Tuesday, October 19, 2010

Air has noise, and other measurements

Unplugging my Parasound HCA-1500A amplifier from the Meguro noise meter, the meter immediately jumps up (not down) to a higher reading: 10.5 mV.  That is apparently the EMI/RF voltage in the air across a pair of banana jacks, in my room at this time.  (I've noticed a little variation over time, the range seems to be 9-11mV so far.)  The Meguro has a bandwidth of something like 1 Mhz, and an impedance of 1 Megohm.

It's particularly funny to remove an amplifier and see the voltage reading go up IN THIN AIR.  It's like the amplifier cables are shorting out the air around the banana jack.  Fortunately the air has a rather high impedance so the cables win.  But one can wonder what affect this has on amplifier circuitry.

BTW, with 6dB's of attenuation dialed in on its level control, but otherwise being fed by the noisy Behringer DCX 2496, I get 1.8mV wideband and 0.3mV "A" weighted noise from the Parasound amplifier.  The majority of that may still be from the Behringer itself.

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