the signal to noise ratio as high as possible. Extra gain provided by the amplifier will reduce the S/N ratio by a similar amount, since the input noise figure is constant. Other values for R1 and R3 of between 1k and 10k ohm can be used if an intermediate gain level is required.

Voltage Gain = 1+ R1/R2 = 1+R3/R4, however the maximum gain with no external feedback is approximately 100, or 40dB. (GdB = 20log Gv)

If driving a pair of headphones, you may also require a 100 ohm resistor in series with each output to reduce the output level, depending on headphone impedance and sensitivity. Make sure you start with the volume right down to check. A number of headphones may be driven from the one amplifier if you wish, since most headphones have at least 16 ohm impedance, or more commonly 32 ohm.

There are only a few external components, the IC contains most of the necessary circuitry. R1,R2 and R3,R4 are the feedback resistors. C1 provides power supply decoupling. C2 and C3 are the input coupling capacitors, which block any DC that might be present on the inputs. C4,C5 block DC in the feed back circuit from the inverting inputs, and C6,C7 are the output coupling capacitors. C8, R5 and C9,R6 act as zobel networks providing a high frequency load to maintain stability at frequencies where loud speaker inductive reactance may become excessive. The pot provides adjustable input level attenuation.


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