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PStamler PStamler is offline
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Default Simple Test Circuit for Tube Noise

On Sep 10, 8:56*pm, (Scott Dorsey) wrote:
PStamler wrote:

In theory. In practice, there are other issues, some of which Scott
has discussed above. But, if the source resistance is appropriate
(either inherently high, or made so with a transformer), tube circuits
can be as quiet as, say, a 5534 opamp.


Unfortunately, the thermal noise in the transformers is sometimes a
bigger worry than the noise of the tubes themselves.... *and certainly
the interwinding capacitance of the transformer is always a bigger
destroyer of bandwidth than the tube stage itself.

I'm a big fan of tubes, it's the transformers I don't like...


Use the right transformer, and it works fine. Try the Jensen JT-13k7;
the thermal noise only adds 1 dB, and the bandwidth is good. It's the
tube used in Dan Kennedy's original preamp design, which is very clean
and neutral. It turns out the same transformer does a fine job with a
vacuum tube.

Peace,
Paul