Lavalier/headset mic tester

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Scodiddly

Well-known member
Joined
Aug 18, 2004
Messages
941
Location
Libertyville, IL USA
This all started as "I need one for my tool bag", though now it's somewhat of a product.

It's a wireless mic transmitter input coupled to a headphone amp, so that you can test lavalier or headset/earset mics without having to go set up a wireless mic system. At my day job we do this a lot, since we rent out a lot of wireless gear.

The design is nothing special, and I'm sure it could be tweezed a lot. But it works, and the ones we've been using at the shop still work just fine. So it's a safe, cautious design.

There's a schematic linked for a basic Shure-compatible design. I've also done ones for both flavors of Sennheiser, and I have a request for Lectrosonics which has a very weird bias voltage thingy in the spec.

http://www.scotthelmke.com/lav-amp.html

http://www.scotthelmke.com/Lav-tester-shure.jpg
 
Thank you for sharing!
So the ne5532 is powered from +/-4,5vdc,right?
And the TLE makes a virtual ground from what I see.
Can you shine a light a bit on the pinouts on the Shure connector and function because we have Shure systems?
I guess pin 1= (virtual) gnd / pin 2 = Suplly voltage for the capsule / pin 3 = Mic signal,but I don't get pin 4 (via 20k to gnd).

And what about Sennheisers (3-pin LEMO),will it be easy to adapt them in the same box?


Really interesting,would be a great helper for sorting things out,especially in a stressful live situation.


Much appreciated,thank you in advance,


best,


Udo.
 
Yup, the TLE thingy splits the 9v battery into +- 4.5 rails for the opamp.

The Shure mic input spec:
1 ground/earth
2 Bias voltage, usually around 5 v through some 1-5k resistance
3 Audio
4 20k resistor to ground, which is used to complete the DC bias circuit in some mics.

Sometimes the shell of the connector is used in the circuit as ground instead of pin 1, though I'm not sure why. It's come up with their lav-to-XLR adapters included in the Beta98  and similar products.

Sennheiser Lemo is pretty simple, it only uses two pins. Ground and then bias/audio. Sennheiser Evolution does the same thing on the tip of the 1/8" plug, while the ring is an unbiased guitar input.

In general it's not really doable to have a simple circuit with both Shure and Sennheiser, because of the shared bias on the Sennheiser side.
 
Awesome,thanks a lot for sharing!



I'll go for the Shure anyway since we swap out our main systems atm from Sennheiser to Shure.
Main use for the tester will be on DPA headworn mics (4066 and the D-Fine series) with 4-pole connectors,
so it seems to be perfect for me.


Will get the parts soon and do some testing on veroboard.


Once again thank you,


best regards,


Udo.
 
Found another mistake on the schematic, it's been fixed. If you built the circuit as shown prior to 2015/1/27 only one side of the headphones will work.  :-[
 
Scodiddly said:
Found another mistake on the schematic, it's been fixed. If you built the circuit as shown prior to 2015/1/27 only one side of the headphones will work.  :-[
Thank you Scott!


Waiting for the next time when I must order from mouser,the tb4m is a bit hard to source here (and way too expensive).Will report back once I'm done.Great service Scott!


Best,


Udo. ;)
 

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