Help with generating negative voltage for car amplifier

There are lots of voltage converters on ebay at nice prices!

 

How much power do you need then?

 

This type of voltage inverters tend to be hard to find, and quite expensive if powerful.
Remember for 30W out you'll need 40W in, unless you're using a class D amplifier.

Here's one possibility but you'll have to ask them about shipping cost and if the output is galvanically isolated from the input.

Here's an example of exactly what you need, though it's more powerful than you want.

 

Of course an amplifier needs to be able to swing about some sort of rail to produce an AC signal. However there is a simple trick often used in low voltage amplifiers.

You have visualised an artificial rail at nominal 6V; I suspect you envisage the output transistors driving the speakers to that rail.
In low voltage amplifiers an inverted version of the signal is often amplified alongside the erect version, and instead of driving the speakers to the artificial centre rail they are driven to the inverted output of the second amplifier.
This is called "bridging" mode.

 

The amplifier configuration you have drawn is bridging mode. The following remarks apply.

You can see that instead of having a maximum possible 6V peak when working to a centre rail you now have a maximum possible 12V peak.
A sinusoidal waveform has RMS power equivalent to a DC waveform about 70% the peak AC voltage.
For 6V peak this is 4.2V, hence maximum power in a single pure tone is about 4.4 Watts.
For 12V peak we obtain 4 times that power, or 17.6 Watts. So theoretically, bridging mode quadruples power.
In practise you won't get full swings to the rails, so these figures are not to be regarded too seriously.
Still you'll probably get better than 10W into your speakers without objectionable distortion and that's a lot of sound to be with in a car - you'll think its loud!

I don't know why you are asking about paralleled amplifiers - perhaps you hope that power may be further increased in this way. Sorry, no.

 

It has just occurred to me that there is a cheeky way to use paralleled amplifiers... use separate speakers as well! In other words take your signal at pre-amp level and feed it to 2 entirely separate power amp / speaker systems. This of course doubles power.

 

Hi again
I expect that the 1 pre-amp could be made to serve more than 1 power amp, so there would be no need to duplicate the pre-amp.

 

Well, OK. I think you could do a lot better than a 741 though - that's a pretty old design and I'm certain that much better op-amps are available today. Even 25 years ago the TL071 was considered an enormous improvement on the 741 and technology has not stood still in the meanwhile.

 

Hi again, Carebare (smile)

So you think you'd like to put 2 amplifier/speaker systems in parallel on each stereo channel to increase sound levels, and wonder how to condition the signal to suit the inputs of the TDA2030A power amps?

I looked up the chip on the manufacturer's page at http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1459.pdf and I don't think you need a separate pre-amp stage at all.

I've copied the cct diagram from the datasheet as an attachment, there are much more knowledgable people than myself who may have another opinion.