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the best 12v amp design/project

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But only provides about 14/16W - far too low for his required 40W.
Not if you parralel two four Ohm speakers. In auto use, the sustained system voltage is about 14V. Allowing about 3V drop on the power devices, you can swing about 11v (peak). That's about 7.7V (RMS) for a sine wave. That gives you about 30W RMS sine wave power driving 2 Ohm speaker load. The TDA 2003 could drive over 3A current so it can swing the voltage. It has data sheet specs for using 1.6 Ohm speakers.
 
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Not if you parralel two four Ohm speakers. In auto use, the sustained system voltage is about 14V. Allowing about 3V drop on the power devices, you can swing about 11v (peak). That's about 7.7V (RMS) for a sine wave. That gives you about 30W RMS sine wave power driving 2 Ohm speaker load. The TDA 2003 could drive over 3A current so it can swing the voltage. It has data sheet specs for using 1.6 Ohm speakers.

You can't drive 2 ohms in bridge mode, each amp only sees 1 ohm if you do.
 
You can't drive 2 ohms in bridge mode, each amp only sees 1 ohm if you do.
The peak voltage swing (in either positive or negative direction) is only about 10V because you only have 14V total rail and you have a couple of volts given to the sat voltage of each of the output stages. The 2003 devices I had would crank close to 4A peak current, so you could drive impedances down to about 2.5 Ohms at full voltage signal swing. It will still work with 2 Ohm load, but it might run out of current right before voltage clipping happens.
 
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The peak voltage swing (in either positive or negative direction) is only about 10V because you only have 14V total rail and you have a couple of volts given to the sat voltage of each of the output stages. The 2003 devices I had would crank close to 4A peak current, so you could drive impedances down to about 2.5 Ohms at full voltage signal swing. It will still work with 2 Ohm load, but it might run out of current right before voltage clipping happens.

The spec you mentioned above said 1.6 ohms, which presumably is the absolute (and completely unusable) minimum?, which would give a minimum of 3.2 ohms in bridge mode.

But why try and force too much power from a poorly designed system?, which will give appalling quality - don't try and bodge a design just because you have a completely unsuitable transformer to hand.
 
A TDA7396 bridged amplifier is rated at 37.5W into 2 ohms when it is clipping a little with 1% distortion and a 15V supply.
 
The spec you mentioned above said 1.6 ohms, which presumably is the absolute (and completely unusable) minimum?, which would give a minimum of 3.2 ohms in bridge mode.

But why try and force too much power from a poorly designed system?, which will give appalling quality - don't try and bodge a design just because you have a completely unsuitable transformer to hand.
I don't know why you are making this so complicated. The single TDA2003 device has specs driving impedances as low as 1.6 Ohms. Read the data sheet.

It will drive 1.6 Ohms, how much voltage it will swing is limited by the peak current. 1.6 Ohms is not the "absolute minimum unusable limit", it is, in fact, what many car audio makers used back in the 80's by paralleling 3.2 Ohm speakers to get the most power they could using a single TDA2003 running of 14V.


What limits the lowest impedance it can drive is peak current which I found to be consistently above 4A on the devices I was using. Just stick with Ohm's Law. If you drive 10V across a 2.5 Ohm load, that's 4A (peak). If you choose to drive a two Ohm load, it will probably only swing about 8.5V. Don't get all hung up on the speaker impedance, the output stage doesn't care. It's where the current limiting cuts in that limits the current drive.

I was not trying to force the most power from a poor design, I was getting the most power out of a pretty good design I ran for many years. It's about all you can get from a 14V rail.

If you read my previous posts, I posted a link to a very good power amp for about $80 that has internal switching power supply and puts out hundreds of Watts at very low distortion.

https://www.amazon.com/Crunch-Power...1?s=electronics&ie=UTF8&qid=1325824080&sr=1-1

I don't know why anyone would choose to build a car amp when good ones can be bought so cheap, but the OP seems fixated on doing it so I posted the schematic of one I built before.
 
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I don't know why you are making this so complicated. The single TDA2003 device has specs driving impedances as low as 1.6 Ohms. Read the data sheet.

It will drive 1.6 Ohms, how much voltage it will swing is limited by the peak current. 1.6 Ohms is not the "absolute minimum unusable limit", it is, in fact, what many car audio makers used back in the 80's by paralleling 3.2 Ohm speakers to get the most power they could using a single TDA2003 running of 14V.

I'm making it simple - it's you who's making it complicated.

I've never seen, or heard of, any car radio using two 3.2 ohm speakers in parallel, nor ever heard of 3.2 ohm speakers at all for that matter.

Car speakers are almost exclusively 4 ohms, and car radio manufacturers used two TDA2003's bridged to give 16W RMS to 4 ohm speakers (each IC seeing 2 ohms).

You seem under the wrong impression that the OP is making a car amp, he's not! - he happens to have a 12V mains transformer and wants to build a 40W amplifier using it. It would make FAR more sense to simply dump the transformer and buy a suitable one, rather than bodging muliple amps and multiple paralleled speakers in order to make an inferior lower quality solution.
 
Okay, I followed Nigel's advice and bought a 25 by 25 volt 5 amp by 5 amp transformer, two LM3886'es and all the other necessary components for a stereo gainclone amp from this website **broken link removed**
But now there are two problems

1) At the bottom of the original website
**broken link removed** (turkish) It giver a parts list with some 0.6 Watt resistors, and I've only got 1/4 watt resistors

2) the layout
Layout.gif
Has more resistors than the schematic

**broken link removed**

What should I do???


Is there any better website for a gainclone like this?
 
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do the wattages of the resistors matter?, because in a project like THIS: **broken link removed**
NOTHING is said about resistors. This pis#es me off quite a bit.
Do they matter?
 
Say I wanted a 1watt resistor, but I only have 1/4 watt resistors of the same value, would this be true, that
THIS
wattage resistors.png
all 4 are 1/4 watt
is equal to a 10k 1 watt resistor.
If not, what sould I do to avoid going to the store again?
 
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If the resistors are well matched that will be ok.
 
do the wattages of the resistors matter?, because in a project like THIS: **broken link removed**
NOTHING is said about resistors. This pis#es me off quite a bit.
Do they matter?

I presume you mean R6? (2.2), that's the only resistor which obviously needs to be a higher wattage.

The series parallel connection you drew is fine.
 
I'm making it simple - it's you who's making it complicated.

I've never seen, or heard of, any car radio using two 3.2 ohm speakers in parallel, nor ever heard of 3.2 ohm speakers at all for that matter.
Whatever.

FYI: In 1980, I developed the TDA2003 at Farichild semiconductor which was a functional replacement of The SGS TDA2003. At that time it was industry standard for many car audio systems to use two 3.2 Ohm speakers in parallel on each channel to get maximum power in car audio systems that ran off 12V. The TDA2002 and later 2003 were products specifically designed to be used for this.

Just read the data sheet.

Such products are no longer state of the art, and today's power amps are so cheap that they make not much sense. The dirt cheap switching converters now available mean that it's easy to boost 12V up to any voltage you want to get any power level you want.
 
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You seem under the wrong impression that the OP is making a car amp, he's not! - he happens to have a 12V mains transformer and wants to build a 40W amplifier using it.
And since that is IMPOSSIBLE, I was offering simple solutions to a similar end which are possible.
 
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I'm making it simple - it's you who's making it complicated.

I've never seen, or heard of, any car radio using two 3.2 ohm speakers
Well, now you have.

"A speaker is a speaker, no mono or stereo. Mono uses one or several on one channel of stereo or monaural broadcast. Single speaker is mono. Two or more may be stereo.
Speakers of this era used 3.2 ohm voice coils"

http://www.aqcollection.com/antique-radio/article-1724.html

There were also a lot of them around in the 70's. One front, one rear on each channel with a F/R fader control.
 

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Well, now you have.

"A speaker is a speaker, no mono or stereo. Mono uses one or several on one channel of stereo or monaural broadcast. Single speaker is mono. Two or more may be stereo.
Speakers of this era used 3.2 ohm voice coils"

http://www.aqcollection.com/antique-radio/article-1724.html

3 ohm speakers were commonly used in the valve era, it's pretty ludicrous to mark them as 3.2 or 3.4 ohms, as the speaker impedance varies greatly with frequency, the value is only a nominal one.

There were also a lot of them around in the 70's. One front, one rear on each channel with a F/R fader control.

And were 4 ohm, not 3.2 - unless the USA for some strange reason was different to the rest of the world?.

I've also never seen a car stereo with paralleled speakers, perhaps this was anpother perculiar American thing?.
 
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