ZAPCO ST-X III Series Class A Amplifiers Owner’s Manual
- June 16, 2024
- ZAPCO
Table of Contents
ST-X III SERIES
Owner’s Manual
Before operating the unit, please read this manual throughly and retain it for future reference.
General Instructions
The installation of the product must be done by professional technicians. Always contact a ZAPCO Authorized Dealer.
Before you start your installation
ZAPCO highly recommends that a fuse or circuit breaker be placed within 18″ of
the battery. The protection device should be placed where it can be accessed
easily and all wiring should be routed safely and correctly according to the
following guidelines:
- Do not run wiring close to hot or spinning objects
- Always use wire grommets when routing wire through the firewall or any other metal panels
- Make sure that the potential for pinched wiring is avoided by routing all wires away from moving objects, including brake, gas and clutch pedals, etc.
Planning your power connections
- The +12V B is the main power input. This must be connected the vehicle battery’s positive (+) terminal
- The GND is the main ground or negative connection. This must be securely attached to bare metal at the vehicle frame
- The terminal between the main power and ground is the +12 turn-on input (REM) and can be connected to the head unit turn-on output wire. If none is available it can be connected to an accessory (ACC) terminal
Mounting your amplifier
Mounting your Zapco amplifier is easy. Just keep in mind a few guidelines:
- The amplifier requires adequate ventilation. Creating power creates heat, and cooling requires air
- Keep the amplifier out of the engine compartment or other locations that may cause excessive heat or moisture
- Do not mount the amplifier to a subwoofer box or other place that may have excessive vibration
Setting Gains
Gain pots are not volume controls and should be used only if absolutely
necessary. Turning up gain controls causes increased noise, makes distortion
more likely and reduces the dynamic range of your system.
Continuous exposure to excessive sound pressure levels may cause hearing
damage. ZAPCO strongly advises that you use common sense when setting volume
levels. Everything written in this manual is for the proper use of the
products. Some features or specifications could be modified during production to
improve the product performance. The technical specifications and
functionalities stated here are current as of the time of publication.
Class, Power, Heat
When buying or selling a car audio amplifier you need to consider more than
just the power output. The basic design platform of the amplifier (Amplifier
Class) will influence how the amp will work in any given situation, for any
given user. All amplifiers make small signals bigger and in doing so create
heat. Class A produces the most heat and Class D produces the least. If the
amplifiers are not properly cooled, they will get too hot and problems will
arise. Either the amp will be damaged, or protection circuits will engage to
shut the amp off until it has cooled down enough to safely work again.
Conversely, better cooling will allow an amp to make more power, longer,
without damage or thermal shut down.
Class A/B amplifiers are used when audio fidelity is the primary goal and
efficiency is of secondary concern. Class A/B amps have superior sound quality
but with lower efficiency, they generate more heat and need more cooling.
Sound Quality and Dynamic Range: Our amps are designed solely for the
best possible sound quality, so we do not current limit the amps. This gives
Zapco amps more Dynamic Range that other amplifiers. Dynamic range, the
ability to go from very quiet to extremely loud without distortion, is a major
reason Zapco amps sound better than others. So, with Z-AP amplifiers,
consumers have more dynamics plus the sound quality of class A/B amplifiers.
If the Zapco Class A/B are used at the maximum dynamic range without
distortion, they don’t need so much cooling and never will shut down. But if
they are driven into its distortion the amplifier will more easily reach
maximum temperature and will shut down.
Critical: Volume does not make a system sound loud. Distortion sounds
loud. With clean sound it is easy to drive an amp to full power and not know
it because it still sounds clean. But when the power requested of the
amplifier takes it into distortion the amplifier will overhead and shut down…
and possibly be damaged. Zapco offers both Class A/B and Class D amps. Class
A/B for the user who puts sound quality and dynamics first, and Class D for
the user who wants big power in a small box.
Installation and Cooling: All the amplifiers need cooling, whether they
are class A/B or class D. For cooling, the heatsink of the amplifier needs to
exchange heat with air around it. So, the amplifier cannot be covered or put
in a space where there is not enough air or ventilation. As noted above, in
many cases a good installation needs to use external fans to make the
ventilation more efficient. Some amplifiers have fans inside, but the problem
is not solved if the fans cannot have an exchange of air with the
environment.
All Wire is not created equal
Do not use CCA wire with Zapco amplifiers
It is easy to think of wire as just wire but the fact is there are major
differences between the types of wires being offered today. The price of
copper has gone up quite a bit lately, but you will notice that you can still
buy heavy primary wire at very reasonable prices. How can this be? Simple…
That lower price wire is not all copper, it is CCA wire. CCA stands for Copper
Clad, Aluminum. That means it is aluminum wire with a thin coating of copper
around the outside of the wire. Does it look like copper wire? Absolutely. But
does it conduct electrical current like copper?
Absolutely Not.
Two things can and likely will happen:
- Because CCA wire can not conduct DC electrical current like copper wire can, your amp will not get the current it needs to produce its rated power. That means you get less power and more distortion. It also taxes the amplifier that is trying to make its power, shortening the life of the amp
CCA wire corrodes quickly and causes terminals that used to be tight to become loose. This causes arcing when electrons to fly around all the open space lookin for more copper. This causes heat that damages connections and can even eventually melt the terminal blocks on your amplifier
In short: While CCA wire is excellent for high frequency AC current (like
tweeter voice coils), it is absolutely bad for high current 12V DC like power
and ground for a car audio amplifier. We have seen CCA wire become a major
cause of amplifier failures as buyers are offered CCA as a low cost
alternative to pure copper wire. So always look at the description of the
contents of wire that you purchase. When someone offers to save you some money
with CCA wire just say “No, thank you”.
Protect your investment with real copper wire.
Wire Size
The second most common cause of under performing amplifiers is insufficient
power current or a poor power connection. The most common cause of under
performing amplifiers is insufficient ground current or a bad ground
connection. 12-volt current: Battery power works only if it travels in a
complete circuit from the battery positive terminal to the battery negative
terminal. Main power input, of course, is attached to the battery positive
terminal. Ground current is returned to the battery through the chassis to the
point where the battery is grounded. The current available for your amplifier
to use to produce power will be restricted by the smallest gauge of wire in
the circuit and by the weakest physical connection in the circuit.
It’s often surprising how many people will obsess about signal wire but
routinely provide the amplifier with only a fraction of the current it needs
to do its job. The most common wire gauge used in car audio is 10-gauge, and
the most common location for amplifiers is in the trunk.
Let’s look at a fairly small system. If you use a 50 watt/ch amp (25
amps) for the highs and a 100 watt/ch amp (40 amps) for the woofers, you need
at least a 4-gauge and maybe a 2-Guage wire to provide 65 amps at the trunk.
Use the Wire Sizing Chart. Add up the fuse values on the amplifier(s) then
choose the proper size wire based on the distance from the car battery to the
amplifier location. Always use the same gauge wire for the main ground as you
do for the main power. Always make your ground as short as possible and secure
it to a clean solid surface, preferably the vehicle frame.
ST-X SQ III Input/Controls
The ST-X SQ III amplifiers have similar functions, but different layout puts
the controls in different positions. Showen here is the ST-4X SQ III 4-channel
model.
1• Power and Protection LED
2• HP Rear frequency control
3• Auto-on switch
4• LP Rear frequency control
5• Speaker level input
6• Rear Gain control
7• Rear L+R RCA input connectors
8• Pass-through RCA outputs so you can “daisychain” multiple
amps while only running one front-to-back RCA| 9• Front L+R RCA input
connectors
10• Speaker level input
11• Rear Crossover Type
12• Bass Boost control
13• Front Gain control
14• Front Crossover Type
15• HP Front frequency control
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ST-X Mono III Input/Controls
The ST-X Mono III amplifiers have similar functions and share the same input
panel. Showen here is the ST-1000XM III model.
1• Power and Protection LED
2• Remote control port
3• RCA Inputs
4• Bridge In and Out to “strap” mono amps so they can work together to drive a
single speaker
5• Gain control| 6• LP frequency control
7• Subsonic filter
8• Bass boost frequency control sets the center point of the boost
9• Bass Boost level
10• Phase control
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Strapping the ST-X Mono III
The ST-X Mono III amplifiers are true mono units and you can double their
power by “strapping” two units of the same model together to drive a single
voice coil. Always keep in mind that each amp must see a minimum load of 2 Ohm
(1V per amp).
- Decide which amplifier will be the “master” and which will be the “slave” amplifier
- Connect the head unit bass output or full range output RCA to the R and L RCA inputs of the first (master) amplifier
- Connect the “Bridge Out” of the master amp amplifier to the “Bridge In” of the slave amplifier with a single RCA cable. Do not connect anything to the regular R and L Inputs of the slave amplifier
- Connect the Bass Remote to the Remote In of the master amplifier
The master amplifier is now the control amplifier. All the adjustments you
make to the bass remote and to the master amplifier’s other controls will be
transferred to the slave amplifier, and the slave amplifier will be driving
the negative side of the signal and have no control functions of its own.
Strapping the Ouputs of the ST-X Mono III
- Connect the master amplifier’s speaker output + terminal to the + (positive) terminal of the woofer
- Connect the slave amplifier’s speaker output + terminal to the – (negative) terminal of the woofer
- Connect the two amplifier’s speaker output – (negative) terminals together
You are creating a much more powerful amplifier in this way and doubling the
output.
Make sure your speaker wire can transfer the power, we recommend a minimum of
12 gauge speaker lead, and for best performances you should use 10 or 8 gauge.
Speaker Wiring of the ST-X SQ III Amplifiers
The Very Basics
No speaker wires can be shorted to, or touching either ground or each other.
This will put the amp into protect and may damage the amplifier. When bridging
the left and right channels of any ST-X SQ III amplifier, you use the left
channel (Ch1) positive and the right channel (Ch2) negative, as indicated on
the chassis by the speaker terminals
2-Ch. Amplifer – Stereo Mode
A simple 2 channels hookup for a right and left stereo pair.
2-Ch. Amplifier – Single Channel Mode
This method is used most often to drive a mono woofer but can also be used to
run separate amplifiers for the right and left channel. The ST-X SQ III
amplifiers are stable to 2Ω stereo and 4Ω Mono so the single bridged speaker
must be of 4Ω minimum impedance
2-Ch. Amplifier
– 3-Ch. Mode
It is possible to run the 2Ch amps in “3-Channel” mode by running a pair of
speakers for the mids and highs on left and right channels, and at the same
time run a woofer bridged between the L+ and R- terminals as shown. However,
since each channel will see 1/2 the impedance of the woofer you must use a
woofer of no less than 4Ω. The amplifier sees impedance by frequency, so you
can have two 2Ω loads but you must use a passive crossover on each speaker in
the three channel mode. With the crossovers in the line, the amplifier will
always see a minimum load of 2Ω on each channel at all frequencies.
- Main speakers can be 2Ω~4Ω. Woofer can be 4Ω~8Ω but cannot be less than 4Ω (as in any bridged situation)
- The active amp crossovers are not used in this system
A 3-Way hookup requires a coil
on the woofer and capacitors on the highs to act as a crossover and maintain
correct impedance. Consult the speaker manufacturer for correct cap and coil
values.
4-Ch. Amplifier – Stereo Mod e
A simple 4 channels hookup for a right and left stereo pair. 
4-Ch. Amplifier – High Power 2-Ch. Mode
Similar to bridging a stereo amp to a mono woofer, you can use the 4-Ch amp in
a dual mono mode to create (in this case) a stereo amp with 190 watts RMS/ch.
As with any bridged setup the speakers must be a minimum of 4Ω impedance. If
you are using the active crossovers you should be sure that they are set to
the same frequency.
4-Ch. Amplifier – 5-Ch. Mode
A 3-way system with front stage, rear stage and subwoofer in mixed mono
configuration.
The 5-speakers system requires a passive crossover between the front highs and
the mono woofer, with capacitors on the front highs positives and a coil on
the woofer positive. All amplifiers chan- nels are full range. 
6-Ch. Amplifier – 5-Ch. Mode
The most popular system for a six channel amplifier is right/left front,
right/left rear, and a mono sub. Note the hookup especially of the sub as Ch5+
and Ch6-. This gives the sub the combined power of the 2 channels. Note that
since the sub is a bridged hookup the sub must be 4Ω minimum.
Technical Specifications
Model| Type| Power (W ) Channel/RMS| THD| S/N|
Frequency Response
---|---|---|---|---|---
ST-2XP SQ III| 2-Ch, Class AB| 2 x 150 (4Ω)
2 x 250 (2Ω)
500 (Br, 4Ω)| < 0.1%| 95dB| 15Hz – 30KHz
ST-4X SQ III| 4-Ch, Class AB| 4 x 70 (4Ω)
4 x 95 (2Ω)
2 x 190 (Br, 4Ω)| < 0.1%| 95dB| 15Hz – 30KHz
ST-4XP SQ III| 4-Ch, Class AB| 4 x 150 (4Ω)
4 x 250 (2Ω)
2 x 500 (Br, 4Ω)| < 0.1%| 95dB| 15Hz – 30KHz
ST-6X SQ III| 6-Ch, Class AB| 6 x 100 (4Ω)
6 x 150 (2Ω)
3 x 300 (Br, 4Ω)| < 0.1%| 95dB| 15Hz – 30KHz
ST-500XM III| Mono, Class D| 200 (4Ω)
300 (2Ω)
400 (1Ω)| < 0.1%| 100dB| 10Hz – 200Hz
ST-1000XM III| Mono, Class D| 500 (4Ω)
700 (2Ω)
1000 (1Ω)| < 0.1%| 100dB| 10Hz – 150Hz
ST-1500XM III| Mono, Class D| 800 (4Ω)
1150 (2Ω)
1600 (1Ω)| < 0.1%| 100dB| 10Hz – 150Hz
ST-2000XM III| Mono, Class D| 1000 (4Ω)
1450 (2Ω)
2000 (1Ω)| < 0.1%| 100dB| 10Hz – 150Hz
ARPA of AMERICA, 801 Davis St. Unit C, Vacaville, CA 95687 – US A
ARPA of EUROPE, Via Isonzo snc, Centro L’Orologio – 04100 Latina – ITALY
ARPA of CHINA, Room201,Unit 7, Dahongshan Industrial zone, No.143 Guanlong
Road, Guancheng Street, Dongguan City, Guangdong Province, CHINA, 523008
APEX GROUP – APEX Business Development (ABD) CO LTD
Bright Way Tower, office 04 7/Fl, 33 Mong Kok Road
Kowloon City, Hong Kong 999077
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ZAPCO ST-X III Series Class A
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