Q-Tech
PUBLIC ADDRESS AMPLIFIER
QTA 1240P
OUTPUT LEVEL
+8Pwr-10 -8 -3 0 +3
POWER
Commercial Series
QTA1120P/1240P
Power Amplifiers
User Manual
WARNING
THIS APPLIANCE MUST BE EARTHED
IMPORTANT
The wires in the mains lead are coloured In
accordance with the following code:
Green and Yellow:
Blue: Neutral (N)
Brown: Live (L)
As the colours of the wires in the mains lead
of this apparatus may not correspond with the
coloured markings identifying the terminals in
your plug proceed as follows:
The wire which is coloured green and yellow
must be connected to the terminal which is
marked with the letter N or coloured black.
The wire which is marked with the letter L or
coloured red.
If a 13 Amp (B.S.1363) plug or any other type
of plug is used, a 5 Amp fuse must be fitted
either in the plug or at the distribution board.
Earth (E)
General Installation
DO NOT run unbalanced high impedance
microphone cables near mains, data,
telephone or 70/100V line cables.
DO NOT run 70/100V line cable near data,
telephone or other low voltage cables.
DO NOT exceed 90% of the amplifiers output
power when using 70/100V line (speech only).
DO NOT exceed 70% of the amplifiers output
power when using 70/100V line (high level
background music).
DO NOT use voice paging horn loudspeakers
for background music unless the loudspeaker
has been specifically designed for this
purpose.
AVOID jointing the microphone cable,
when this is unavoidable make sure a good
screened connector is used.
ALWAYS use balanced low impedance
microphone cable terminating to balanced
inputs on long cable runs.
ALWAYS use a mains grade double insulated
cable for the loudspeaker cable runs when
run in conduit together with power cables.
ENSURE that all loudspeakers are in-phase.
ENSURE that there are no short circuits on
the loudspeaker line before connecting to the
amplifier. It is also advisable to check the final
impedance to the amplifier with a dedicated
impedance meter to determine power draw is
within the amplifiers limits.
QTA-1120P/1240P
User Manual
Contents
Introduction ..................................2
Description
Front Panel Layout
Rear Panel Layout
Power Source
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
.............................3
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Installation Practice
Operation
Trouble Shooting
Specifications
Technical Notes
....................................5
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
...............................7
. . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1
Q-Tech Commercial Series
QTA-1120P/1240P
User Manual
QTA-1120P/1240P
User Manual
User Manual Q-Tech Commercial Series
QTA-1120P/1240P
2
Introduction
Congratulations on your purchase of a new
Q-Tech Commercial series amplifier. Quest
Engineering Q-Tech Series amplifiers are
engineered and built to a standard that will
satisfy the most demanding environments of
commercial installation audio.
For your safety and continuing reliability of
your Quest amplifier, please read all the safety
instructions and familiarize yourself with the
amplifiers functions and installation procedure
section before installing and operating the
amplifier. Quest has paid great attention
to detail in order to maintain strict quality
assurance standards of all Q-Tech Series
amplifiers.
It follows that if your audio installation is
completed with the same attention to detail,
your amplifier will deliver its best results.
Please red the section: Constant Voltage
Distributed Speaker Systems Demystified.
Unpacking: Please inspect the amplifier
carefully immediately after unpacking. If
you find any damage, notify your supplier/
dealer immediately. Only the shipper may file
a damage claim with the carrier for damage
incurred during shipping.
Description
QTA series of Power Amplifiers cover
models from 120W RMS to 480W RMS. This
manual is to for 120W QTA-1120P and 240W
QTA-1240P.
• Easy to use booster Amplifier
• 7 step LED Ramp for signal presence
• XLR and phone jack input
• Rear mounted Input gain control
• Parallel/Mono selection for the use
of additional power amplifiers
• Rear mounted switch for selection
of 100mV or 1v sensitivity
• 8 ohm, 70V and 100V speaker output
• XLR and phone jack output
• Overload, over temperature, and
speaker short protection.
• 115v-240v AC and 24v DC power in
• 2U height
• 19” rack or table mounted
Rack ears supplied.
• 3 year replacement warranty.
QTA-1120P/1240P
User Manual
User Manual
Q-Tech Commercial Series
QTA-1120P/1240P
3
Front Panel Layout
PUBLIC ADDRESS AMPLIFIER
QTA 1120P
OUTPUT LEVEL
+8Pwr -10 -8 - 3 0 +3
POWER
1
2
3
VOLTAGE SELECT
AC 115/240V 50/60Hz
FUSE 250V T5A
24V DC
COM8Ω70V 100V
CAUTION
RISK OF ELECT RIC SHOCK
DO NOT OPEN
CAUTION:
TO PREVENT ELECTRIC SHOCK
DO NOT REMOVE COVER (OR BACK)
NO USER SERVICEABLE PARTS
TO QUALIFIED SERVICE PERSONNEL
BALANCED OUTPUT
@ 10K ohms
SENSITIVITY
Parallel Mono 100mV 1V
GAIN
BALANCED INPUT
@ 10K ohms
230V
1
2 3 4 5 6
7 8 9
10 11 12 13
1 Power On Indicator LED
2 Level Indicator LED
3 Power Switch
Rear Panel Layout
1 AC Voltage (115V/230V) Selection Switch 8 XLR Output
2 AC Fuse 9 Parallel/Mono Switch
3 AC Power Input Socket 10 Sensitivity (100mV /1V) selection Switch
4 Earth Connection Screw 11 Gain Control
5 DC Power Supply Terminal 12 MIC 4/Aux 1 Selector Switch
6 Speaker Output Terminal 13 Phone Jack Input
7 Phone Jack Output
QTA-1120P/1240P
User Manual
User Manual Q-Tech Commercial Series
QTA-1120P/1240P
4
132
Plug
1
3
Socket
2
Viewed from Solder
Side of Plug/Soceket
Power Source
AC Power Source
The supply transformer has been designed for
AC 240V /115V (±10%) 50 /60 Hz.
DC Power Source
Battery Connection (24Vdc)
When using external batteries, please ensure
the amplifier is grounded via the screw
terminal. (Electrical stability of the system
will be improved by providing a good earth
ground.) When connecting batteries, please
ensure correct polarity.
Main Connections
Each input has XLR and Phone jack input.
Use the one you want
Pin Assignments:
Speaker Output Connection
The speaker output screw terminal is on the
rear panel. It can connect low impedance 8
ohm, or high-level 70V or 100V speaker. Use
only one of these output connections for
corresponding speaker.
As a guide for the correct gauge of wire, we
recommend the following:
Up to 50m AWG25-26 (0.15mm2)
100V
70V
Low
Impedance
(4Ω)
50m - 200m AWG20 (0.5mm2)
Over 200m AWG18 (0.75mm2)
Up to 50m AWG24 (0.20mm2)
50m - 200m AWG17 (1.0mm2)
Over 200m AWG16 (1.5mm2)
Up to 10m AWG18 (0.75mm2)
10m - 30m AWG13 (2.50mm2)
Sensitivity Selection Switch
Place the switch on 100mV or 1V position for
corresponding sensitivity of signal source
from other devices.
Balanced Audio (3 pole XLR):
Pin 1: Ground / Screen
Pin 2: In phase / +ve / Hot
Pin 3: Out of phase / -ve / Cold
Unbalanced Audio (3 pole XLR):
Pin 1: Ground / Screen
Pin 2: Signal
Pin 3: Ground / Screen (connect to pin 1)
For best performance when using long lines
between microphones/mixer and or amplifier
use balanced lines. These have the effect of
cancelling out any noise or hum that may be
induced into the cables. the amplifier to be
processed externally and then returned to the
power amplifier section of the amplifier. The
connecting link must be plugged in for normal
operation as a mixer/amplifier. “PRE OUT” is
after the tone controls and the master volume
Booster Output Connection
Use XRL (female) or phone jack to connect
booster output to another amplifier.
Parallel / Mono Switch
The amplifier includes both male and female 3
pin XLR connectors, labeled input and output.
While the female is normally used as the input
to the amplifier, both XLR’s are connected
in parallel so either will work. When signal
is connected to one XLR, the other XLR
becomes a line level output allowing the
input signal to be distributed (split) to other
amplifiers. In some projects, the same input
may be looped through to multiple amplifiers
using this method. Up to 6 amplifiers can be
looped together without any noticeable loss
in level. A distribution amplifier should be
used when more than 6 amplifiers need to be
looped.
QTA-1120P/1240P
User Manual
User Manual
Q-Tech Commercial Series
QTA-1120P/1240P
5
Please ensure the switch is on the Mono
position when you are not connecting to
another amplifier.
When it is connected to another amplifier, put
the switch on Parallel position to maintain
maximum gain.
Installation Practice
Step 1. Take a piece of figure-8 cable,
connect the stripe/coloured wire to the 100V
terminal and the uncoloured wire to the COM
on the amplifier terminal strip.
Step 2. Connect the other end of the wire
(uncoloured) to the Com/EARTH connection
on the ceiling speaker transformer and the
other + (strip) wire to the required voltage
taping.
Step 3. Take a second piece of figure-8 cable
and connect the plain wire to the parallel
COM connection and the other + (stripe) wire
to the parallel output from the transformer
terminal block and connect it in the same way
to the next ceiling speaker.
Step 4. Continue this process until all the
ceiling speakers are connected in a parallel
connection with all the COM connections
and all the wattage connections following a
parallel connection.
The only way to test this is with an
impedance meter on a single speaker. A
15% discrepancy can mean that a 100
watt system will only be able to power 7
or 8 x10 watt speakers safely. Be aware of
this booby trap. Always plan to have 20%
more power than you think you will need.
2. Incorrect output connection: If you accidentally connect your terminal strip
on the amplifier to the 8 ohm output
instead of the 100/70V line, you will have
distortion and risk damaging the amplifier..
3. Short circuits and no circuits: Check that
your wiring has not been accidentally cut,
miss-connected or generally damaged
in the course of installation. This can be
common with building sites with multiple
trades people installing equipment into the
same ceiling cavities as the audio system.
Operation
After all connections are completed, turn on
the power. If necessary, turn the gain control
on the rear panel to what you desire. We
suggest turning the gain level to maximum
always.
Common problems with ceiling
speaker installations
System is distorting. Check for the following
causes:
1. Too many speakers set to too high
a power tapping for the power of
the amplifier Solution: Calculate
the total power draw and re
connect the speakers to a lower the
wattage tapping. (See below)
Some cheap ceiling speakers have
incorrect taping labels. A 10 watt speaker
may really be drawing 15 or 20 watts.
QTA-1120P/1240P
User Manual
User Manual Q-Tech Commercial Series
QTA-1120P/1240P
6
Trouble Shooting
If the amplifier fails to work as required,
please check the following:
Specifications
Type Booster Amplifier
Model QTA-1120P QTA-1240P
No Power, No Lights
Make sure amplifier power switch is on. •
Make sure mains power switch is on at •
the wall.
Check the mains and DC fuse. •
Replace with only the correct type and •
rating.
Distorted Output
Check that the speaker type is correct for •
the output that you are using (ie. 4-16Ω, or
100V line).
Check for any short circuits on the speaker •
line.
Very Low Output Volume
Make sure that the speaker line is not •
shorted.
Check speaker types and ratings.•
Check that the parallel/mono switch is •
correctly set.
Continually Blows Fuses
Make sure that the speaker line is not •
shorted.
Check speaker types, ratings and if on •
correct output.
Output Power (RMS): 120W 240W
Mains
Voltage
Power
Supply
Battery
Voltage
Total Harmonic Distortion
Sensitivity 1V, 100mV @ 10K ohm
Outputs
Signal to Noise Ratio4 86 dB
Indicator Power On, Level
AC Power Consumption 320W 640W
DC Power Consumption 8A 15A
Dimensions (mm) 88(H) x 425(W) x 305(D)
Weight 8.2 Kgs 10.6Kgs
Mounting options Desktop or 19” rack
AC 115V or 230V
50/60Hz
DC 24V
<= 1% @ 1KHz,
rated power
8
Ω, 70V, 100V
Amplifier Keeps on Cutting In & Out
Make sure that there is adequate •
ventilation around the amplifier.
Check the vent slots on the front are not •
covered or blocked and the fan on the rear
is functioning correctly.
Check also speaker types, ratings and for •
any short circuits on the speaker line.
QTA-1120P/1240P
User Manual
User Manual
Q-Tech Commercial Series
QTA-1120P/1240P
7
100V Line Public Address System
Remote Speaker
with 100V Line
Transformers
Technical Notes
Constant Voltage Distributed
Speaker Systems Demystified
In a typical paging and background music
speaker installation, quantity loudspeakers are
placed across a single amplifier in a parallel
wiring configuration (see Fig 1.).
Each ceiling speaker will contain a small
transformer and you will notice that the
connection block near the transformer will
have a common terminal (C or earth), and a
number of wattage terminals.
Connect the wattage setting terminal for the
desired acoustic output (volume) level you
need from each individual speaker.
This will be a 100V setting in Europe and
most of Asia and 70V in the USA. (See the
explanation below)
Fig. 1
Often some speakers need to be set at
different volume output levels, and the
calculations involved in determining the actual
load impedance at the amplifier’s output
can be quite involved but there is a simple
technique for not overloading the amplifier
As for the amplifiers, there are two common
standards, 100 Volt line in Europe and Asia
and 70 Volt line on the American continent.
For the purpose of simple calculations, we will
use the European standard for this exercise.
On the rear of a 70/100V amplifier you will find
an output terminal strip. This terminal strip
will contain a number of + voltage outputs
(70V 100V) and a terminal at one end for the
negative return wire (COM).
A low impedance terminal will be for
8-ohm speaker installations and is under
no circumstances to be connected to a
transformer type speaker system.
How to calculate the correct
number of speakers and what
wattage connection for a given
amplifier power.
If you connect too many speakers to an
amplifier you will have distortion, overheating
of the amplifier and generally poor
performance. The problem is not really “too
many speakers”, it is more a problem of “too
much wattage draw exceeding the output
capability of an amplifier. A similar problem
would be trying to draw 2,000 watts from
a 1,000 watt generator. Sooner or later….
Expect a system failure.
Let us take a 100 watt amplifier. If you have
20 speakers and you set them at the 5 watt
taping, you will have a total 100 watt draw
which is the maximum output of the amplifier.
This is correct in theory but in practice you
will be safer connecting 18 speakers, not 20.
The reason is that most ceiling speakers draw
more than their claimed wattage.
The alternative would be to connect the
speakers to the 4 watt transformer terminal
giving you a theoretical total draw of 80 watts
and thus, plenty of “headroom”. One watt
difference is not very noticeable as far as
output sound pressure level in concerned.
A system that does not distort will give
much clearer voice reproduction than a
louder system that is distorting or loosing
the sibilant frequencies.
There is a formula for testing the potential
power of the system by measuring the
impedance of each speaker and then adding
all the figures to a total impedance, which is
then compared to the amplifier’s expected
impedance/power figures. The quick way is
to just add up all the wattages and then give
yourself 10-20% headroom by reducing the
number of speakers per amplifier or lowering
the wattages slightly.
QTA-1120P/1240P
User Manual
For the benefit of those who want to calculate
the power of the system with a formula. See
below:
Determining power by calculating
total impedance
The alternative to counting the speaker taping
watts is to calculate the total impedance of
the line, which will also indicate the wattage
necessary to drive the system correctly.
The computational formula is voltage squared
divided by impedance:
Power = Voltage2 / Impedance.
High impedance of speakers and output calculation table for 100Volt systems
8
Output Impedance Output Impedance Output Impedance
0.1W 100KΩ 10W 1KΩ 40W 250Ω
0.5W 20KΩ 15W 667Ω 50W 200Ω
1W 10KΩ 20W 500Ω 75W 133Ω
2W 5KΩ 25W 400Ω 100W 100Ω
3W 3.33KΩ 30W 333Ω 150W 66.7Ω
5W 2KΩ 35W 286Ω 200W 50Ω
(100V plan) P = E x E / Z = 100x100 / Z = 10,000 / Z
P: Power(W), Z : Impedance (Ω), E : 100V(Designed voltage of a general-use amplifier)
When the speaker line reaches its top voltage
of 70 Volts, the formula is:
Power = 5000 / Impedance (because 70
squared equals 5000).
To measure impedance a dedicated meter is
required. These use a 1k frequency to send an
alternating current through the transformer(s).
The resulting figure indicated by the meter’s
dial can be cross referenced with the meter’s
impedance chart to see what value should be
expected and the power that will be required.
User Manual Q-Tech Commercial Series
QTA-1120P/1240P
www.questaudio.net
Quest Engineering Pty Ltd
86 Derby St. Pascoe Vale VIC 3055
Ph 613 9354 9133 | Fax 613 9354 9233
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