TDA2030A distortion

[caxxxxxx]

I just built my first working TDA2030 on a 5 hole protoboard. I had some success, but I get very audible distortion mostly at low volumes, but still audible at higher levels. I used the datasheet schematics and values, but I omitted R5 and C8 for the moment.

It's near dead quiet with no input connected, a very slight hum if I put my ear right on top of the speaker. It doesn't run hot at all, a tad warm if no input is connected.

Here's my PCB layout, the green lines with very large pads are wires. Smaller red lines are the PCB copper lines:

Untitled3.jpg

and here is a bad pic from my cameraphone of my completed build:

Untitled4.jpg


My Power supply consists of a 24VCT 1.5 amp trafo (from the spec sheet)connected thru a rectifier circuit from a LM3886 kit I use regularly with 20000uF per rail (a little much I agree but it's all I have atm). It reads 36.5V total DC power. Heres a pic of the board:

Untitled5.jpg

Edit: Noticed my 100uF caps were backwards on the board layout above, and corrected the pic.

[geraldfryjr]

I dont understand what the diodes are for as they may be the source of your distortions.
If you post the schamatic it will be easier to analyze.

Also it looks as though the .1uf cap on the v+ rail is connected to the output instead of the ground as it is a bypass cap.
I just saw this and could be the cause of your distrotion.
As I know what the diodes are for but I don't think that they are necessary.
jer

[caxxxxxx]

Originally Posted by geraldfryjr

I dont understand what the diodes are for as they may be the source of your distortions.
If you post the schamatic it will be easier to analyze.

jer

OK, thanks:

Untitled.jpg

Corrected PCB layout:

Untitled3.jpg

Why cant I edit my first post now?

[Mooly]

Try it with R5 and C8. I suspect it is unstable if you could see the output on a scope.

[caxxxxxx]

Originally Posted by geraldfryjr

Also it looks as though the .1uf cap on the v+ rail is connected to the output instead of the ground as it is a bypass cap.
I just saw this and could be the cause of your distrotion.
As I know what the diodes are for but I don't think that they are necessary.
jer

Oops, I didn't do this on my actual PCB, gotta fix the pic. The .1uF is going straight to ground, not output pin #4 as shown. I will fix the board layout pic (again...) and repost new picture.

I didn't think the Diodes were necessary as none of my kits have them, but better safe than sorry. Would save me some space if I removed them tho......

Originally Posted by Mooly

Try it with R5 and C8. I suspect it is unstable if you could see the output on a scope.

I was hoping to avoid this, but perhaps your right. I guess I'll make room by removing the diodes. Thanks guys!

[caxxxxxx]

I'm scratching my head trying to figure out what C8 value is. I'm guessing 20K is the cutoff frequency?

From the datasheet:
Untitled2.jpg

Google search info:
What is the component value in tda2030a circuit???

I come up with 2040 for R5
C8=361pF

So, 2K Resistor and 390pF cap should be ok, right?

[Mooly]

Remember you are using the cap as a means of increasing the stability margin rather than defining a specific bandwidth. In practice a small value may well be all that's needed, say 22 or 47pf. Without seeing what is actually happening on a scope we have to just best guess it.

[caxxxxxx]

I soldered together a 390uF and 2K resistor, it sounds way worse now. It always "farted" a little on powerdown for a brief couple of seconds, but now it really does it badly, lol.

Mooly, I'll try the smaller values next

[Mooly]

390uF ???????????

we are talking pf for the compensation, little more than the capacitance a few cm of parallel wires would have.

Try something like 22pf

[caxxxxxx]

Oops, as stated in post #6, I used 390pF. Typo on my part.

Anyway, tried the 30pF with 2K resistor, still sounds a lot worse. I don't have a 22pF, I have a 10 and a 30pF