Re: Low volt noise gen

On Thu, 10 May 2007 20:44:21 -0400, John Popelish <jpopelish@xxxxxxxx>
wrote:

John Larkin wrote:
On Thu, 10 May 2007 18:27:01 -0400, John Popelish <jpopelish@xxxxxxxx>
wrote:

Thanks for an actual data point,
instead of an unsupported opinion.

My opinion isn't unsupported. I have two of these boxes, and they both
hiss.

Is the hiss originating from the LM386 chips or from some
other component? Phil's data shows the result of a test of
the LM386 generated noise.

He did specify that the input pins were grounded. In real life, simple
chips like this tend to run the input stage at high currents, which
skews things towards low voltage noise and high current noise. So if
the input were driven from a reasonable non-zero impedance, or just
left open, there would be a bunch more noise.

Amplifiers with grounded input pins tend to have a bad s/n ratio,
especially if you measure it in dB.

I wonder what's the absolutely worst noisy amplifier thing around. I
recall seeing opamps that ran over 100 nv/rthz somewhere.

John


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