User Manual

Townsend Labs Sphere L22 Precision Microphone System Guide Using the Sphere L22 System
32
Preamps
Although a Sphere microphone can work with virtually any two-channel mic preamp with 3-pin XLR
inputs and 48 V phantom power (P48), we recommend preamps with precision digital gain control or
analog stepped gain adjustment so the channel levels can be easily matched.
NOTE: Digitally controlled preamps may also be referred to as “recallable” or “remoteable.”
Preamps with digitally controlled gain include those found in Universal Audio's Apollo series interfaces
(except Apollo 16), the Presonus Studio 192, and other products from companies including Apogee,
RME, MOTU, Avid, Roland, and Focusrite. Digitally controlled preamps have the additional advantage
of linking channels so their levels move together when one of them is adjusted.
Many preamps with analog stepped gain adjustment, such as the Neve 1073, work well with Sphere.
Since the mic modeling assumes some of the character of the preamp used, great results can be obtained
from devices with more vintage color. However, for best results, set your preamp gain to avoid clipping
and disable all of the preamp's filters, pads, phase switches, and EQ.
Some analog stepped gain preamps also have a continuous fine adjustment knob, which must be set
properly. Usually the maximum or middle position works best to easily match levels between channels.
We recommend running a calibration procedure with the Sphere mic, especially if the preamp has a
fine adjust knob, to verify that the levels are properly matched.
NOTE: To help determine which preamp to use, we compiled an extensive list of over 250 mic preamps
that have precision stepped gain adjustment. See http://townsendlabs.com/prelist.
We recommend a preamp with a 2000-ohm (or higher) input impedance, although the mic is designed
to work down to about 1000 ohms. If the preamp has variable impedance, we recommend setting it
to the highest value because that generally best matches the gain between channels.
The preamp must have 48 V phantom power in accordance with the IEC 61938 specification and be
able to deliver up to 8 mA of current per channel. The mic draws about 8 mA at maximum sound
pressure level and about 5 mA at more typical levels.
Preamps with Continuous Gain
It is also possible to use Sphere with preamps that have continuously adjustable gain, such as those
from API, Midas or SSL, although it is necessary to recalibrate the gain to match levels each time the
gain is adjusted. To learn how to calibrate your preamp, see Preamp Calibration on page 14.