how to connect sub amp

jarcher12 · 17th May 2009, 07:51 AM

Hi frst of all I have built 3 chip amps with the help off this forum and only had to ask once. Excellent forum. But now i have a question that I can't find the answer.
I have an amp with two 3876 for 8 ohm speakers and one 3886 for a 4 ohm passive sub. My question is how do I connect the sub amp , where does the input come from. I dont really want to add a whole lot of extra circuits. I think i found a thread once that said connect a 10k r to the output and use this as input to the sub amp. is this a good idea ? any help appreciated.

jarcher12 · 17th May 2009, 03:01 PM

I found this http://www.tkk.fi/Misc/Electronics/c...r_to_line.html page is this an ok way to do it ?

AndrewT · 17th May 2009, 05:21 PM

no,
that is just an attenuator.

You need at least a low pass filter (= half a crossover) to feed the bass amplifier.

You should fit a high pass filter (=the other half of the crossover) to feed the two mid/treble amplifiers.

You should also fit a summing circuit to couple the two channels together to feed the single bass speaker.

You may need a phase invert or phase adjust for the bass amplifier.
You may need a high pass filter for the bass amplifier.

You will need a PSU to feed the new circuitry.

Conclusion:
It's far easier to feed the wideband signal to wideband amplifiers feeding full range speakers, with or without passive crossovers.

jarcher12 · 18th May 2009, 01:11 AM

Ok thanks, I will experiment and see what comes out of it.

dangus · 18th May 2009, 11:07 PM

Watch out for a used car audio electronic crossover, and power it from a 12V AC adapter.

jarcher12 · 19th May 2009, 12:12 AM

Thanks that sounds like a good idea. For now I just took the signal from one of the speaker outs with a 10k to the input pot of my sub amp. then a passive crossover for the sub woofer. It seems to work fine. but there is always room for improvement.

I open it about once a week to tweak

17th May 2009, 07:51 AM	#1
jarcher12 diyAudio Member Join Date: Apr 2009	how to connect sub amp Hi frst of all I have built 3 chip amps with the help off this forum and only had to ask once. Excellent forum. But now i have a question that I can't find the answer. I have an amp with two 3876 for 8 ohm speakers and one 3886 for a 4 ohm passive sub. My question is how do I connect the sub amp , where does the input come from. I dont really want to add a whole lot of extra circuits. I think i found a thread once that said connect a 10k r to the output and use this as input to the sub amp. is this a good idea ? any help appreciated.

17th May 2009, 05:21 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	no, that is just an attenuator. You need at least a low pass filter (= half a crossover) to feed the bass amplifier. You should fit a high pass filter (=the other half of the crossover) to feed the two mid/treble amplifiers. You should also fit a summing circuit to couple the two channels together to feed the single bass speaker. You may need a phase invert or phase adjust for the bass amplifier. You may need a high pass filter for the bass amplifier. You will need a PSU to feed the new circuitry. Conclusion: It's far easier to feed the wideband signal to wideband amplifiers feeding full range speakers, with or without passive crossovers. __________________ regards Andrew T.

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17th May 2009, 03:01 PM	#2
jarcher12 diyAudio Member Join Date: Apr 2009	I found this http://www.tkk.fi/Misc/Electronics/c...r_to_line.html page is this an ok way to do it ?

18th May 2009, 01:11 AM	#4
jarcher12 diyAudio Member Join Date: Apr 2009	Ok thanks, I will experiment and see what comes out of it.

18th May 2009, 11:07 PM	#5
dangus diyAudio Member Join Date: May 2004 Location: Vancouver Island	Watch out for a used car audio electronic crossover, and power it from a 12V AC adapter.

19th May 2009, 12:12 AM	#6
jarcher12 diyAudio Member Join Date: Apr 2009	Thanks that sounds like a good idea. For now I just took the signal from one of the speaker outs with a 10k to the input pot of my sub amp. then a passive crossover for the sub woofer. It seems to work fine. but there is always room for improvement. I open it about once a week to tweak

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