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How to convert speaker-level AVR outputs to mono to drive passive SVC subwoofer.

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  • How to convert speaker-level AVR outputs to mono to drive passive SVC subwoofer.

    Hello Everyone.

    I have a six year old Pioneer SW-8MK2 active mono subwoofer that I purchased from here a while back.
    The built-in amplifier gave up the ghost and there are fried components burned on the circuit board.
    Knowing I would spend more than I wanted to repair the amp (cheaper to buy another used one on CL), I removed the amp boards from the metal cover and wired the subwoofer speaker wires directly to the left channel of the speaker-level inputs.
    Now I have a "passive" subwoofer.

    My AVR is a typical Yamaha HTR-5650 with the (now unused) subwoofer RCA output and no subwoofer speaker outputs.
    I want to connect the subwoofer directly to my "B" speaker L and R terminals to get the low end sound back.
    I have a cheap low-pass subwoofer filter to install inside the box to take away the highs.

    What I need to know is how to wire the AVR L and R speaker channels to make them mono into the subwoofer's single channel to avoid burning anything up.
    I heard you can solder resistors to the L and R red wires and they combine them after the resistors.
    The black wires just get combined together.
    The subwoofer speaker is 8 ohms and can handle 100W of power.
    The AVR puts out 80W per channel, according to the specs in the manual.
    What value of resistors should I use and is this a cheap and safe way to get use of my subwoofer back?

    Thanks!

  • #2
    Unfortunately that will not be possible. There's no way to combine the signals without shorting the amp out, and if you place series resistors to avoid killing the amp you lose the power to the sub in exchange for heating the resistors.

    My suggestion would be to put some money back and get a new plate amplifier for the sub so you can run it from the RCA output.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music

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    • #3
      Plate Amp to make the sub active again ...

      As Wogg said, do not try to combine the speaker level outputs into a mono signal.

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      • #4
        Way back in the early 70’s in my teenage car stereo days I once wired a center speaker that was in the dash with the positives from each channel. It worked and didn’t blow anything up. And sounded kinda cool!

        Could this work for Michigan Yamaha?

        Have fun! Mark

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        • #5
          In addition to the issues already pointed out the AVR A/B speaker outputs may well be series wired. Get a plate amp.
          www.billfitzmaurice.com
          www.billfitzmaurice.info/forum

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          • #6
            Originally posted by Psycoacoustics View Post
            Way back in the early 70’s in my teenage car stereo days I once wired a center speaker that was in the dash with the positives from each channel. It worked and didn’t blow anything up. And sounded kinda cool!

            Could this work for Michigan Yamaha?

            Have fun! Mark
            That will give you the difference signal to the speaker, so whatever is in the L and not R or vice versa. Bass in omni-directional and gets the most power out of both channels pushing it in phase, so almost all content has the low frequencies matched in both channels, so there wouldn't be any content for a sub like that.
            Electronics engineer, woofer enthusiast, and musician.
            Wogg Music

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            • #7
              Originally posted by wogg View Post

              That will give you the difference signal to the speaker, so whatever is in the L and not R or vice versa. Bass in omni-directional and gets the most power out of both channels pushing it in phase, so almost all content has the low frequencies matched in both channels, so there wouldn't be any content for a sub like that.
              It could be additive L- & R+ (or vice versa). The real questions: Are the channels bridgeable? And are they bridgeable while in use on the L-R? And what impedance would the amp see bridged with an 8 ohm woofer while driving the L-R? Highly unlikely it would be successful (and likely damage the amp).

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              • #8
                Any amplifier can use the LFE from the Yami to power the sub. A low pass may not be needed. There are lots of options for a sub amp including building one and used pro amps.

                Might check if the woofer has a dual voice coil then there would be no problem running separate low passes and b channel L R to the separate voice coils.
                John H

                Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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