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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all products

7 posters

    Subwoofer question


    Posts : 8
    Join date : 2019-11-14

    Subwoofer question Empty Subwoofer question

    Post by docswanson Sat Aug 07, 2021 5:25 pm

    Hi again,
    Now it's time to enjoy my newly rebuilt ST70. I will be using it with some Klipsch bookshelf speakers and an powered subwoofer.

    I will be using the high level inputs on the subwoofer from the speaker outputs of the ST70. The Klipschs will be using the 8 ohm outlet.

    My question, is there a preferred speaker terminalI should hook the subwoofer up to? I had assumed I should use the 16 ohm, since the sub presents a very high impedance load. But I am not sure if my reasoning is sound. Any thoughts on the optimal choice for connection?


    Posts : 36
    Join date : 2019-10-26
    Location : Kansas City

    Subwoofer question Empty Re: Subwoofer question

    Post by AmpedUp Sat Aug 07, 2021 9:59 pm

    The optimal setup would be to connect your sub/s to a preamp that has sub terminals. Powered subs need only a weak (non-amplified) signal thus they should not be connected to your ST-70 outputs. If you decide to not add a preamp you would need to split the signal from your music source with one feed going to your sub and the other going to your amp. This is not a good idea but will usually work. Matching impedance levels is important for quality sound and are good questions for you to ask of the seller of any preamp before you purchase. Roy sells a range of quality preamps that might just fit your budget.
    Good luck...

    Posts : 148
    Join date : 2018-03-20
    Location : NY

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    Post by New2Tubez Sun Aug 08, 2021 2:00 pm

    Have you looked here..? I'm sure it's come up.

    Posts : 136
    Join date : 2012-07-08
    Age : 62
    Location : Livermore, CA

    Subwoofer question Empty Active Crossover from Speaker Level Input

    Post by aguaazul Sun Aug 08, 2021 3:54 pm

    For a while I used an Energy EAC, Like here:

    EAC Active Crossover NetworkActive Crossover Network.

    It can accept line level inputs from the back of your amp, & send the adjustable sub frequencies to your powered sub & pass through the rest to your main speakers.

    I still have mine, if you are interested in purchasing it, my wife & I are actually cleaning out the garage today I can locate it & we can privately negotiate a price.

    Here is the PDF of the owners manual, hosted on my Google Drive:

    EAC Owners manual



    PS: This also shows how to attach a PDF. Hope this helps.

    PSS: EDIT: it also can take in Line Level from your Preamp, do the same. These are nice little units.

    Last edited by aguaazul on Sun Aug 08, 2021 3:56 pm; edited 1 time in total (Reason for editing : Remembered a cool feature... Now second thinking selling it ;-))

    Posts : 48
    Join date : 2019-12-28
    Location : Rochester, NY

    Subwoofer question Empty Re: Subwoofer question

    Post by knotscott Mon Aug 16, 2021 9:54 am

    I've been running an inexpensive Dayton SUB1200 powered subwoofer off my Dyna/VTA ST70 with very good results, but I run the sub off the same outputs that the main speakers use...8 ohm.  I actually prefer the sound in this setup, vs running the sub from preamp outputs to line level input of the sub.

    Posts : 59
    Join date : 2019-05-20
    Location : Northern Illinois

    Subwoofer question Empty Re: Subwoofer question

    Post by ttocs Mon Aug 16, 2021 11:22 am

    I've been running my subs via the High Level (Speaker Level) inputs on the subs for a long time, and just daisy chain from the speaker's terminals which are fed by by the 4Ω outputs of the M-125 amps. I daisy chain because each pair of subs is adjacent to each Front speaker, shortest solution.

    For whatever reason, this resulted in a tiny, tiny, increase in treble output from the electrostatic speaker panels in the area of drop-off above 10KHz where the impedance takes a dive. It's less than 1dB, but I'll take it.

    Posts : 1
    Join date : 2023-01-13

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    Post by sweden Sat Jan 14, 2023 5:58 pm

    Hi, using the high input terminals on the sub when using the output terminals on the st70 is the right way to connect the sub! Use the same connection as on your speakers, for example 8 ohm.
    I have currently one Quad Integrated connected to my Magneplanar and two subwoofers, yes..two! The amp does not have sub outputs so I have to connect them to the same terminal as the Maggies. Works like a treat and sounds…marvellous!! The impedance on the subs are so high that they will not affect anything! cheers

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