Electronics > Beginners

Loud Speaker?

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mariush:
Of course you can adjust the gain with those TDA chips, the datasheets explain what each capacitor and resistor in the example circuits do and what increasing or decreasing their values does.

Of course these chips will get warm or hot without a heatsink, they're not 100% efficient, they're class AB amplifier chips, not class D chips (but class D chips are more expensive and can be much more difficult to make on your own, these are super easy to use). Their efficiency is about 65-70%, so if you'll give them 40v and output 20-25w to the speakers, you'll get about 10-15w wasted as heat, so you'll need a large heatsink for them.

But if you power them from 12v and they output 2.5-4 watts, a small heatsink would be enough, something recycled from an old power supply, or even some metal sheet screwed to the back of the chip may be enough.

Your LM386 may not get hot, but that's only because it won't output much power anyway, it's limited to 1.5w or something like that, you only get about 0.7 watts on a speaker... if it doesn't take much power in and doesn't put much power out, what's there to heat?
It's not a powerful audio amplifier and no matter how you put it, it's just not designed for those big speakers. Honestly, I wouldn't use it to power something bigger than headphones.

The point is that it's a very easy project to tackle, it doesn't cost much money, these chips are very generic and you may find them in stores around you (stores that sell parts for tvs and radios, maybe even people repairing tvs have them around if you ask them), they're cheap. The capacitors and resistors are also cheap...You can find everything needed on eBay if you don't find in Greece, it's really not a problem.
It would be a nice simple project for you to make and enjoy.


I have an audio amplifier board taken out of an older Phillips TV (I'm attaching it to this message) that uses TDA2040 and never had to adjust the gain, I found that adjusting the volume in Windows was enough. Nowadays I have a 5.1 system and don't use it anymore. The circuit in the datasheets is much simpler, this one has headphone output and some other additions that I don't use and you wouldn't need anyway.

The heatsink is sized so that the amplifier would output up to 20-25w per channel, the 35w printed on the board is peak, with 10% distortion. tda2040 is designed for about 40v input voltage, the transformer in the picture is +/- 15v and low current.  When I used it with two 10w 4w speakers, the heatsink barely got warm, even at high volume.
 

ChrisGreece52:
Nevermind i saw the datasheet and the site in depth and i saw that instead of a capacitor the TDA uses a resistor :D

ChrisGreece52:
I think i am going with the TDA 2050 because of its output power.
Ill feed a 12 volt DC voltage to it and reffering to the diagram it says that with about 12 volt input voltage the power output is about 10 watts.
Also i will use the same gain configuration that i wanted to used with the LM386
its a double pole single throw switch the one pole is connected to an led (to indicate the status of the gain) and the other pole to the main capacitor (in this case resistor)

ChrisGreece52:
From the datasheet i got this info.
I will operate it at 12 volts
At this voltage the output power is about 10 watts
the distortion at 20 watts (1 khz) is 0.03%
and at 15khz is 1% (non existant at 10 watt)
also the power dissipation at 10 watt is also 10 watt (i hope i am wrong at this one)

mariush:
No.

Pay attention to what the graphs say:



The graph is for SPLIT POWER SUPPLY  (a power supply that has negative AND positive voltages feeding the amplifier). 
The voltage values below are listed as +/- VOLTAGE.

In the first picture (on the left), you're not interested in 10% distortion, so you look at the second curve that's a bit lower than the first, which is for 0.5% distortion.

On the Y axis, you have the output power, on the X axis you have the input voltage, in +/-V. If you're going to use a single power supply ( just ground and +v), you have to double that value.

You can see that it crosses the 5w output at +/-10v, so you'd need +20v to get 5w output on the speaker. With 40v (+/-20v) you get about 20w output.
With just 12v, you have to look at +/-6v , so you're somewhere between +/-5 and +/-10v, at about 2-3 watts.  This is still way better than about 0.5-0.7w you get with LM386, with 10% distortion.

Since these have such large input voltage range (up to +/- 25v or 45-50v for single power supply) it makes them great to use with recycled transformers - 24-30v AC transformers are relatively easy to find (but remember it's not just the volts with a transformer, the VA rating must be big enough, let's say about 40-60VA at least, this would make it a heavy transformer, about 0.5 Kg at least).
Until you do find one, you can simply use a 12v from a computer power supply and only get a lower number of watts. 

In the second picture, on the right, you have the Distortion versus output power, WHEN the IC is powered from +/- 22v (so with a single power supply that would be 44v - the IC tolerates a maximum of +/-25v or 50v).  This is close to the IDEAL way the amplifier would like to work, the maximum voltage it supports.
That one says that with 8 ohm speakers, the distortions are typically below 0.1% from 1kHz to 15kHz. 
But the graph is only correct for +/-22v or about 44v. If you power the amplifier from only 12v, the distortions may be a bit higher... but should be below 0.5% as the graph in the first picture say.


Later edit:   The graph there on the left is for  8 ohm speakers. If you use 4 ohm speakers, the output power changes a bit, and you can see that in Figure 8, on the following page in the datasheet.  And notice that with 4 ohm speakers, the amplifier is no longer able to work at up to +/-25v (50v), the graphs stop at about +/-22v (44v)  and on the right side of the page, you see those distortion graphs made for +/-18v (36v) , not for +/-22v like before.

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