My First Build

[Nurbit]

Hi Guys

I thought I'd show off my first attempt at building an amp.

I acquired several old Coomber tape players which have TDA2040 chips inside them so I thought I'd build an amp based around those first and hopefully build a gainclone later on based on an LM3886.

I did make an attempt to use stripboard but that failed misserably so in the end I used the board layout from the datasheet.
I had to edit it on the PC and resize it before it could be used but that didn't take long to do.

I then etched my first circuit board using the toner transfer method and ferric chloride. I was very happy with the results for a first attempt.

Here is the pic of the etched board......


I then started adding parts to the board. As you can see in the next image, I didn't have the correct value for some of the resistors so I had to improvise and add 2 resistors together to get the desired value



Once it was finished, I used a small heatsink at first but then replaced it with a larger one.





The next step after that was to throw together a PSU to run it.
I should note at this point that I opted for a single supply version of the circuit due to the fact that I only have single output transformers.

For the PSU I used a 20v transformer, then ran it through a KBU 6D bridge rectifier and then used a 4700uf capacitor before it connected to the amp board.





And there it is.
It's bloody loud. I haven't added a volume control yet.
I plan on building another one and casing the PSU so that I can use the system in my shed

I have noticed that without an input source, the speaker hums like mad but stops when I plug an audio cable in, even with no music being played.

Is this normal?

Is there anything I seem to have done wrong/badly/stupidly?
What changes would you all suggest?

One other thing I don't understand.....

Should I be using a single power supply or the split type power supply that supplies both a plus and minus voltage?

What are the advantages to the split type?

Sorry if I sound thick but I'm still learning

-- edit --

I'd also like to mention that one of the most usefull resources I used was Nuuk's Decibel Dungeon website.
I've have read his site more times than I care to remember but each time I managed to absorb something new.

Thank you Nuuk for such a brilliant website

[AndrewT]

Check the amplifier alone.

Short the input hot to input ground.
Leave the output without any external load.
Power up and check the output voltages, Vac and Vdc.
Both should be near 0mVdc & ac.
power down.
Connect your source.
Repeat the measurements. Have they changed?
Report back.

[Nurbit]

will do, thanks

[danielwritesbac]

Originally Posted by Nurbit

. . .
I have noticed that without an input source, the speaker hums like mad but stops when I plug an audio cable in, even with no music being played.
. . .

Add the load of a resistor or the load of a potentiometer to the input.

[Nurbit]

Andrew T - I did as you suggested.
I am getting 0vac but I am getting 11vdc with and without the input shorted.

I have now built an identical circuit and have found the same results on both so it sounds like a circuit design issue rather than a faulty part issue...... or am I just being silly

Thanks

[Nurbit]

Even though my last post hasn't been authorised by the mods yet, please ignore it
I'm an idiot.
For some reason, I had the test leads in the wrong holes on the meter.
I'm actuslly getting 0vac still but only about half a volt dc......

On both circuits.....

[AndrewT]

50mVdc is too much.
You should be getting <<500/10 mVdc
Aim for 0.5mVdc to 10mVdc, with and without the source connected.

[Nurbit]

Sorry if I sound thick but how do I do that?
Do I simply add resistors to the output stage or is there something else I should be doing?

Thanks

[AndrewT]

Post your schematic with component values and component labels.

[Nurbit]

This schematic is the single power supply version taken directly from the TDA2040 Datasheet