Microphones Old EV Microphones Dying!

[JD]

So, I had a few old EV microphones, a couple of 635A's and a RE-16, good old workhorse microphones still in their bags. Had to test a mixer out, and I grabbed one and plugged it in.... nothing! Picked up another... nothing. Picked up the third... nothing! Picked up an old SM57 and that worked fine. Ok, these mics used to work great, and were almost indestructible. Metered 2 to 3, Open circuit! Autopsy time.
What I found was a little disturbing. There is a glue that is used near the diaphragm that turned into a semi-liquid state and it had dissolved the fine copper wires that led to the coil. It was a sad discovery as I suspect whatever they used, they used on all the models of that vintage. Anybody else run into this?

 

[RonHebbard]

So, I had a few old EV microphones, a couple of 635A's and a RE-16, good old workhorse microphones still in their bags. Had to test a mixer out, and I grabbed one and plugged it in.... nothing! Picked up another... nothing. Picked up the third... nothing! Picked up an old SM57 and that worked fine. Ok, these mics used to work great, and were almost indestructible. Metered 2 to 3, Open circuit! Autopsy time.
What I found was a little disturbing. There is a glue that is used near the diaphragm that turned into a semi-liquid state and it had dissolved the fine copper wires that led to the coil. It was a sad discovery as I suspect whatever they used, they used on all the models of that vintage. Anybody else run into this?

@JohnD Nope! My 635A's date from approximately 1974 or 5 or so and are still going strong.
Toodleoo!
Ron Hebbard.

 

[JD]

@JohnD Nope! My 635A's date from approximately 1974 or 5 or so and are still going strong.
Toodleoo!
Ron Hebbard.

I would have said the same thing two days ago! These are from 1980/81. Could be they changed the glue. I've had a run of "bad plastics" lately, such as Anvil cases with foam that turned to black tar and crumbs, Speakers where the voice coil adhesive broke down, and of course the ever-present "foam" suspension problems. Feels like the move "The Andromeda Strain."

 

[RonHebbard]

It feels like the movie "The Andromeda Strain."

@JohnD Wasn't that the film where Canadian actress Kate Reid's character zoned out when her epilepsy kicked in due to watching the rhythmic pulsing of the illumination in her microscope when she's searching through a bazillion samples for hours on end and misses the sample that held the solution to the problem? I overlapped with Miss. Reid on one of her many seasons at Stratford. She wore glasses over contacts to get around off stage but never appeared on stage with glasses. Whenever Miss. Reid was on stage, she was essentially blind with other actors often helping her to enter and / or exit from time to time.
Toodleoo!
Ron Hebbard.

 

[FMEng]

A lot of audio equipment of that era suffered from "space age" materials that deteriorate with age. I can show you JBL speakers with foam rubber surrounds that turned to dust.

To this day, the venerable EV RE-20 has an aging problem that causes their sound to change over time. The really old ones have the internal shock mount come apart, leaving the mic element to rattle loose in the case. I'll never understand why EV seems to ignore the issues, instead of correcting it. EV used to have a great refurbishment program where they'd make them like new for a very reasonable, flat rate. That ended, probably when Bosch bought the company. Now the repairs cost almost as much as a new mic.

By contrast, Neumann still services every mic they made since World War II, at affordable cost. And their mics age gracefully. I gave up on RE-20s for radio studio use and switched to Neumann.

To EV's (slightly deserved) credit, they recently lowered the price of the RE-16 from obscene to reasonable. I think the competition between EV's Variable-D and Shure's new Dualdyne in the KSM-8 woke them up. The RE-16 is still a very good mic for uses where you need a very uniform polar pattern versus frequency, and no proximity effect. In fact, I just bought two. Just don't try to hand hold a Variable-D mic, because blocking the ports changes the acoustics.

We buy quite a few RE-50 mics for reporters to use. They never seem to fail, unlike some similar, omni-directional dynamics.

 

[RonHebbard]

A lot of audio equipment of that era suffered from "space age" materials that deteriorate with age. I can show you JBL speakers with foam rubber surrounds that turned to dust.

To this day, the venerable EV RE-20 has an aging problem that causes their sound to change over time. The really old ones have the internal shock mount come apart, leaving the mic element to rattle loose in the case. I'll never understand why EV seems to ignore the issues, instead of correcting it. EV used to have a great refurbishment program where they'd make them like new for a very reasonable, flat rate. That ended, probably when Bosch bought the company. Now the repairs cost almost as much as a new mic.

By contrast, Neumann still services every mic they made since World War II, at affordable cost. And their mics age gracefully. I gave up on RE-20s for radio studio use and switched to Neumann.

To EV's (slightly deserved) credit, they recently lowered the price of the RE-16 from obscene to reasonable. I think the competition between EV's Variable-D and Shure's new Dualdyne in the KSM-8 woke them up. The RE-16 is still a very good mic for uses where you need a very uniform polar pattern versus frequency, and no proximity effect. In fact, I just bought two. Just don't try to hand hold a Variable-D mic, because blocking the ports changes the acoustics.

We buy quite a few RE-50 mics for reporters to use. They never seem to fail, unlike some similar, omni-directional dynamics.

@FMEng Was the RE-50 the model which had a complete 635A encased within it or am I confusing it with another model? The DS35 is another of their mics from approximately the same era which so often sounded great on whatever you put it in front of.
Toodleoo!
Ron Hebbard.

 

[FMEng]

I believe the 635 and the RE-50 have the same capsules. The RE-50 has a better shock mount and improved wind screen over the 635.

The DS35 was very similar to the RE-16, but without the Variable-D proximity effect control. I wouldn't be surprised if they shared capsules.

There was a time when Electro-Voice was quite an innovator in microphones. Sadly, they haven't done much in recent years.

 

[JD]

@FMEng Was the RE-50 the model which had a complete 635A encased within it or am I confusing it with another model? The DS35 is another of their mics from approximately the same era which so often sounded great on whatever you put it in front of.
Toodleoo!
Ron Hebbard.

If you take apart a RE-16 / DS-35, you'll find what looks like the case of a 635A! The element is completely different (as you would expect because omni/card), but if you back off the little hex screws and drop the lower windscreen, Surprise!

 

[JD]

Interesting extra tidbit: I measured about 1 meg between pins 2 and 1. I am thinking that although there should not be a problem running a passive mic on phantom power, in this case there was. I suspect the watery glue was somewhat conductive and the coil lead-in wire dissolved due to electrolysis.

 

[FMEng]

The problem with that theory is that electrolysis takes time, and it sounds like the mics were working when stored then failed immediately. They would also be noisy during the time the electrolysis was taking place.

Let's not leave anyone with the impression that phantom power damages dynamic mics. It does not. Or, at least I've never heard of a convincing example of where it has.

The only, rare exception that I know of is vintage ribbon mics, such at the RCA 44-BX and 77-DX. The problem is those ribbons that have grounded center-tap transformers. If pins 2 and 3 don't mate during connection at precisely the same instant, or one of them goes open, the change in DC current flow can cause the ribbon to be driven and stretched. When using vintage ribbon mics, the rule is to make sure phantom power is off and discharged before plugging or unplugging the mic. Once connections are made and solid, phantom can be safely applied, if necessary.

 

[TimMc]

The problem with that theory is that electrolysis takes time, and it sounds like the mics were working when stored then failed immediately. They would also be noisy during the time the electrolysis was taking place.

Let's not leave anyone with the impression that phantom power damages dynamic mics. It does not. Or, at least I've never heard of a convincing example of where it has.

The only, rare exception that I know of is vintage ribbon mics, such at the RCA 44-BX and 77-DX. The problem is those ribbons that have grounded center-tap transformers. If pins 2 and 3 don't mate during connection at precisely the same instant, or one of them goes open, the change in DC current flow can cause the ribbon to be driven and stretched. When using vintage ribbon mics, the rule is to make sure phantom power is off and discharged before plugging or unplugging the mic. Once connections are made and solid, phantom can be safely applied, if necessary.

Since phantom power +48 is on both pins 2 &3, with - on pin 1, a mis-wired cable or a cable modified for unbalanced use could permit phantom to reach the capsule in a destructive way.

 

[JD]

Since phantom power +48 is on both pins 2 &3, with - on pin 1, a mis-wired cable or a cable modified for unbalanced use could permit phantom to reach the capsule in a destructive way.

Phantom is delivered through 4700 ohm resistors in the mixer, so the max current on short would be about 10 ma. Dissipation across a standard dynamic microphone element would be roughly .005 or 5 mw. Tend to throw more than that across the element just by metering it on the times one scale of most multimeters.
The mics in question were in a church on an old Biamp mixer that ran phantom. That mixer was on for years 24/7. Still, as FMEng said, they worked when they were put away, so who knows.

 

[FMEng]

Since phantom power +48 is on both pins 2 &3, with - on pin 1, a mis-wired cable or a cable modified for unbalanced use could permit phantom to reach the capsule in a destructive way.

The way I have always prevented that is to never wire an XLR to XLR cable anything other than straight through*. New cables are rung out before going into service.

For any combination besides XLR to XLR, I have a system. Adapters are purposely built short in length, typically <12", and clearly marked with a label under shrink tubing*. Most of my adapters convert from something to XLR, so that adding length is done with XLR to XLR.

*This policy applies to portable cables, not to cables made for permanent installation in racks and studios.