Bargain Gear- the EV CO90

Most people can tell from my resume that I’ve been doing audio for a while. One of the advantages that I have over someone just out of school is in the gear department… I’ve used a lot of it. Some works great, others, not so much.

I first encountered Electro-Voice CO-90 lav mics at WCBD TV in Charleston, SC, nearly 25 years ago. These were wired lavs, and came with a transformer base to drive a balanced cable. While they weren’t particularly small or easy to hide, they are quite rugged… I’ve seen pissed-off news anchors slam them on a desk dozens of times, and they still work. They are omnis, which increases their usefulness in certain applications… even though I used to swear at them when we went to a tight 2-shot, since they would pick up the other anchor and phase cancel, especially when Jill Franco was wearing something busty and place the mic a long distance from her mouth.

The later version of this mic was the EV CO94, which had a TA3m connector on the mic head. This allowed them to be used with a wireless unit. The downside it that the 94s came with a slightly bulkier  rectangular “belt pack,” but it did work with 9v batteries which are easier to find. The head was the same size.

Here's a look at my latest eBay score… a CO90 complete kit. This one came with all paperwork, a battery (if you get one with a dead battery, please don't toss it in the trash for obvious reasons... save it for recycling), a single mic clip, a windscreen (easily broken and/or lost) and a second phantom power base... the only one I've seen.

So at the risk of driving the eBay price up, I can suggest buying a few of these as backups or extra mics. They are occasionally seen on eBay for about $25-35. Just a few things to be aware of before you buy:

1) The E625 batteries they used are no longer made, since they contained mercury. There are some substitutes that work (Z625PX, Energizer E625G). You might have to special order a few of these, since they aren’t commonly found at the pharmacy. But the current draw is miniscule– 150 microamps– and a battery will commonly last over 1000 hours.

2)Repairs. Electro-Voice was sold to Telex years ago, and the current company is a shell of its former self. Forget about factory service… I’ve called their parts department, and they have no replacement parts to speak of. There are two main failure points… the cable and the battery spring. The cable will often be just plain worn out, with cuts and breaks in the insulation. I’ve replaced the cables, but it’s quite a difficult task, as one end was soldered to a FET and potted in resin. If you buy one with a bad cable, then plan on quite a few hours at the bench to repair it, unless you get lucky. Sometimes a break in the insulation will be close to the base. In that case, the cable can be clipped ahead of the bad spot and re-soldered to the base, which is a good bit easier than re-soldering near the head. If you really want to change out the cable for new, you can buy replacement cable from Trew Audio’s repair department. It’s tiny and difficult to handle and solder, of course, so I wouldn’t recommend this as your first repair project.

A second place for these to go bad is the battery spring. These were special little dealies that EV made, kind of like a spring steel washer with three tiny leafs that press the battery against its negative contact and conducted current through the positive side. These little leafs are a weak point… I’ve had one with two of the three leafs broken off, so until I can come up with a suitable re-design, that mic will stay off-duty. You wouldn’t want to chance a dropout during operation because of a bad battery contact. A viable option in this case would be to skip the battery altogether… EV made a special phantom-powered only base, the CO90PM. These are gems if you can find them, but they’re extremely rare. It is possible to do your own conversion… details can be found here:

Another application for these mics that may be more useful is a plant mic, where the mic is hidden somewhere on the set. I’ve found a few EV model 370 Barrier Adapter Plates on eBay that just came in. These are simple glass-reinforced plastic plates, about 2-1/2 inches square, with a small recess and a clip to hold a CO90 head.

Electro Voice EV 370 boundary plate

The EV 370 boundary plate clipped to the CO90 head… an easy plant mic, surface mic, etc.

This will allow these mics to be used as a pseudo-boundary mic, though they will probably be improved by taping them down to a larger flat surface. The configuration isn’t a true boundary, like a PZM… a PZM(Pressure Zone Microphone) has the mic diaphragm parallel and very close to the boundary surface, 1/10-1/50″ away. A PCC configuration (Phase Coherent Cardioid) has the diaphragm set perpendicular to the boundary, except the CO90 isn’t a cardioid… so I guess that makes this a “PCO” mic, or Phase Coherent Omni. (To quote John Cleese, “He’s making it up as he goes along!)

Gear like this isn’t for everybody. To be honest, I rarely use these mics, and nearly always reach for my Countryman EMWs. But it’s good to have some hardwire choices in your kit in case the wireless situation gets buggy.

2 responses to “Bargain Gear- the EV CO90

  1. Hello, are you aware of anyway to power the Co90 externally instead of using the battery? Thanks, Fred

    • Hi Fred… Check the post again, especially the part about the EVco90PM, and the link to Uneeda audio page about powering EV mics with phantom. Best, BG

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