Myth-Buster Mic Splitter

The sound of a microphone is greatly affected by the preamp it is plugged in to. You may choose a preamp just as you would choose a mic for different applications. I do a lot of custom microphone modifications and rebuilds in my shop and it's always interesting to try the different builds out with different mic preamps.

The classic "shootout" way to do this is to record something and record it again with a different preamp and then listen to the two takes. Needless to say, this is not a very clinical way of going about this. Two different performances with you at two slightly different positions to the mic does not really yield a very good comparison file.

You need a splitter - and not just any splitter but a really good splitter! Without a splitter, you can convince yourself that you hear all sorts of differences between preamps. Some are real, some... not so much. Comparing using a splitter settles it - hence I call it my "Myth-Buster".

The most common way to build a mic splitter is with a transformer. And when you use "really good" and "transformer" in the same sentence, Jensen is often what you're talking about. The circuit is simple. In fact, Jensen even supplies the schematic for a simple mic splitter right on their website. For a simple two-way splitter, the Jensen JT-MB-C is what you want. They are not cheap but they are definitely worth it if you are trying to make a high quality splitter. Here is a simple mic splitter schematic based on the JT-MB-C.

Shootouts done with a splitter are very clinical and accurate. The signals are so identical that you are sure that the only differences are due to whatever comes after the splitter. In a DAW, you can flip the phase and trim the levels of one track and see how well they null out. If the signals were identical, you could make this "difference" signal approach -inf in level. In reality, even with the same preamp model, I've been able to null out signals to about -70dB with this technique.

You'll notice on the schematic that in addition to the split outputs from the transformer, there is a Direct Out. You may think this is optional but for Phantom Powered Mics, it really isn't. Since DC will not go through the transformer, you will use this connector to plug into "any old preamp" to provide the P48 to your mic. If you don't use this, you would need some sort of inline phantom power provider to go between your mic and the splitter.

• Jensen JT-MB-C transformer
• Project Box (I used a Hammond box from Parts Express)
• 15/16" Chassis Punch for XLR Jacks
• 3 Male Panel-Mount XLR Jacks
• 1 Female Panel-Mount XLR Jack
• Drill
• Fasteners
• Hookup wire

• Choose how you want to lay out your XLR connectors. In my Hammond project box, I have the input on one of the short sides, the direct out on the opposite end and the two splitter outputs on one of the long sides.
• Choose where you want the Transformer Mounted
• Mark and drill center holes for all XLRs
• Use your 15/16" chassis punch to cut the holes for the XLRs
• Set an XLR jack in each hole and mark the mounting screw hole positions
• Drill holes for all XLR mounting screws and the mounting screw for the transformer
• Mount all the parts
• Refer to the Jensen Schematic and wire it up.