repairing an electret microphone

To replace a wire which broke in the swivel of the boom, I reconstructed the boom of an Altec Lansing headset. This included resoldering the wires to the back of the electret capsule. The speakers still work but the mic does not after this repair.

Found a similar failure after soldering a new electret onto the wires of an inexpensive Creative/Telex desktop mic.

Is the electret mic particularly heat sensitive? If so, what technique is recommended? Already I was careful to apply minimal heating.

Thanks, ... Peter Easthope

If your continuity is good, try another capsule. Try attaching small wires first with speed. The only thing that could go wrong is melting the flexible parts of the diaphram.

You should heat sink the outer container.

I've never found them to be particularly heat sensitive within common sense limits, but note that they are polarity sensitive, as they contain a FET preamp which is phantom powered via the output terminal ...

Arfa

It's a job that needs a lowish power or thermostatically controlled iron ( or a fast hand ! ). As someone else mentioned, the capsules are polarised.

Graham

My experience with soldering hundreds of Panasonic WM 55A103 electret capsules is that it takes quite a bit of abuse and clumsy soldering/desoldering before anything goes seriously wrong. You wouldn't normally expect to experience a problem from using ordinary soldering techniques. If the job looks as though it might turn into an awkward one and require a bit of messing-about, it may then be a good idea to provide some sort of heat sink on the capsule body.

Where you might have got a problem, however, is if you have accidentally smeared a whisker of solder or dross from the live contact to the capsule body and cause a short-circuit. That can sometimes be difficult to spot unless you are really looking for it. It is best removed mechanically with a scriber point; if you try to unsolder it, the chilling effect of the casing on the solder blob will just create a worse and worse mess.

A few electret mic are phantom powered but the majority use a form of AB power for the capsule.

I'm using the term "phantom powered" loosely Dave, in that the audio out is floating on the DC in, because there are only two connections, one of which is the FET drain terminal, the series DC 'feed' resistor therefore actually being the drain load resistor. The other terminal (also the capsule case) is of course ground or FET source. Where there is this type of power / signal setup, it is often considered generically, to be 'phantom powered' ... Excuse my ignorance, but what's "AB power" ?

Arfa

Scroll down to A-B or T power.

I've never run across any T power mics or adaptors in my 35 years of being around the equipment.

Not a good idea to use it where mics are concerned, though. Can cause confusion.

Other thing is not all electrets have the same ground polarity. But hopefully are marked.

AB or T power is where the DC is fed up the audio pair on a balanced mic. Dates from before true phantom and has the disadvantage it puts DC across a moving coil mic - although when it was common many used a PS for each mic, rather than getting it from the mixer.

Only really used on some older top end mics. Mainly Sennheiser. Favoured by outside broadcast types as it's more robust over long runs than phantom.

Certainly still commonly in use 35 years ago in broadcasting. But some mics that could use it also had an internal battery as an option.

Phantom to T power adaptors are the spawn of the devil. ;-)

( or a fast hand ! ).

If the job is heat sensitive, you want the iron HIGH power, up to temperature, and do the joint fast. A low power iron, especially if it's not thermostat controlled, is likely to take too long to get the joint up to temperature, and THAT cooks the nearby items.

If a joint takes more than three seconds to heat and draw solder, your iron is too cold. If your iron stays on the joint for more than five seconds, the operator is too slow.

If the work is or might be critical, I always use an artist's small paintbrush with water-washable flux to prepare it. And, I wash it afterward (small squirt from a poly bottle with distilled water).

I've never seen T powered and I run a music studio that has some pricey vocal mics. Must be a broadcast studio/remote site favorite as you mention.

Would you know what makes them more robust? Can't be just the fact that they run on 12 volts rather than 48. I suppose the voltage is an advantage for remote use requiring less batteries or a more standard available source.

They pre-date phantom mics - and good quality mics have a long, long life.

But they may well have been originally designed for location drama etc - where they could get the power from a Nagra.

Plenty of theories but can't be definite. Perhaps the fact they will always work if the audio pair is ok - unlike phantom which needs the screen. So one less pin/cable to go wrong. Perhaps a lower impedance supply?

You still see new pro equipment with phantom and T power switchable - the ubiquitous SQN, for one

OK, but seems that all of this is tending to look at 'whole' mics as in something that a newsreader would clip to himself, whereas the original poster was talking about just the capsule inside, which was also what I was referring to. As far as the polarity of electret mics varying, I can't remember ever seeing a capsule where the case wasn't a negative-side ground, and over the years, I have dealt with and replaced many in cordless phones and similar.

I appreciate that to a sound engineer, the term "phantom power" has a slightly special meaning in terms of voltage level etc, but that still doesn't change the fact that generically, any system where DC power is supplied to an active signal source, using only the wires that are carrying the signal rather than any additional power carrying wire, are considered to be 'phantom' powered, irrespective of the voltage involved. TV antenna amplifiers for instance, are often described as being phantom powered, as also are satellite LNBs.

However, all that said, I do take your point that it could give rise to confusion between a sound engineer reading it, and an electronics engineer, who might better understand the overall concept. Perhaps it would be better to call the electret capsule 'line powered' ...

Arfa

Indeed - that's always how aerial pre-amps etc which use this technique are described. At least in my experience.

Phantom power is so called because it is invisible to the actual required signal. Line power doesn't qualify in this way.

Makes sense to me. Unfortunately the term Phantom Powered can be used too loosely and gets misinterpreted.

No Dave, they aren't. The term "phantom power" is used for many situations where an active device needs powering and only the signal cable is available. Antenna amplifiers, satellite LNBs, cable operators' distribution amplifiers and so on, are all routinely described as being "phantom powered". There are plenty of web references to the technique of phantom powering in these applications. Long ago, when I worked in the early days of cable TV, all of our line amplifiers were powered in this way, and it was always referred to as phantom powering, both by all of the high-end network engineering bods, and also our in-house lecturers, responsible for training of all of the company's engineers.

In fact I would go as far as to say that the technique has been around and called that for a very long time, and the 'hi-jacking' of the term by sound engineering to try to mean something very specific, is actually the questionable use of the phrase.

How so ? What do you perceive as being the difference ? If DC is travelling one way, and signal the other on a single cable, they must be mutually invisible (or made so by appropriate circuitry techniques at the active device, and what it's feeding at the far end of its cable). I have never seen any distinction made before. As far as I am aware, "Line powered" is just a slightly more technically descriptive way of expressing "phantom power".

Arfa

Phantom powering was first used by the telephone industry long before TV of any sort. If the cable TV industry - hardly a bastion of good practice

- hijacked it for something which is patently not phantom, they're the ones that are wrong.