Wednesday, January 11, 2017
Q. Should my Valve Mic be this noisy?
SOS Forum Post
Technical Editor Hugh Robjohns replies: Valve mics are generally more noisy than solid-state condensers. The M9 is specified with a self-noise figure of 15dBA, which is roughly 8dB higher than the best of the large-diaphragm solid-state designs — the Neumann TLM103 has a self-noise figure of 7dBA, for example.
However, while it is possible that your mic is faulty or requires a new valve, the high noise floor you describe could also be down to poor mic technique.
With vocals peaking at -6dBfs, a noise floor of -38dBfs does seem poor. The question is, how much of that noise floor is due to the mic, and how much is due to the recording environment? Are you recording a low-volume source at a considerable distance, or in a noisy room, or with a poor-quality mic preamp, for example?
If you have access to another large-diaphragm mic, I would suggest you rig that alongside the M9 and adjust the gain to get the signal peaking at the same level for both mics, and then compare the background noise floors. If both mics deliver similar noise levels, then the room or your technique are at fault. If the M9 is more than a few dBs noisier than a solid-state large-diaphragm mic, then the M9 is in need of repair.
It could be that the valve is faulty or worn out, and certainly that's the easiest thing to replace yourself. However, there could also be a problem in the power supply or elsewhere in the mic's output circuitry, which would require a return to the supplier to be fixed.