How to Build a Microphone

For decades condenser microphones have been the staple for high-quality recording and live sound assignments. Unfortunately, not everyone can afford to own a good one. Well that's about to change. I've written this article so that anyone who wants a great condenser mic (or those who just want more of them) can have their wish. For around $20 (US) anyone can build an extremely accurate, life-like condenser microphone. DO NOT let the cost fool you, this mic's frighteningly good performance will blow your mind -and it's easy to build!

This microphone is largely based on a posting I found on the internet showing how to modify Realistic (Radio Shack) PZMs for better performance. I have simply finished the design so people can build a complete mic from scratch. After making a pair of these, I was shocked to find out how amazing they sound. In fact, these little buggers have become my first choice for capturing unhyped, totally natural stereo images, beating-out pairs of choice small and large-diaphragm condensers, and some nice ribbons too!

There are several good points worth a quick mention regarding this microphone:

Firstly, it uses an extremely simple circuit with very few components. As such there's not much stuff in it to screw up the sound. In audio design simple is generally better, and this is the epitome of simplicity.

Secondly, because it is such a simple circuit, it is very easy to build, even if you have no previous electronics building experience. With moderate care and attention anyone can easily build a pair of these mics in an afternoon.

Thirdly, this mic uses a proprietary, portable power supply instead of phantom power. This makes it a great choice for location recording, binaural nature recordings, or anyone forced to rely on dynamic mics because their gear lacks phantom power capability.

Lastly, because this mic uses a tiny 6-mm diaphragm, it has incredibly fast impulse response, which essentially means that its sound reproduction is extremely accurate and life-like. This factor has contributed to the recent popularity of ultra-small-diaphragm condensers. Larger diaphragms (even those used in traditional, high-quality small-diaphragm pencil mics) simply cannot reproduce this kind of accuracy. Recording with a pair these mics sounds just like being there!

Enough rambling-let's get started.

Circuit components

(1) Panasonic WM-66AY Omnidirectional Microphone Cartridge (available from Digi-Key at 800-344-4539, part # P9959- ND). This capsule is a high-quality back electret type with a frequency response that is ruler flat from 20Hz to 20kHz. It contains an internal FET impedance converter making an external FET unnecessary.

1000 pF ceramic disc capacitor 10uF mylar or metalized polypropylene capacitor (DO NOT substitute an electrolytic!)

(1) .2Kohm 1% metal-film resistor 

(1) 9-volt battery terminal w/leads 

(1) 9-volt alkaline battery

Insulated copper wire

Hardware:

(1) Metal enclosure for the power supply (important for proper grounding)

(1) 9-volt battery mount (clip types can be purchased at Radio Shack or you can use industrial velcro, etc...)

Panel-mount male XLR connector Panel-mount female XLR connector

(1) Male XLR cable connector (for the mic output to PSU)

(4) Rubber feet (not necessary, but I like them for the bottom of the PSU!)

This project consists of two main parts: Fig. 1 — the microphone, and Fig. 2 — the power supply. Fig. 2a is power supply used when driving a balanced input. This is the one most people will want to build. When using it to drive an 1/8" unbalanced mic input (such as those on many cassette and

mini-disc multitracks), simply use an XLR female to 1/8" male adapter cable connecting pin 2 to tip and pins 1 and 3 to sleeve. If you are certain that you will never want to drive a balanced input, you can opt for the supply shown in Fig. 2b designed for use with unbalanced inputs only.

You may notice that there is no "power" switch on the power supply diagrams. This is because the battery will only drain when the mic is plugged in. Each time you finish using the mic, simply unplug it from the supply. There is no need to remove the battery.

Construction tips:

When building the circuit make sure to shrinkwrap all bare leads to prevent the possibility of shorting against the chassis or other leads. If shorting occurs, your mic won't work. Shrinkwrap is available from any electronic supply store.

After you connect the wire leads to the mic cartridge seal the entire back of the cartridge with non-conductive epoxy making sure to overlap a touch where the back meets the sides. This seal provide additional dampening of the phenolic backplate of the capsule which further extends its low frequency response.

You can mount the cartridge just about any way you want. I chose to mount mine in the end of the rubber boot of a Neutrik XLR connector (see photos). This allows for a compact package, reasonable sonic neutrality, and perhaps even a touch of shock-mounting because of the rubber's ability to dampen vibration. If you choose to mount your cartridge the same way, sink it by pressing gently on the edges of the cartridge. Do not mash down dead center or you risk damage to the diaphragm. Note that mounting the cartridge this way will also require that you handle the finished mic with care so as not to damage the exposed capsule.

Buy or borrow a simple multi-meter for use during construction. Mine is an inexpensive Radio Shack model 22-802 which costs about $25. Use this to check all solder points as you go just to make sure that they are good (sometimes a connection may look good, but, for some reason, won't be making solid electrical contact). By checking as you go you can identify a problem when it occurs rather than having to go through the entire, completed circuit to find a single cold joint (which can easily become a hair- pulling experience!).

For my power supply chassis I used a single- wide electrical junction box which cost me 79-cents at Home Depot. The solid cover for it (to complete the enclosure) cost another 35-cents complete with screws! This is an excellent choice because it's cheap, it's metal, it's sturdy, and the punch-outs are already the right size for most XLR panel mount connectors. I used Neutrik XLRs which required that I file four grooves around the edge of the hole for the right fit, but the hole was already there!

Work slowly! This is not a complicated project, so it won't take long. Check and recheck your progress. I know it's easy to get impatient and want to have it done, but work methodically. When you are finished the mic will give you years of excellent performance!

Using your new mic(s):

Despite the fact that these mics are omnidirectional they do possess directional characteristics at higher frequencies. Therefore using a pair in an X-Y configuration can yield an incredibly natural stereo image. This also allows you to back- off the top-end a touch (acoustically!) by simply pointing the tip of mic 90-degrees from the source. The impulse response and realism remain unaffected!

These mics are awesome for stereo recording. Try them as drum overheads and room mics. Jecklin-disc and spaced-omni stereo techniques also work fabulously. They are great for acoustic guitar, piano, percussion, choral groups, or just about anything that you want to sound like "being there".

If you have never used omnidirectional mics before, be aware that they hear much more of the room in which the source is recorded than cardioid mics do. Therefore, if you want a "dead" sound, you will need to either record in a "dead" room or use baffles and/or strategic placement to reduce ambience. I was able to effectively control the ambience in a vocal track by placing the mic below the singer's head in a carpeted room, pointing up at him while he sang down at the mic. Since his voice projected primarily into the carpet, much of it was absorbed leaving very little to reverberate in the room.

Also, omnidirectional mics do not exhibit the proximity effect (low-end boost when used up close) that directional mics do, so you can place these mics extremely close to a source without the unnatural boominess that can result from using a cardioid. This also means that when you want that low-end effect (for say, a lead vocal) then you will need to dial in a touch of low-frequency equalization.

Because these mics sound so natural, they are great for capturing just about any good- souding source. Use them on guitar cabinets, acoustic instruments, brass sections, ensembles, inside kick drums, you name it. Experiment and have fun!

A word of caution: NEVER connect these mics to a phantom powered input without first turning off the phantom and allowing 5-10 minutes for discharge. Though it is designed to drive a balanced input, the mic's output is not a true balanced design, so the DC-voltage provided by phantom power on pins 2 and 3 will not cancel as it would with a balanced mic. This could easily damage the cartridge, which is rated for a maximum of only 10-volts DC!

Many thanks to Phil Rastoczny for writing the article on the Realistic PZM modification that is the basis for this microphone.