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Old 20th July 2007, 02:35 PM   #1
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Default Line driver?

Is there anyway to build just a RCA line driver to take one input signal and have it put out 4 or 5V output on 3 outputs? Has to operate off of car voltage.
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Old 20th July 2007, 05:24 PM   #2
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Forget the "line driver" car audio mumbo jumbo. What you want is called a preamp.

Here is a circuit designed specifically for use in a car....

If you don't like that circuit you can build nearly any preamp and use it. There are plenty of them around if you do a search.

The power supply for a preamp in a car is probably more complicated then the preamp itself. If your up to building your own you can try this one.....

I've taken the easy way out for some Linkwitz Transform circuits I'm building. I went ahead and bought some DC-DC converters.

If you find a project that you feel confident building and need a supply, I can sell you one of mine (I have extras).

These sell for $70 new, but I can sell you one for $10.....

DATEL BWR-15/330-D12

OR, you can just BUY a "line driver".
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Old 14th August 2007, 12:10 PM   #3
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Default Datel DC-DC Converter

Do you still have any of the Datel DC-DC converters? I would -love- to get my hands on one for an equalizer project I've been working on. I prototyped the equalizer and was almost ready to solder everything together when I realized that supplying power wouldn't be straightforward in a car. I found the Datel units after a lot of research but was turned off by the $70! $10 is a lot more in the range of what I was thinking

As an alternative, would it be possible to use a PWM to regulate the battery voltage down to 5V and then upconvert again using the following from TI:


I was hoping that the output from such a pairing would give me a steady power supply since the fluctuating battery V is regulated upfront.

I'm really interested in the Datel units regardless, but also curious if the strategy I have proposed would work for low-power devices. Thanks for any insight!
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Old 14th August 2007, 01:11 PM   #4
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I've already let a few go and would like to keep most of whats left, but I can spare another I guess.
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Old 15th August 2007, 03:15 AM   #5
dangus is offline dangus  Canada
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There's little DC-DC converters at Mouser and Digikey... they start at around $15 and up. I'd suggest getting one that does +/-15V and regulating down to 12V with 3-terminal regulators if you're fussy.
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Old 15th August 2007, 04:53 AM   #6
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If you don't find anything else, you can have this one for the price of shipping (~$7).
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Old 15th August 2007, 10:34 AM   #7
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Default DC-DC converters

Anonymous1: A few other alternatives seem to have opened up so let me explore those before I request one of your Datel units. Thanks very much for the offer though!

Dangus: If I'm thinking of the same units that you are referring to, I had one major concern that held me back from using those. Namely, the given input range is either 12V or 15V +/- 10%. This gives me a range of 10.8-13.2V or 13.5-16.5V. I'm expecting the car battery to fluctuate between 12-14V conservatively (although I thought it would be better to account for at least 10-14V). Thus, a 12V version will be overloaded when the car is on (14V) and a 15V version will be under-volted when the car is off.

I'm guessing that the 12V version uses components that cannot tolerate >10% input. However, from what I understand, an underpowered component can still be functional but will not always give predictable results. If this is true, I can use a 15V version and then regulate down to 12V as you suggest in order to smooth out irregularities brought on by voltage drops . Am I on the right track here?

This was also the thinking behind the solution I posted above, except that I figured a PWM could regulate a very wide range of V very efficiently. If anyone has comments on that setup vs. the above they would be appreciated!

Perry: That's a very kind offer and I am definitely interested depending on the validity of my statements above. The only thing that I'm a bit worried about is that your solution is a full-strength PS for higher-wattage projects and I'm afraid it would be wasted on my little equalizer. Also, should I decide to produce a couple more of these equalizers it would be nice to have something that is readily available vs. a custom one-off solution. I will definitely get back to you though regarding your board. Thanks!
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Old 15th August 2007, 12:23 PM   #8
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Default Re: Line driver?

Originally posted by audiobahnkid592
Is there anyway to build just a RCA line driver to take one input signal and have it put out 4 or 5V output on 3 outputs? Has to operate off of car voltage.
In an automotive environment you have to contend with noise and (potentially) long cable lengths. The line driver chip takes a single-ended output, converts it to a balanced output -- then the line receiver does the opposite -- in this way you avoid noise pickup over the cable.

You don'thave to use the specialist chips like the Analog Devices SSM2141 and 2142 shown in the attachment -- the same thing can be cobbled together with discrete opamps and some resistors -- and ADI shows how on their website.

With respect to bipolar power for the line driver -- the transistors in inexpensive PWM chips like the SG3524 and SG3525 are sufficient to drive a push-pull DC-DC converter -- you can get the transformer core you need from a busted PC power supply.

Take a look at the SSM2142 data sheet on Analog Devices website.
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