Although the CMC 5 Ug has a more modern successor (the CMC 6 Ug), some people place a special value on its discrete circuitry, or require an exact match for an existing microphone.
The chief task of a CMC microphone amplifier is to convert the extremely high-impedance signal from the capsule to a very low-impedance one suitable for transmission through a microphone cable. Several versions are available which differ only in their powering, connectors, output levels and surface finishes. They all feature a symmetrical class-A output stage with neither coupling condensers nor an output transformer. This design helps them to achieve extremely low distortion and light physical weight, while their very low output impedance helps make them insensitive to electrical interference.
On the choice of amplifier type:
If a recording device has balanced inputs but lacks phantom powering, it may be possible to add 12 Volt powering rather easily by using a supply voltage that is already present internally. In most cases 48 Volts would need to be generated with a voltage multiplier circuit, which is more difficult to implement. That is why we recommend the CMC 6, which works with both 12 V and 48 V phantom powering so long as the relevant standard is followed.
If it is certain that 48 Volt phantom powering will be available in all foreseeable recording situations, the CMC 5 should be fully satisfactory. In addition to the CMC 6's dual-voltage circuitry versus the CMC 5's single-voltage circuitry, the two amplifiers differ in their response at the very bottom of the audio frequency range.
The CMC 5 rolls off below 30 Hz, while with digital recording in mind, the CMC 6 is essentially flat to 20 Hz.
The CMC 3 is designed for 12 Volt phantom powering. If necessary it can also be driven from certain 48 Volt phantom supplies, but it will draw significantly more current than a CMC 5 or CMC 6 without offering any particular advantage for doing so (a CMC 3 draws 11 mA at 48 V).
The CMC 4 works only with 12 Volt parallel powering (T-feed), which is rarely encountered nowadays except in video and film sound.
For installations in which 48-Volt powering will always be provided and in which RFI is not an issue, the model CMC 5 Ug is available.
Variant Amplifier Versions
Special versions of the CMC 5 Ug are available with different gain (amplification factor) or extended low-frequency range. Either type of amplifier can be specially ordered, or retrofitted at the factory, to have a different low-frequency limit from the standard version (see, for example, the "linear" version listed below).
The two amplifiers in a stereo pair of microphones should be of the same type.
CMC 5 Ug linear
The CMC 5 Ug microphone amplifier normally has a gradual rolloff in response below 30 Hz to guard against infrasonic disturbances from various sources such as air movement and vibration. However, when using pressure (omnidirectional) transducers, particularly with digital recording, it can be desirable to pick up frequencies below 20 Hz without attenuation. The special technology of the CMC 5 Ug linear microphone amplifiers makes this possible; on request we can deliver microphone amplifiers with response that is flat to as low as 3 Hz.
Caution must be advised with respect to infrasonics, however. Since pressure transducers can pick up very low frequencies, ventilation systems in large spaces (churches, concert halls) or traffic rumble can create a problem. With pressure gradient transducers the risk is even greater. They are far less sensitive to very low frequency sound, but respond much more strongly to low-frequency mechanical stimuli such as air currents and solid-borne noise. Such signals may be below the audible range of frequencies, but they can overload electronic circuitry and produce severe distortion, particularly in transformer-coupled circuitry.
CMC 5 Ug +5 dB
The sensitivity of a microphone using this type of amplifier is 5 dB higher than with the standard version, but the equivalent noise level and maximum output voltage are not materially affected. Thus the highest sound pressure level which the microphone can accept without distortion is 5 dB lower than in the standard version, while the signal-to-noise ratio is essentially the same with either gain setting.
This version might be chosen in order to raise the microphone's signals above the noise level of the equipment to which it will be connected, and / or for working with sounds that occur mainly at low levels.