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Old 10th March 2004, 06:24 PM   #1
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Thumbs up Class A in CAR AUDIO???

Just a real quick question (if thatís possible ). How easy is it to convert a smaller home audio amp that people build around here to work in your car? For example, what would it take to run an Alpha X in your car setting aside all heat issues?

You've got a DC 12v battery, 14.4v when the car is running, and an 80 amp alternator. Obviously, the amp couldn't take 80 Amps directly so there has got to be something in between. I would guess a Transformer to up the voltage, but are there other factors in play here?

Thanks

Brian
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Old 10th March 2004, 06:55 PM   #2
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Depending on what power you intend to get from your Aleph-X you can purchase an inverter or DC to AC converter. A transformer will not work because a transformer does not work with DC. If you put a transformer across a car battery you will have all the fireworks you can handle. Inverters are rated in watts and you will need to purchase an inverter large enough to handle the power requirements of that particular amplifier. It's as simple as that.
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Old 10th March 2004, 07:08 PM   #3
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Default That simple

hmm. I thought about the idea of building an amp exactly like it would be for home use and than using an DC to AC converter I just figured there was a way to cut out that kind of transition. Thanks Kilowattski

Brian
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Old 10th March 2004, 08:32 PM   #4
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Default alternative

in stead of a step from 12VDC to 220VAC and back to + and - 30 VDC you could try a set of Switched PSU's which you could design to produce eg 20V to 30 V DC directly from 12V, so you end up with a + and - supply which will power any diy project for your car.

You have some trouble filtering out the noise which a Switched PSU will introduce.
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Old 10th March 2004, 08:33 PM   #5
mwh-eng is offline mwh-eng  United States
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Default Re: That simple

Quote:
Originally posted by Killjoy99
hmm. I thought about the idea of building an amp exactly like it would be for home use and than using an DC to AC converter I just figured there was a way to cut out that kind of transition. Thanks Kilowattski


You could possibly buy a DC to DC converter in which the secondary voltage matched the DC mains on your amp, but you would also have to provide the lower voltages to the pre-amps.

If you want a good learning experience, study on how to build your own DC to DC converter and use one of the National Semiconductor chip amps. Won't be class A, but I bet it will sound fine, as long as you can keep the switching noise away from the chip amps. I built an amp this way for amplifying frequencies above 20 KHz to drive away nuisance animals. I built a DC to DC converter and used the chip amp. I was not careful with the secondary filtering and did get some switching noise in the chip amp. With a little more filtering, I think the switching noise can be removed. Not a problem for my application since I'm trying to make high frequency noise, but for clean audio you will need well filtered secondaries, and you must minimize the conducted and radiated noise from the converter. Building a high efficiency DC to DC converter with modern parts is not too difficult.
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Old 10th March 2004, 09:30 PM   #6
urosst is offline urosst  Slovenia
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I bild balanced MOSFET POWER FOLLOWER work perfect.

only problem is amp constant use 30 A dc curent.
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Old 10th March 2004, 10:03 PM   #7
Tensop is offline Tensop  Lebanon
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Switching noise shouldent be too hard to keep away, i bet keeping the switching speed many times above the audible frequency range will reduce the noise inhibited lower down on the frequency scale. heres a picture of my unfinished SMPS design, which should be capable of around 300watts electrical power, and with some reworking.. should be capable of around 1kw, but at that stage the amount of noise being generated purely by the flow of current would be enourmous.

P.S this is unfinished, so dont go attempting to copy it
Click the image to open in full size.

as you can see on the right end, it goes through a bridge rectifier and into a set of inductors, it can supply +35/0/-35 or any voltage you want.. for class A car audio i would want to be keeping that a bit lower
output capacitance totals 9400uF per rail, which is quite alot considering the switching frequency would be 90khz - 150khz, depending on how well the transformer can handle it, the capacitors ability to handle the frequency, diodes, mosfets, switching controller etc etc etc

also, this circuit is based on immo_G's design, and furthermore rod elliots..

,

tensop
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Old 11th March 2004, 04:04 AM   #8
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My driving force behind this thread is based on that fact that almost every car audio amplifier out there is class AB. I was asked about the ability to build car audio amplifiers so I figured I would pitch the idea to everyone here. Just to make sure it's clear and keep this thread heading in the right direction: I'm not saying that Class A is in any way better sounding that Class AB. lol .

I think it would be pretty interesting to create a PURE CLASS A car audio amplifier to power some MB Quart Q's or Focal Utopia's. The only amplifiers that I have scene other than many of the mcntosh amps to run power as "clean" as Class A was made by Tru technology. There has been a few threads about these car amps as they have the BiPolar transistors mounted in plain site on the top of the chassis. That alone is one of a kind.

Thanks

Brian

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Old 11th March 2004, 09:31 AM   #9
Tensop is offline Tensop  Lebanon
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It's a rice of its own kind
imho class A in cars is pointless, too much road noise, engine noise, low internal volume, bad soundstage etc

you will have a very hard time making an SMPS circuit for a class A amp inside a car. the constant current draw is huge.
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Old 11th March 2004, 09:52 AM   #10
sss is offline sss  Israel
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Quote:
Originally posted by Tensop
imho class A in cars is pointless
agreed
why to make 10W amp with more then 70W power supply that will draw high current constantly !!!
i think u should stick to class ab because u wount hear any difference in sound specially inside a car
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