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Old 20th January 2008, 06:20 AM   #1
Cxrazy is offline Cxrazy  United States
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Default 12vDC to 12vAC

Hey guys,

I built and amp recently that runs off of 12vAC.

I want to use this amp in my car (12vDC). The amp draws a max 30-40Watts. I doubt using a bridge rectifier would be enough -> too much current.

How could I go about cheaply and effectively doing this?

Thanks!
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Old 20th January 2008, 06:31 PM   #2
Bone is offline Bone  United Kingdom
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It would be a good idea to give us details of the amp you have built and its power supply before expecting someone to give you advice.

Tony
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Old 20th January 2008, 06:34 PM   #3
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Use a vibrator.
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Old 20th January 2008, 08:05 PM   #4
sandyK is offline sandyK  Australia
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Use a vibrator.





I am sure he means a Vibrator, as used in early car radios to generate a HV AC supply from a 12V DC source ?. It is rather like a buzzer, which uses metal contacts to momentarily interrupt current flow, thus resulting in a buzzing noise.

SandyK
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Old 20th January 2008, 09:50 PM   #5
Cxrazy is offline Cxrazy  United States
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uh... Its a kit I bought at a local electronics store. its a stereo 30W RMS amp.

I'm using a 12v transformer now to take the mains voltage down to 12v.

What else would you need to know?
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Old 20th January 2008, 10:36 PM   #6
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Quote:
Originally posted by Cxrazy
What else would you need to know?
Well there are a few possibilities here that rely on knowing how your amp functions.

Amplifiers run on DC, not AC, so what does the other part of the power supply on the amp look like? Is it a voltage doubler, or does it just make a single DC supply?

Going from DC -> AC -> DC in a car would be pointless if your amp just runs on a low voltage single supply. In that case you could just power it straight from the cars DC.
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Old 21st January 2008, 12:34 AM   #7
Cxrazy is offline Cxrazy  United States
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Click the image to open in full size.

Quote:
This small amplifier is constructed around the TDA1521 IC, capable of delivering 2x15W RMS
(4 ohm) or 2x10W RMS (8 ohm). The IC is thermally and short circuit protected. THD: .07% (1W/1 kHz). Frequency response: 7 to 60,000Hz (-3dB). Requires 2x12 VAC, 2A transformer (sold separately). Net weight: 1 lb.
Thats what it looks like. maybe it uses those diodes to rectify AC to DC.

Anyone?
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Old 21st January 2008, 01:01 AM   #8
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OK, your amp needs a symmetrical DC supply of up to around +/- 16v. The only real way to accomplish this in a car is with a switch mode power supply.

Building a SMPS is far more complicated than your amp kit. See the link below for details on a SMPS for car audio use.

http://sound.westhost.com/project89.htm
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Old 21st January 2008, 03:05 AM   #9
Cxrazy is offline Cxrazy  United States
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I have a broken car amplifier.

Could I somehow salvage the powersupply from this? Building that SMPS is a bit over me tech level
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Old 21st January 2008, 04:37 AM   #10
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As long as the power supply still works it should be possible. The voltage might be too high, in which case you can take some turns off the transformer to reduce it.
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