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Old 21st April 2001, 02:48 AM   #1
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I have an Active Xover for my sub in my car but it runs off 12VAC, is there any way to invert this to 12VDC, any help would be great
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Old 22nd April 2001, 12:42 AM   #2
blmn is offline blmn  Brazil
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I didn't understand what is your problem. Usually audio gear for car needs 12 VDC. and not 12 VAC. Are you sure you need 12VAC? Would you tell us the brand/model of your crossover, if it is a commercial one?
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Old 22nd April 2001, 06:23 AM   #3
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It isnt a commercial product as i built it It was designed for mains supply and i was using it for my home HiFi. I just thought i could adjust it to work in my car.
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Old 22nd April 2001, 11:10 AM   #4
blmn is offline blmn  Brazil
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OK, I think it's clear now. Your crossover is a home type and needs 120VAC to work. You want to use it in your car.

I know two ways to solve this problem, but I think some of them would be a little complex if you don't have some experience in electronic design and mounting.

You can put an inverter (12VDC to 120VAC) to feed your crossover, but, as far as I know, most of the commercial types produce output waveforms that are not very good for audio applications. Maybe some fellows here at the Forum know some commercial types designed for audio.

You can modify the power supply of the Xover and adapt there a simple switched mode power supply, working with 12VDC at the input.

Another possibility is on building your own crossover. There is another thread here with indications about "ESP audio projects", when you you find information about how to build a simple car crossover and preamp.

Regards
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Old 22nd April 2001, 11:39 AM   #5
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no it doesnt run on 120VAC, It runs on 12VAC, i did have it running from mains power (240VAC here in OZ) into a transformer stepping it down to the 12VAC. Sorry if i wasnt clear enough in my description of it . My question was simply if i could turn 12VDC into 12VAC. The way i thought i could was maybe to use a diode (one that converts AC to DC) and to reverse the polarity. This probably wont work its just a thought. Unfortunately power supplies are not my forte.
thanks for your help By the way it is based on the 3 way active linkwitz (I think thats how its spelled) design.

[Edited by bwoca on 04-22-2001 at 06:49 AM]
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Old 22nd April 2001, 07:01 PM   #6
blmn is offline blmn  Brazil
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It will not work as you think with the diode and it seems your Xover has just the transformer placed out of the box to avoid hum or to allow little box mounting.

There are many possibilities here too. I'm assuming two wires from the transformer to the Xover:

- full wave rectification and unregulated power supply inside the xover: you don't need nothing more than connect the battery to the 12VAC input of the xover with no worries about polarities. Usually works fine since you take care of ground loops;

- full wave rectification and regulated power supply inside the xover: You might might have problems if the regulated output is over 9 or 10V, but it can work too at the same way of the first possibility;

- half wave rectification in both cases above: take care about the polarity of the ground of the Xover, it must be the of the rest of the components of your system (usually negative battery tap) and must be considered when connecting the battery to the 12VAC connector of the Xover;

- any kind of voltage doubler or switched mode circuits inside the Xover: considering you don't want to change nothing inside the xover, you will need an circuit called inverter or an sinusoidal generator with enough power and output amplitude to support the Xover, working in 60Hz or more. I think there are projects about it in the Internet.

I think the first think to do is discover how this xover is powered and analyse the possibilities above. I think the first or the second are the bigger probabilities of working.

Regards,



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Old 22nd April 2001, 07:06 PM   #7
blmn is offline blmn  Brazil
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By the way, the ground polarity must be considered in the two first possibilities to. It must be the same of the rest of your system, ok?
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Old 23rd April 2001, 08:15 AM   #8
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Thanks for your replies
After more inspection of the schematics it in fact runs off +/-16VDC. I should have looked at it before i posted Just so you know im not that familiar with electronics but very interested as im in my first year of an Electronics degree Is there an easy way to supply a negative and positive rails off of the 12VDC source. If you need the schematics i can email to you. Again thanks for all your help
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Old 23rd April 2001, 09:17 AM   #9
Geoff is offline Geoff  United Kingdom
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Yes. See the car pre-amp/active filter project at the ESP Audio Pages (www.sound.au.com) for details of a virtual earth arrangement.
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Old 23rd April 2001, 10:30 AM   #10
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I may have read it wrong but wasnt the article about how to make the +/- supply rails plus the ground, but does not talk about stepping up the voltage. Thanks for the link as it has solved half of my problem
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