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What are the mic wiring differences between the new SM transmitter and the other older Lectro transmitters such as the UM400? What should I do with my current microphones?


The SM input is a radically different input system compared to our previous microphone inputs. It is so superior to the old way of doing things that we will eventually introduce this input system on all our UHF transmitters. We realize this causes some confusion for our customers but the advantages are very real. The improvements are audible and make the transmitters easier to use and much harder to overload. It is no longer necessary on some mics to introduce pads to prevent overload of the input stage, divide the bias voltage down for some low voltage mics, or reduce the limiter range at minimum gain settings. For a more detailed technical discussion of the improvements in the SM servo input stage, see FAQ#061-WIRELESS. We have spent many, many hours trying to make the change from the old system to the new system as painless as possible.

For 90% of the microphones in common use, no changes are necessary to the wiring of the 5 pin connector. For some microphones the wiring can be simplified. For line level inputs, our custom musical instrument cables, adapter cables and so forth we have managed to keep the 5 pin wiring the same for old and new transmitters. You can find complete wiring diagrams for the SM transmitter on our web site. The exceptions to this compatibility are all three wire microphones (including our own M150) and a few odd wirings such as the 40 dB attenuator wiring for line level inputs. All this can be found on our web site under the Support tab, but I will list some of the more popular mics here after I discuss some of the headings on the diagrams on the web site.

The first section discusses what each pin of the 5 pin connector does. The most radical change is that pin 4 is now a voltage selector pin. You can skip this technical section if you just want to know how to wire your mic.

The next section is is boxed and labeled "Works with SM only". These wirings are specific to the SM transmitter and make wiring a Countryman B6 or E6 or a three wire microphone such as a COS-11 very quick and easy. However, these wirings won't work with older Lectro transmitters such as the UM400, UM200, etc. If you need the two wire Country B6 or any three wire mic to work with both older transmitters as well as with the SM go to the last section below labeled, "Compatible with SM and other Lectrosonics Transmitters". 

Countryman B6 and E6 are shown in the first diagram of the section labeled "Compatible with SM and other Lectrosonics Transmitters". TheB6 and E6 are two wire mics but still need special wiring because they are unhappy if run from more than about 3 Volts. The added 1.5k and 3.3k resistors shown in the diagram make the microphones compatible with any Lectro transmitters. This wiring bypasses the servo section and runs the Countryman from the 5 Volt bias supply directly. If you can use the easy wiring above in the "Works with SM only" section for the B6, it gives a little better control of sub sonics and voltage drift with humidity; otherwise there is no difference in audio response. If you have a Countryman B6 or E6 already wired for attenuation for use with a UM200 or UM400, it should still work fine with the SM. font-family: 'Times New Roman'; font-size: medium; line-height: normal;"

Sanken Cos-11 microphones, the Lectrosonics M-150 and other three wire microphones to be used with the SM will all require new wiring. If the wiring is not changed, they will have much higher output than usual and extra distortion at high levels. The reason is that the source follower wiring used with the UM200 and UM400 series is not compatible with the SM virtual ground input. The second diagram in the "Compatible with SM and other Lectrosonics Transmitters" section shows a compatible wiring that will work with all 5 pin Lectro transmitters. This wiring converts the three wire microphone to a two wire system with no changes in audio quality. The microphone polarity will be reversed so you may want to enable the phase switch on the Lectrosonics receiver. This wiring is electrically equivalent to the easy wiring in the "Works with SM only" section above.

All two wire mics (except the Countryman B6 and E6 as described above) such as the MKE-2 and the Lectro M-152 will work with the SM with no changes. The two wire setup is shown in the third diagram in the "Compatible with SM and other Lectrosonics Transmitters" section. 

The fourth diagram and fifth diagrams in the "Compatible with SM and other Lectrosonics Transmitters" for unbalanced and balanced line level inputs are the same as for previous transmitters.

The sixth diagram at the lower right for low z dynamic microphones is changed compared to previous transmitter wirings and has the addition of a jumper wire from pin 4 to pin 1. This tells the servo bias supply to shut down and set the pin 3 input voltage to 0 Volts. This additional jumper will reduce the mic output by less than a decibel when used with older transmitters.

Posted 1 year agoby LectroAdmin