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Old 13th February 2004, 09:35 PM   #1
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Default line driver/preamp

i`m wanting to build a nice line driver/preamp.
the driver needs to push from 2 to 10 volts.
any ideas.plans you`ve seen on line?
any help...
thanks
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Old 14th February 2004, 03:20 PM   #2
Did it Himself
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Just make an op-amp non-inverting buffer using an NE5532 with a gain of 2-3. Any application note for op-amps or standard book will have a suitable circuit.

Note that NE5524 is a single version of NE5532, but it requires compensation to be stable under gains of about 5. Again, the app notes cover this in detail.

An alternative chip is the OPA134 (single) or OPA2134 (dual).
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Old 16th February 2004, 06:42 PM   #3
maylar is offline maylar  United States
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A 12V power supply will only give you about 5V RMS output before clipping. You need a +/- 15V power supply to get the range you want. There are small premade DC-DC converters that'll do that for you. This also lets you run direct coupled I/O and eliminates the low freq rolloff you'd get with coupling capacitors.

"Nice" line amps have very low output impedance that you won't get with standard opamps. A 50 ohm source at 10 volts means you need 1/2 watt per channel. You can get by with much less power since the input impedance of a power amp is lots higher than that... but what's the point of a line driver if it lets noise get in on the cable?

I made one myself a while ago with capacitor coupled 12V opamp circuit and it sounded like ***. Poor low freq response and more noise than without it. If I did it again I'd do it differently.
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Old 19th February 2004, 11:46 PM   #4
rwaudio is offline rwaudio  Canada
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I designed and built car stereo line drivers for a few years.. mostly for SPL applications as I was the only company to build 16-32 channel line drivers. I have since stopped building them because it took too much time for a "hobby" I have parts and prototype boards leftover, and a few prebuilt. it's based on an unregulated dc/dc converter which at 12v(battery) gives 9v rms of signal, at 14.4v(battery) it gives 12v rms of signal...
I could assemble a kit for not alot of $$
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Old 20th February 2004, 05:14 PM   #5
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rw
i`ve sent you an email
if you don`t get it let me know.
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Old 20th February 2004, 06:39 PM   #6
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rw, how well did the hobby buisness work for you. i was concidering making some custom signal processors for car audio, but wasn't sure how much demand to expect. like 1 board a month or 100...
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Old 20th February 2004, 07:30 PM   #7
rwaudio is offline rwaudio  Canada
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offroadbum - got the email I'll reply after work
theChris - sales varied alot, and I never advertised, there was only word of mouth spreading of RW Audio.. but in a good month I'd sell 10+ units (about $1500+can worth) as a hobby I also designed a 48db/oct linkwitz riley crossover but never got it to market... there was alot of interest in it though.. wish I had gotten it finished and buildable.. I enjoyed it, I had sales in germany/puerto rico/guam/us (inc alaska/hawaii) canada etc.. so word does spread if you have a good product.. there were dozens of world records set in db drag racing with my products.. so I'd say if you build it and take pride in your work, with a good RELIABLE design you'll sell...
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Old 21st February 2004, 07:53 AM   #8
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i still chuckle ever time i hear of the LR filters in car audio. i'm sure there is demand though.

i was thinking of making precision 3khz crossovers, effective 60db/octave.

i found a good source of opamps which seem to be decent and popular -- i've seen it in a PPI amp and a lanzar amp.

i think i'll start up work again sometime soon. i'm debating how high quality i want to make the filter. dual psu or single.
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