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Old 28th October 2004, 02:11 AM   #1
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Default Looking for starting points on car amp (first real post here)

Hello everyone, this is one of my first posts on this site.
If I have posted in the wrong section, I apologize, and Mods please move this thread.
I've done a search. In similar beginner's posts, the replies have been "tell us what you want to build, and tell us how good you are at DIY stuff." So here goes!

At this point, I am very interested in building my own car amplifier. I have basic knowledge of electronics and an understanding of audio concepts.
I am looking to build 2 moderately powerful amplifiers for my front stage. My main reason for doing this is that I am looking for excellent sound quality. Brands I have been impressed with for amplifiers include Audison, McIntosh, and U-Dimension, and I'd like to have comparible sound if that is possible.

my questions:
Where should I get started? Can anyone recommend some good plans for DIY car audio amplifiers? Im looking for around 150watts RMS per amplifier.
I want my amplifier to be able to adjust input voltage (gain), and have a crossover built in if possible (active). I have seen some crossover designs on the ESP site, could i just combine it with an amp?

I am a complete noob to this, so any help is very very appreciated.

For reference, I have an extensive background in custom car audio, and have built my own enclosures and components. However, I have not tried building the actual amps. I am fairly competent with electronics, and have a good knowledge base for audio.

Thanks for reading this, hopefully you can help me out!

-KC, from Canada.
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Old 31st October 2004, 12:42 AM   #2
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Default heretical...

Hi,

This may sound heretical, but you might consider buying a cheap car amp that is not necessarily the best sounding, but is *known* to deliver a good number of watts, say 100w x 2, shouldnt be hard to get recommendations from people...you can find 'em quite cheap used. Then rip out the amp section and install a few of the nat semi chip amps (LM3875 etc). If the PSU in the car amp is good for the power, the chips are really, really good...you can get about 60w per chip and various designs exist to parallel them to drive low impedance loads, or bridge them for high impedance loads...the BPA200 thread describes a 200w solution...read a bunch in the chip amp section and you'll see how simple, and high complex the designs can be. Gutting a car amp also has the benefit of providing a case, terminals, fuses, all the stuff thats otherwise gonna be hard to find...

If you really want to spin it all yourself check out Rod Elliots website, www.sound.au.com, it has a modestly simple SMPS for car uses, then you need to choose an amp for your output, there really arent that many (that I am aware of) published for 1-4ohm loads, but modifying existing designs is possible, though perhaps not a good place to start...oh and Sanyo claim to have modules designed for sub 4 ohm loads...

Have fun

Stuart
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Old 31st October 2004, 12:47 AM   #3
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thanks very much for the help!

Actually, I've done a ton of reading up on amp building now. I was considering your suggestion, but hadnt asked anyone yet! I have an Alpine t707 that should serve as a great donor!~

Thanks again!
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Old 14th February 2005, 05:56 AM   #4
kita is offline kita  United Kingdom
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Question heretical follower

stuart- i really like the simplicity of the gut it and transplant approach. I think I've got just the candidate too, a cheap 'tornado' amp, 4x30w rms, but they're bridgeable to 2x60w (seperate rca inputs for each pair of channels tho which is weird...I seem to need a preamp/ line splitter for my single source).
I tried chasing the bpa200 thread and found quite a few different schematics for bridging and paralleling chips- did you have in mind anything particular?
Also, have you heard of anyone who's pulled off this trick already or is it an original brainwave? Just to know whether I'm a guinea pig. (I've always wondered)
Thanks

kita
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Old 14th February 2005, 07:05 AM   #5
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Default original, not really...

In the course of fixing car amps I have acquired a number of car amps suitable as donors for chassis and power supply. In the main the amp sections were crap to start with, so fixing them 'good' as new was pointless, the only simple high quality amp I could fit in the chassis was going to based on a GC...you can make the things using simple point to point wiring, so no PCB's needed, they have good protection circuits, etc overall just seemed like a good fit...

For driving normal to low impedance loads, from 4 down to 1ohm, I'd just use a simple parallel approach, build the GC channels much as normal, but use accurate (1% or better) resistors to set the gain and then before the input network unite the inputs with resistors of a few K and after the feedback point join the outputs with some low value power resistors, perhaps 0.15ohm @ 3w. The more channels paralleled the more current you can deliver and the lower the overall output impedance.

Since 2 channels are already available in one chip, doubling the output into 2ohms, or quadrupling it to drive 1ohm (2 chips/4 channels paralleled) should be quite straightforward, though I have nothing but theory at this point. Too many projects, not enough hours...Just finished an aleph amp, started a krell, and I'm fixing broken stereo to help out a friend at a local stereo store...and if I remember correctly I have a fulltime job too...

For bridging with parallel channels, such as the BPA200 I'd be following one of the other threads closely, I'm just not convinced I'd ever use that much power in a car. Part of the attraction of a GC in this situation is the simplicity, as you get into the BPA200 level projects you lose some of that.

If you decide to move ahead with your project, let us know how it goes, I will be following along as soon as I can clear the decks...

Stuart
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Old 14th February 2005, 06:23 PM   #6
maylar is offline maylar  United States
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The LYNX power amp here..

http://www.audio-circuit.dk/

.. would be a great start at what you're trying to accomplish. There is of course a power supply issue to contend with whenever you do a car amp, and most people say it's more daunting than the audio portion. There are SMPS threads here all the time.
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