Earth lift resistors on PC-3 and VTA driver boards

knowledge base for the classic Dynaco ST70

Earth lift resistors on PC-3 and VTA driver boards

Postby mugsy » Sun Oct 04, 2009 5:58 pm

Hi folks.

Question regarding the original ST70 driver board, vs the VTA upgrade:

There are two 10R earth lift resistors on the original board. Here in the UK I got a hum on my ST70, until some kind soul informed me that if I leapfrogged the 10R resistors the hum would go, which indeed it did :)

So far so good.

I am going to fit my (upgraded - new caps) VTA board to the ST70, and need to know whether I need to do something similar with this board?? I seem to remember I had some hum with this board originally (It's been a while), but I'm not sure if that was due to earth lift resistors or the metal stand-offs which the board came with and could have been creating a loop. Will be mounting it with nylon stand offs this time.

So basically, are there any earth lift resistors on the VTA board - there don't appear to be from what I can see?

Cheers,

- John
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Postby mesherm » Sun Oct 04, 2009 6:26 pm

Those 10 ohm resistors were installed in ST-70s because the preamp plugged into the octals in the front and in that instance it reduced noise. They are totally not needed if you don't use the monaural Dynaco preamps.
The VTA board has a normal input configuration.
Mike's N-1 Rule: When looking for N number of components to finish a job, you have a 95% chance of only finding N-1 of them.
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Postby mugsy » Mon Oct 05, 2009 1:41 pm

Many thanks Mesherm that's great :))
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