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Old 3rd April 2004, 10:36 AM   #1
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Default Anyone built the BPA200 - 200W amp shown in AP1192 ?

Hi all,

Just wondered if anyone has built the 200W amp shown in the the one and only AN1192 pdf? And if so, have you got any words of wisdom to pass on about it?

Also, noticed the transformer suggested is 385VA 60V rms - is this not a little too big?

- chris
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Old 3rd April 2004, 12:57 PM   #2
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I have 4 spare BrianGT Boards right now. I just completed a 4 channel amp. I am banking on him sending me boards for my completed amps so that I can finish my BPA200.

What resistors might you use? I am just thinking of getting some .1% holcos from Newark, and then some sweet looking HS moutables from them as well.

What is the best solution to coming up with the inverted polarity signal? I was thinking that TI chip the INA2134.

-Paul Hilgeman
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Old 3rd April 2004, 03:10 PM   #3
JohnJ is offline JohnJ  United States
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Chris,

I built one about 2 years ago. Still works great!

The two things I found were a problem building it related to heat.
Firstly, get a huge heat sink. Because of the protection circuits in these amps, the key to getting clean power is keeping them COOL. I used a chunk (about 1/2) of a heat sink from a 16kw power inverter. It measures 12"x6"x6". I just stuck it on the top of the amplifier case. The fins stick upward. Then I took a PC fan and put it on top, blowing downward so the air comes into the middle and out the sides.
THe second problem is intermediate testing (I test every little sub circuit as I go). Turns out the the idling power of these modules is larger than the free air power dissapation of the pakages(i.e. without heat sink). That means when you try to fire the amp up without a load and the heat sink not attached, they go into thermal limiting! Frustrating .
I used a strip of AL about 1/4" thick and 12" long and used those big paper clips (clamps?) to hold them against the strip for testing.
Next is the module to use: LM3886T not LM3886TF! The original app note from National showed a 1/3 more power output before the protection kicked in without the plastic coating on the heatsink! (since that app note doesn't seem to be around I'll attach a copy here, They left some good development note out of AN1192 ). The problem is that the bare heat sink tab is at the negitive supply voltage! I don't know how safe it is to have high current 35 volts just a coat of paint from the outside world. That mean investing in the best heat sink insulator you can get for it (yes, there is a big difference) . Digi-key carries a good selection, (Digikey.com is a great source for info. Just follow the links to the data sheet and the MFG of anything! They also only have a $25 minimum!)
The cost of the transformer had kept me from building an AMP for years before this. Helps when I startind working in a Transformer factory that specialized in BIG toroids! Mine is the same size as my amp and about 40 pounds. OVERKILL Good thing is I can drive 4 channels with it.
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Old 4th April 2004, 08:16 PM   #4
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Hi Crismann

Have a look at this tread:

200 watts Gäjnklon (Gainclone) - BPA200

It should give you some different views on stuff like DC-servo, ways of mounting the devices, needed heatsink and so on.

If you want to go "all the way" the 385 VA is not to big.

Have fun

Thomas
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