Portable Stereo Project: Amp Woes

[scwhiteley]

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.

[audioguru]

The TDA2003 is very old and it and TDA2030A ICs do not match well enough to make a bridged amplifier. A TDA7240A is a bridged amplifier made for a 14.4V supply and works well.

The pcb design showed on the datasheet should be used. A supply bypass capacitor or two should be used that are also shown on the datasheet.

RadioShack proto-board has very low quality with the copper too thin and the holes too big. It is made from cheap phenolic-paper that warps instead of good quality epoxy-fiberglass.

[pyrohaz]

I made a simple amplifier with the TDA2030 in a tech lesson at school, after looking around at what parts my school had, I found an old unsoldered TDA 2030, after soldering some solid core wires onto it, I made a 5W or so audio amplifier out of it, I know this is probably not the way to do it but I:

1. Connected the +Vs to my 12v Supply and the -Vs to 0v.
2. Biased the Non-Inverting input half way between the supply voltage using a simple resistive divider (two 10k's and a 100uF capacitor to make sure I got no ripple)
3. I then wired it up as a standard Op-amp based audio amplifier, 10k resistor between the input capacitor and the inverting input, then a 100k resistor between the inverting output and the output for a gain of 10. Before the input capacitor, instead of directly inputting the the sound source into the amplifier, I made a simple Preamplifier based on the LM741 (I know you guys aren't too fond on the chip but it worked fine for this project!)
4. I added a Miller circuit (? I forgot the name of the actual circuit lol) 1R resistor in series with a 100nF capacitor on the output, I think the increases stability or something?
5. I placed a 2200uF Capacitor between the output from the chip and the speaker, my speaker was a single 4R speaker with a built in crossover and tweeter.

The sound was actually quite impressive, after trying it with my bass guitar and comparing the sound of that amplifier to the sound of my standard amp, I was quite impressed at how small my distortion levels were.

Obviously, there were some problems with this design such as: Negative feedback for the whole design I think? I will obviously keep that in mind for when I next build a circuit like this again.

Audio, I don't think that he was intending to use them bridged, just using each chip for each channel.

All I can personally say is I don't think you will be able to get much power as the TDA2003 at full power will cause quite a bit of distortion (10% at 10w through a 4ohm speaker) so if you did end up using the TDA2003 and TDA2030, you'd have to limit the TDA2030 to a much lower level.

[audioguru]

I made a simple amplifier with the TDA2030 in a tech lesson at school, after looking around at what parts my school had, I found an old unsoldered TDA 2030, after soldering some solid core wires onto it, I made a 5W or so audio amplifier out of it.

With a supply of only 12V its output at clipping is only 1.0W into 8 ohms and 1.75W into 4 ohms.

5W into 8 ohms is 17.9V p-p. The amplifier has an output voltage loss of 4.5V so the supply must be at least 22.4V for 5W into 8 ohms.

[pyrohaz]

I calculated massively wrong then XD I dont understand how it got so loud then, was my speaker just massively efficient or was it overdriving but where I couldn't hear it? I was only using a single 12v Supply while my Bass amp (Hiwatt 10w blah blah...) seemed quieter :S And I had got the speaker wrong. After looking, it was 4 Ohm phillips speaker with tweeter, only a 5.25" speaker though :S Sealed enclosure....

[audioguru]

An amplifier produces almost double the power into 4 ohms compared to 8 ohms. Double the power is just a little louder.
A 0.5W clock radio is pretty loud. My 140W stereo is much louder.
At work my demo sound system had 1600W. I tried not to break the windows with it. I am lucky it didn't deafen me.