29 May Updated: Wiring the Vega Transmitter and changing input impedance from microphone to guitar
Member Mike has another update for us. Below, after the wiring instructions, you will find detailed instructions for the 50 kohm modification which is needed to operate the Vega transmitter (initially built for microphones) correctly with guitars. Thanks, Mike!
Note. Since this article was originally written, it has been found that raising the input impedance to 100k is more suitable for guitar use. Therefore, this article was amended again on December 05th 2011 by Rob
(Edited by Banane (Franz) with extended wiring instrucrions from Member Mike)
If you have the Vega transmitter that goes with your R42, you probably noticed that you can’t plug your guitar into it because it has a 4-pin LEMO connector and there is not enough room to add a 1/4 inch jack. Of course you could remove the connector and wire an instrument cable directly to the TX as Guido did with Fil’s unit but I liked the idea of being able to utilize the existing jack. I had some difficulty finding proper strain relief wiring a guitar cable direct.
Things you will need:
-LEMO half moon connector. Find it HERE
-1/4 inch plug (I like Neutrik because the strain relief fits the thin cable nicely)
-thin 1/8 inch OD shielded cable such as Belden 8451-regular instrument cable is too large to accomodate the LEMO. This type of cable is commonly used in amps for master volumes.
Now open up the transmitter to verify that its input looks like this:
While you have the transmitter open, it would be a good time to add the impedance-changing resistor described below.
You will notice a yellow wire (ground) that is soldered to pin 4 of the LEMO jack. The brown wire is the signal wire and is on pin 1. The green and orange wires power the lavalier microphone and will not be used for guitar.
You will need thin 2 conductor shielded cable to do this. On the LEMO end strip ¼ inch of insulation from the cable. Peel back the braided wire and foil and trim as short as possible and tuck any remaining braided ends and foil back into insulated jacket.
The goal here is to make sure the outer shield does not touch the LEMO connector on the Vega end. This isolates the cable from excess noise. Slip the threaded nut of LEMO onto on to the cable, then the compression clamp, then the notched spacer.
The LEMO clamp is too tight to use heat shrink here. Now solder black wire or ground wire to pin 4 of the LEMO and red or signal wire to pin 1.
On the guitar or ¼ inch plug end strip cable and solder braided wire and black or ground wire to the plug shield together. Then solder the red or signal wire to the tip.
Changing input impedance from microphone to guitar
The Vega transmitters (TX) that we have seen are matched for microphone input. Many of these units measure 10-20k ohm between signal and ground. In order to match the guitar input we need to raise the Vega’s resistance to 100k. We do this by installing a 91k resistor from signal to ground on the Vega TX. It would be a good idea to measure your own Vega TX to see what its resistance is. The idea here is to get to 100k. There are 2 ways to add the dropping resistor. The easiest is to connect the resistor into the guitar plug in series with the signal wire and the plug tip or alternatively wire it internally on the Vega T.X LEMO jack. I chose to wire mine into the Vega thinking that would be best for noise suppression.
- Open up the Vega TX and you will see a brown wire (pin 1) and a yellow wire (pin 4) soldered to the LEMO jack. Remove shrink tube insulation and unsolder these 2 wires.
- Now take a 91k ¼ watt resistor and trim/bend the leads so one leg fits into LEMO pin 1 and the other leg into pin 4. Solder resistor into place.
- Then take the yellow and brown wires and solder them to the correct exposed resistor leads. You should now measure close to 100k across pins 1 and 4. (Please note that a 47k is pictured here-result of an earlier mod
Vega Receiver to guitar amplifier patch cable
The rear boost on the C.V R42 has an XLR output so you will need to make a patch cable to convert to ¼ inch plug that will be accepted by your amp. This is pretty straight forward so here is the proper wiring:
Contributors: Guido Borghesani, Filippo Olivieri