crown glm microphones how to wire and power requirements

[momgrel]

Hello. I am new to this forum and have some questions about some crown glm microphones that I have. I would like to use them to mic some acoustic instruments such as guitar ,banjo and so on. The problem is that I do not know what voltage is needed for phantom power or how to wire them. Some of the mics have what looks like a mini xlr plug on the end of the wire and others have no plugs. I think that my dad used these with an old vega wireless mic system. Some of the mics have openings on both sides and some only on one side. I am thinking that the ones with two openings are the glm 100 and the ones with only one opening are glm 200. If anyone could help it would be much appreciated. Thanks in advance.

[Hugh Robjohns]

You're going to need to know what models you have, as there are two power options depending on version:

GLM-100 and GLM-200: Phantom power, 12 to 48 volts DC, positive voltage on pins 2 and 3 with respect to pin 1 of output connector. Supplied with 8-foot, black, permanently attached cable with rugged strain/flex relief and 3-pin pro audio connector.

GLM-100E: Unipolar powering is +1.1 to 20 VDC on red lead relative to shield. White lead is audio. Bipolar powering is + voltage on red lead and – voltage on white lead relative to shield. Supplied with 4-foot, black, two-conductor shielded cable with no connector. White: audio, red: B+, shield: ground.

Mics of this type are always back-electrets and are designed to run on a relatively low single-sided voltage as per the 100E version. This kind of powering is provided by default by radio mic transmitters etc. However, where the mic is to be used in a conventional wired system, a powering adapter is typically built-in to the XLR plug to convert standard phantom power into the required single-sided arrangement internally.

A mic with an Omni pattern will only have one opening, in front of the diaphragm to allow 'pressure operation', whereas anything directional will always have two openings (or vents), allowing sound waves to reach both sides of the diaphragm for 'pressure gradient' operation. So the single opening models are, indeed, the 100 or 100E version, and the dual opening models are the 200 version.

If you have 200 versions without the XLR then I'd hazard a guess that they've been purchased or modified specifically for use with radio mics and single-sided powering. The manufacturer's blurb implies that phantom models are shipped with standard XLRs on the cables, not mini-XLRs, and it sems more likely that the mini-XLRs were added to connect with a specific radio mic transmitter system.

The manufacturer's info sheet is here:

http://www.crownaudio.com/media/pdf/legacy/136453_glm100-200...

H

[momgrel]

Hello Hugh, and thanks for your kind and complete response to my questions. After looking closer the mini xlr is not xlr at all but rather a four pin LEMO connector which is the same as the one on a mini sony mic that I know for sure was used with the vega system. It must be that the mic was powered by the vega transmitter. It sounds like you are saying that these cannot be used by wiring to a regular xlr connector and flipping the phantom power switch. Another thing that I failed to mention is that the glm 200s have in their cable a small rectangular segment with four screws marked EQR. I removed the screws to look for batteries and found only some small electronics enclosed in shrink tubing. Perhaps you you know what these things are. Is it possible that these electronics are a variation on the powering adapter that you mentioned that would normally be built into the xlr plug for standard phantom power conversion? From the info found on the link you sent I think i could easily build the second power supply pictured, and possibly the first with the help of a friend. Do you know which would be best? I realize that there are many questions here and it would take you some valuable time to answer them all. If you have time great if not,no problem here the answers you have already given I think have put me on the right track to figuring this out. Thanks very much,Mike G.

[momgrel]

Sorry one more thing. Do you think that the fact that all of the permanently
attached cables exceed four feet is enough to be certain that none of these are glm 100e. Thaks again, Mike

[Hugh Robjohns]

After looking closer the mini xlr is not xlr at all but rather a four pin LEMO connector which is the same as the one on a mini sony mic that I know for sure was used with the vega system. It must be that the mic was powered by the vega transmitter.

That makes a lot more sense.

It sounds like you are saying that these cannot be used by wiring to a regular xlr connector and flipping the phantom power switch.

Nope. There needs to be a small circuit which extracts a suitable single-sided power rail and balances the audio output onto the XLR.

Another thing that I failed to mention is that the glm 200s have in their cable a small rectangular segment with four screws marked EQR. I removed the screws to look for batteries and found only some small electronics enclosed in shrink tubing. Perhaps you you know what these things are.

'EQR' sounds like some kind of equalisation module, but I guess it could possibly be a powering unit. Probably best to contact Crown Audio directly and ask them. I wouldn't recommend plugging phantom in and seeing what happens! If the mic is expecting a few volts and receives 48V it's likely to go pop!

H