LM3885 BPA200 200W Mono Subwoofer or Stereo Amp ASSEMBLED & TESTED w/heatsink! - diyAudio
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Old 19th November 2010, 03:32 AM   #1
MartyM is offline MartyM  United States
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Default LM3885 BPA200 200W Mono Subwoofer or Stereo Amp ASSEMBLED & TESTED w/heatsink!

As much as I hate to do it, I am breaking down the 7 channel car amplifier I built and selling the individual lightly used National Semiconductor LM3886 chip amplifier subwoofer from my amp. I built the amp originally as an original solution for the 5.1 surround sound from my Alpine 5.1 decoder/DSP in my car.

I have here a single-channel 200W paralleled dual-chip amplifier, consisting of two PA100 amplifiers run in a bridge configuration, with a compact size, based on the National Semiconductor BPA200 design example. I designed the PCBs and assembled & tested the amplifiers myself. Of course, I ran them in my car, in between using my other amplifiers.

This can easily be converted to a ready-to-go stereo PA100 amplifier!!

The amplifier pair has a large heatsink (electrically isolated) and a custom 12V DC fan I added later.

The amps run in single-channel subwoofer bridged mode, with an external op-amp bridging board I built and will include (along with schematic).

Each amplifier feature 0.1% Dale resistors for the audio feedback & gain paths, and 1% 0.1 Ohm parallel resistors on the output.

Each amp board features a 10K adjustable potentiometer on the input, Molex .062" connector for the audio in connection, and Molex .093" 2 & 3 conductor connectors for the +V, -V, and ground connections, along with the speaker + & - connections.

It sounds really good, and was never been abused. I designed them and ran them based not on the need to run them at 200W, but that my maximum need might be in extreme cases, 100W. In reality my listening habits would keep them below half of that. This will drive a 4 Ohm speaker or higher.

If you need the Molex connectors removed, other small things like that done, I don't mind. Also, the amplifiers are wired for an external time delay circuit to enable a time-delayed mute circuit, but I will remove that if you like.

Of course I'll supply the schematics if you like. One image of the schematics is attached below.

These were originally power by my inverting power supplies and ran off of +/-28V DC, from my +12V inverting SMP supplies.

Let me know what we can do! My amp was HUGE and VERY HEAVY, looking to get rid of a lot of the projects I've collected over time.

I have an excellent eBay feedback rating [micro_engineer (703)] and will ship responsibly and promptly.

I guess my asking price is about $40. It will be very hard to beat that price for the sum of the price of all items, including the heatsink. (Also includes necessary mounting hardware)

Thanks!

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Old 19th November 2010, 07:24 AM   #2
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would these work at 14.4V and if so how well?
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Old 19th November 2010, 02:17 PM   #3
MartyM is offline MartyM  United States
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Hi, they can be run at 14.4V, with some modifications:

1. Will need to add a large output capacitor on each for DC blocking (see Nat. Semi. LM3886 data sheet, Single Supply Application Circuit).

2. Will need minor modifications to the supporting components like the feedback/capacitors in the design.

If you want to use this as a stereo amplifier, it will do ok, but bass will be limited for the DC 14.4V application. As a subwoofer amplifier, you'll still need split rail power to deliver any real power, the same as any amp.

However, I built a +12V to +/-28V power supply (see other post) that will take care of that in either case. Plugs right up to the amp set.
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Old 19th November 2010, 05:42 PM   #4
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Old 19th November 2010, 05:43 PM   #5
MartyM is offline MartyM  United States
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What? I don't understand.
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Old 19th November 2010, 05:57 PM   #6
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Old 21st November 2010, 03:09 PM   #7
MartyM is offline MartyM  United States
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Default SOLD! :)

Subwoofer / amp set is SOLD!

Thanks for those who expressed interest in the set.
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Old 21st November 2010, 04:41 PM   #8
JZatopa is offline JZatopa  United States
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There are a few guys on mobilesoundscience.com who would have loved to buy that whole amp from you. Why didn't you just sell the whole amp? Are you building another one? I would love to know a whole lot more about how well this DIY amp worked for you and what you will be replacing it with. I wanted to build a DIY class A amp for my horns but I don't know how to make a power supply and I have never truly built an amp from scratch.
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Old 21st November 2010, 04:52 PM   #9
MartyM is offline MartyM  United States
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Hi there. Actually some how I've never heard of that site, but I'll check it out from now on.

Actually the amplifier in its entirety was prohibitively heavy and not exactly easy to carry around!

But mainly the issue I had not resolved 100% was dealing with ground loop noise. I did not implement good noise control from the beginning. Also I should have made it much more compact. Otherwise, it did sound really good.

On the other hand, not many people need a 7 channel amplifier, so what are the odds I'd sell the whole thing? Not good, I suppose.

I'm going to either redesign the whole (or part of) the amp, and replace it or build a pure vacuum tube amplifier.

If you're going to build your own amplifier, I would suggest buying an SMPS supply like this:

eBay +12V to +/-32V 180W SMPS LINK
eBay seller: along1986090

By the time you buy all the parts, design/build the PCB, then resolve things like noise & other issues it can get expensive in terms of time & money. But not terrible if you have a design to base it off of, like I did.

Well, just some ideas. Thanks
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