Q-Tech
Q-Tech Commercial Series
QTA 2120P/2240P
2-Channel Power Amplifiers
User Manual
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.
IMPORTANT
The wires in the mains lead are coloured In
accordance with the following code:
Green and Yellow: Earth (E)
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.
WARNING
THIS APPLIANCE MUST BE EARTHED
QTA 2120P/2240P
User Manual
User Manual
Q-Tech Commercial Series
QTA 2120P/2240P
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Contents
Introduction ..................................2
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Front Panel Layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Rear Panel Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Power Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Main Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Installation Practice . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Operation ....................................5
Trouble Shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Technical Notes ...............................6
QTA 2120P/2240P
User Manual
User Manual Q-Tech Commercial Series
QTA 2120P/2240P
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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 read 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
The QTA 2120P and QTA 2240P are 2 channel
power amplifiers designed for 2 zone
applications.
Each channel has XLR and phone jack input
and outputs, each with its own gain control
• 2 channels Power Amplifier
• Signal, Peak and Protection Indicators
• Individual gain control of each input
• 8 ohm, 70V and 100V speaker output
• Choice of XLR and phone jack inputs
• 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
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User Manual
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Rear Panel Layout
Front Panel Layout
1 AC Power Input Socket 7 Channel 2 Phone Jack Input
2 Earth Terminal 8 Channel 2 XLR Input
3 Channel 2 Speaker Terminal 9 Channel 1 Link Output
4 Channel 1 Speaker Terminal 10 Channel 1 Phone Jack Input
5 24v DC Power Input 11 Channel 1 XLR Input
6 Channel 2 Link Output
1 Power On/Off Switch 4 Signal Indicators
2 Power On Indicator LED 5 Peak Indicators
3 Channel Volume Controls 6 Protection Indicators
7
65 8 9
10
11
1 2 3 4
1
2 4 5 6
3
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User Manual Q-Tech Commercial Series
QTA 2120P/2240P
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Power Source
AC Power Source
The supply transformer has been designed for
use AC 240V(±10%) 50 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:
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)
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:
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.
For best performance when using long lines
between microphones/mixer and or amplifier
use balanced lines. These have the effect of
canceling out any noise or hum that may be
induced into the cables.
100V
Up to 50m AWG25-26 (0.15mm2)
50m - 200m AWG20 (0.5mm2)
Over 200m AWG18 (0.75mm2)
70V
Up to 50m AWG24 (0.20mm2)
50m - 200m AWG17 (1.0mm2)
Over 200m AWG16 (1.5mm2)
Low
Impedance
(4Ω)
Up to 10m AWG18 (0.75mm2)
10m - 30m AWG13 (2.50mm2)
1
3
2
Plug
1
3
Socket
2
Viewed from Solder
Side of Plug/Soceket
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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.
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.
Trouble Shooting
If the amplifier fails to work as required,
please check the following:
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.•
Continually Blows Fuses
Make sure that the speaker line is not •
shorted.
Check speaker types, ratings and if on •
correct output.
Amplifier Keeps on Cutting In & Out
Make sure that there is adequate •
ventilation around the amplifier.
Check the vent slots 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.
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User Manual Q-Tech Commercial Series
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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)
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).
Specifications
Type Booster Amplifier
Model QTA 2120P QTA 2240P
Output Power
(RMS):
120W x 2 240W x 2
Power
Supply
Mains
Voltage
AC 115V or 230V 50/60Hz
Battery
Voltage
DC 24V
Total Harmonic
Distortion
<= 1% @ 1KHz, rated power
Sensitivity
XLR, Phone Jack (balanced) 1v
@ 10K ohm
Outputs
8
Ω, 70V, 100V
Signal to Noise
Ratio4
86 dB
Indicator Power On, Level
AC Power
Consumption
440W 880W
DC Power
Consumption
8A 15A
Dimensions (mm) 450 (W) x 184 (D) x 132 (H)
Weight 14.3 Kgs 18.8Kgs
Mounting
options
Table top or 19” rack mountable
100V Line Public Address System
Remote Speaker
with 100V Line
Transformers
Fig. 1
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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.
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.
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 2120P/2240P
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User Manual Q-Tech Commercial Series
QTA 2120P/2240P
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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)
High impedance of speakers and output calculation table for 100Volt systems
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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