Input Conditioning & Impedance
48 V phantom power
Press a channel’s +48V switch to supply phantom power. The supply is 48 V ±4 V at 10 mA per channel and complies with DIN 45596. It is suitable for phantom-powered condenser microphones and ribbon microphones with active onboard head amplifiers.
Mute the monitoring path and turn phantom power off before connecting or disconnecting a microphone. Only enable phantom power for microphones or active devices that require it.
−10 dB pad
Channels 1 and 2 have a −10 dB pad for hot input signals. The actual attenuation varies with the selected microphone-preamp input impedance, so use the meters and listen when setting the channel.
Polarity reverse
Press ø to reverse a channel’s polarity by 180 degrees. Use careful microphone placement first, then compare polarity settings across a multi-microphone setup to find the fullest and most solid low-frequency result.
Common examples include the kick microphone relative to drum overheads, or an underside snare microphone relative to the top snare microphone.
Always remember to check phase.
Sweepable high-pass filter
The high-pass filter is a second-order, 12 dB/octave filter sweepable from 25–250 Hz. Press the filter switch to engage it, then set the cutoff with the channel’s HPF control. Use it to increase headroom and remove low-frequency rumble or unwanted low-frequency energy.
Variable input impedance
Each channel provides three microphone-input load settings:
| Setting | Input impedance |
|---|---|
| LO | 220 Ω |
| MED | 1.2 kΩ |
| HI | 2.8 kΩ |
The microphone’s source impedance and the preamp’s load impedance form a frequency-dependent voltage divider. Changing the load can therefore change the microphone’s level, transient response, frequency response, detail and perceived tone.
Transformer-output microphones, such as an SM57, SM7 or Coles 4038 ribbon microphone, may show a noticeable change. The source manual uses an SM57 with an illustrative 310 Ω source impedance at 1 kHz to demonstrate the interaction. Ribbon microphones are noted as often favouring high-impedance inputs.
When comparing settings, listen for:
- Change in level
- Change in speed or transient response
- Change in tone or frequency response
- Change in detail
The source manual describes the broad listening range as moving between fast/detailed, soft/hard and glued/slow, with HI, MED and LO positions providing different points in that “triangle of tone”.
Transformerless condenser microphones with electronically buffered outputs may change little or not at all because their output impedance is more linear with frequency. If in doubt, consult the microphone manufacturer’s data.