Functions in detail – Aphex 188 Eight Channel Mic Preamp User Manual
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188
4. Functions in Detail
Channel Select and Channel Status Readout
Use the encoder to select the channel. Only one channel can be selected at a time.
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displaying the input setting. While setting the gain you may want to scroll back to the Meter
Screen. The vertical 12 segment meter indicates the available peak headroom measured in dB
(4dB increments). To indicate that functions (Polarity Reverse, Low Cut 75Hz, 26dB PAD, and
Phantom +48V) have been engaged, there is a check mark. If the funciton is not selected, there
will be a dash.
8
Input Gain Control
The input gain is the actual gain of the front-end preamp section. Use Input Gain to bring the
microphone’s signal level up to the appropriate range as indicated on the channel’s Headroom
Meter. The available range of control is from +26dB to +65dB in 1dB stops (not “steps”) with
individual precision within +/- 0.08dB.
NOTE: The gain does not move in 1dB steps. It ramps in small increments (1/20dB steps)
between 1dB “stops” to eliminate all gain adjustment glitches.
This brings us to making a comment about gain steps. While there are several remote controlled
preamps on the market, the problem is that they have stepped gain control and the step size
can be as large as 10dB. Even a 3dB step, up or down, in a microphone preamp will cause an
audible click or pop when it is changed. The Aphex 1788A and the 188 use different but equally
effective circuitry to eliminate pops and clicks and zipper noise. This is especially appreciable
when you have to roll through a gain change of 6dB or more very quickly. The 1788A and the
188 just sound like a fader was moved with no jumps, pops or zips. Both preamps roll through
the full span of 26 to 65dB in 250 milliseconds. A single 1dB stop is completed in less than 15
milliseconds. In other words, the smooth gain control is also fast and responsive.
Polarity Reverse
The POLARITY REVERSE reverses the microphone preamp’s output polarity. This can be a
very useful feature in tracking down polarity differences in microphones and/or cables. It is
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Aphex Model 188