# Unexpected results with TDA 7052

I built the TDA 7052 circuit from the datasheet and connected it to my computer's sound card and a 50 $\Omega$ speaker.

Here's the circuit:

The $R_s$ is the source impedance, which I can't measure and sound card manufacturer isn't providing any useful information. I also used 100 nF electrolytic capacitor, since I don't have any ceramic at the moment.

I already know that the speaker and the amplifier can work well together, because they were salvaged from another circuit.

Now about my problems:

First problem is that the amplifier won't work on voltages above 3.1 V. The minimal voltage listed in the datasheet is 3 V, typical is 6 V and maximum is 18 V, so this looks a bit strange.

The next problem is that I get crackling and noise when I set the computer volume to more than 50%. The speaker is quiet (much more than in the radio I got the amplifier and speaker form) and from time to time it seems as if the amplifier is clipping (I'm not sure if that's the right word. The peaks seem to get distorted).

Here's the effect of increasing volume on a sine wave:

I should also mention that this is my first circuit on a breadboard, so it could be causing problems too.

So where do I start fixing this?

• The 100nF has to be ceramic for a reason (low ESR). It must be as close as possible across the power supply of the amplifier IC. – starblue May 14 '11 at 7:02
• You can measure the sound card's output impedance, but it's probably low enough to not matter. – endolith Oct 18 '11 at 2:05

## 1 Answer

Why are you using a 50 ohm speaker? The TDA7062 was designed for an 8 ohm unit.

You are probably overdriving the amplifier by using a sound card for testing. Try a few mV input.

Try putting a pot on the input, as a volume control. Sound cards have a low impedance output, so 10k (log) will be fine.

It's a high-gain amplifier and might be oscillating if you built the circuit on a breadboard. Put it on a PCB.

I've never had any problems with the TDA7052.

• Thanks a lot! The potentiometer fixed the problems with power supply voltage. When I set input voltage to say 100 mV, the output volume is really low, but there's no interference. I also tried with 8 $\Omega$ speaker and there was no difference in the output. I'll try with a PCB and a 100 nF capacitor next. – AndrejaKo May 14 '11 at 10:12