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    Is there a difference between the VTA driver board for the ST-70 and the ST-120?

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    1bigpig

    Posts : 11
    Join date : 2015-03-12

    Is there a difference between the VTA driver board for the ST-70 and the ST-120?

    Post by 1bigpig on Tue Apr 21, 2015 7:52 pm

    Bob (and everyone else),

    Is there a difference between the VTA driver board for the ST-70 and the ST-120?

    I am starting to get some popping and volumn jumps in the right channel of VTA-120 with the step attenuator and when I touched the knob the other night, it made a loud hum.  So, I am thinking about removing the step attenuator completely and upgrading to the new CCS VTA driver board with the lower gain 12AU7 tubes. With my current preamp, I can only get to about 9 o'clock before I am almost at full volumn.

    I saw someone had a modern VTA driver board for an ST-70 for sale on eBay, but it was removed from an upgraded ST-70.  So, if I was to purchase this board, what changes would be required to make it work on an VTA-120?

    Lastly, could the hum and jumping in volume be a bad solder connection on my step attenuator?

    Thanks,

    Bruce

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: Is there a difference between the VTA driver board for the ST-70 and the ST-120?

    Post by MontanaWay on Tue Apr 21, 2015 8:54 pm

    the VTA driver boards, circuits and components used are identical for the ST70 and ST120, so they are totally interchangeable in their ORIGINAL execution.

    Yes, check all your solder joints around the attenuator, input jacks etc., especially the ground connections! If you are still getting that noise, good chance it will be the attenuator. Either bypass it or get yourself a good quality ALPHA of BOURNS 100K stereo AUDIO taper potentiometer. Size wise it should fit into the same spot, you may need to enlarge the hole for the pot mounting shaft though.

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Is there a difference between the VTA driver board for the ST-70 and the ST-120?

    Post by j4570 on Wed Apr 22, 2015 7:28 am

    I would be leary of buying someone else's used driver board considering how realtively inexpensive they are from VTA (Roy or Bob), you could end up with another issue to diagnose. I built mine and it wasn't too bad, but if that's not for you, you can get a prebuilt one for not much more. I'm to the point in my life I have too many projects and not enought time, so I only have time to do it once, which means do it right.

    I've thought about the CCS driver board myself (I have an older one as well) with the Octal tubes though. But that would be another project and my VTA board is still working great...so I will wait.

    One last thought. Before I started doing anything else, I'd remove the tubes and clean all the sockets and fire the amp back up and rebias. Once I had that done, if the problem persisted, I would take out the attenuator to diagnose that issue before I ordered a new board or attenuator.

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Is there a difference between the VTA driver board for the ST-70 and the ST-120?

    Post by tubes4hifi on Wed Apr 22, 2015 10:21 pm

    to answer the original question FULLY . . .
    the VTA70 and VTA120 use the exact same driver board . . .
    BUT, there was a revision about 3 years ago.
    The original board from 10-20 years ago used 12AT7 tubes, then they were switched to a LO-GAIN version using 12AU7 tubes about 5-6 years ago.
    About 3 years ago the phase splitter was improved by using a CCS and removing the balance pot.

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Is there a difference between the VTA driver board for the ST-70 and the ST-120?

    Post by Bob Latino on Thu Apr 23, 2015 8:55 am

    1bigpig wrote:Bob (and everyone else),

    Is there a difference between the VTA driver board for the ST-70 and the ST-120?

    I am starting to get some popping and volumn jumps in the right channel of VTA-120 with the step attenuator and when I touched the knob the other night, it made a loud hum.  So, I am thinking about removing the step attenuator completely and upgrading to the new CCS VTA driver board with the lower gain 12AU7 tubes.  With my current preamp, I can only get to about 9 o'clock before I am almost at full volumn.

    I saw someone had a modern VTA driver board for an ST-70 for sale on eBay, but it was removed from an upgraded ST-70.  So, if I was to purchase this board, what changes would be required to make it work on an VTA-120?

    Lastly, could the hum and jumping in volume be a bad solder connection on my step attenuator?

    Thanks,

    Bruce

    Hi Bruce,

    More than likely one of the solder connections on the attenuator or a solder connection on the input jacks or driver board have gone partial. The simplest thing to do is to RESOLDER the six connections on the attenuator and see if that cures the issue you are having.

    Bob

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