In the 1970s I modified an MX-100 by installing three subminiature Beyer input transformers which are no longer available, unfortunately. It wasn't too difficult and it seemed to work well. If I recall correctly (and I might not ...) the preamp already had tip-ring-sleeve phone jacks built in, so I didn't even have to change those out.
The thing is, depending on your particular microphones and the phantom power supply that you're using with them, you may not really need transformers to unbalance their signals. You should ask the manufacturer of your microphones how to unbalance their signals--the answer varies considerably with different microphone types. Sometimes it's as simple as leaving one lead unconnected, and making sure that the 48 VDC isn't coming out of the power supply and going into the preamp.
You could use in-line transformer adapters with unbalanced 1/4" output plugs and avoid having to modify your mixer. Unfortunately all the Shure "problem solver" in-line transformers that I see on their Web site look as if they step the signal voltage up or down. I don't think you want that for this application. Oddly they don't seem to offer a simple 1:1 input transformer for low-impedance microphones--I guess this isn't a very common application any more.
Lundahl, if I recall correctly, actually has a better adapter available for this specific purpose than anything they show on their Web site. It's on their professional price list, or it was as of a couple years ago. I seem to recall $195 apiece, which does seem steep. Alternatively for that kind of money you could get a Jensen MS-2XX "Iso-Max" box with two of their excellent transformers (
http://www.jensen-transformers.com/ms2xx.html).
The big problem with subminiature transformers, especially if they step up the incoming voltage at all, is that they're easier to saturate (overload) than larger transformers, particularly at low frequencies. When a transformer saturates, the distortion increases very rapidly. You should totally forget any notion of "transformer warmth" with this class of transformer--you can use them to couple a signal and block DC, but you really don't want to play around with their overload limit.
Keep in mind also that with directional (pressure gradient) microphones, low-frequency disturbances such as moving air or vibration picked up by the microphone can have strong low-frequency components that might not seem audibly significant but could saturate an undersized input transformer, particularly a step-up transformer.
--best regards
Topic: Nakamichi mx100 with condenser mic / balanced to unbalanced (Read 4081 times)