measuring resistor noise is not as simple as connecting
a low-range voltmeter and reading the result. Joe Geller,
KO2Y has determined that several problems exist that prevents
low-cost methods from working.
He has successfully overcome these problems and has implemented
an interesting solution using modern components. He has
named this device the Geller JCan.
his website Joe says "Whether
you are an audiophile, an instrument designer, an EE or
physics student or an electronics enthusiast, you might
find these problems in measuring resistor noise interesting.
You might even want to build a JCan and try it out yourself!
JCan is a very sensitive instrument that can directly
measure resistor noise when used with a standard AC voltmeter
capable of measuring AC voltages in a range of 1 mV to
20 mV AC at audio frequencies. The JCan can also measure
thermal noise plus shot noise by injecting a small current
into resistors under test."
JCan circuit board is mounted
under the lid of the shielding enclosure.
J-Can is a battery-powered special amplifier that is completely
shielded from outside interference. Even the target resistor
is enclosed inside the JCan during testing. A shielded
signal connector is the only thing visible on the shield
older HP 400 series AC voltmeters are very useful and
widely available as surplus instruments. An HP400 AC voltmeter
is also a good companion instrument for working with the
decided to use an additional audio amplifier to allow
hearing the output from the instrument. This definitely
added an interesting dimension to the project and allows
comparing the near white noise with no power to the occasional
clicks of shot noise under power.
found that building and using the JCan is fun. I also
learned more about the underlying fundamentals and problems
of resistor noise measurement. A mentor said to me a long
time ago "remember the first three letters of the
word 'fundamental' spells FUN!"