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WARNING: The headphone amps are
designed to drive any standard head-
phones to a very loud level. We're not
kidding! They can cause permanent
hearing damage. Even intermediate
levels may be painfully loud with some headphones.
BE CAREFUL! Always start with the PHONES level
turned all the way down before connecting headphones
to the PHONES jack. Keep it down until you've put on
the headphones. Then turn it up slowly. Why? Always
remember: "Engineers who fry their ears, fi nd them-
selves with short careers."
8. 48V Phantom Power Switch
Most professional condenser microphones require
phantom power, which is a low-current DC voltage
delivered to the microphone on pins 2 and 3 of the XLR
microphone connector. Push in the 48V button if your
microphone needs phantom power. An LED lights next
to the button to indicate that phantom power is active.
This is a global phantom power switch and applies
48V to the XLR input connectors on channels 1-4.
Dynamic microphones, like Shure's SM57 and SM58,
do not require phantom power. However, phantom
power will not harm most dynamic microphones should
you accidentally plug one in while the phantom power
is turned on. Be careful with older ribbon microphones.
Check the manual for your microphone to fi nd out for
sure whether or not phantom power can damage it.
9. Channel GAIN
The GAIN controls adjust the input sensitivity of the
mic and line inputs on channels 1-4. This allows the
signal from the outside world to be adjusted to optimal
internal operating levels.
If a mic-level signal is plugged into the XLR combo
jack, there is 0 dB of gain (unity gain) with the knob
turned all the way down, ramping up to 60 dB of gain
fully up.
When using the balanced line input of the combo jack
(1/4" TRS connector), there is 20 dB of attenuation
all the way down, and 40 dB of gain fully up, with a "U"
(unity gain) mark at about 10:00.
ONYX MIC PRE
30
OL
U
20
-10
-20
48V
U
-
20dB
+
40dB
-40
GAIN
1
ONYX MIC PRE
30
OL
U
40
20
40
-10
-20
60
U
60
-
20dB
+
40dB
-40
GAIN
10. Signal Level Indicators
These LEDs indicate the channel's signal level after
the GAIN control and the INSERT jack.
If you've followed the "Set the Levels" procedure on
page 6, the –20 and –10 LEDs should light frequently,
and the OL (Overload) LED should not light at all. If
the OL LED is blinking frequently, the signal is probably
distorted from overdriving the input. Either turn down
the GAIN control or turn down the signal at its source.
11. Instrument Switch
Channels 1 and 2 have an extra button for switching
between the MIC/LINE and Instrument inputs. When
the button is out (MIC/LINE), the XLR MIC input or the
1/4" LINE input is used, and the Instrument input [12]
on the front panel is disconnected. When the button is
pushed in (Instrument), the 1/4" Instrument input is
used and the XLR MIC and 1/4" LINE inputs are discon-
nected. The input stage of the Instrument inputs is
specially designed for the high-impedance pickups on
electric guitars, basses, acoustic guitar pickups, etc.
Plugging a guitar straight into a typical
line input can result in the loss of high
frequencies, causing an unnatural and
dull sound. Normally, you must use
a direct box between a guitar and a
mixer's or preamplifi er's input, which serves to convert
the impedance of the guitar from high to low. The In-
strument inputs on channels 1 and 2 make the need for
a direct box unnecessary.
HOWEVER: The Instrument inputs are unbalanced, so if
you are running a long cord between the instrument and
the Onyx 400F (say over 25 or 30 feet), it is best to use
a direct box with a balanced output to avoid picking up
noise over the length of the cord.
12. Instrument Input
This is a 1/4" TS connector that accepts an unbalanced
instrument-level input signal from a high-impedance
instrument like a guitar.
2
3
ONYX MIC PRE
ONYX MIC PRE
30
OL
OL
U
20
40
-10
-10
-20
-20
U
60
-
20dB
+
40dB
-40
-40
GAIN
4
30
U
20
40
U
60
-
20dB
+
40dB
GAIN
Owner's Manual
13
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