Aphex
Thermionics
- Division of Aphex Systems Ltd.
Model 1100 MkII Mic Preamp - Owner’s Manual
With LoCaf you get as much as 20dB of improved
headroom below the low cut corner frequency
to reject input overload when compared with
other products. Use this filter to eliminate wind
or breath rumble, handling noise, or other low
frequency problems.
1.14 Power Switch
Pretty simple: it turns the power on and off.
Power indication is by means of the window
backlights. The windows will always be lighted
when the power is on unless the fuse is blown or
the electric supply is disconnected.
Notes:
1. Diode contact effects commonly occur when-
ever microphone signals are routed through ordi-
nary mechanical switch contacts. Here’s how that
happens. The well established fact is that only a
small number of points actually touch between
any two facing contacts. Eventually, all metal sur-
faces begin to oxidize including these points of
contact. When that happens, metal oxide point
contact diodes are created that rectify the audio
signal causing distortion. The extremely minute
current from a microphone signal cannot break
down these diodes and eventually the diode
effect grows worse and worse until it is plainly
audible. We chose to avoid the problem alto-
gether , albeit at a higher cost, by using sealed
bifurcated gold contact relays to do mic level
switching. Bifurcation (multiple metal contacts
for each circuit) overcomes the odds of getting
a diode in the path, while gold contact surfaces
oxidize at a rate thousands of times lower than
other materials.
2. One wouldn’t want the reference tone to be
accidentally switched on during a session. That’s
why we put in a delayed reaction. You must
intentionally hold down the button for a period
of time to get the tone.
3. dB(fs) refers to “decibels in reference to full
scale” and is the common digital audio meter ref-
erence. 0dB(fs) is the maximum peak value that
can be converted to digital.
Figure 1-3 Low Cut Characteristics
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