Build an audio amplifier

Build a good Audio Buffer Amplifier
By Kevin K. Custer W3KKC

General Description:
This circuit will amplify voice audio in the range of 50 to 10,000 Hz with little distortion, and have the ability to drive a low impedance load to 16 ohms. The circuit will run from 5 to 18 vdc and give about 20 dB of gain.

Concept:
To build an inexpensive audio amplifier with little parts count that is very reliable and easy to build and implement. Parts are available from many online sources.

Construction:
Build the circuit on a breadboard and use a socket so when the lightning hits, well you know...

If the audio input is biased above ground (audio floats on a voltage) a coupling cap will need installed in the "Audio In" lead to the pot. The pot can be any value from 5k to 100k. This pot can be left out if the circuit ahead of it already includes a potentiometer. The 100pF helps make it immune to RF, making it suitable for higher RF environments. Don't leave out the 100uF cap or the circuit will oscillate, or otherwise be unstable.

Many op-amp circuits don't drive low impedance loads well, this circuit will handle a load impedance to about 16 ohms but doesn't need to be loaded down to that impedance. The output cap is a 10uF non polarized electrolytic for impedances to 600 ohms. The output capacitance should be raised to 100uF for impedances to 100 ohms and to 1000uf for impedances below 100 ohms (speaker).

Operating bandwidth is from 50 Hz to 10 kHz Over 10 kHz the unit suffers from poor slew rate, causing distortion, but for NBFM this bandwidth is acceptable. Actually, for this purpose slew rate limitations work to our advantage as it helps make the amplifier less RF susceptible. Increased audio amplification can also be had with the addition of a feedback loop. Consult the TI part manual for examples.

This extra is from Danny Musten KD4RAA:
With the addition of a .0047 uF capacitor in series with a 15k resistor from pin 1 to pin 5 of the IC, gives a -6 dB per octave de-emphasis slope to the circuit.
I am using your audio buffer template w/the LM-386 on all my link radios using disc audio for uniform sound throughout. See picture below.

If you have further need of information, or if you have enjoyed this construction article, please e-mail me at: kuggie /at/ kuggie /dot/ com and let me know.
I may take the time to do more quality construction projects in the future.

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This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.