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    Driver microphonics-a funny result

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    eickmewg

    Posts : 41
    Join date : 2014-08-29

    Driver microphonics-a funny result

    Post by eickmewg on Sat Jan 10, 2015 3:59 pm

    When I got my VTA ST-120 kit Bob included Sylvania 5963 drivers for the VTA board. They worked well for several months but then got very noisy on startup. He suggested I try a platinum Mullard ECC82 from Upscale audio for the voltage amplifier. I supplemented that with two GE 12BH7A outboard drivers. This seemed to work but I noticed that they were rather microphonic when I tapped any of the transformers, the chassis, or the drivers themselves. I had previously built a Transcendent Sound grounded grid preamp that originally came with three rather lowly JJ ECC82 tubes. I had replaced those in the grounded grid with RCA clear-top 12AU7 tubes. So, I decided to roll the JJ ECC82 tubes into the ST-120. These are like $15 tubes vs. the $60 for the Mullard tube alone. No more microphonics! I then put the platinum-grade Mullard tube back in the center with two JJ's and the microphonics returned, I was surprised at the result. Furthermore, the JJ's sound as good to my ear as the Mullard/12BH7A combination. I guess tubes can be funny things!

    MontanaWay

    Posts : 781
    Join date : 2014-02-06
    Age : 58
    Location : Brookings, Oregon

    Re: Driver microphonics-a funny result

    Post by MontanaWay on Sat Jan 10, 2015 7:11 pm

    I've had very good results with JJ tubes, I really cannot fault them at all!

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Driver microphonics-a funny result

    Post by sKiZo on Sun Jan 11, 2015 9:54 pm

    If microphonics is an issue, try isolating the amp better. I put Vibrapods under the legs on mine and they worked wonders. I could feel a pretty good buzz in the chassis prior to that, now it feels dead steady ...



    The pods come in different pound ratings ... I used two #4's on the back under the heavy iron, and just needed #1's in the front. I noticed the amp wasn't sitting level after due to the rear feet getting squished a bit (that iron is heavy if you haven't noticed), so I stacked an extra #1 with the #4's ... perfect!


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