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Old 21st April 2005, 11:50 AM   #1
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Default bridged opa549 problems

i built a bridged opa549 amp and it worked perfectly sounded perfect. well i went to build the second channel and im not sure where i went wrong. when i power up the music comes out, but also the woofer pushes completely out, it seems there is alot of DC on the output or something. does anybody know what the problem could be?
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Old 21st April 2005, 01:20 PM   #2
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Seems that one part of the bridge indeed has a lot of offset. Can you measure which side it is? Don't connect the speakers for now, you could blow them. Do you have a load resistor (5-20 ohms will do).

If you can identify that, can you measure (without signal) the DC at the input pins of the good and the bad channel?

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Old 22nd April 2005, 11:41 AM   #3
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thank you for your help i have figured out the problem. somehow, the ground got connected to the input and that was the reason for the huge dc output. thank god my speakers are fine thow.


But, i have another problem. both channels work fine when hooked up individually to the transformer (42,0,42V after rectification) i have the +42V and the 0 hooked to a rectifier and then i have the -42V and 0 hooked to another one. so each of my channels is getting +-21V. it works perfect when one of the channels isnt conected to power but when i connect the other one, one of the channels just puts out a huge amount of distortion. any ideas?
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Old 22nd April 2005, 12:09 PM   #4
joensd is offline joensd  Germany
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Hi,
can you post in detail how you wired the power supply and the amps?
Ideally including a schematic for the amps.
Either I misunderstood you or there is something fundamentally wrong with your power supply wiring/concept.

Quote:
+42V and the 0 hooked to a rectifier
I assume with +42 and 0 you mean the AC from the transformer?
Rectified that´d be roughly 60VDC. Now how do you get +-21V from that?
You can split a 60VDC-supply to get +-30V but that is not recommended for a power amplifier and anyway +-30V would be on the edge of what the OPA549 can handle.

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