hey guys,
i've just finished a paralleled LM3886 based power amp and i'm having a weird problem.
The two LM3886 amplifiers are on separate boards and have their inputs connected by a wire between the two boards.
One board has the zobel network and damped series inductor, the output of the other board again is connected to this one by a wire.
When i turn it on, even if the volume pot is set to 0, a weird low pitched noise, which isn't particularly loud, comes out of the speaker and the mains fuse blows after a second or two.
If I disconnect the wire connecting the outputs of the two boards however, both of them work fine. this problem only occurrs when the outputs are actually connected.
I've read that if the two circuits outputs aren't well matched, they might try to 'drive each other'? i have used 1% resistors in all places that have an effect on the output signal.
I've attatched the schems of both boards. Where it says 'to board 1' etc are the points at which the two boards are connected.
Anyone have any idea what the problem might be/ how i can fix it?
edit: forgot to mention, the series inductor is 12 turns of enamelled copper wire around the 10 Ohm resistor on the output of the first board. and the reason I have used 5 parallel resistors at the output of each is that the LM3886 documentation recommends .1 Ohm resistors but I couldn't get 1% accuracy .1 Ohm resistors with high enough power rating, so I used 5 x 1 Ohm resistors to get close.
i've just finished a paralleled LM3886 based power amp and i'm having a weird problem.
The two LM3886 amplifiers are on separate boards and have their inputs connected by a wire between the two boards.
One board has the zobel network and damped series inductor, the output of the other board again is connected to this one by a wire.
When i turn it on, even if the volume pot is set to 0, a weird low pitched noise, which isn't particularly loud, comes out of the speaker and the mains fuse blows after a second or two.
If I disconnect the wire connecting the outputs of the two boards however, both of them work fine. this problem only occurrs when the outputs are actually connected.
I've read that if the two circuits outputs aren't well matched, they might try to 'drive each other'? i have used 1% resistors in all places that have an effect on the output signal.
I've attatched the schems of both boards. Where it says 'to board 1' etc are the points at which the two boards are connected.
Anyone have any idea what the problem might be/ how i can fix it?
edit: forgot to mention, the series inductor is 12 turns of enamelled copper wire around the 10 Ohm resistor on the output of the first board. and the reason I have used 5 parallel resistors at the output of each is that the LM3886 documentation recommends .1 Ohm resistors but I couldn't get 1% accuracy .1 Ohm resistors with high enough power rating, so I used 5 x 1 Ohm resistors to get close.