Car amplifier understanding

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Most amplifiers I see use a dual polarity power supply to power it. The ones I have seen that just use positive and gnd are normally low wattage circuit for like headphones ect.

A car uses +12 rem(+12) and gnd to power the radio, what kind of circuit could be used to convert that to a dual polarity supply.

Or is it that car amplifiers are designed differently?
 

To apply twice the voltage to a speaker, a convenient method is by bridging it between two amplifiers. Each amplifier has the same positive supply. The load gets true AC.

Another option is to install a buckboost converter. It inverts supply polarity, and is ground referenced, thus you can continue to use the chassis as 0V ground. If you wish you can use a boost converter to raise +12V to 24V, etc.

Another option is to create a +12-12 split supply, by pulsing 2 stacked capacitors (possibly add an inductor, buck converter style). This method isn't ground referenced, so you might decide it's inconvenient.
 

A low power car amplifier has a supply that is 0V and a little higher than +12. Its maximum output is about from +2V to +10V then it is coupled through a capacitor to the speaker that gets half going positive to +5V and half going negative to -5V. These are peak voltages, the RMS voltage is 3.54V so the power in a 4 ohm speaker is (3.54V squared)/4 ohms= 3.1W.

A bridged amplifier also uses a 0V and +12V supply and each wire of the speaker goes from +2V to +10V but with opposite phase. Then the speaker gets 7.1V RMS which is 12.6W into 4 ohms.
The power is actually a little higher when the car battery is charged to about +14V by the alternator.
 

Ommit the rectifier and the transformer could the circuit be hooked up like this.

The only thing is between the capacitors I would not have where to connect it to.



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So battery positive goes to where the positive is on the schematic and battery natural to negative on the schematic but ground between the capacitors could I tap off the battery negative, would that work.
 

To obtain a bipolar supply from a single transformer winding, 2 diodes is sufficient. Designate one end of the secondary as ground 0V.

This simulation has a simple class B amplifier powering a 4 ohm speaker.



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The load gets true AC.
The 1k resistor is unnecessary.
 

That looks different from what I had in mind. Check this image

6109904300_1475711903_thumb

Is this a possibility, getting the 12v from your car and connecting it to a regular amp say a TDA amplifier circuit.

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Your link does not work so we do not know what it is about. I fixed it and it is attached to this post. It is completely wrong.
You want to make a converter circuit to connect a TDA amplifier to the 12V in a car but you did not say which TDA amplifier (there are many of them), but in your other thread you talked about a TDA7294 amplifier IC that has a minimum supply of +/-10V or 20V. The datasheet shows a graph with a +/-12V supply the TDA7294 provides only 15W into 4 ohms about the same as a 12V bridged car amplifier IC. But the TDA7294 needs an additional negative supply generating circuit.
 

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Yes I need a converter, I don't have a specific circuit in mind, just that most amplifiers I know use dual polarity supply, and the car uses 12v and gnd so I'm asking how would I use the cars 12v and gnd to make a dual polarity to power an amplifier circuit.
 

A car amplifier does not use a TDA7294 IC with a +/-12V supply to make only about 15W into 4 ohms. Instead it uses a bridged car radio amplifier IC to make 15W into 4 ohms without a negative supply generator. A bridged amplifier circuit does not need a negative supply and does not need an output coupling capacitor.
The TDA7294 IC is expensive because it is rated at 100W with a supply voltage of +/-27V to +/-35V that is produced by a complicated Switched-Mode power supply that has an input of 12V and ground.
 

OK so something like the TDA 7350 would work grate, I didn't know they used different circuits for cars, so is it possible to get high wattages like 1000w from a car? That would probably require a 95amp hour battery and the engine turned on? Just asking for knowledge nothing that I plan to attempt
 

Yes, a TDA7350 and others were used a long time ago as a car audio amplifier but they are obsolete now. It produced 17.5 Whats into 4 ohms with horrible clipping distortion or about 14 Watts with fairly low distortion.
A switched-Mode power supply takes +12V and ground and generates any supply voltage you want including a dual polarity supply. Then it powers an ordinary high power amplifier circuit.
 

Well the idea behind using a switch mode power supply to power a regular amplifier is what I had in mind first I just didn't know how to make the dual polarity switch mode power supply for such a case.



For a low power amp so 20 watts at 4ohms from 12v and gnd do you know any circuit I could try, wattage can be higher or lower, just something that could play possibly 2 12" speakers or would you reccomend using an ordinary amplifier with a switch mode power supply.
 

Simple arithmetic shows that 20W at low distortion into 4 ohms is a signal that is 8.95V RMS that is 25.3V peak to peak. An audio amplifier has voltage loss at its output so for 25.3V p-p the power supply must be about +/- 14.6V or 29.2V, not 12V.

A switched mode power supply in a high power car amplifier uses a high frequency (so you do not hear it) high power oscillator driving a custom made high frequency transformer. Then the resulting higher voltage AC is rectified and filtered into higher voltage DC.
 

I found this schematic but I only see one issue so far, I don't know how many turns I would wrap on T1

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The Elliot Sound Products switched mode power supply for a high power car audio system that you found is pretty good. The article talks about the transformer.
**broken link removed**
 

Ok its a good article I have been reading it and it seems straight forward.

I will definitely try this circuit and see what i can learn through that experience.

What about building a switch mode power supply for a Power amplifier with 110v input can you recommend me to anything.

I would like to switch from linear power supplies even if its just high power amplifers.
 

A 110VDC power supply to an audio amplifier might be +-55VDC. Then the amplifier max output will be about +-50V peak and produce 156W into 8 ohms or about 280W into 4 ohms with low distortion.
The Elliot Sound Products site is down so I cannot see its car amplifier power supply project.

Or do you want to power an amplifier from the 110VAC mains without a transformer? No, it is very dangerous since it will not be isolated.
 

the part about power supplies for cars was just to gain some knowledge I never built a car amp before, I normally build amplifier and use 110v and a transformer with a linear regulator but its very hard and expensive to get good transformers to build those types of power supplies so I wanted to learn about switch mode.

your saying building a power supply from mains 110v is dangerous with a transformer because there will be no isolation due to the fact that there is no transformer.

What I wold like to know is how do the companies build those thing amplifiers without iron core transformers, how do they manipulate mains 110v? I am wondering how that power supply works ( I assume its switch mode) but again if it is they wont be able to use a ferrite core transfrmer to step down mains voltage at that low frequency 50hz, so how does it work.
 

This is a theoretical demo of a simple buck converter, to give an idea how it can work using a small inductor value.

The 110V supply is a hazard to work with, for components as well as humans (see post #17).



This is a single step-down converter. It would need another section to make a split supply, or to make a negative supply.
 
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