For AAs and AAAs, I have selected the Maha Powerex Imedion cells which retain a charge for an extended period of time (spec’d at 15% loss per year). I have invested in two of the MH-C9000 Wizard One chargers for my office and two MH-C401FS Mini chargers, one for my bedroom and one for the church sound booth. These are both available alone and in kits with cells from Paul’s Finest where he is selling the international version with a multi-voltage “wall wart” for a reasonably good price with great service.

While the MH-C401FS charges batteries individually, and does a good job of it, the MH-C9000 Wizard One is amazing. It will determine the remaining capacity and will even test and condition cells to the IEC standard. For example, I was having a problem with some cordless phones that used 3-cell NiMH battery packs. I took the pack apart and put the three cells in the MH-C9000 and it told me that they had a capacity of about 70, 40, and 40 mAh for each of the three cells. I immediately replaced these three cells with three new Imedion AAA cells that have about 800 mAh capacity each.

I have been using the Maha cells and chargers since April and am very pleased.

A special-purpose option in this are the 3.7 V 14500 lithium polymer AA-sized cells. These will obviously damage many devices that could physically accept them, but for the latest breed of LED flashlight, such as the 4Sevens Quark AA lights (USA site),  these provide superior peak output at the highest setting with the understanding that you can also use standard NiMH cells in an extended emergency with the loss of some peak output.

I have been using the AW-139 dual-cell fast charger also since April with great success. These will charge the 14500 cells mentioned above as well as 17670 cells which are the size of two 123 cells and work well in some LED lights that use two disposable 123 cells. I have been using the Pila version of these cells for about five years in my SureFire L4 LED light and have now bought four more cells for other flashlights. These are available from 4Sevens (USA) as well as other places such as www.dealextreme.com. Make sure you get the protected cells.

Recently, I did a thorough search for 9 V rechargeable batteries for wireless microphones at church. I was pleased to discover that iPowerUS (they have a Toronto office) was able to provide lithium polymer 9 V batteries that far outperformed the available NiMH offerings. We bought one DC9V charger and eight DC9V-520mAh batteries for alternate use in four wireless transmitters that we use regularly. We expect this system to pay off in a year or less.

I also bought their GC-60 tester/charger for my NiMH AA and AAA cells which, so far, looks excellent. Both chargers come with a “wall wart” and a car cord.

See updates in this article.

As with much equipment–and especially with lower-cost equipment–the performance specifications and the actual operational data is not published. There are reports of the H2 clipping on the line inputs in some of the reviews and it appears that a lack of understanding how the inputs were configured exacerbated that situation.

There is nothing wrong with the line inputs on the H2. BUT there are some caveats:

1. DO NOT use the input level control on the line inputs to go below 100 or the preamps will clip before the signal reaches 0 dBFS.
   ALTERNATE WORDING (thanks Greg H.):
   Set Zoom H2 RECORD LEVEL to 100 or greater to avoid clipping at the Line In preamp stage.
2. Use an external attenuator with the gain set at 100 to avoid overdriving the line inputs.
3. The noise floor is not spectacular, but is not too bad. With the inputs terminated in 150 ohms, the peak noise was -70 dBFS, but that improved to about -85 dBFS or better, measuring it as an A-weighted rms figure, which is how most noise is measured. While this certainly isn’t what one would expect out of the Sound Devices, it is far better than the 50-60 dB(A) that one can achieve with an analog cassette tape without Dolby.
4. The maximum input level to the line input should be no more than -5 dBV or -3 dBu.
5. Try to avoid clipping as there appears to be a delayed recovery in some instances.

With this information, you can optimize a pad between the source and the H2 line input so that the recorder is never overloaded. Try to keep the levels as high as practical as there is a relatively limited dynamic range. On the other hand, I have found that the recorder noise is not objectionable even when I’ve boosted the levels 20 dB for a quiet choir piece from our church. The room ambience totally swamps the recorder noise–at least as far as I hear.

The H2’s internal mics are reasonably good for many purposes. While I still prefer the SD722 for many things, I think the H2 is one of the better oral history conversation capturing devices I’ve seen. It uses SDHC cards which may require a new card reader. Don’t use the built-in USB connection unless you’re recording MP3 files as you’ll be there all day. The internal card-reader mode is limited by the USB 1.1 interconnection. This interconnection is adequate, however, for using the H2 as a 16-bit live audio interface/microphone connected to your computer (at either 44.1 or 48 ks/s). The unit will record up to 96,000 samples per second, 24 bits,  but many of those bits will be noise.

Please let me know if this has helped or if you have any questions or comments.This work was done with version 1.50 of the H2 firmware.

Please note that connecting any microphone other than the intended one to any of the adapters shown in the link may severely damage the microphone. In general, while the vast majority of dynamic microphones and some ribbon microphones can work with phantom powering, it is a good idea not to send power to microphones that don’t need it.

In the 1960s, transistorized microphones from AKG, Neumann, Schoeps, and Sennheiser became available. There are several niches of early microphone powering that continued on for many years. Perhaps the easiest way to look at it is backwards.

I have adopted the terminology “hot” and “low” to refer to the audio signals in a balanced line. Hot is defined as the voltage going positive in respect to the low lead with a positive pressure at the microphone diaphragm. I’m using “hot” in this context rather than “hi” because so many people have heard of “pin two hot” or “pin three hot” that I wanted to be consistent with that nomenclature.

PHANTOM POWER

Today, 48 V phantom powering is almost universal. In phantom powering the positive voltage is fed through a pair 6k81 ohm resistors, one to each modulation lead. The matching of these resistors is often done to 0.1% to maintain common mode rejection. The negative power runs on the mic shield. XLR: Pin 1-shield; Pin 2-audio hot, +48 V; Pin 3-audio low, +48 V. Tuchel: Pin 1-audio hot, +48 V; Pin 2-shield; Pin 3-audio low, +48 V. This was standardized in the 1960s in DIN Standard 45596.

A caveat about phantom powering voltages. There are a wide range of microphones that will work with phantom voltages from 9-52 V, but many that are rated at 48 V will not work well outside of the +/- 4 V tolerance in the standard. AKG, Audio Technica, and Schoeps, for example, make many 9-52 V powered microphones, while DPA, Neumann, and Sennheiser mics generally need 48 V. Some devices (e.g. the first version of the MicroTrak digital recorder) had an odd 30 V phantom that probably worked with a number of mics, but might have degraded their performance. M-Audio took this to heart and the MicroTrak II has real 48 V phantom power. There once was a 24 V phantom power option in the standards, but apparently it was never adopted in practice and it has since disappeared.

Prior to standardization, in 1964, Schoeps produced the CMT-20 microphone which used negative 8.5 V phantom power. The CMT-200, according to Schoeps drawing SB316, dated 1964-10-14, used the same -8.5 V phantom. Later this was broadened to negative 8-12V phantom followed by the switch to positive phantom at some later point. With vintage microphones, at least from Schoeps, be very careful as they might be negative phantom.

For more details about phantom power, please see Rick Chinn’s page here. This page on Wikipedia has some further history.

NOTE: You can use a polarity-reversal cable with phantom power, but not with any of the other schema.

CAUTION: Phantom Power can damage some battery-operated microphones like the Audio Technica AT822 stereo mic. It can also damage ribbon microphones which are not floating (i.e. those that have their centre tap grounded).

T or AB POWER

Moving backwards in time, the next most widely used microphone powering scheme is called “AB power” “T-power” or “Tonader Power” and is standardized in the 1960s in DIN standard 45595. In this design, both the power and the audio are on the same wires. The hot audio and the positive power is on one conductor while the low audio and the negative power is on the other conductor. The shield is just a shield in this scheme. This was widely used by Sennheiser and Schoeps in the film industry. Neumann made a FET-70 series that used this powering scheme and many of the mics in that series are the same as the much more widely known FET-80 series (as in U-87 and KM-84, for example). Rick Chinn has more information here.

If you have T-powered microphones, you can power them off phantom power WITH THE APPROPRIATE ADAPTER.  These adapters can be purchased or made. Rick Chinn has a transformer design and a transformerless design. I developed a similar transformerless design,  but used 680R resistors instead of the 4k7 resistors that Rick used and I placed a 180 ohm resistor between the zener and the filter capacitor to reduce the noise of the zener even more.

T-Power, as introduced by Schoeps with the CT100 series in 1965 was wired to XLR connectors with the hot/+ connected to pin 3, following the Ampex standard. This polarity practice is documented on the same Schoeps drawing referenced above. Sennheiser, to the best of my knowledge, always connected the hot/+ to pin 2, which became the international standard. Many Nagra recorders came with pin 3 hot, but I believe they could be ordered either way. Sennheiser introduced this powering scheme in late 1963 based on catalog research by Lonn Henrichsen.

It got to the point where there was the term “red dot” microphones which had been rewired for pin 3 hot/+. If in doubt, this is the one legitimate use of a polarity reversal cable with T-power. Sennheiser adopted T-Power with the MKH-105/405/805 microphones in the mid 1960s. They later provided “P48″ versions of these microphones and at that point also designated the T-powered mics with a “T”. So there could be an MKH-416T and an MKH-416P48 which differed only with the powering. This appears to have been introduced with the XX6 series of microphones.

CAUTION: T-Powering WILL damage ribbon and may damage dynamic microphones.

EARLY ANOMALIES

In addition to the Schoeps NEGATIVE phantom mentioned above, Sennheiser introduced their first line of RF condenser microphones with an unbalanced, negative power connection. The MKH-104/404/804 have odd wiring. Pin 1 of the Tuchel connector is audio output. Pin 2 is ground (audio low and power +). Pin 3 is -8 V power. This series of microphones was introduced in 1963 and discontinued between the 1968 and 1969 catalogs.

Later, Sennheiser introduced the extended-low-frequency special-purpose microphones, the MKH-110, with the same powering scheme, except Pin 3 is +8 V power!

It is trivial to power an MKH-x04 microphone from a 9 V battery, and after having noise problems with an inexpensive off-the-shelf DC-DC converter, I ended up with an alternate powering scheme, described here.

I’ve decided that this will be an application to keep in the Tuchel connector domain, so this oddball powering doesn’t get into any other microphones and possibly fry them.

CAUTION: These powering schema can damage many types of microphones.

CONCLUSIONS

While this may sound complex, in practice certain combinations of mics/recorders are used together and it’s fairly trivial to keep track of what’s what.

For example, for almost four decades, I’ve had AKG C451 microphones in my kit, and I’ve adapted almost everything to power them. Other mics that take 9-52 V phantom obviously will work there as well. I’ve had several (currently three) Sennheiser MKH-416T short shotgun mics for about a decade (I got them used). I made a P48-T12 adapter for each of them, and I keep them with the mic. When I grab the mic, I grab the adapter. Sometimes it goes right on the mic, other times it goes at the end of the first mic cable coming from the mic. Placing this at the mixer increases the risk of damaging other microphones.

When I first got the MKH-416T mics, I made a stereo powering box that had a toggle switch that could select T12 or P12 so I could use one box with a pair of short shotguns or C451s. This had unbalanced outputs (all resistor-capacitor networks, not transformers) that connected to the portable DAT Walkman recorder and used 8 AA batteries for long running time.

I recently got an AKG C460/CK63 and that’s still 9-52V.

Some of the newer mics in my collection (Neumann TLM-103, KMS-105; DPA 4006 TL) are P48 only and, in fact, most of the new equipment I have has true 48 V powering. This includes a Sound Devices 722 portable recorder, a MOTU 828MK II multichannel FireWire audio interface for my laptop, a Mackie 1402VLZ mixer, and a Shure FP410 mixer. The church I do sound for has a Mackie 1604VLZ that I previously owned, so P48 is very common in my world. People who have used Nagras in the field report adapting everything to one scheme. In one case it was the “red dot” mentioned above.

All in all, don’t be afraid of some of the oddball powering schema, just work through what is needed. Since all of these schema are low-powered, the likelihood of any significant damage to a microphone is probably low, but still, don’t take chances with expensive, excellent performing antiques.

It is my understanding that European broadcasters at least influenced the various powering schemes by requiring compliance to their specific powering standard across several manufacturers. When I started working at ABC-TV in New York City in the early 1970s, there was a system of remotely powered microphone preamplifiers built into extended length female Cannon UA cable connectors. So this is yet another odd scheme, although it was an accessory to the microphones rather than in the microphone itself. This preamplifier was used to boost the signal level at the microphone in an attempt to overcome hum and noise on the long lines.

In the process of doing this work, I have learned a few things which might be of assistance. This is the first post in the blog in the live sound and recording category. Many of the posts relating to microphones will also be tagged in the oral history category.

One of the challenges for good sound reinforcement or speech recording is keeping the speaker “on mic”. There are many ways of handling this, but some work better than others. Here are my favourites:

• If the room is quiet and you can do a proper setup, a pair of Sennheiser MKH-416 short shotgun mics, one for the interviewer and one for the interviewee, gives very natural and unselfconscious results.
• For larger groups, I’ve had good results with an Audio Technica AT-822 (or the phantom-powered AT-825) stereo microphone, but the actual voice quality of that mic is inferior to the MKH-416. The high-end is harsher, but, used at a greater distance that is often not as noticeable. The room needs to be very quiet for this to work well, however. This is currently my least favourite approach (of those listed).
• So far, some of the best pickup I have found is a headworn mic–the main subject of this post.

At our church, they had tried headworn mics from Shure and they really were uncomfortable. Whoever selected the units, selected dynamic units and they did not sound all that good. They were retired in favour of the Countryman E6 units (also available from Shure, although I prefer the direct-from-Countryman version with the 2mm cable for robustness).

The Countryman units were working reasonably well, but never seemed to stay in the same place. It was frustrating as it was causing a widely varying sound quality, so we decided to try a DPA 4066 headworn mic on our head priest. The results were outstanding. The unit is comfortable (no more sore ears), it stays put, and it sounds better!

It is no surprise that these are taking over the religious and theatre markets. I am not sure I’d want to try to fit one of these on 87-year-old Aunt Tilly who is trying to tell us some family histories as it may make her self conscious, but probably no more so than a large microphone stuck close to her face. That’s where the short shotgun Sennheiser MKH 416s come in handy, they get the same sound pulled farther back–as long as Aunt Tilly talks in that direction.

As mentioned in a recent post about Story Corps, it appears they are using the Neumann KMS-105 in their mobile recording units. These are reputedly also excellent microphones and would be worthy of consideration when a more conventional, close-talking microphone is required.

A clip-on lavaliere microphone (such as the DPA 4060 miniature microphone, essentially the same capsule as on the 4066 headworn microphone) is useful, but the positioning is critical and often the sound is not as good as one would hope due to body resonances and clothing absorption and rustling.