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Thread: Biamping Vintage Altec 803B/804A/8/11B with Tube Amps

  1. #11
    Senior Hostboard Member bowtie427ss's Avatar
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    Re: Biamping Vintage Altec 803B/804A/8/11B with Tube Amps

    The document also says:
    Caution: Below the cutoff frequency of the capacitor, the power amplifier will be unterminated. If the power amplifier has an output transformer (typical of tube amps...), a 20 W resistor equal to ten times the compression driver impedance should be installed across the amplifier output terminals.
    Not sure i subscribe to this.

    A series cap only filters 6 db per octave below the effective kneepoint of the cap. 5 octaves down there is still signal passing thru, allbeit attenuated ~30db. Even with safety cap installed, there is "some" load all the way down, surely enough to prevent voltage buildup and ultimate implosion of the OPT, no?

    Additionally, if your tube amp is producing disproportionate signal below the filter points of the active network driving it, then your tube amp is not in good health.
    Not all vegetables make good leaders.

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    Senior Hostboard Member Elitopus1's Avatar
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    Re: Biamping Vintage Altec 803B/804A/8/11B with Tube Amps

    I agree with Bowtie about the resistor. I have biamped with tube amps and have never used a resistor.

    The rest of that PDF is pretty accurate though.

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    Junior Hostboard Member FriendlyVolcano's Avatar
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    Re: Biamping Vintage Altec 803B/804A/8/11B with Tube Amps

    I'm bi-amping, too, using an Ashley XR1001. I've got Mcintosh MC60's (tube) on the top and and a MC250 (SS) on the bottom. I'm running Emilar EA175 HF drivers 16ohm.


    Altec had their own Bi-Amp protection cut-off publication, which I followed:

    http://alteclansingunofficial.nlenet...ers/TL_205.pdf

    Based on their suggestion for a 16ohm driver, I'm using a 22mfd cap in-line, which would let me go down to about 480hz. I'm crossing at 800hz so that should be OK. I'm also not using a resistor across the terminals as suggested by the JBL document.

    Can anyone comment on the disparity between these two tech manuals? And what is the lowest frequency that a HF driver should experience before needing to be cut off?

    Should I be following the JBL approach?

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