Microphone Care

No matter what mics are in your collection, you want to take care of them. No matter how cool or boutique or amazing a mic is, if you go to use it and it’s got a problem, it’s worthless at that moment. I’ve learned a lot from doing the Custom Microphone Mod Shop and I’ll share some of that here.

microphone Mods

Storage

Mic Cabinet, Mic Shelf, Shoe Box… Everyone has their own version of the “mic locker”. Besides questions of theft security, the main things you should be worried about here are

  • Moisture
  • Dust
  • Accidental Damage

Microphones have very sensitive elements. Condensers and Ribbons especially have extremely low mass surfaces which pick up the sound waves. It takes a very small amount of dust and/or moisture to significantly alter this mass and therefore the ability of the element to translate sound pressure into voltage.
I’ve had some mics come into my shop for rebuilding and the capsules were actually corroded and pitted from years of being in high moisture environments. And when they get wet, they also get caked with dust.

Desiccant (Do Not Eat)

Those little desiccant packets are your friends.  We all get them when we buy junk from Amazon. It does no harm to throw a few of them in where you store your mics. If you are in a high humidity environment (get a Hygrometer to measure), I’d strongly suggest storing your mics in a room that has a Dehumidifier running. Keeping the capsule dry is probably the single most important thing you can do. 

Microphone Dominos

Another obvious tip for storage is to keep the mics in such a way as to avoid accidentally damaging or dropping them. Standing a bunch of mics up on a shelf may look cool, but sooner or later you’re going to knock one over (which will certainly knock the rest over). This, I know first-hand.

Hot-Plugging

I see some variation of this question on Facebook all the time.  Is it safe to plug in in a mic with Phantom Power already on?  The other related question is if it is safe to apply Phantom Power to Dynamic or Ribbon Mics (often you don’t have any choice when using low-end mixers with one phantom switch for all channels).

If everything is working right with Phantom Power, there is an equal voltage potential on pins 2 and 3 with respect to ground (pin 1).  That means there is NO potential across the output transistors or transformer.  The reason there is any question about hot plugging is that unless you can insert the XLR jack at the speed of light, there is going to be some tiny instant of time where pin 2 or pin 3 makes contact before the other. During that time, there IS a potential across the output transistors or transformer.  Notice I said “If everything is working right”. Having a bad mic cable with pin2 or 3 disconnected or intermittent is going to cause the p48 to be applied across your output device. Maybe it can take it… maybe it can’t.

Does it matter?

This is what everyone wants to know. To me it’s like asking if it’s safe to cross the street.  My answer is that it is usually perfectly safe. Transformerless condenser mics (at least all ones that I am familiar with) have protection diodes in the output section to provide protection to the output transistors. Some mics use transistors which can easily tolerate this voltage even without the diodes.  Most transformer-coupled Condenser mics should tolerate this too.

Bottom line, I’d avoid hot-plugging, but I wouldn’t worry too much about it.

Ribbons

Ribbons are a different animal.  They don’t need phantom power but they may have it applied for one reason or another. You might switch it on by mistake or again, if it’s plugged in with an all-or-nothing type device that puts phantom on all inputs. I have less experience with Ribbons, but I believe it should be ok to have a stable phantom voltage applied (I’ve certainly done it with no problems). I think it is probably best to avoid hot plugging ribbons and if you can’t avoid having phantom applied, make sure the mic cable is a good one with no intermittent connections.

Dynamics

In my experience Dynamic mics are pretty bulletproof. They can tolerate hot plugging (and pounding in nails).

Shipping/Transporting

One thing I’ve learned the hard way over the last year is that Shipping Carriers are very good at wrecking microphones.  The opening scene of “Ace Ventura, Pet Detective” is probably a bit of an exaggeration but maybe not by much. Large Diaphragm Condenser microphones do not like rapid Deceleration (ie: sudden impact).  The capsule is heavy and typically suspended with a pretty feeble mounting cradle.  Why not make the mounting stronger?  Because the optimal microphone would have NO cradle at all – the capsule would be magically suspended in mid air by some unseen force. Since this technology does not yet exist, we use cradles that are as strong as possible while being as thin as possible. The net result is several broken capsule cradles which were not broken when they left my shop.

rode nt2 repair
Rode NT2 after UPS got through with it.  The capsule cradle broke and the capsule is destroyed.

When mics come to be for rebuilds, I am often horrified at the packaging. The mics are slamming around inside the box and they are wrapped with one thin layer of bubble wrap (if that).  I generally don’t care because I am typically replacing the entire guts of the mic anyway.

You can’t prevent careless handling all the way through the chain. I recently shipped a mic to a customer (with six red “Fragile!” labels on the box) and watched the clerk toss it onto a pile of boxes about five feet away.  This was at Point A with me watching!  Imagine what happens between point A and B.

Deceleration

The best you can hope to do is slow down that rapid deceleration (absorbing the shock) when the mic inevitably gets thrown, dropped, kicked, whatever.  

Contrary to popular belief, bubble wrap is really not very good at absorbing shock. You want elasticity/cushioning, and bubble wrap doesn’t really offer much of that. It’s great at taking up space (also important). If you have the original packaging for the mic, it will typically be in some soft cushioning foam. This is what you want. If you don’t have the original foam, I suggest getting some soft shipping foam (1 or 2 inch thick) and wrap the mic in it. You want to absorb shock on all axis  – they might drop it upside down!

If your only choice is bubble wrap, use a lot of it.  Spend the extra money on the larger package and wrap it in a big fat cocoon!

Shake Test

Once closed up, shake the box. There should be NO movement inside the box. This is where bubble wrap and craft paper are valuable. They are great at filling the space so the mic can not move (accelerate / decelerate) inside the box. 

Crash Test

After my third customer had a mic arrive with a broken capsule cradle (and an expensive ruined capsule), I upped my packaging game and decided to do a little test. With my latest packaging, I tossed a mic out of the second story window to the pavement below. It survived perfectly.  (I’d like to point out that this was my microphone, not a customer’s mic).

Troubleshooting

Believe it or not, there are not that many things that can go wrong with a mic. There’s an element, a circuit and/or transformer and a connector.  Depending on the type of mic, different symptoms can mean different things. 

A good first step is to make sure the problem IS the mic and not the mic preamp. Plug in a similar type of mic and verify that it does not have the same problem. 

Hum – 

Condenser mics are extremely susceptible to hum pickup. Inside that body, they are converting a very weak high impedance signal from a capsule to a signal capable of driving a low impedance input on your mic preamp.  Hum almost always means that the body shielding has lost some integrity. Very often this is simply some oxidation on where the various pieces of the body fasten together.  The idea is to have a very good connection from pin 1 of the XLR through all of the body and headbasket parts.  It’s usually possible to take the body apart and clean the edges and surfaces. You can even take a scotch brite pad to the edges.  Normally, this will solve the hum.   If the hum continues or is intermittent, it may be that the circuit board is not making a good grounding contact for some reason. This might get a little harder to figure out on your own.

In the case of Tube mics, another likely culprit is the power supply itself. It probably has a failing filter cap.  One hint to this is if the tone actually sounds more like 120/100Hz rather than 60/50 Hz.  If so, it is definitely a power supply problem because you are hearing full wave rectified AC mains.

Hiss – 

In my experience, this is always the result of one of the zener diodes failing in a Condenser Mic. Depending on the design, there is at least one zener for the power supply and additional ones for hot-plugging protection (see above).  Any one of those could be the culprit but in my experience, it’s always been one of the protection diodes. If you have some basic soldering and desoldering skills, these are not hard to replace. The protection diodes are typically 6.2v.  You could also just try removing them (and then be extra careful about hot-plugging).

Whistle – 

This is a strange and interesting one.  Many transformerless condenser mics actually have an oscillator in them. This is used to step up the voltage to polarize the capsule.  That oscillator runs at around 2 Megahertz so you should never hear it. But sometimes, a problem with the oscillator circuit can cause it to produce a component in the audio range. Another strange thing that can happen is if some of that oscillator tone leaks into ground, it can cause interference with other mics.  If the two mics’ oscillators are within 20KHz of each other, you may be hearing a difference frequency.

Low Output – 

If a condenser mic suddenly has a low output, there are a few possibilities but before we look at the mic, remember the part above about checking the preamp. This could be a problem with low phantom power voltage. Some mics perform very poorly with low p48. I had a Behringer device on my bench that on a good day would only put out about 14 volts! Most of my mics worked ok, but I had an oktava that was totally silent.

Assuming it’s the mic, this is probably not good news. It might be the capsule itself. If the mic has a pattern switch, flip it to omni mode and see if the output is still low. If not, it probably means that the front diaphragm of the capsule has failed.  Otherwise, we’re into the circuit (or transformer) and this is probably a job for a tech.If a condenser mic has a low output on power-up, give it a minute to warm up. I mean this for non-tube mics too. Some mics (like the Rode NT2) have a very slow charge up time for polarizing the capsule. Until I learned that, I thought I broke a customer’s mic – it was silent on power-up.  The NT2 takes 70 seconds to fully charge the capsule!

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