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Portable Stereo Project: Amp Woes

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scwhiteley

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Hello!

I'm working on a portable stereo project and could use a little input. I've built a few stereos over the past couple of years with varying success. So far I've only used TDA2003 and TDA2030 IC's in my projects, but I'm open to suggestions.

Here are some of the hardware parameters of the current project:

The speakers: Two cheap 4 inch, 4 ohm, 100 peak watt speakers

The power: I was planning to use a 12 cell pack of NiMH AA's, so a 14.4 volt pack. The cells I've been looking at are rated anywhere from ~2500 to ~3500 mAH.

Finally, the aspect of these projects that gives me the most trouble: the amps...

My original intent for this particular project was to use a pair of bridged TDA2030's for each channel (which, according to the schematic specs, will provide 20W per channel) The biggest problem is this, my success rate in building amps with TDA2003 and TDA2030 IC's is about 50%. So really not very good at all... I lovingly assemble and solder them, and about half of them work. I have been building them on perf. project boards from Radio Shack, and my best guess at the problem is that I'm a subpar solderer. The joints look good to me, and I painstakingly inspect them for even the tiniest of macroscopic shorts. Alas, the pair of amps I built for this project (on one project board) aren't functioning properly. The left unit seems to work okay by itself (it doesn't seem to sound as good as some of the others I've put together), and the right sounds like absolute staticky, frothy excrement. And they both sound terrible when running together. Frustration abounds.

To be completely honest I'm sub-amateur at all of this stuff, but I'm willing to learn. If anyone had some input on good literature regarding simple electronics and amplifiers, I'm all ears. That being said, I'm not sure that I'm pairing the proper amps to the rest of the get-up. I know very little about what amp IC's are available and which would work best in my projects, I'm going entirely off what I learn from the internet. I'd greatly appreciate some wisdom in this area. What amp would you use? I'm willing to budge on the power supply and maybe even the speakers, but it needs to be rather compact... and cheap, of course.

As I have apparently been cursed by the god's of solid state amplification, perhaps a good question would be this:

In you're experience, what is the greatest pitfall of the home-made amp? Bad solder jobs? Bad schematics? Bad implementation of schematics on a perf. board?

Thank you for reading, sorry for rambling.
-S. Chad Whiteley

P.S. - Of course, all of my schematics and diagrams are available for, well, entertainment probably.
 
TDA2030A ICs are not matched so they make a poor bridged amplifier. With a 14.4V supply their power into 4 ohms is only 15W, not 20W at clipping.
Use one TDA7240A bridged amplifier IC instead for each channel. Its power is also 14W into 4 ohms at clipping.
 
Awesome, thanks for the speedy replies!

It looks like the TDA7240A could be really handy for this project. It would definitely reduce the size, which is good for the enclosure I'm intending to use. Also, less components means I'm less likely to screw the whole thing up.

Thanks,
-Chad
 
I've been reviewing the specs and schematics for the TDA7240A circuit and I've come up with a question. A potentially silly one.

If you take a brief look at the schematic here:
https://www.electronica.ro/audio/images/TDA7240A.gif

It refers to a "standby" switch on pin 2. It appears to me, the sub-amateur, to simply be a power switch. I was under the impression that "standby" mode existed to keep tubes warm, a feature that this IC (by the very virtue of being an IC) does not need. Is this a misnomer?

The reason this even bothers me is that I would be using this circuit on a battery powered stereo, so a constant power drain in the off (or "standby") position would be detrimental. Perhaps I'm just reading too much into it.

Anyhow, based on it's simplicity alone, this looks like the IC I should have been using all along.

Thanks again,
Chad
 
In Standby position, the amplifier's current is very low (200uA instead of 65mA when it is normal without a signal).
Its Standby switch passes a very low current so it can be small and cheap.
Coming out of or going into Standby eliminates a loud PLOP in the speaker that happens if the amplifier is simply turned on.
 
Okay, quick question.

I've been dinking around working out how I'm going to assemble these amps while I wait for parts. I came across a small hiccup, it may be nothing.

I'm building the circuit according to the TDA7240A specs:

**broken link removed**

Strangely enough however, the application circuit shows capacitor C4 (220uF), but it is mysteriously missing from the PC Board layout... The application suggestion lists C4 as a supply filter...

So my plan is just to stick C4 on the perf. board next to C5 and hope it all works out.

...unless, of course, that is a bad idea.
 
C4 is part of the power supply. It must be added if you use a battery.
 
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