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Old 15th April 2004, 04:57 AM   #1
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Default 12 volt DC to 9 volt AC

OK, did a search, didnt come up with anything. I'm wondering how hard/easy it will be to make something that can convert 12 volt DC to 9 Volt AC. It needs to be fairly regulated and clean, as its for a piece of audio equipment, but not super sensitive like a computer.

What im doing is trying to use an Alesis Nanoverb in my car. It has a 'wall wart' power supply of 120 volt in and 9 volt AC out. Not sure what frequency AC out. Im assuming 60 hz. I dont really think using a 12 volt to 120 volt setup up inverter will work that well. Maybe thres another component that has 12 volt DC input... hmm. Any thoughts?
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Old 15th April 2004, 05:14 PM   #2
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Hi, It is a litle tricky converting DC to AC. Part of the process involves injecting a square wave or sign wave into the signal to create alternating current.

If I were you I'd rather find the DC powersupply in the component you are trying to connect, and attach a regulatd DC supply there. Actually depending on how accessible the DC supply is in this device, you might either attach an unregulated stepped down DC source after the rectifier or a regulated DC supply of the right value after the regulator circuit.

If you are looking to experiment, consider using a 12VDC to 120VAC step-up converter. Take care in considering the current limitations on the converter. However considering the powersupply is a wall wart, an inexpensive ~$30USD converter might work.

Good luck,

-David
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Old 16th April 2004, 03:46 PM   #3
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You could probably get away with a 9V regulator followed by a mosfet full bridge. Run the full bridge from a 60Hz oscilator. The result would be a 9V square wave. This should be fine for the Alesis since its only going to convert back to DC anyway.
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Old 16th April 2004, 03:59 PM   #4
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Why mess around trying to make AC. My guess, and it's just a guess, is that the 9VAC goes to a bridge rectifier and then a filter cap. That combination will give about 12 VDC. You could just input 13 VDC with a little over 1.2 volts for diode voltage drop every thing will be fine. I've done this sort of thing lots of times and unless there is some internal need for the AC signal it will work great.

Do check out to make sure that the 9 VAS goes straight to the bridge or the power switch and then the bridge, if so your home free.

Later BZ
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Old 17th April 2004, 12:08 PM   #5
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Quote:
Originally posted by HDTVman
Why mess around trying to make AC. My guess, and it's just a guess, is that the 9VAC goes to a bridge rectifier and then a filter cap. That combination will give about 12 VDC. You could just input 13 VDC with a little over 1.2 volts for diode voltage drop every thing will be fine. I've done this sort of thing lots of times and unless there is some internal need for the AC signal it will work great.

Do check out to make sure that the 9 VAS goes straight to the bridge or the power switch and then the bridge, if so your home free.

Later BZ
I have taken appart similar Alesis gear before, and the bridge is not connected directly to the power input socket. There are some caps in series with the bridge to prevent a DC power supply from working. The supply must be AC or it will be blocked by the caps.
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Old 17th April 2004, 02:42 PM   #6
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hmm...maybe he can short out the caps...and then a simple 12V input sould suffice??
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Old 17th April 2004, 04:44 PM   #7
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Quote:
Originally posted by ClassD


I have taken appart similar Alesis gear before, and the bridge is not connected directly to the power input socket. There are some caps in series with the bridge to prevent a DC power supply from working. The supply must be AC or it will be blocked by the caps.
That's why I suggested that the power input be checked out before just trying the 12 VDC input.

It's possible that Alesis is using a voltage doubler type of circuit to get + / - supplies and that would require an AC input.

Later BZ
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Old 18th April 2004, 12:09 AM   #8
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can he just try to tap from one of those regulating caps and apply straight DC?? It would solve the problem of having to use AC in a voltage doubler and filter....creating a pure sine wave is not that easy....
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Old 18th April 2004, 11:32 AM   #9
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No need for a pure sinewave. The voltage doubler (if thats what it is) should work fine from a square wave input. By the way, I'm thinking that the voltage doubler is probably being used to create dual rails from a single AC supply?
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Old 18th April 2004, 12:16 PM   #10
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May not even be a doubler, just 1 diode and a regulator each side to give the two rails. Still should work from a square wave.
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