• +1 505 892-4501
  • This email address is being protected from spambots. You need JavaScript enabled to view it.

How should I wire a Sanken COS-11 or other three wire microphone to a MM400 transmitter? I've seen several recommended wirings.

0

See also FAQ (What is the correct wiring for different versions of the Sanken COS-11 microphone and various Lectro transmitters?) for wiring a COS-11 for more normal sound levels than the 114 dB SPL assumed in this FAQ( How should I wire a Sanken COS-11 or other three wire microphone to a MM400 transmitter?.)

We recommend a 2k to 4k source resistor. Wire the white lead to the resistor and the other end of the resistor to ground. The black drain lead is wired to the center pin. We do not recommend just wiring the source lead (white) to ground. Below is a long post to the RAMPS group that explains why:

After my post about the COS-11 wiring, I was asked by a dealer if the lower output COS-11 red dot wasn't a simpler solution than building a resistor into the connector to simulate a three wire hookup on a MM400, which is a two wire system. So we went back and made more measurements. Lectro isn't set up to make precision sound level measurements but we faked it fairly well. I used some B&W 602's (7" Kevlar cone) to produce a surprisingly low distortion 400 Hz audio signal (less than 0.3%) and a Radio Shack sound level meter for level measurements. The Radio Shack was calibrated to a B&K sound level meter and is actually pretty decent. As further proof of the pudding, some lavaliere mics that were spec'ed as overloading at 118 dB, indeed did overload at those levels. We placed the mic about 3 inches from the loudspeaker cone so we could easily get levels of 125 dB at the microphone.

With 114 dB into the mic and using a two wire mic setup (signal taken from the black wire or drain), we set a mixer level of 0 dBm for a COS-11 grey dot(?) with a shorted-to-ground source, and measured -8.8 dBm for the same mic with a 2.2k source resistor. A COS-11 red dot measured -9.1 dBm shorted to ground and -18 dBm with a 2.2k resistor. Distortion levels in the same sequence were grey dot shorted 9%, grey dot with 2.2k 1%, red dot shorted 2%, and red dot with 2.2k 0.44%. These results are pretty much what would be expected; the source resistor reduces gain and provides negative feedback to the FET, both of which reduce the distortion. In addition, the red dot is a lower gain mic and therefore has less distortion at high sound pressure levels. What is most interesting here is that a grey dot with a source resistor has less distortion than the red dot shorted at the same sound pressure level and at the same output level (gain).

We now increased the sound pressure level to 124 dB and ran the same sequence. Distortion levels were grey dot shorted (unusable)%, grey dot with 2.2k is 1.75%, red dot shorted is 8%, and red dot with 2.2k, is 0.7%. Again, these results are pretty much what would be expected; again the source resistor reduces gain and provides negative feedback to the FET, both of which reduce the distortion. Again,the red dot is a lower gain mic and therefore has less distortion at high sound pressure levels. This is a repeat of the previous findings and once again a grey dot with a source resistor has less distortion than the red dot shorted at the same sound pressure level and at the same output level (gain). 

These numbers jive fairly well with info from Sanken's site. So my recommended hookup for a MM400 is to use a 2k or 4k source resistor with either of the Sanken microphones. The MM400a transmitter will be driven about 6 dB into compression when set for minimum gain before the microphone starts to clip and this will be at sound pressure levels of 120 dB and 130 dB respectively. Without the source resistor, the levels will be more than 10 dB lower. For the UM200 or UM400 transmitters, always wire the microphones as three wire microphones which is shield to pin 1, black to pin 2, white to pin 3, and pin 4 grounded back to pin 1.

Posted 1 year agoby LectroAdmin
#58