Stereo Amplifier with Subwoofer

[rafaelandreatta]

Hello,

I have a Logitech 2.1 Speaker System, it has obviously 2 speakers and 1 subwoofer. I also have a home theater with 2 speakers and 1 subwoofer, but it is not working.

My goal is to build another amplifier to use with these speakers + subwoofer of the home theater. I am thinking in cloning the Logitech project. I have opened the amplifier and it looks like simple to build. I have found so far the components:

2x 2200uF
8x 100uF
4x 220uF
1x 47uF (did I read wrong? should it be 470uF?)
1x BT2025BH (here is our problem)

All capacitors are eletrolytic 16V.

I have another CI that has a heat sink, I will have to use the solder to remove and see the CI model.

But, this BT2025BH, I cannot find the datasheet anywhere. I put in google and a lot of chinese and korean websites are shown. I read in a link that it could be replaced by KA2026 or TEA2025B.

Does anyone know a CI replacement for this BT2025BH?

Sorry if I'm telling something wrong, I'm not an expert in electronics.

Thank you all for the help

 

[bountyhunter]

Sorry if I'm telling something wrong, I'm not an expert in electronics.

I am or I was, so I'll give some free advice: buy an amp, they are dirt cheap these days and will have all the stuff it takes to keep your speakers from being destroyed like soft-start at turn on. And, you can buy one cheaper than you can build one.

 

[audioguru]

Recently I bought a 2.1 audio system that sounds good. It cost only $25.00.
The 150W and 75W power ratings are a joke. Its total output power is about 7W.

I cannot attach (upload) its image today.

EDIT: I still cannot upload an image.

 

[transistor495]

I cannot attach (upload) its image today.

EDIT: I still cannot upload an image.

You've praised those little speakers a lot and it gone out of your hands..

It is now not ready to sit and show up in this little forum...

 

[audioguru]

My $25.00 2.1 speakers system is here:
NOPE. Uploading does not work here today.

 

[rafaelandreatta]

Thank you for the replies.

Well, I know I could buy one for cheap etc... but I do want to build it, for practice etc, you know?

I have looked around for some 2.1 amplifier circuits but I cannot find a good one (that I could buy for some cheap). So I have decided to first make a simple stereo amplifier, and maybe attach a low pass/subwoofer filter to it. What do you think?

Independently of if attach the filter to the stereo amplifier is good or not, could someone tell me if the following circuit would work?

I have found this link: **broken link removed**

But I have been reading a topic where you audioguru made some corrections to the circuit.

https://www.electro-tech-online.com/threads/help-need-for-audio-amplifier-la4440-ic.114214/

You told that we should follow the circuit in the datasheet, which is: https://1.bp.blogspot.com/_B8Dh2WXN...mA/s1600/stereo+Amplifier+circuit+LA4440..jpg

But, the circuit in electroschematics.com looks a bit more sophisticated than the datasheet one. For instance, the datasheet circuit does not include the potentiometers. But if it is really better than the other one, where should I put the potentiometers in order for it to work? It could be used double potentiometers (I just want to control the volume), right?

Thank you for the great help!

 

[audioguru]

EVERY power amplifier has an input volume control. The manufacturer of the obsolete Sanyo LA4440 IC assumes that you know how simple it is to add volume controls.

Yes, use input coupling capacitors and a double pot.

 

[rafaelandreatta]

EVERY power amplifier has an input volume control. The manufacturer of the obsolete Sanyo LA4440 IC assumes that you know how simple it is to add volume controls.

Yes, use input coupling capacitors and a double pot.

Considering that LA4440 is obselete, I think it is better to use the following circuit. What do you think?

https://www.electro-tech-online.com/custompdfs/2012/04/3088.pdf

Permit me to ask two more questions.

1 - If I understand correctly, in this case, the middle terminal of the potentiometer would be connected to the capacitor C1 (for channel 1 and the other middle terminal to the C2). And the other terminal (don't matter what is) should be connected to the channel input. Am I right? But, what should be the max resistance of the pot? I really don't know how to calc this, could you give me an advice?

2 - When the circuit is finished and working, is it hard to add a subwoofer output by coupling some kind of low pass filter? Do you have a link or something to a circuit that I could couple to the amp in order to make the subwoofer to work?

I really appreciate your help!

 

[bountyhunter]

Thank you for the replies.

Well, I know I could buy one for cheap etc... but I do want to build it, for practice etc, you know?

OK, go ahead.

 

[audioguru]

Considering that LA4440 is obselete, I think it is better to use the following circuit. What do you think? TDA2009A

Its output power is fairly low but it is available and it works fairly well.

1 - If I understand correctly, in this case, the middle terminal of the potentiometer would be connected to the capacitor C1 (for channel 1 and the other middle terminal to the C2).

Yes.

And the other terminal (don't matter what is) should be connected to the channel input.

no.
The input and ground terminals must be correct or the volume control will work backwards.

what should be the max resistance of the pot? I really don't know how to calc this, could you give me an advice?

Look at the INPUT RESISTANCE in its datasheet. it is from 70k to 200k so a volume control can be 10k, 22k or 47k ohms for each channel.

2 - When the circuit is finished and working, is it hard to add a subwoofer output by coupling some kind of low pass filter? Do you have a link or something to a circuit that I could couple to the amp in order to make the subwoofer to work?

You need a separate power amplifier to drive a sub-woofer. Usually the sub-woofer amplifier is fed from a lowpass filter and the stereo amplifier is fed from two highpass filters. My favourite audio site does not have a project of the filter circuits but there are many on the internet.

 

[transistor495]

Bit complicated but should give excellent performance. You should be able to build this using couple of TL071/72s. Try this active filter circuit:

View attachment 62979

You can use single TDA2009A for stereo section and may be a TDA2030 for the woofer part. Combining all these, you've a very nice hifi 2.1 performer!