User Manual

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User’s Guide OctaMic XTC © RME
12. Analog Inputs / Outputs
12.1 Mic / Line In (XLR)
The OctaMic XTC has 8 balanced full range XLR inputs on the back panel. The electronic input
stage is built in a servo balanced design which handles unbalanced and balanced signals cor-
rectly, automatically adjusting the level reference.
When using unbalanced cables be sure to connect pin 3 (-) to 1 (ground). Otherwise noise
may occur, caused by the unconnected negative input of the balanced input.
The pin assignment follows international standards. With XLR, pin 2 is + or hot, pin 3 is – or
cold, pin 1 is ground. Pin 1 is connected to the chassis directly at the socket (AES48).
The OctaMic XTC offers an adjustable amplification from -20 dB up to +65 dB. This equals a
sensitivity of +32 dBu down to –53 dBu, referenced to full scale of the AD-converter. Changing
the gain is usually done click-free, as the gain change is performed during the zero crossing of
the audio signal, if possible.
The soft switching, hi-current phantom power (48 Volt) provides a professional handling of con-
denser microphones. The usage of a hi-end integrated circuit (PGA 2500) plus a fully symmetri-
cal signal path guarantees outstanding sound quality, stunning low THD, and maximum Signal
to Noise ratio in any gain setting.
Due to the XTC’s flexibility, its signal to noise ratio is not easy to determine. The EIN value is
constant across a very wide amplification range, typically 127 dBu at 150 Ohm input imped-
ance. Even at a gain setting of 30, which corresponds to 0 dBFS at only -18 dBu, the EIN still
reaches 122 dBu.
12.2 Line In (TRS)
TRS sockets of inputs 1-4 operate as line inputs. Compared to the XLR inputs they have slightly
higher input impedance (6.6 kOhm) and a fixed attenuation of 9 dB. This jas no influence on
noise or distortion. Even the adjustable gain range is still 65 dB. But the PAD attenuates only by
18 dB, so that the input sensitivity covers +39 dBu down to -44 dBu, referenced to full scale of
the AD-converter.
12.3 Instrument In
The main difference between a line and an instrument input is its input impedance. Channels 5-
8 offer an input impedance of 800 kOhm at the TS socket, with adjustable gain from +10 dB up
to +65 dB. This equals a sensitivity of +21 dBu down to -34 dBu, referenced to full scale of the
AD-converter.