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Old 30th October 2002, 04:29 AM   #1
griff is offline griff  Australia
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Default DIY car audio class D 1500watt and above amp

Any ideas on how to get such a project started?
Any schematics around?
Does anyone know why hardly anyone tries this and insists on paying muchos dollars for commercially produced items?
What would the implications of such a project be?


Thanks for any assistance guys, I think this would be quite a first project for me to attempt after exams.
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Old 30th October 2002, 07:03 AM   #2
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on a basic functional unit scale you will need: crossover, DC/DC power converter, and some kind of H bridge driver with output transistors. Not impossible but at maybe 90% efficiency for the DC/DC converter and 92% for the H-bridge you would need over 1800W. Which is over 150A for 12V (worst case of course). If you think a car can take this go ahead (i think it would be neat but would not put it in my car). For the DC/DC converters you can buy them ready made that output 48V (even this wont get you 1500W). For the H-Bridge look for something that is set up to run a 3HP or so DC motor. Then all you would need is a PWM IC to stitch them together.

Not exactly impossible but it is probably cheaper to buy one, but i have to say i dont know if the are availabe or what they cost. I think its possible but you will need lots of SPICE sims, an oscilloscope and lots of time. Not to mention an extra alternator.
hummm.... maybe you could just get a 60V alternator
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Old 30th October 2002, 10:38 AM   #3
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Default Reads like a product brochure it does...

"Then all you would need is a PWM IC to stitch them together."
Hi Lligior. The way you describer it makes me think you write glossy brochures for power semiconductor manufacturers in your spare time! "Just choose this ic and plug it into that mosfet, add an inductor here, a diode there, plug then all together as simply as Lego(TM) blocks and hey presto! you have a working 50kW inverter / converter / UPS / AC motor drive / rail gun / uber amplifier / welder / doomsday engine / whatever, that goes like Black Sabbath on 78. Our products will save you years of ratsnests, explosions, fires, noise, emi, black faces, red faces and unexpected faeces." etc etc etc.

I think this kind of project even to hardened, experienced professionals is really really hard. I work side by side here http://www.setec.com.au/ with some of the best in the southern hemisphere (I don't include myself BTW) and I get to see first hand what goes into making this kind of thing work properly. If you wanna have a go, be my guest, but at least start small and work your way up. Give your ears a chance to get accustomed to smaller explosions first.
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Old 30th October 2002, 11:20 AM   #4
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Default Re: DIY car audio class D 1500watt and above amp

Quote:
Originally posted by griff
Any ideas on how to get such a project started?

Thanks for any assistance guys, I think this would be quite a first project for me to attempt after exams.
Hi!

Ok, cool to design a 1.5kW amp but still, 150 A is near a start motor...

When these questions comes up, I always wonder what type of listening in a car need 1500 watts?

1 W -> 93 dB (example)
10 W -> 103 dB
100 W -> 113 dB
1000 W -> 123 dB (if the speakers can take it...)

Listen to music in a car at more than 110 dB, isn't good for your hearing neither your concentration at your driving.... or

I don't want to sound too negative but I suggest that you start with a DC-DC converter which is fast enough for a power amp. That's your real challenge! To make a good (low distortion) power amp with 1500 watts out is also a challenge.
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Old 30th October 2002, 12:27 PM   #5
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Default Re: DIY car audio class D 1500watt and above amp

Quote:
Originally posted by griff
Any ideas on how to get such a project started?
Any schematics around?
Does anyone know why hardly anyone tries this and insists on paying muchos dollars for commercially produced items?
What would the implications of such a project be?


Thanks for any assistance guys, I think this would be quite a first project for me to attempt after exams.
Hi Griff, first thing is that there are no 1500W drivers around.
So that means multiple amplifiers or very low load impedence capability.
The usual method is line level crossovers and multiple amplifiers, but you still need to specify load impedence.
Then you can think about specifying and thinking about the practicalities of the issues.
Get a look at and study the inside of a modern high power No Break UPS.
These things have a serious incoming power rectifier section, serious battery section, and a serious horsepower (1500W = 2 Horsepower) AC output stage according to rating.
These are complex and necessarily physically big and component costly, and go expensively splattttt when they go wrong.

Another approach might be to modify multiple cheap modern PC UPS boxes (many of these run on a single internal 12V gel-cell battery) to give multiple (min 2) rectified and isolated output DC rail voltages that you need for multiple suitable medium to high power amplifier modules.

Have you had a good look in modern DC-DC supply car power amps ?.
You should get a service manual of an amplifier example that you can use and study both and have a play.
The switchmode supply techniques used are not expensive nor complex (they are mostly made in China nowadays) and could be reasonably duplicated if you can get hold of, or make suitable transformers and suitable semiconductor parts can be had easily from WES Components, Sydney.
The practicality is that you only need to run at max power for "sound-out competitions", and this can be 240V powered I think.
For impresssing your mates and your new girlfriend a few hundred watts is fine, and for being a responsible and aware driver a few watts is plenty (Father hat on ).

Eric.
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Old 30th October 2002, 04:38 PM   #6
griff is offline griff  Australia
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I forgot to mention that it will probably be running a 15" Brahma or 2, not components 1500 watts or above into 1 or 2 ohm

I choose 1500 watts as that would make it worth my time sort of thing, 1200 clean watts can be bought (ie JBL 1200.1) that is stable to 1 ohm for $250USD, ($1500 AUS ).

Maybe it would be better to start with a JBL for example and mod the life out of it? Would that be a good learning experience?

Thanks for the replies guys!
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Old 30th October 2002, 04:38 PM   #7
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Im not saying it would be easy, but if you wanted to build a kind of proof of concept all you would need is three parts. A DC supply like a computer power supply, TL494 PWM converter, and UDN2998 H-bridge. This would only supply 2amps but it should work. This would let you find what switching speed you would need. I dont think it would be a good idea to try and build the DC/DC converter yourself, its just complicated to be in any way amusing. Same goes for the H-bridge, I built one and never could get it to work correctly. It would control the motor it was for but its efficency was poor. A 1500W project may be a bad idea, but one made from the parts above is definitely possible, cheap, and informative.


I doubt you can beat JBL's price. Maybe a schematic project DC/DC would work but if it didn't you would need an o'scpoe and lots of semiconductor knowledge.
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Old 30th October 2002, 08:02 PM   #8
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oke i have a power supply with the rankings of 40V 75A !!!!
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Old 31st October 2002, 06:48 AM   #9
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Good PWM amplifiers ARE NOT made with modulators like a TL494 !

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Old 31st October 2002, 11:02 AM   #10
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Charles

I have no doubt there is something better than TL494. One of the things I really like about the forums here is that there are lots of ideas floating around. The TL494 would have some problems here, the biggest is that it would give a constant current draw. This alone would make it almost impractical for a large amp. I have a powered sub but have not opened it up to see what is in it. What do these things usually have in them?
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