tearing my hair out over a silly little IC amp project with about 8 components

[Michael Shiloh]

I hope none of my students are reading this.

This semester, I decided to upgrade from the old LM386 (which is sort of
a '65 Plymouth Valiant) to something a bit newer. Poking around a little
bit, I saw many references to the TDA2822M, which boasts somewhat better
sound and is a stereo amp still in an 8 pin DIP.

Circuit is dead simple, basically variations straight from the
datasheet, e.g.:

http://electronics-diy.com/low-power-stereo-amplifier-tda2822.php

although I've tried a few others.

My problem is, as soon as I power up, I get a loud buzzing sound, even
with the inputs shorted to ground. So the amp must be oscillating, but why?

Output signal, before the bypass caps, is roughly a square wave with
some exponential rise and decay, around 170 Hz. I'm driving a pair of
small 8 Ohm speakers.

Power supply voltage is showing the same oscillations, but a more square
wave. I'm using a 9V battery, so likely when the speaker goes on it
drags down the power supply. I tried adding more bypass caps but this
didn't help.

Perhaps my 9V battery can't provide enough current for this? Tried it on
two bench power supplies. The ripple drops drastically but the
oscillation does not cease.

I double and triple checked my wiring. I took it all apart and rebuilt
from scratch.

What am I doing wrong?

[Jeff Keyzer]

Try ditching the breadboard for some copper clad and (short) point to point wiring.

Regards,
Jeff (mobile)

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[Michael Shiloh]

Hi Jeff,

Thanks for your suggestion. That was my initial thought, but I hoped the
circuit is not that sensitive. The old LM386 worked fine on a
breadboard, as built some 50 different ways by previous students.

I took your suggestion. I didn't have a solid piece of copper clad, so I
built it on a small perfboard, with very short wires. It doesn't
oscillate now, and works, but I'm not sure I want to use such a
sensitive chip with my students, unless it is to teach precisely this point.

Apart from that, the sound quality isn't so great, so I'm going to stick
with the 386 for now.

Thanks,
Michael