Converting Wireless Lavalier to Wired XLR

N

nolken

Member
I have a Countryman EWM Lavalier. I also have a Rolls DB25 Direct Box. I would like to be able to use my lavalier as a wired lavalier. So my question is this:

To avoid purchasing an $80 adapter, can I attach a 3.5mm TRS connector onto my lavalier mic into a 3.5 to 1/4 inch adapter, wire in 1 or 2 AA batteries with some resistors and a diode for the plug-in power? The direct box would balance the signal while the battery would provide the plug-in power.

A couple of assumptions I have made (which may be incorrect, please correct me if I am wrong) through knowledge and/or experimentation.

1) The direct box will not allow the phantom power to pass through to the mic. This allows me to use phantom power for a shotgun on the same preamp as the lav, and it protects the mic in case I accidentally have the phantom power on.

2) The sound quality will degrade some, but not enough to make a huge fuss about.

3) The battery power will last forever and a couple of days since the lav uses so little power. I may even use CR2032 so I can fit it all within the direct box. I will add a switch to activate/deactivate the plug-in power.

The only thing I do not have readily available in my home is the TRS connector.

So what are your thoughts? Has anyone done anything like this before?
 
There is no reason you can't do that... providing one has the electronic skills and the specs for a particular mic. It's not as easy as making a simple mic cable, and the mic element could be permanently damaged if something is not right. A $70-$80 Phantom Pwr. XLR adapter would be worth the cost.
 
Well I'm actually a mechanical engineering student, but I switched from electrical. I know enough about circuits to be a danger to myself.

My direct box has a 50k ohm to 600 ohm step-down transformer. That will drop my lav mic (1500 ohm impedance) down to 18 ohm, going into my 600 ohm pre-amp. I've always heard that the higher the pre-amp to mic impedance ratio the better off you are, which makes sense since the dB drop will be less, but 18 ohms seems really low. That being said, the 18 ohms should in theory be better. I've also heard that going too low can create imbalances in the tone. Countryman's XLR version of the mic outputs a 600 ohm impedance. I could add a resistor or a series of resistors in the line to bring the mic impedance up to the 600 ohm range, but that doesn't seem logical. I could also unwind some of the primary side of the transformer. I really don't want to do that, as I don't want to damage the transformer. Purchasing a new transformer wouldn't be logical for a price perspective since the cost if individual specialized components is quite high.

Is an 18 ohm mic output impedance too low?
What problems or audio distortions could that cause?
I can't seem to find any non-propriatary phantom power/XLR adapters. Maybe I'm not looking in the right place. Countryman doesn't seem to want to sell me one of their XLR connectors. Any recommendations on one of these just in case I don't decide to go through with this idea?
 
Last edited:
nolken said:
...
I can't seem to find any non-propriatary phantom power/XLR adapters. Maybe I'm not looking in the right place. Countryman doesn't seem to want to sell me one of their XLR connectors. Any recommendations on one of these just in case I don't decide to go through with this idea?
Click to expand...
Ambient's "Eumel" is one such non-proprietary adapter. The problem with finding adapters is the wireless transmitter manufacturers use such a wide variety of terminators and wiring schemes. There are a number of different Eumels varieties avaiable so you can choose the one that mates your particular mic's cable connector. http://www.ambient.de/en/products/ambient-recording/mic-power-supply/emp.html
 
Nice. Don't know what they cost but I would lean very heavily toward buying a prebuilt unit over fabricating one from scratch. And I have built a lot of devices/ mixers etc. over the years.

The reasons are that as mentioned there are a ton of wiring variations for wireless lavs and getting it all in a neat box that isn't a PITA to haul around can be a major challenge. These things are small compact and look like they would do a good job and be pretty seamless. If they are running $150 a pop that would change the balance a bit but if they are around $50 you are probably going to spend more an a clunkier box that is less reliable.
 
. . .and Ambient gear is in general excellent. I forgot they made these and I really need a couple.
 
Noiz2 said:
...If they are running $150 a pop that would change the balance a bit but if they are around $50 you are probably going to spend more an a clunkier box that is less reliable.
Click to expand...

The Ambient one is running for $130 everywhere I've seen them. Countryman (lav mic brand I'm considering doing this with) posts their mic specs and wiring diagrams nicely.
There is also the Sennheiser MZA900P for $159. The say it's proprietary, but I've heard of others who have used it with success. The Audix APS910 is $35. It is supposed to be proprietary as well, but I may end up going with that one to try it. More than likely though I'm going to try to build one that doesn't use phantom but a battery instead. That should cost me less than $5 and if it works I know I have a low cost solution for other mics saving money on not just one mic but several. Also If i build build one I can cater it to the needs of each individual mic.

I'm considering other options as well, including tossing the battery power idea and using a step down voltage circuit for use with Phantom Power.

The size shouldn't be an issue, it should all easily fit into an inclosure no larger than the average wireless transmitter. If I go the battery route everything will fit within the access space in the direct box, which is pretty small.

I just don't understand why they are all so expensive. My only thought is that maybe because there is not a high demand so manufacturing cost is higher.
 
If you build your own you need to block the Phantom power. The transformer alone should be over $5.

You could though make a powering unit and connect it to a balancing transformer. Say $35 plus whatever you spend to power the mic.

You could buy the transformer bare and build it into your box but again you will probably pay more for a bare one (of decent quality) than you will pay for the adapter.

Quality transformer plus powering circuit plus housing, gets you along way there. And as you say low demand. Also you need to figure that there is probably about a 100% markup over cost (between the companies profit and the resellers profit).

In reality for a comparable product, and it's not really comparable since yours is not going to be that small, you are probably talking $30 - $50, not counting your labor.

Which puts me more in your camp. At 1/2 to 1/3 the price I would probably make it since I know I could. Unless I had a budget, then I buy hands down.

You might be able to get a unbalanced female 1/4" to male XLR balancing transformer you can modify (since you will have a fair amount of room on the 1/4" side. I would probably use Phantom to provide power just because it keeps it simple and small but? YMMV.
 
John,
so I guess these are a personal recommendation? :)
I don´t know what could go wrong quality wise in such an adapter, but they do offer the same quality as the Sennheiser or Ambient adapters, don´t they...?
Because then I could get two for the price of one Ambient for my MKE2s.
Anyway thanks for the info!
 
So Countryman finally got back to me. The said they would sell the connector for $140. I can send it in for "repair" and have them install the connector/circuit on to the mic for me for $85 plus shipping. Considering the mic costs $177 new with the connector on it I'm going to go ahead and try my original solution. I'll probably try it this weekend and I'll report back as to how it went.
 
Well I tried it really quick. didn't work. at all. I guess i'll just sell the mic and buy a new on with XLR already on it. $85 plus shipping is too much to have an adapter put on the mic when it only costs $177 at bh. I don't really want to buy a power supply from anyone else since they are all proprietary and not guaranteed to work either.

Any other ideas?
 
You never did say how the stock cable for your EMW lav was terminated. Lavs usually come either with an XLR / phantom power adapter hardwired or terminated in a connector specifically wired to mate with a specific manufacturer's wireless transmitter. For example, your EMW could have come with a 3.5mm TRS for use with a Sennheiser Evolution series transmitter, a 3-pin LEMO for use with other Sennheisers or Zaxcomm, a TA5F so it can be used with a Lectrosonics, etc etc. So what does your's have, or does it terminate in a bare pigtail? When you say the adapters are proprietary, what it means is they're also specific to a particular connector and wiring scheme. For example, Sennheiser's MAZ900P adapter is sold for use with the ME2 mic but it will work just fine with any other mic that is wired for use with the G2/G3 transmitters.
 
I've used the ($70) OST Phantom Power XLR adapters on a variety of different mics and all worked fine, provided they're wired for a specific wireless transmitter connector. (Lectro UM200/400 and Sennheiser SK100 G2/3 transmitters in my case)
 
You must log in or register to reply here.
Back
Top