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Y connector with an inline filter

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oneartist

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I need to build a RCA Y connector with an inline filter. This will send a full range audio signal to a powered pair of subwoofers with lowpass filters. The filtered signal will go to a stereo amp. What size cap do I need for an amp with 22K input impedance to drop the signal by 6db at 40hz?
 

MikeMl

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100nF

D4.jpg
 

audioguru

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A Y connector shorts two signals together usually so that one signal can feed two amplifiers. Maybe you are wrongly shorting together left and right channels to feed a single subwoofer amplifier? What do you have that feeds what?
Why do you need such a simple RC filter that it very gradually cuts low frequencies below 300Hz?

Usually a stereo amplifier has a 3rd order highpass filter and the subwoofer amplifier has a 3rd order lowpass filter with the cutoff frequency at 80Hz to 150Hz.
 

oneartist

New Member
A Y connector shorts two signals together usually so that one signal can feed two amplifiers. Maybe you are wrongly shorting together left and right channels to feed a single subwoofer amplifier? What do you have that feeds what?
Why do you need such a simple RC filter that it very gradually cuts low frequencies below 300Hz?

Usually a stereo amplifier has a 3rd order highpass filter and the subwoofer amplifier has a 3rd order lowpass filter with the cutoff frequency at 80Hz to 150Hz.
Here is the whole story. My 7.1 surround mix uses 7 Magnepan dipole speakers. The FL & FR speakers are model 1.7 floor speakers and they do not go into the very low frequencies well. To fill out the missing bottom I'm using two GR Research Open Baffle W-Frame subs. I'm using a Oppo 105 as a preamp. The 105 has two dacs. One for stereo and one for multichannel audio for the 7.1 mix. Oppo says you can use the stereo dac for the FL & FR speakers while you use the other dac for the remaining speakers. The owner/designer of GR Research suggested running the stereo signal through the splitter and allowing full range signals to the powered subs with a 80hz low pass filter. The cap which Mike calculated would drop off the signal below 40 hz by 6db to the 1.7 amp (Odyssey Stratos). Since Oppo uses speaker configuration to allow you to set the front speakers as small to limit the low frequency range, I sent a question to Oppo for an opinion.
 

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audioguru

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Connecting the splitter to FL and FR outputs shorts the outputs together:
1) It might damager the outputs.
2) It causes L and R to be the same so no stereo.

A single RC makes a very poor filter because it cuts frequencies you want and it passes frequencies you don't want. A 3rd-order active filter has a sharp cutoff.
 
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