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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 Dynakitparts.com products


    VTA ST-70 with 12 or 16 ohm speakers

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    vinylb

    Posts : 7
    Join date : 2020-09-08

    VTA ST-70 with 12 or 16 ohm speakers Empty VTA ST-70 with 12 or 16 ohm speakers

    Post by vinylb on Wed Sep 30, 2020 3:53 pm

    I had my ST-70 on the bench running for a week before putting into my main system and really impressed with it. Have had various CJ, ARC, Rogue Audio's to name a few and this  beats them in detail, dynamics and soundstage.

    I was curious as to how it would handle speakers with a 12 or 16 ohm impedance? Would I need to put a resistor on the speakers binding posts to match the 4 or 8 ohm tap?

    Thanks
    Bob Latino
    Bob Latino
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    Location : Massachusetts

    VTA ST-70 with 12 or 16 ohm speakers Empty All VTA amps may be set up for 18 ohm speakers

    Post by Bob Latino on Wed Sep 30, 2020 8:37 pm

    vinylb wrote:I had my ST-70 on the bench running for a week before putting into my main system and really impressed with it. Have had various CJ, ARC, Rogue Audio's to name a few and this  beats them in detail, dynamics and soundstage.

    I was curious as to how it would handle speakers with a 12 or 16 ohm impedance? Would I need to put a resistor on the speakers binding posts to match the 4 or 8 ohm tap?

    Thanks

    All VTA amps may bet set up for 16 ohm speakers on one of the RED output binding posts. The YELLOW secondary wire which now goes to the NFB eyelet on the driver board is actually the 16 ohm secondary wire. What you do is just run the YELLOW wire to one of the red speaker binding posts and then run another wire from that binding post to the NFB eyelet on both channels. If you forget to add in the extra wire to the NFB eyelet, then the amp will have no feedback, the gain of the amp will go UP, the bandwidth will be restricted and the amp's overall distortion level will go UP slightly.

    Bob
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    vinylb

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    Join date : 2020-09-08

    VTA ST-70 with 12 or 16 ohm speakers Empty Re: VTA ST-70 with 12 or 16 ohm speakers

    Post by vinylb on Wed Sep 30, 2020 9:05 pm

    Good to know I can add an extra tap on the back. In layman’s terrms, what does it do to the sound/synergy between speaker and tube amp if we don’t add 16ohm tap at the rear of st70 or add a resistor at the speaker posts?

    Thanks
    Bob Latino
    Bob Latino
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    Posts : 2959
    Join date : 2008-11-26
    Location : Massachusetts

    VTA ST-70 with 12 or 16 ohm speakers Empty Re: VTA ST-70 with 12 or 16 ohm speakers

    Post by Bob Latino on Thu Oct 01, 2020 7:52 am

    vinylb wrote:Good to know I can add an extra tap on the back. In layman’s terrms, what does it do to the sound/synergy between speaker and tube amp if we don’t add 16ohm tap at the rear of st70 or add a resistor at the speaker posts?

    Thanks

    Adding a 16 ohm tap won't change the sound of the amp as long as you remember to also connect a jumper wire from the 16 ohm tap you added to the NFB eyelet on the driver board.

    Bob
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    vinylb

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    Join date : 2020-09-08

    VTA ST-70 with 12 or 16 ohm speakers Empty Re: VTA ST-70 with 12 or 16 ohm speakers

    Post by vinylb on Thu Oct 01, 2020 4:55 pm

    Thank you for your replies Bob. Two more questions: if I don’t modify my st70 as instructed, will any damage be done to the speakers or st70? Because speakers are 12/16 ohms, shouldn’t it be an easier load on st70 transformers?

    Thanks
    Bob Latino
    Bob Latino
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    Posts : 2959
    Join date : 2008-11-26
    Location : Massachusetts

    VTA ST-70 with 12 or 16 ohm speakers Empty Re: VTA ST-70 with 12 or 16 ohm speakers

    Post by Bob Latino on Thu Oct 01, 2020 5:16 pm

    vinylb wrote:Thank you for your replies Bob. Two more questions: if I don’t modify my st70 as instructed, will any damage be done to the speakers or st70? Because speakers are 12/16 ohms, shouldn’t it be an easier load on st70 transformers?

    Thanks

    No .. It won't cause any harm but it is not an ideal situation. That said > Some audiophiles have found sometimes that they like the sound better when the speaker is on a different tap than what the speaker manufacturer recommends ..

    Bob

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