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Old 16th November 2003, 06:31 PM   #1
audioPT is offline audioPT  Portugal
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Default OPA541 Bridged

Hi!

How to bridge 2 OPA541?

I've tried and fried 2 of them

Pedro Martins
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Old 16th November 2003, 07:59 PM   #2
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firstly there is now a chip amp forum. it's more likely you'll find answers there much quicker.

my bet would be that you are not useing a large enough load, or that you are using insufficient heatsinking or that the themal interface to the heatsink is poor.

bridging can be seen as each amplifer playing into an impedance equal to half of the load. this is actually easy to show with circuit diagrams. so if you have a 4ohm woofer the opa is trying out the 2ohm load.

if you have no heatsink the chip will fry. this isn't a class D amplifer chip that runs cool.

a more detailed summary of things like how the chip is setup, how long the chip lasts, and if the heatsink is isolated from the chips would aid in troubleshooting.
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Old 16th November 2003, 08:13 PM   #3
audioPT is offline audioPT  Portugal
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Tanks for answering.

1. I know there is a Chip Amps Forum... Sorry, I forgot!
2. The load is 8Ohm and the PSU is 30-0-30V 5A
3. The OPAs are in a heatsink large enough to some Aleph's
4. Both OPA's are isolated from the heatsinks.
5. These OPA's have worked in a stereo configuration...

Helped?
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Old 16th November 2003, 10:25 PM   #4
B.VDBOS is offline B.VDBOS  New Zealand
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When you bridge two amps they will try to put out 4 times the power, this could be why your chips are frying

Two things you could do to solve this are

1: Reduce the gain in each amp to half of what it was so that in bridge mode it will be
putting out only two times the power which should be fine for two chips

2: Keep the gain the same for four times the power in bridge mode and use four chips in bridge parallel arrangement to deal with heat.

Download this PDF file, its for national chips but the theory will be the same for the opa's

http://www.national.com/an/AN/AN-1192.pdf
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Old 17th November 2003, 07:21 PM   #5
audioPT is offline audioPT  Portugal
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He! He! he!

At the time you are writing your reply, I was reading that application note from National...

Now they are working, but not the two first ones, as they are dead!

Fried, is the right word...

The gain I'm using is low, but is sufficient for my purposes.

BTW, I can put 1 Hz into the woofer!!! Really! It drops the full PSU current! I've used another toroidal with 600VA with the same voltage 30-0-30, and the ampmeter goes full scale, dropping from 6 to 4 amps between 15 and 1 Hz.

I know the chip only hangs 5 Amps, but at 35 Hz it jumped to 8 A!!

As the temperature

Regards to all

Pedro Martins
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