...OK, I thought I'd chime in to update the status of the M49b I purchased from Dany a week ago...since the mic had no power supply (and I'm not gifted in the DIY skillset) I had Dany forward the mic to Brian Fox (Foxaudioresearch.ca) who is also in Canada...I've admired Brian's work, and his exceptionally informative website, so I thought this might be a good opportunity to establish a dialog and commission him to modify a PSU to service the M49b...
...Brian has carefully researched the build options (both b and c) and the specific needs in reference to modifying a standard OEM Chinese power supply...he asked me from the get-go if I was locked in to keeping the mic true to Dany's B build specs, or if I would be open to some minor tweaks that might benefit the mic's performance, as per my particular needs...I told him to feel free to suggest options and we would go from there...
...Brian's initial testing focused on the mic's filament bias circuit...noting that in the revised C version, Neumann converted to a cathode bias, he suggested making that modification, to limit the amount of filter capacitance needed in the power supply...he noted the only thing special about the kit supply was that it had enormous amounts for filament power filtering just so the filament bias method would not inject hum into the mic (this was not needed with an indirect heated tube like the 5840)....with my approval, he made the adjustment to generate the bias in cathode as in the C, but it with a fixed voltage of 1.6 like the B...Brian does this by using a red LED in the cathode circuit instead of a resistor, which creates a fixed 1.6 volts with perfect low end response, but with much lower hum and noise than using a filament based bias voltage...
...with that he could re-wire the M49 7pin XLR so that the mic will work with any Chinese supply that is voltage adjusted to 120 volts or less...he modded the OEM chinese supply to produce 116 V volt B+...measurements showed the preamp has a net gain of +1 dB and can produce -10 dBu output before hitting 1% 2nd Harmonic distortion, and distortion is pretty even from 100Hz to 20KHz....
...I hope I have detailed Brian's approach properly (as I'm no "tech" by any measure)...this morning he sent some graphs and a sound file...he offered me the opportunity to further "sculpt" the mic's sonic character, by implementing an EQ cap (270 pF and 470 pF)...but I'm pretty satisfied with what I hear, and would prefer to stay as close to Dany's build, other than the biasing modification...so here is the response graph and sound file...any input or comments are welcomed...
Soundfile: https://soundcloud.com/kidvybes/bouchard-m49-sample-converted
*** Brian assured me that the preamp section of the mic was very flat in it's response, so that the dips in the mic's frequency response chart (from 2K-8K) may be a direct result of this particular M7 capsule's tuned response...
is that you're probably slightly tuned to the brighter side (more than I am, that is). So that could play a part here.
