Thanks for the useful info, Michael, but I feel like you're dancing around the edge of my question.
To be specific (for those of us that bought the GC mics
not supplied with frequency response graphs), do you have any experience or information, objective or subjective, positive or negative, that these mics, once modified, are any different than the "mainstream" Oktava mics? In other words, have you noticed any of the widely touted QC issues in these mics, particularly in the capsule construction or frequency response?
Do you do any testing, once modified, other than go/no go? Do you test any before and after parameters of the mics?
Sorry to be such a PITA. If you don't want to answer, no problem.
Well, I think you had several questions, my apologies if I didn't answer them clearly. I'll step through these in order.
Q: To be specific (for those of us that bought the GC mics
not supplied with frequency response graphs), do you have any experience or information, objective or subjective, positive or negative, that these mics, once modified, are any different than the "mainstream" Oktava mics?
A: I'm a bit confused, are you asking if a later-period (no graph) Guitar Center Oktava MK-219 or 319, once modified, is any different than a stock "mainstream" Oktava mic or a modified "mainstream" Oktava mic? Since I'm not sure what your intended meaning is, all I can say is that a full suite of modifications to an authentic 219 or 319 is going to produce a better sounding mic - no matter when it was purchased.
Q: In other words, have you noticed any of the widely touted QC issues in these mics, particularly in the capsule construction or frequency response?
A: In my opinion the "widely touted QC issues" are really more of an oft-repeated Internet legend than fact. The legend has its origins in Scott Dorsey's comments about parts substitutions in the MK-012. There have been no variations in MK-219 capsule construction from the mid 80's through the most recent production runs. However, with over 90,000 MK-219 and MK-319 mics in use there does exist the possibility that if 219s or 319s were sold through Guitar Center without a frequency response chart AND if some of the capsules had deviations from spec, then yes, there is a possibility that some listeners may have heard out-of-spec Oktava mics. But in my opinion, this would be a very low percentage of microphones.
At the beginning of my business relationship with Oktava I requested they build me two special mics so I could evaluate both "high resonance" and "low resonance" tuning in diaphragms. These were presented to me with frequency response graphs. The mic with the "low resonance" tuned diaphragm resembled an SM-57 spectral response - peaking at 5-7kHz then a drop-off beyond that. It sounded that way to the ear as well. I have never heard a stock 219 or 319 with anything close to the sort of HF loss heard in the mic I intentionally asked to be tuned to a low resonance.
Q: Do you do any testing, once modified, other than go/no go? Do you test any before and after parameters of the mics?
A. In my Premium Electronics mods I bias each FET for minimum THD with a spectrum analyzer at a level that represents the maximum intended SPL at the capsule. The 2nd harmonic distortion component is usually 12-16 dB lower than a stock mic. I bench test and verify noise floor which, post-mod, is lower in the critical 2kHz band than it is at 150Hz. And, like Klaus Heyne, I use a trusted set of headphones and my own speaking voice reciting phrases chosen to evaluate sibilance, HF extension, midrange clarity / phase integrity and proximity effect. Having heard nearly one thousand stock and then modified Oktava mics I have a pretty good feel for both the qualities exhibited by the stock mics and the improvements possible through the mods.
