Hi. I recently got a mic pre-amp. It has an advertised noise floor
of -140dB (at minimal gain) . However, when I began using the unit, I
started hearing an unusual pulsing in the output. A deep pulse around 500Hz.
I ran the unit into Vegas, with all software meters at unity gain, and the
mic pre-amp at minimal gain. Vegas showed the noise floor at -70dB, as does
my soundcard at input.
I did this test by sending the data through the Coaxial S/PDIF output of
the mic pre, to the Coaxial input of my soundcard. I tried this with and
without a mic attached. In both cases, I heard this pulsing. The sound gets
louder when I turn up each pot on the pre, and seems to change tempo
depending on where they are. It usually cycles around 5 times per second.
I also have a Nomad Jukebox 3, which records to 16/44.1 .Wav files. It
has S/PDIF input, and when I send the mic pre to this unit, the same noise
I sent the unit back, and was told it is working order with a noise floor
of -138dB at minumal gain, and that I was somehow measuring the unit\'s noise
inaccurately. I\'ll receive the unit again shortly, so I can test it once
more. Am I missing something here? I\'m no audio wizard, but I thought this
would be fairly simple to figure out. Please, any assistance is appreciated!
:::Please Note::: I am not assuming the pre-amp is faulty. I trust that it is working order, on the manufacturers words.