Portable amplifier

Because I was bored and had the parts at hand, I decided to build a small portable amplifier. It uses a TDA7057AQ chip from a broken computer monitor with built-in speakers (actually it wasn’t broken until I decided to take it apart and take all the interesting parts out!). The TDA7057AQ is a 2 * 8 W amplifier IC requiring very few external parts. The circuit I use comes straight from the datasheet:

That’s a very simple circuit indeed! Because I didn’t have 5 kΩ resistors, a 22 k potentiometer and two 470 nF capacitors (I did have more of them, but they were all of different shapes and sizes), I used the following values:

• R_s -> 5,6 kΩ
• 470 nF capacitors -> 47 nF capacitors (in the monitor they also used 47 nF so it should work fine)
• 22k potentiometer -> 20k potentiometer

My speakers are 8 Ω 7,5 W and come from the very same monitor as the amplifier IC.

Finished product

Update 23 august 2007

Finally I had the courage to put everything together so I guess this project can be called “completed” now. One small detail, I decided not to add a DC input for reasons I am unable to remember. The sound quality can be described as “pretty bad, but still better than that of mobile phones and most cheap speaker sets for mp3 players”. The finished product:

Work log

June 2006

The amplifier is working. In fact, only one channel is working properly. The positive output 2 (pin 8) does nothing. To get sound from channel two anyway, I connected the speaker between the negative output 2 (pin 10) and ground. This way everything seemed to work fine but after some more testing I noticed that this caused a quiescent current draw of more than 350 mA instead of the normal value of about 20 mA! After many measurements I concluded that the IC must be dead (well, half-dead). I ordered a new TDA7057AQ to solve this problem. In the meantime, I’ll design a suitable box for this amplifier and choose a power supply (probably six RL14 alkaline batteries in series).

Update 22 june 2006

Today the new TDA7057AQ arrived. I’ll test it soon.

Update 26 july 2006

I finally started to work on this project again. Today, I made the beginnings of what should become the front panel. Here’s a picture showing the lashup:

I still don’t have a power supply for it. Now the best choice seems to me a rechargable 6 V lead-acid battery of about 3 Ah. With 6 V, the output power will be only 2 W (1 W for each channel), though. However, that should be enough in most cases. Maybe I’ll reserve room for a second battery so they can be hooked up in series for 12 V (which should give an output power of 10 W total, according to the TDA7057AQ datasheet).

Update 5 october 2006

Every project seems to take longer than you expected, and that’s especially true for this one. After a long pause I finally picked up the project again. I acquired a brand new 6 V 4 Ah rechargable battery which is what I will use as a power supply. I’m thinking of adding a connection for an external DC power supply, too.

I also continued building the enclosure for the thing. It’s a box measuring 22,5 x 11 x 10 cm and it’s made of 4 mm thick MDF. Here are a few pictures of the building process:

Personally, I think it looks pretty decent. Due to a stupid miscalculation however, the back panel doesn’t fit (it’s 8 mm too large). But I don’t think that’s going to be a big deal. When the enclosure is finished I’m going to spray paint it silver.

Update 6 october 2006

Just a small update to keep you informed. Yesterday I put everything in the box for a test run. It sounds definitely better than without the box. Of course it’s not über high quality, but it’s acceptable. Here are two pictures:

Altough I cut 8 mm off the width of the back panel it still doesn’t fit because it’s 2 mm too high. I asked for a piece of 11 cm high in the shop, but they cut off a piece of 11,2 cm instead. *sigh* Before I start painting, I have to fit in a few extra connectors, namely the sound input and the DC input. Because there’s no electronics shop anywhere near where I live, I had to order these parts online so I have to wait a few days before I can continue work.

A new update will follow when I feel the need.