Stewart Audio AV25-2 NET+ User manual

AV25-2 User Manual Rev A Page 1
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AV25-2 User Manual
1Important safety instructions
1. Please read carefully prior to product installation or operation.
2. Read these instructions.
3. Keep these instructions.
4. Heed all warnings.
5. Follow all instructions.
6. Do not use this apparatus near water.
7. Clean only with dry cloth.
8. Do not block any ventilation openings. Install in accordance with manufacturer’s instructions.
9. Do not install near any heat sources such as radiators, heat registers, stoves, or other apparatus
(including amplifiers) that produce heat.
10. Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has
two blades with one wider than the other. A grounding type plug has two blades and a third
grounding prong. The wide blade and/or the third prong are provided for your safety. If the
provided plug does not fit into your outlet, consult an electrician for replacement of the obsolete
outlet.
11. Protect the power cord from being walked on or pinched particularly at plugs, convenience
receptacles, and the point they exit from the apparatus.
12. Only use attachments/accessories specified by the manufacturer.
13. Use only with the cart, stand, tripod, bracket, or table provided by the manufacturer, or sold with
the apparatus. When a cart is used, use caution when moving the cart/apparatus combination to
avoid injury from tip-over.
14. Unplug this apparatus during lightning storms or when unused for long periods of time.
15. Refer all servicing to qualified service personnel. Servicing is required when the apparatus has
been damaged in any way, such as power-supply cord or plug is damaged, liquid has been spilled
or objects have fallen into the apparatus, the apparatus has been exposed to rain or moisture,
does not operate properly, or has been dropped.

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2Approvals
This equipment has been tested and found to be compliant with the limits for Class A Digital device
pursuant to part 15 of the FCC rules.
This equipment has successfully passed UL Standard 2043 - Fire Test for Heat and Visible Smoke
Release for Discrete Products Installed in Air-Handling Spaces.
3Warnings
3.1 Explanation of Warning Symbols
3.1.1 Lightning Bolt
The lightning bolt within arrowhead symbol, within an equilateral triangle, is intended to alert the
user to the presence of un-insulated “dangerous voltage” within the product’s enclosure that may be
of sufficient magnitude to constitute a risk of electrical shock to person.
3.1.2 Exclamation Point
The exclamation point within an equilateral triangle is intended to alert the user to the presence of
important operating and maintenance (servicing) instruction in the literature accompanying the
appliance.
3.2 Warnings
WARNING: TO REDUCE THE RISK OF ELECTRICAL SHOCK, DO NOT EXPOSE THIS AMPLIFIER TO RAIN
OR MOISTURE. DANGEROUS HIGH VOLTAGES ARE PRESENT INSIDE THE ENCLOSURE. DO NOT OPEN
THE CABINET. REFER SERVICING TO QUALIFIED PERSONNEL ONLY.
Use only the power supply shipped with the device.
3.3 User Responsibility
3.3.1 Mains Connection Grounding
Your amplifier must be connected to a grounded outlet. Do not defeat the safety purpose of the
polarized or grounding-type plug.
3.3.2 Speaker Output Hazard
Power amplifiers are capable of producing hazardous output voltages. To avoid electrical shock, do
not touch any exposed speaker wiring while the amplifier is operating. External wiring connected to
the speaker terminals shall be installed by a qualified person. Do not connect or disconnect speaker

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wires while the mains power is on. Do not connect speaker wires together or to ground as this may
result in permanent damage to your amplifier.
3.3.3 Radio Interference
This product has been tested and complies with the EMC directive, and with FCC part 15 Class A. If
this product is not used in accordance with these operating instructions, it may cause interference
with to other equipment, such as radio and television receivers.
3.3.4 Speaker Damage
Loudspeakers may be damaged or destroyed if overpowered. Always check the loudspeaker’s
continuous and peak power ratings to prevent such an occurrence. Do not rely solely on the
amplifier’s volume control to reduce output power to a level safe for the loudspeakers.
3.3.5 Maintenance
Clean regularly with a soft cloth to remove dust and debris. Also check that there is adequate
ventilation for convection cooling.

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4Table of Contents
1 Important safety instructions .............................................................................................................................. 1
2 Approvals ............................................................................................................................................................. 2
3 Warnings .............................................................................................................................................................. 2
3.1 Explanation of Warning Symbols ..................................................................................................2
3.1.1 Lightning Bolt ........................................................................................................................2
3.1.2 Exclamation Point..................................................................................................................2
3.2 Warnings .......................................................................................................................................2
3.3 User Responsibility........................................................................................................................2
3.3.1 Mains Connection Grounding ...............................................................................................2
3.3.2 Speaker Output Hazard.........................................................................................................2
3.3.3 Radio Interference.................................................................................................................3
3.3.4 Speaker Damage....................................................................................................................3
3.3.5 Maintenance .........................................................................................................................3
4 Table of Contents................................................................................................................................................. 4
5 Welcome .............................................................................................................................................................. 5
5.1 Features.........................................................................................................................................5
5.2 Unpacking and Visual Inspection ..................................................................................................5
5.3 Installation and Setup ...................................................................................................................5
5.3.1 Pole Mounting.......................................................................................................................5
5.3.2 Universal Mount Installation.................................................................................................6
5.3.3 Cooling and Ventilation.........................................................................................................6
5.3.4 Operating Voltage .................................................................................................................6
6 Rear Panel ............................................................................................................................................................ 7
6.1 Operation ......................................................................................................................................7
6.1.1 Input Connections .................................................................................................................7
6.1.2 Speaker Connections.............................................................................................................8
7 Specifications ..................................................................................................................................................... 10
8 Troubleshooting................................................................................................................................................. 10
9 Warranty Information........................................................................................................................................ 11
9.1 Warranty Summary.....................................................................................................................11
9.2 Eligibility Requirements ..............................................................................................................11
9.3 Non-warranty Repairs.................................................................................................................11
10 Return Procedure............................................................................................................................................... 12
10.1 Shipment Instructions.................................................................................................................12
10.2 Packaging Instructions ................................................................................................................12

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5Welcome
Congratulations on the purchase of your new Stewart Audio AV25-2 audio amplifier. This amplifier
has been designed and built to provide you with years of high-quality audio performance and trouble-
free operation. If after reading this operation manual you have questions concerning amplifier
installation and operation, please contact your Authorized Stewart dealer, or you may contact us
directly using the contact information provided on the back of this guide.
5.1 Features
The AV25-2 audio amplifier offers 2 channels of clean, full-range, dynamic audio with 25W output
power per channel in a sub-compact ¼ rack enclosure. It has been optimized for 4Ω and 8Ω
loudspeakers. The Signal Detect circuitry automatically places the amplifier in sleep mode and
wakens it when a signal is present. The contact-closure terminals mute the audio output for fire
alarm applications. There are multiple mounting options to fit a variety of applications. The external
in-line power supply provides plenty of power to achieve full, rated audio output power.
This product is proudly manufactured in the USA.
5.2 Unpacking and Visual Inspection
Every Stewart Audio product is carefully tested and inspected before leaving the factory and should
arrive in perfect condition. If any damage is discovered, please notify the shipping carrier
immediately. Save the packing materials for the carrier’s inspection and for any future shipping.
5.3 Installation and Setup
5.3.1 Pole Mounting
The AV25-2 amplifier is Stewart Audio’s first line of pole-mountable amplifiers. The AV25-2 has
mounting holes on both the top as well as the side of the unit, which can be used with the AV-Pole
bracket available from Stewart Audio.
Part Number: AV-Pole

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5.3.2 Universal Mount Installation
The AV25-2 also has a universal mount bracket available
which allows the unit to be mounted against a wall or
under a table. Two screws are included in the kit, which
will affix the bracket to the top or side of the unit. Two
holes in the bracket are available for mounting the unit
where desired.
5.3.3 Cooling and Ventilation
The AV25-2 is a convection-cooled amplifier. Ensure that
there is sufficient open space around the amplifier to
allow for free air flow. Do not stack amplifiers on top of
each other or mount amplifier in a way that air flow
around the unit will be impaired. Inadequate airflow
around the amplifier may cause the amplifier to overheat
and potentially become damaged as a result
5.3.4 Operating Voltage
The AV25-2 is shipped with an in-line power supply. This is a universal power supply that operates on
AC mains from 100-240V at 50 or 60 Hz. The 48VDC output from this supply is connected to the rear
of the amplifier. Use only the power supply shipped with the amplifier.
Part Number: AV-Bracket

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6Rear Panel
1. Speaker Output Connectors –3.5mm Eurostyle connections to low impedance speakers (4/8Ω).
2. Contact Closure Mute connectors –3.5mm Eurostyle mute connector. Short terminals to mute;
open to unmute.
3. 48VDC Power Conector –Connect 48VDC output from in-line power supply shipped with unit.
There is no on/off switch; the amplifier is on whenever the power is applied. Stewart Audio
recommends connecting the power to the amplifier before the in-line power supply is plugged
into the AC receptacle.
4. Power Indicator –This blue LED illuminates when DC power is applied. Note that this will dim
when the amplifier is in sleep mode (approximately 5 minutes with no input signal on either
channel).
5. Clip Indicators –These red LEDs illuminate when an excessive input signal levels are applied.
Reduce signal level to avoid distortion.
6. Signal Present Indicator –The green LED illuminates to indicate an input signal is present on
either channel.
7. Input Connectors –Connect audio sources via these 3.5mm Eurostyle connectors.
8. Channel 1 Level Control –Turn fully clockwise for maximum output on output 1. Note that the
input sensitivity of the AV25-2 is 0.5Vrms. Do not overdrive the amplifier.
9. Channel 2 Level Control –Turn fully clockwise for maximum output on output 2.
In normal operation, the DC voltage on the speaker output connectors is approximately 24VDC.
Do not connect any speaker output to ground or to the amplifier chassis. Do not connect
speakers across speaker outputs. (Bridge mode is not supported.)
6.1 Operation
6.1.1 Input Connections
Your AV25-2 amplifier is provided with a 3-pin Phoenix connector for each input. This connector will
accept balanced or unbalanced connections, however some modifications must be made for an
unbalanced connection. See the next two sections for instructions on connecting your amplifier to its
input source.
③
①
②
④
⑤
⑥
⑦
⑧
⑨

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6.1.1.1 Balanced Connections
When using a balanced input
source and connector, you must
ensure that the hot, cold, and
ground pins of the connector are
matched up to the +, -, and
ground pins of the AV25-2’s
Phoenix connector respectively.
Diagrams have been provided for
standard XLR and TRS
connectors. Please refer to the
manual of your input source in
case it does not follow the standard pin-out
6.1.1.2 Unbalanced Connections
When using an unbalanced input
source and connector, a jumper
must be added between the
negative (-) terminals and the
ground terminals. Then the
unbalanced source can be
connected to the positive (+) and
ground terminals. Diagrams
have been provided for standard
RCA and TS connectors. Please
refer to the manual of your input
source in case it does not follow
the standard pin-out.
6.1.2 Speaker Connections
Stewart Audio recommends using high-quality, heavy-gauge speaker wire and connectors to send the
output signal of your amplifier to the speakers. Use the following table as a guideline when selecting
your wire gauge.
Distance
Wire Gauge
Up to 25 ft.
16 AWG
26-40 ft.
14 AWG
41-60 ft.
12 AWG
Speaker leads connect by means of removable terminal block connectors supplied with the unit. Strip
speaker leads 1/4” and insert into connector observing proper polarity. With a small, flat-blade

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screwdriver, tighten the screw until the leads are held securely in place. Inspect for possible shorts or
broken wires.
In normal operation, the DC voltage on the speaker output
connectors is approximately 24VDC. Do not connect any
speaker output to ground or to the amplifier chassis. Do not
connect speakers across speaker outputs. (Bridge mode is not
supported.)
NOTE: Class 2 wiring must be used on the speaker terminals to comply with UL
requirements.
CAUTION: Do not connect either speaker terminal to ground. This will cause a short circuit
which may damage the amplifier, speaker, or both. Similarly, do not connect any speaker
terminal to ground.

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7Specifications
Max. Output Power (all channels driven)
4 ΩStereo Power
35W/channel
8 ΩStereo Power
25W/channel
Performance
Frequency Response (+0, -3dB, 1W)
30 Hz –20 kHz
Power Bandwidth
30 Hz –30 kHz
Signal to Noise Ratio
>95 dB
THD+Noise
<0.1% @ full power
Signal to Noise Ratio
>100 dB
External Mute
Contact Closure
Slew Rate
30V/microsecond
Input Sensitivity
0.5V (-6 dBV)
Standard Voltage Gain
28X (26.5 dB)
Input Impedance (Balanced/Unbalanced)
20kΩ/10kΩ
Standby, Idle Current Draw; 1/8 Power Draw
5mA, 10mA, 7.2W
Characteristics

Amplifier Class
D
Input Connectors
3.5mm Euroblock
Output Connectors
3.5mm Euroblock
Power Supply
External in-line 48VDC (included)
Cooling -----------------------------------------------------------
Convection (no fan)
Controls
Level, Mute
LED Indicators
Power, Signal Present, Clip (2)
Construction
Aluminum Enclosure
Dimensions (Length, Width, Height)----------------------
3.2” X 4.35” X 1.25” (81mm X 110mm X 32mm)
Weight------------------------------------------------------------
< 0.37 lbs. ( 0.16kg))
Warranty---------------------------------------------------------
3 years
Plenum Rating
UL2043 Compliant
8Troubleshooting
Power indicator (LED) is not illuminated.
Check that the amplifier is plugged into a live outlet. Apply an input audio signal to one or
both inputs to wake the amplifier from sleep mode. After you have ensured that it is not a
power issue and that the amplifier is not in sleep mode, disconnect any speakers. If the
amplifier turns on after a few seconds delay, then the problem is in the output connection.
Check wiring and speakers for short circuits. Make certain that the speaker leads are not
grounded.
No output on one or both channels; Power indicator is lit.
Check that level controls are not turned down. Check that input and output connections are
secure. Ensure signal present LED is illuminated to denote a signal. If there is no signal
detected check signal source and that level controls are set high enough.

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Amplifier overheats and/or shuts off.
Review section5.3.3 on proper cooling procedures. Check the signal lights on the rear of the
amplifier to see if the signal is overdriving (the clip light flashes red frequently). Overdriving
the amplifier for extended periods of time can result in a thermal shutdown.
Output sound is distorted or cracking.
Check all cables for damage or loose connections and reduce the gain on the input signal at
the mixer or preamp level. Replace the cables and loudspeakers temporarily to see if this
resolves the problem. If problem still exists, contact your Authorized Dealer for service.
9Warranty Information
9.1 Warranty Summary
All Stewart Audio amplifiers and accessories, unless excluded in this summary, are covered by a 3-
year limited warranty on parts and labor from the data of purchase. In order to be eligible for
warranty repairs, the amplifiers and accessories must have been purchased through an authorized
Stewart Audio dealer and submitted by the original purchaser. This warranty is only valid in the
country in which the amplifier was purchased.
9.2 Eligibility Requirements
Stewart Audio warrants against all malfunctions which come as a result of component or
manufacturer defect. The amplifier is also covered from all failures which arise during the warranty
period (3 years from date of purchase) that are not a result of misuse. The following actions will void
your warranty:
The power cord or AC plug has been damaged through misuse.
The amplifier has been exposed to moisture or extreme temperatures.
The amplifier has been dropped, items have been dropped on the amplifier, or the enclosure
has been damaged.
The amplifier has been opened by the operator.
The amplifier was improperly packaged when sending to the factory for repair, resulting in
damage.
Any of the precautions or instructions found in this manual were not followed.
Damages resulting to the amplifier which are not covered under this warranty can be factory-repaired
at cost to the customer. Use the contact information below to initiate the repair process.
9.3 Non-warranty Repairs
An estimate for all non-warranty repairs will be provided to the customer once the unit has been

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shipped to the factory. The customer is responsible to approve this estimate within 7 days. If the
repairs are not approved within 14 days, Stewart Audio reserves the right to consider the unit
scrap and may discard it. Payment for non-warranty repairs must be submitted to Stewart Audio
before the product will be returned to the customer.
10 Return Procedure
All returns to the factory for service must be accompanied by a Return Authorization (RA) number.
One can be obtained by contacting Stewart Audio at [phone] or via e-mail at
[email protected].
NOTE: Any defective products received without an RA number will be returned to sender at
their expense.
If Stewart Audio is unable to contact the sender in 14 days, the merchandise will be considered scrap
and may be disposed of.
10.1 Shipment Instructions
If Stewart Audio requests that you ship the defective product back to their service center,
please refer to the guide below. To ensure prompt warranty service, be sure to follow all
instructions.
Return Authorization (RA) is required for product being sent to the factory for service.
See packing instructions in Section 10.2.
Ship the defective product using a method which provides for order tracking or order
confirmation. The service center is located at the following address:
Stewart Audio
14335 Cuesta Court Suite C
Sonora, CA 95370
Use a bold black marker and write the RA number on three sides of the box.
Record the RMA number for future reference. The RA number can be used to check the repair status.
10.2 Packaging Instructions
Should Stewart Audio request that you ship your product to their service center, these instructions
must be followed in order to ensure safe delivery. If they are not followed, Stewart Audio assumes no
responsibility for damaged goods and/or accessories that are sent with your unit.
1. Please write the RA number on three sides of the box. Include the Stewart Audio RA number
inside the box and a brief description of the problem.
2. You will be advised during the RA process what accessories should be included with the
amplifier (power supplies, connectors, cords, etc.). This is dependent on the failure

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assessment.
3. When shipping your amplifier, it is important that it has adequate protection. We recommend
you use the original packing material when returning the product for repair. If you do not have
the original box, see number 4.
4. If you provide your own shipping pack, use materials adequate to prevent damage during
transit. Make certain that the amplifier is NOT free to move within the package, as this is the
most common cause of damage.
5. Securely seal the package with an adequate carton sealing tape.
6. Do not use light boxes or “peanuts”.
NOTE: Damage caused by poor packaging will not be covered under warranty.