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Advice making electret mic cables please Audio Interfaces
Old 20th March 2019
Here for the gear

Advice making electret mic cables please


I want to make some electret microphones with XLR connectors (so I can extend using other xlr cables if needed) but the electrets I have found only have 2 pins. Can I use them with XLR? How should the pin connections work? or should I stick to using jack plugs?

This is what im looking at:

The cable is screened. I potentially want the cable to be up to 50m long.

Any advice gratefully received!
Old 20th March 2019
You need a way to power the capsules DC voltage of less than 10 volts according to the specs. You should also get a transformer from unbalanced to balanced if you want to run any length of cable. The output impedance is 2.2 K ohms. You will also need a capacitor in front of the transformer to keep DC from getting into the transformer. Maybe Richard will chime in with a good solution. By the way the S/N is not very good.
Old 20th March 2019
Lives for gear

What are you plugging the other end into?

Assuming it's a normal professional audio mixing console or similar XLR microphone input with phantom power available, I would suggest something like the Rode VXLR+ adapter at the microphone end. This both balances the line (which will greatly help avoid noise pickup on a long 50m connection) and converts from standard phantom power to plug-in power that your microphones need.

If you google around a bit, you can find schematics for similar circuits should you prefer to do it yourself; but frankly, at the price of the Rode gizmo, I am not sure I personally would bother.
Old 20th March 2019
Here for the gear

Thanks for the responses.

Im only using the mics to pic up environmental background noise so I hope the s/n is adequate for that. Ive made a short one before that sounds ok.

I did not know about the voltage! That explains why the one I made previously will work when plugged in to my Zoom H4n recorder but not into my Zoom TAC 8 interface Im guessing! In this new scenario I want to plug the mics directly in to the Zoom TAC-8, it has phantom power so the rode adapter sounds like a good way to go.

Old 21st March 2019
Gear Head
vogelchr's Avatar

You need something similar to (to list a known brand) Sennheiser MZA 900P (with a 1/8 inch TRS connector). There are dozens of different pinouts, connector types, Input impedance and supply voltages. They all convert the 48V phantom power (or 12 or 24 or internal battery) to a lower supply voltage of the mic and convert the single ended output to symmetrical XLR. Most use a variant of what you can find when search for „Schoeps Circuit“.

Also you can connect the typical electret microphones in two ways: using the fet in the microphone as a voltage follower, with three pins (supply, output, ground) or as a common source amplifier with two pins. The former has more linearity when recording loud sounds, the latter potentially less noise and simpler cabling.

Get yourself a cheap clone of the aforementioned sennheiser part, crack it open and learn how it works and how good it matches your type of microphone. If it doesn’t, get a different cheap clone or adjust the parts in it.
Old 22nd March 2019
Lives for gear
Richard Crowley's Avatar

Sennheiser, Shure, Rode, and likely several others all make suitable adapters from "raw" electret condenser mic capsules to proper XLR balanced, low-impedance, phantom powered, etc. The Rode VXLR+ is emminently the most sensibly priced of all the commercially available converter products.

You will need a shielded-pair cable with a 3.5mm TRS plug to connect from the electret condenser capsule to the input of the Rode VXLR+ While I make most of my own cables, I would prefer to buy a molded cable/connector as you can find a nice small-diameter cable pre-terminated to the 3.5mm TRS connector. For that matter, you could rescue/recycle such a cable from some discarded product for free.

Of course, once you go through the XLR adapter/power supply you have an ordinary low-impedance balanced XLR signal as from any other microphone and you can connect to any XLR cable that you fancy.

If you wanted to DIY the XLR to electret converter circuit, there are many different schemes, circuits, PC boards, etc available. And I used to do that regularly. But the price of the Rode VXLR+ is so low it is hardly worth DIY anymore. Life is more convenient, but not as much fun anymore. If you really want to DIY, I can cite several online resources.

I am ordering a Rode VXLR+ myself to confirm the "pinout" of the input TRS connector. I will conduct the experiment and report back in a few days.
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