1W STEREO KA2209 AMPLIFIER MODULE (3087v2)

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Circuit Description : 

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. The data sheet contains further information about the KA2209. You may download it from the software download page on our website :

http://www.quasarelectronics.com/3087.htm

Assembly Instructions :

This is a 1 watt stereo amplifier module Kit using the KA2209 IC from Samsung, which is equivalent to the TDA2822. It will operate well 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 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. We have also provided input attenuation via the potentiometer which can  be used as a volume control.

You should keep the IC gain 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 = 20*log 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. 

Testing : 

Check the voltage and polarity before connecting the battery or power supply. If it does not work, recheck all component positions and polarity. Check all solder joints, and all  external wiring. The IC itself is quite robust, and there is very little else to go wrong. Remember when testing, it will not produce full output for more than a short duration because of limited heat dissipation. We found it easily exceeded the manufacturers specifications however.