Features of the PRO-125
• 125W RMS Mos-Fet Amplifier
• Open & Short Circuit Protected
• Crow-Bar Speaker protection
• 4 × Microphone inputs
• Separate channel 3-band tone controls
• Echo facility with depth and delay controls
Caractéristiques du PRO-125
• Amplificateur Mos-fet 125W RMS
• Protection contre les courts-circuits
• Protection haut-parleur
• 4 entrées microphones
• Réglages de tonalité séparé à 3 bandes
• Réglage de l'écho avec contrôle de la durée
PRO-125
IMPORTANT
Installer and Users please note:
These instructions should be read carefully and left
with the user of the product for future reference.
The PRO-125 must be installed by a competent
electrician in accordance with the current IEE wiring
regulations.
The PRO-125 is fan cooled, so it must be installed where air
can flow freely into and out of the slots in the case. Also, the heat
generated must be allowed to escape, so do not install the
amplifier in a cupboard.
Install the PRO-125 away from sources of moisture; avoid
areas where drinks can be spilled onto the amplifier as this may
cause serious damage.
Connect the PRO-125 to the mains supply with the lead
provided. The wires are colour-coded as follows:
• Brown = Live (phase)
• Blue = Neutral
• Green/Yellow = Earth
• The PRO-125 must be earthed for safe and reliable
operation.
•
NEVER
disconnect the earth, even in an attempt to prevent
‘hum’. If the earth were disconnected, it could result in equipment
connected to the input (even indirectly through a mixer), such as
microphones, becoming live in the event of a fault (such as a liquid
spillage into the amplifier).The supply must be fitted with an
isolating switch, or plug and socket, and protected by fuse or
circuit breaker rated at between 6A and 16A. If the PRO-125
circuit is connected via an MCB then it is recommended that a
time-delay MCB is used (Type 3 or Type C to BS3871). This will
reduce the possibility of "nuisance tripping" due to the large inrush
current of power supply.
User Guide PRO-125
© N.J.D. Electronics 2007 -Page 2-
Inputs
Connect the microphone to one of the four sockets on the
front panel using the XLR to XLR lead provided.
If using additional microphones, or line level inputs, connect to
the sockets on the front panel, using single core screened cable
for unbalanced microphones, screened twisted pair for balanced
line microphones and twin individually screened for stereo line
inputs. Connections are as follows:
Unbalanced microphone:
Use a mono jack
plug. Connect signal to tip and screen/earth to
sleeve.
Balanced microphone:
Use a 3-pin XLR
connector or a stereo jack plug. For an XLR
connector, connect
signal+
(also called "phase"
or "hot") to pin2,
signal−
(also called "non-phase"
or "cold") to pin 3 and
earth/screen
to pin 1; for
a stereo jack connect
signal+
to the tip contact.
Connect
signal−
to ring, conect
earth/screen
to
sleeve.
Line inputs:
Use a mono jack plug. Connect
signal to tip and earth/screen to sleeve. This is
the signal level from a mixer, a CD or tape player,
or the audio output from a video player or
satellite TV receiver. This signal level is generally
referred to as 0dBm or 775mV.
Note: The output from a radio microphone
receiver is often at line level.
Note: It is much less likely that hum will be a problem, if
balanced-line inputs are used.
Do not connect the speaker output of another amplifier
to any of the inputs, this will result in damage to the PRO-
125.
The PRO-125 mixer is earthed, so the screen of input cables
should not be connected to earth at the signal source in order to
avoid hum loops. If the signal source has a connection to mains
earth then this MUST NOT be removed. If a hum loop occurs then
User Guide PRO-125
© N.J.D. Electronics 2007 -Page 3-
signal
Ground
"cold"
"hot" Ground
signal
Ground
cold
Hot
Screen
1
2
3
the connection between the cable screen and mains earth should
be removed. It may be necessary to consult a dealer if this
involves modification to either unit.
Loudpeakers
Connect the loudspeakers to the Speakon connectors on the
rear panel using the leads provided. The PRO-125 can operate
two loudspeakers of the type in the kit. Connecting additional
loudspeakers may damage the amplifier.
Operation
ALWAYS
connect the speakers and turn the Level controls to
zero before switching on; do not touch the speaker outputs whilst
the amplifier is running as this could result in electric shock.
If using a line level input, set the gain control to its furthest
anticlockwise position (labelled "1")
If using a microphone input, set the gain control so that the
red "peak" light illuminates on only the loudest peaks.
Set the bass, mid-range and treble controls to their centre
positions (labelled "0")
Set the echo controls to their furthest anticlockwise positions.
Set the master level control to its central position (labelled
"3").
Rotate the level control clockwise until the desired output level
is achieved.
Adjust the bass, middle and treble controls for the correct
frequency balance, rotate clockwise to increase the amount of
bass, mid-range or treble, anticlockwise to decrease.
If echo is required, rotate the master level control to "3" and
each input control for the desired amount of echo. The echo
depth and delay controls can be used to adjust the echo effect.
"Delay" sets the amount of time before the first echoed signal
appears, "Depth" sets the number of times the signal echoes
before decaying away.
The overall output level can be adjusted using the master level
© N.J.D. Electronics 2007 -Page 4-
User Guide PRO-125
control.
If the amplifier is being asked to produce more power than it
can supply it will ‘clip’ the signal, and if this happens the output will
sound badly distorted. In this state, the amplifier can produce an
output in excess of 175 Watts per channel at levels of distortion
up to 30%, which could cause damage to speakers. This distorted
signal has a large amount of extra treble which can damage high
frequency units.
If the "peak" indicators are on excessively, or the signal is
distorted, there is only one solution:
TURN THE VOLUME
DOWN.
(Otherwise damage will occur to the amplifier,
loudspeakers or both)
The echo can be disabled using a footswitch connected to the
¼" jack socket on the rear panel. When the footswitch is on, the
echo will be disabled and the yellow LED on the front panel will be
illuminated.
Short circuit protection.
The PRO-125 is protected against short-circuits on the
outputs. If this happens, it will limit its output current to a safe
level until the short circuit is removed. A short circuit should be
removed as soon as it is discovered, as the amplifier is not
intended to be run indefinitely into a short circuit. Short circuit
protection does not protect the amplifier from having too many
speakers connected to the output.
If speaker leads are too long or too thin, their resistance may
prevent the short circuit protection operating in the case of a
short circuit at the loudspeaker end of the lead - in this case the
impedance of the cable may be indistinguishable to the amplifier
from a low impedance speaker.
© N.J.D. Electronics 2007 -Page 5-
User Guide PRO-125
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