hook the left and right channels together?

[x. onasis]

Will it hurt a stereo 3875 amp to do this?

I've got a single input sub plate amp and I'd like to sum the outs from the chipamp to get low freq. from both channels.

Would it effect the signal from another line out to the left and right main speakers?

[jackinnj]

you can parallel the inputs and outputs of an LM3875 -- but note that the input impedance will drop in half -- take a look at how it is done on the LM4780 datasheet.

[preiter]

I'm confused.

You want to send the output from an LM3875 based amplifier, into a subwoofer amplifier?

Please explain more.

[Sherman]

If I understand his question, he wants to sum the low frequencies of both channels of his chip amp because his sub amp only has a single input, not a stereo input. That way the chip amps do the high frequencies in stereo and the sub does the low frequencies in mono.

I believe the answer is to place a low-pass filter on the outputs for both chip amp channels before the speakers of course. Take the outputs from the low pass filters together to the sub.

You need to decide the crossover frequency you want to use in order to build the low-pass filters.


Edit- my diagram didn't show up right, so removed.

[x. onasis]

Originally posted by Sherman
If I understand his question, he wants to sum the low frequencies of both channels of his chip amp because his sub amp only has a single input, not a stereo input. That way the chip amps do the high frequencies in stereo and the sub does the low frequencies in mono.

This is exactly right.

I wanted to slam together two sets of speakers for distant friends today out of available parts: 16 TB 871's and a couple DVC woofers and two plate amps. Got the boxes together and drivers in for tomorrows trip. After a quick listening test, one's gonna get a set with two active subs and the other will have to purchase a sub.

Oh well, I tried.

Thanks for the responses.