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Author Topic: Using an Audio-Technica Lav with a Shure Wireless Pack  (Read 258 times)

Geoff Doane

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Using an Audio-Technica Lav with a Shure Wireless Pack
« on: November 27, 2017, 02:09:47 pm »

This is really an interface problem, not RF, so if the mods feel it is more suited to a different forum and move it, I won't feel hurt.  :)

I recently purchased a used A-T Pro35 lav microphone that includes the AT8538 phantom power adapter.  This has a TA3M at one end and male XLR at the other for connection to a regular input with phantom power.  Since I already own a couple Shure wireless packs (with TA4M mic connector), I thought that it might be convenient to be able to use the Pro35 mic with one of them.  Obviously, I'll have to build an adapter from TA4 to TA3, but there will have to be some bias considerations too.  Shure is very open with information regarding what each pin on the pack is used for.  A-T, not so much...  In fact the standard answer when somebody asks this kind of question in their FAQ is "buy an A-T wireless system".

So, the quick question is, "Has anybody here already done this, and what did you have to do?"

My early attempts at reverse engineering the mic and power adapter indicate that pin 1 of the AT 8538 adapter is ground, and pins 2 and 3 have between +3.25 and +3.5 VDC (ref to ground), with a maximum current source of 0.40 mA.  When the mic is plugged in the voltages stay virtually the same, and there is audio on both pins 2 and 3.  It appears that the audio is identical and NOT differential (same polarity) on both pins when I look at them with a dual trace scope.  Pins 2 and 3 are not simply connected together at the mic end, because I measure 1.8 kΩ between them when they're not plugged in.

My inclination is to bias one of those audio lines with about 10 kΩ from the 5V in the Shure pack (limiting DC current to about 0.5 mA), and see if that gets me audio.  But while I'm waiting for TA4F and TA3M connectors to arrive, I thought I should solicit some advice here.

GTD
« Last Edit: November 27, 2017, 03:42:53 pm by Geoff Doane »
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Geoff Doane

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Re: Using an Audio-Technica Lav with a Shure Wireless Pack
« Reply #1 on: December 07, 2017, 10:41:34 am »

Well, after some trial and error (mostly error), I came up with a workable solution.  It works, although it sounds like its running through a LPF at 5 kHz or so compared to the A-T wired adapter.  I'm hoping that might not be too undesirable for close mic'ing things like sax or trumpet that I would usually roll off the top end anyway.  It reminds me of the sound of an '80s vintage AKG D12E.  Definitely would not be acceptable for voice.

Here's what it looks like and the wiring scheme that worked.  Connectors are viewed from the wiring side.

GTD
« Last Edit: December 08, 2017, 03:46:10 pm by Geoff Doane »
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