Series One

v v v v
Model 1100 Model 1200 Model 1400 Model 1700

Owners Manual

*TD-000027-00*

Rev. C

Series One Power Amplifier Operation Manual TABLE OF CONTENTS
I: INTRODUCTION 1.1 Welcome.. 1.2 Warranty... 1.3 Overview of Amplifier.. 1.4 Specifications..
EXPLANATION OF GRAPHICAL SYMBOLS
The lightning flash with arrowhead symbol, within an equilateral triangle, is intended to alert the user to the presence of uninsulated dangerous voltage within the products enclosure that may be of sufficient magnitude to constitute a risk of electric shock to humans.
The exclamation point within an equilateral triangle is intended to alert the users to the presence of important operating and maintenance (servicing) instructions in the literature accompanying the product.
II: BASIC INSTRUCTIONS 2.1 Unpacking and Inspection. 5 2.2 Important Precautions.. 5 2.3 Quick Instructions.. 6 III: OPERATION 3.1 Cooling.. 8 3.2 AC Requirements.. 9 3.3 Input Connections.. 9 3.4 Octal Module Accessories. 12 3.5 Input Switches and Mono Bridging. 12 3.6 Speaker Connections. 13 3.and 70 Volt Systems.. 15 3.8 Protection Features.. 15 3.9 Operational Troubleshooting.. 16 IV: SPEAKER PROTECTION 4.1 Background... 4.2 DC Protection.. 4.3 Horn Driver Protection.. 4.4 Power Capacity.. 4.5 Power Limiting.. 4.6 User Responsibility.. V: MAINTENANCE AND SERVICE 5.1 Cleaning... 5.2 Dust Removal.. 5.3 User Maintenance. 5.4 Obtaining Service..
EXPLICATION DES SYMBOLES GRAPHIQUES
Le symbole clair avec point de flche lintrrieur dun triangle quilatral est utilis pour alerter lutilisateur de la prsence lintrieur du coffret de voltage dangereux non isol dampleur suffisante pour constituer un risque deltrocution. Le point dexclamation lintrieur dun triangle quilatral est employ pour alerter les utilisateurs de la prsence dinstructions importantes pour le fonctionnement et lentretien (service) dans le livret dinstruction accompagnant lappareil.

CAUTION

RISK OF ELECTRIC SHOCK DO NOT OPEN
CAUTION: To reduce the rish of electric shock, do not remove the cover. No user-serviceable parts inside. Refer servicing to qualified service personnel. WARNING: To prevent fire or electric shock, do not expose this equipment to rain or moisture.
RISQUE DE CHOCK ELECTRIQUE NE PAS OUVRIR
ATTENTION: Pour enviter les risques de chock electrique, ne pas enlever le courvercle. Aucun entretien de pieces interieures par lusager. Confier lentretien au personnel qualifie. AVIS: Pour enviter les risques dincendie ou delectrocution, nexposez pas cet article a la pluie ou a lhumidite.

SAFEGUARDS

Electrical energy can perform many useful functions. This unit has been engineered and manufactured to assure your personal safety. Improper use can result in potential electrical shock or fire hazards. In order not to defeat the safeguards, observe the following instructions for its installation, use and servicing.

PRECAUTIONS

Lnergie lectrique peut remplir de nombreuses fonctions utiles. Cet appariel a t conu et ralis pour assurer une scurit personnelle entire. Une utilisation impropre peut entraner des risques dlectrocution ou dincendie. Dans le but de ne pas rendre inutiles les mesures de scurit, bien observer les instructions suivantes pour linstallation, lutilisation et lentretien de lappareil.

I. INTRODUCTION

1.1 WELCOME
Thank you for selecting a QSC Series One power amplifier for your audio system. Our goal is to ensure your complete satisfaction with your amplifier purchase. Please do not hesitate to call your QSC Dealer or QSC Audio Products if you have any service problems or questions not answered in this manual. Your QSC Series One power amplifier can be readily operated by anyone familiar with professional audio systems. The four models covered by this manual, the 1100, 1200, 1400 and 1700, have similar features and connections. Any differences will be covered in the following detailed instruction sections of this manual. Because not all amplifier features and characteristics are standardized, we recommend that both experienced and first-time users review the contents of this manual. Please consult the table of contents for quick reference to sections of interest. We recommend that all users review the Basic Instructions section of this manual before installing or operating the amplifier.

automatically as soon as safe operation is assured. An equally important muting circuit protects the loudspeakers from unexpected damage, by muting the amp during turn-on and turn-off and by blocking DC faults, whether caused by the amplifier or preceding components. The front panel presents essential user information and is recessed to prevent damage. The green power indicator serves as a pilot light and individual red clip indicators monitor overall performance of each channel. The AC switch and circuit breaker are front mounted for convenience and quick resetting. Except for the Model 1100, the Gain controls and input programming switches have been placed on the back of the amplifier to protect them from damage, inadvertent adjustment, or tampering. The Gain controls, as well as a pair of headphone jacks, have been placed on the front panel of the Model 1100 to allow easy access in monitoring applications. The amplifiers use a separate bipolar power supply for each channel, for minimum crosstalk, cross-distortion, and greater reliability. A single dual-secondary transformer feeds isolated, separately fused rectifiers and filter capacitors for each channel. Thus the remaining channel can keep running in case of breakdown. In order to interface properly with a variety of pro-audio systems, we have included all of the popular input and speaker connectors. Balanced or unbalanced inputs can be made using XLR plugs, screw lugs to the barrier strip, or 1/4-inch phone plugs (ring-tip-sleeve for balanced inputs). Speaker connections are made with 5-way binding posts. The steel chassis, of the 1200, 1400 and 1700, is a 14 gauge, single piece design with integral rack mounting ears. The 1100 chassis features single piece aluminum extrusions that form the sides of the chassis and feature integral rack mounting ears and heatsinks. The extra strength chassis and rugged mounting of internal parts contributes greatly to QSCs reputation for reliability by protecting the circuitry from years of road abuse. All of these points are more fully explained in the following Sections.

1.4 SPECIFICATIONS

OUTPUT POWER (per channel) Both Channels Driven 8 ohms, 20-20 kHz, 0.1% THD 4 ohms, 20-20 kHz, 0.1% THD Bridged-Mono Operation 8 ohms, 20-20 kHz, 0.1% THD DYNAMIC HEADROOM dB 8 ohms 4 ohms DISTORTION, THD @ 8 ohms 20-20 kHz, at rated power SMPTE-IM at rated power FREQUENCY RESPONSE DAMPING FACTOR @ 8 ohms NOISE (A-weighted) VOLTAGE GAIN, dB SENSITIVITY, V RMS (for rated power, 8-ohms) INPUT IMPEDANCE

50w 70w 140w

100w 150w 300w

200w 300w 600w

325w 500w 1000w

2.0 2.3

2.0 2.5

1.9 2.9

Less than 0.1%, 0.01% typical Less than 0.025% 20-20 kHz, +0, -1.0 dB at 1 watt Greater than dB below rated power 26 1.1.1.1.0
10K unbalanced inverting 20K balanced or unbalanced non inverting -70dB, 20-20 kHz AC Switch, Circuit Breaker, Gain Knobs, Input Programming DIP Switches, and Bridging Switch Power: Green LED Convection Clip: Red LED 2 speed fan 2 speed fan

CROSSTALK CONTROLS

INDICATORS COOLING 4

Convection

AMPLIFIER PROTECTION
Full Short Circuit, Open Circuit, Over-Temp, Ultrasonic and RF Protection. Stable into reactive or mismatched loads. DC Load Fault Protection 3 Second Turn-on, Instant-off Muting 16 32

SPEAKER PROTECTION

COMPLEMENTARY OUTPUT DEVICES POWER SUPPLY
Single Transformer with Independent Isolated Secondary Windings, Fault Fuses, Rectifiers, and Filter Capacitors
DIMENSIONS Faceplate Width Faceplate Height Chassis Depth WEIGHT Shipping, Lbs Net, Lbs
Standard 19" Rack Mounting 1.75" 5.25" 8.7" 9.5"

5.25" 9.5"

7.0" 11.75"

II: BASIC INSTRUCTIONS

2.1 UNPACKING AND INSPECTION
All QSC Series One amplifiers are fully tested and inspected before they leave the factory. Despite the protective carton and rugged amplifier design, it is possible for shipping abuse to damage the amplifier. Check for obvious carton damage while unpacking the unit. After removing the amp from the box, rotate it in all directions to check for loose parts inside. Please save the carton for return shipment, if required. QSC does not warranty against damage caused by sending amplifiers back in the wrong carton. If shipping damage is evident, notify the transportation company immediately. Only the consignee can file a claim with the carrier for shipping damage. QSC will cooperate fully in such an event. Be sure to save the carton for the shipper to inspect.
2.2 IMPORTANT PRECAUTIONS
2.21 2.22 2.23 The power must be OFF when making any connections. If you connect plugs with the power on, especially in dry environments, static sparks or bad cables can cause pops or hums which can damage speakers. When first powering up the amp, have the amplifier Gain controls all the way off, in case of defective cables or hookups. Turn the Gain controls up gradually until normal operation is verified. Check the AC voltage printed on the serial number label to ensure your amplifier is properly configured for the AC voltage supplied in your area before connecting the AC plug. CONNECTION TO A VOLTAGE SOURCE OTHER THAN THE ONE SPECIFIED WILL IMMEDIATELY DAMAGE THE AMP, AND VOIDS THE WARRANTY. 2.24 Never connect the speaker terminals (red binding posts) for two channels together on any power amplifier. The two channels will fight each other and possibly fail. Do not connect the speaker ground terminals (black binding posts) to chassis or signal grounds, as the resultant ground loop could cause ultrasonic oscillations. In other words, keep all speaker wiring separate for each channel, and separate from input wiring. Do not remove the amplifier cover, as there are dangerous voltages inside. Do not expose to rain or moisture. Refer all servicing to qualified personnel. The warranty will be void if the amp is tampered with by non-QSC repair centers or personnel. The QSC Warranty does not cover tampering by unqualified personnel, or repairs made at non-QSC repair centers. Please call the factory for Service Center information and locations.

2.27 2.28

High voltages can be present on the speaker terminals. Always connect speaker terminals with the power off, and use heavy gauge cable with no frayed strands or damaged insulation. Please be aware that power amplifiers have high power circuitry inside with potential for fire and shock hazard; never plug in a damaged amplifier until the condition of the internal insulation is checked. If a circuit breaker blows quickly when turning the amp on, the amplifier is defective and should not be restarted until the amplifier has been repaired. Failure to observe these precautions could lead to fire or shock hazard. Power amplifiers are inherently heavy and may become hot after use; provide adequate support and be careful how you hold the amplifier when handling it.

2.3 QUICK INSTRUCTIONS

2.31 2.32 Stereo Operation These instructions cover the normal use of the amplifier in two-channel or stereo applications. See Section 3 for detailed installation instructions and special cases. AC Power Connect the AC cord to a standard GROUNDED outlet only. The amplifier will operate satisfactorily over a +/- 10% range of voltages, but full rated performance will be met only at the rated voltage. Failure to properly ground the amplifier may result in unwanted hum and noise and will create a potential shock hazard. Floating Chassis Ground There is no provision for lifting signal ground relative to chassis ground on Series One amplifiers. For safety reasons do not lift the ground pin on the AC cord. Electronic balanced inputs are provided for hum rejection. Use balanced input cables to avoid hum, interference and ground loops. Input Programming Switches 8-pole mini DIP switches are located on the rear panelsee the rear panel illustration for details. They come factory set for normal stereo operation (switches 1,2 and 7,8 up). See section 3.5 for other cases. Octal Socket For normal operation, nothing should be plugged into the octal socket. It comes from the factory with a protective label to prevent corrosion of the pins. Input Connections The input polarity is as follows: 1/4-inch plug: tip is minus or inverting input ring is plus or non-inverting input barrel is ground, as always pin 1 is ground, as always pin 2 is plus or non-inverting input pin 3 is minus or inverting input (AES Standard) GND is circuit ground + is plus or non-inverting input - is minus or inverting input

2.35 2.36

XLR plug:

Barrier Strip:

When making unbalanced connections, the barrel of an ordinary two-wire 1/4 inch plug will ground the plus side of the balanced input; XLR plugs will need to have the unused pin grounded inside the plug, and the installer will need to ground the unused screw on the barrier strip. It is still possible to use the balanced inputs to reject hum with an unbalanced signal. See Section 3.3 for details. 2.37 Speaker Connections Banana plugs, spade lugs, or bare wire ends can be connected to the 5-way binding posts. Be sure to observe correct polarity (red/black terminals) for each speaker to insure that all speakers move in the same direction. The 1100 features a pair of standard 1/4" headphone jacks on the front panel. They are connected to the speaker outputs of the amplifier through a resistive pad that prevents excessive power levels from damaging the headphones. 2.38 Power Up Start with the gain controls off until proper operation is verified. Upon turning on the switch, the power LED should come on green. After three seconds, the muting circuit should release and turn on the sound. The amp should now be working, and the Gain controls can be advanced. In case of difficulty consult Section 3.9.

The Model 1400 and 1700 amplifiers feature High Turbulence Flow-Through Cooling. An internal, two-speed fan forces air across a light-weight, high-turbulence heat radiator. Air flow is from the rear, so that warm air is exhausted to the front rather than baking the rest of the rack. This prevents the recirculation of heated air and reduces internal rack temperatures. Be sure that plenty of inlet space is allowed in the rack for free air flow. Dust filters are not provided on the amplifiers since small filters tend to clog quickly and reduce airflow. However, dust can be a problem and it should be removed from the insides of the amplifiers by using a compressed air jet through the vents several times a year. If amps are used in a fixed installation, where removal is not convenient, consider an additional fan pack in the bottom of the rack with a large external dust filter. The additional fan will maintain air flow, and the external filter can be removed and cleaned from the front of the amp rack. When installing the 1400 or 1700 in the same rack with passively cooled amps or fan cooled amps that exhaust into the rack, locate the 1400 or 1700 on the bottom. This will assure the coolest air for all amps.
Thermal cut-out The amplifier should normally run a little warm to the touch, and under high-power operation may get quite warm, especially around the heat sinks. If the heat sink temperature becomes excessive, internal thermostats for each channel will remove power temporarily. (See Section 3.8)

3.2 AC REQUIREMENTS

3.21 AC tolerances Series One amplifiers are designed for safe operation at AC voltages l0% higher than rated; however, temperature rise and transformer hum may increase somewhat. Operation on lower-than-normal AC voltages is not harmful to the amp, but performance will be progressively lost. For voltages down to 75% of rated voltage, no effect other than loss of peak power should be noticed. If voltage declines further, short-circuit protection (current limiting cutback) may be experienced during heavy peaks into low impedance loads. The muting circuit may not come on at less than 70% of rated voltage, but once on, it should stay on down to about 30% of rated voltage. There should be no sub-audio or DC transients caused by fluctuating AC voltages; you should suspect poorly regulated preceding components if thumps or voice-coil excursions are observed during peaks. AC supply In order to maintain full rated power, power amplifiers require well-regulated AC voltage of the proper rating. This is not always easy to assure when large banks of amps are used. The problem is further complicated by the fact that virtually all practical amplifier power supplies use peak rectification of the AC waveform. This means power is drawn only from the tips of the AC sine wave. When many amps are used, or there is an excessive length of inadequate gauge AC wiring to the amps, these tips can be seriously eroded without a major effect on measured RMS voltage. Bulk-power devices, such as lamps, on the same circuit may not be greatly affected, but other electronic components, which normally use the same type of rectification, may be seriously affected during high-power peaks. This is especially true of sensitive devices like computers, video gear, etc. This is why power amps should have their own electrical circuit if possible.

3.31 3.32 3.33

INPUT CONNECTIONS
(See illustrations in Section 2.3 for location)
Input Labeling All input functions are located on the rear panel of the amplifier and are labeled. Input Jacks 1/4-inch ring-tip-sleeve, female XLR, and three-circuit barrier strip terminal blocks are provided for input connections. Input Circuit An electronic balanced input is standard. This uses matched, 20 k resistive dividers and the differential input of a high performance 5532 op-amp to accept balanced input signals and reject common-mode signals. For best performance in the balanced-input mode, the source should have equal impedances for both signal conductors, so that the loading effect on each leg will be the same for common mode (noise) signals. Minor
mismatches will result in slight loss of common-mode rejection, but will still have much greater noise rejection than unbalanced inputs. 3.34 Balanced Inputs For proper balanced-line operation, the cable shield should be connected at the power amplifier end only and kept separate from both signal conductors. The cable shield should be connected to the barrel of a 1/4-inch plug, to pin 1 of an XLR plug, or to the GND terminal of the barrier strip. Balanced-line cables contain two signal conductors, a plus polarity, often called high or hot, and a minus polarity, often called low or return. The plus conductor should go to the ring of a 1/4-inch plug, to pin 2 of an XLR plug or to the plus input of the barrier strip, for the amplifier to reproduce the signal in the same polarity (non-inverting operation). This conforms to the international standard for XLR connections. The minus conductor goes to the tip of a 1/4-inch plug, to pin 3 of an XLR connector, or to the minus terminal of the barrier strip.

Amp Input

Figure 3.34a 1/4-inch RTS Balanced Output Connection
Figure 3.34b 3-Pin XLR Balanced Output Connection
3.35 Unbalanced inputs Since the input signal responds to the difference between the plus and minus signals, if only a single-ended, unbalanced signal is available, the unused input terminal must be grounded for operation without loss of gain. The ability to reject cable-induced hum and noise is lost, but this may not be needed in well-shielded environments with short distances between audio components. For unbalanced signals, the barrel of an ordinary two-conductor (mono) 1/4-inch plug will ground the sleeve terminal when pushed all the way into the 1/4-inch jack, so no special wiring is required. For XLR plugs, the signal conductor should be connected to pin 2, and pin three should be connected, inside the plug , to pin 1 (ground). On the barrier strip, the minus terminal is tied to the adjacent GND terminal, and the signal conductor should be connected to the plus terminal. In all cases, of course, the shield goes to the ground terminals. The tip of an unbalanced 1/4-inch plug has been made negative (inverting) because it is far more stable in systems which are subject to complex ground loops.

3.5 INPUT SWITCHES AND MONO BRIDGING
3.51 Input Programming Switch An 8-pole input programming DIP switch will be found on the rear panel of the amplifier. The switch functions are as follows: (move levers up to turn on, down for off) Switches 1,2: Bypass the Octal Socket for Channel 2. Keep on for normal operation (i.e. when no octal accessory in used). Turn off when an octal accessory is plugged in (see the instructions with the octal accessory). Switches 7,8: Same as above for Channel 1. Switches 3,4: Connects the output from an octal accessory plugged into Channel 1 to both amplifier channels. Turn on to feed the octal accessory to both channels. Turn off for normal operation or for using separate octal accessories. Switches 5,6: Connects the inputs of Ch. 1 and Ch. 2 in parallel (see Section 3.37). If octal accessories are used, the inputs (not the outputs) of both accessories will be combined. This may be used in place of a Y-cord for feeding a common input signal to both channels. 3.52 Mono Bridging Most stereo amplifiers have a method of combining both channels in series to give the combined power into a single load. This is a way to fully use both channels when only a single speaker is driven. To engage the bridged-mono mode of the Model 1100, a slide switch must be set through a hole in the bottom of the amplifier. Due to the danger of touching live terminals inside the amplifier, BE SURE TO REMOVE ALL POWER AND DISCONNECT THE AC PLUG before resetting the switch. In accordance with the label on the bottom, set the switch towards the front for bridged-mono use, and towards the rear for normal stereo use. To engage the bridged mono mode on the Model 1200, 1400, or 1700, there is a separate slide switch located below the barrier strip inputs on the rear panel. Follow the directions on the label to engage the switch in the Bridge position.
Connect the amplifier input to Ch. 1 only, and use only the Ch. 1 Gain control, which now controls the entire amplifier. Do not feed another input into Channel 2. The Ch. 2 Gain control should be kept off for safety. An 8 or 16 ohm speaker load should be connected across the two red speaker terminals, using the red terminal of Ch. 1 as the + or hot terminal, the red terminal of Ch. 2 is the - or common terminal. Mono Bridge Precautions a. Minimum load impedance is 8 ohms, which will be the equivalent, to the amp, of 4 ohms per channel. If a fourohm load is used, the amp will have to work very hard and may overheat. b. Both sides of the speaker cable are hot or active. Be sure there is no ground or other circuit connected to either side of the speaker cable. c. If the parallel-channel switches (#5,6, see Section 3.51) are switched on,the signal into Ch. 2 will cancel the mono-bridge signal. To prevent this, and still permit patching to additional amps, keep the Gain for Ch. 2 fully off.

3.66 3.67

loss of 10% is barely audible, the resultant low damping factor will prevent the amplifier from fully controlling the peaks and dips in frequency response caused by speaker impedance variations. This will result in greater coloration and muddiness.

Cable Length 5 ft.

Wire Gauge 8
Cable Resistance 0.063 0.040 0.025 0.016 0.010 0.126 0.080 0.050 0.032 0.020 0.252 0.160 0.100 0.064 0.040 0.504 0.320 0.200 0.128 0.080 0.050 0.640 0.400 0.256 0.160 0.100 0.800 0.512 0.320 0.200 1.024 0.640 0.400
Power Loss, 8 Load 0.79% 0.50% 0.31% 0.20% 0.13% 1.58% 1.00% 0.63% 0.40% 0.25% 3.15% 2.00% 1.25% 0.80% 0.50% 6.30% 4.00% 2.50% 1.60% 1.00% 0.63% 8.00% 5.00% 3.20% 2.00% 1.25% 10.00% 6.40% 4.00% 2.50% 12.80% 8.00% 5.00%
Power Loss, 4 Load 1.58% 1.00% 0.63% 0.40% 0.25% 3.15% 2.00% 1.25% 0.80% 0.50% 6.30% 4.00% 2.50% 1.60% 1.00% 12.60% 8.00% 5.00% 3.20% 2.00% 1.25% 16.00% 10.00% 6.40% 4.00% 2.50% 20.00% 12.80% 8.00% 5.00% 25.60% 16.00% 10.00%
Damping Factor, 8 Load 18

Damping Factor, 4 Load 9

10 ft.

20 ft.

40 ft.

80 ft.

160 ft.

320 ft.

Table 3.69 Speaker Wire Table

3.AND 70 VOLT SYSTEMS

3.71 Introduction Commercial sound systems commonly use dozens or even hundreds of speakers for sound distribution. Special methods for connecting and controlling many separate speakers have been worked out by commercial sound contractors. 25 Volt lines 25 volt distribution systems are popular in small to medium sized installations where local codes require conduit for 70-volt lines. The Model 1100 amplifier will deliver up to 120 watts directly to 25 volt lines by using the mono-bridge mode. Please note that, as with any system using the mono-bridge mode, neither side of the speaker line should be grounded. The Model 1200 amplifier will deliver up to 150 watts per channel directly to 25 volt lines. The Model 1400 and 1700 have excessively high output voltages and are not recommended for directly driving 25 volt lines. 3.Volt lines All Series One amplifiers may be used with our 70-volt output transformers, the OT-300a and OT600, to power 70 volt distribution systems. See the following table for details on transformer model and power ratings. Consult the transformer Owners Manual for additional information on 70 Volt distribution applications.

Model 1400 1700

Output Transformer OT-300a OT-300a OT-300a OT-600
Voltage Tap 17 V 25 V 35 V 45 V
Power,Per Channel 70w 150w 300w 500w

Table 3.Volt Output Power
3.74 Low Frequency Rolloff In commercial sound systems, a rolloff below 50 Hz or so is desirable to prevent excess wasted power at frequencies below the range of the speakers and their small transformers. Contact the QSC Sales Department regarding the availability of Octal Modules for this application. The roll-off may also be provided by preceding signal processing equipment, such as EQs, active crossovers and mixers.

3.8 PROTECTION FEATURES

3.81 Summary We have ensured that accidents, mistakes, and abuse will have the minimum possible chance of harming the amplifier or speaker. The major challenge was to do this without impairing the audio performance into normal loads. Short Circuit Protection The active region in a power transistor is surprisingly smallperhaps 1/5 of a inch wide. This little piece of silicon must control hundreds of watts of power. If not managed properly, this can burn out the silicon, instantly destroying the transistor. Under normal conditions, most of the power passes through the transistor, into the speaker, producing useful power and only some waste heat. If too many speakers (too low of an impedance) are connected, excessive power will be drawn through the transistor, and more heat will be wasted. If the load impedance drops to zero, which might happen if the speaker wires are shorted together, then there would be almost no limit to the power drawn through the transistor, and the waste heat will be so high that the transistor will burn out. This is why solid state amps need short circuit protection. The patented QSC Output Averaging short circuit protection acts by monitoring the load impedance. As long as it is within rated limits (above 2 ohms), the amount of waste heat in the power transistors is acceptable, and full audio power is allowed to continue. If the output impedance is reduced below 2 ohms the instantaneous current peaks will be limited, but to a fairly high value, which the transistors can handle for a short time; if a strong signal persists for more than a fraction of a second, the current limit is smoothly cut back to a lower value which the transistors can handle indefinitely. The result is full performance into rated loads, ability to handle normal program peaks into marginal loads, and good protection into short circuits. At no time will the circuit cause abnormal distortion spikes or loss of sound.
Thermal Protection In case of blocked ventilation, improper loading or prolonged short-circuit operation, the temperature of the power transistors can rise to excessive levels. If the temperature of the heat sink rises to 85C, a thermostat will remove power to that channel. Power will be automatically restored when the channel has been allowed to cool down. Please note that Channel 1 can shut down without affecting channel 2, but if channel 2 shuts down, the muting circuit for both channels will operate and mute channel 1 as well. This was done so that whichever channel might overheat in the bridged-mono mode, it would remove the signal for both channels and prevent damage to the muted channel. The amplifier should come back on within a minute or two. If thermal problems occur, check for blocked ventilation, proximity to a heat source, short circuit, or improper load (too many speakers).

DC Fault Protection The Model 1100, 1200, and 1400 amplifiers employ a unique Bi-Capacitive output circuit that combines the tight, well controlled audio performance of direct-coupled (DC) designs with the inherent ability to block DC output in the event of amplifier failure. Because this circuit requires dual power supplies, protection is independent on each channel. A DC fault in one channel will not affect operation of the other. Since no relays or other external devices are employed, the amplifiers are free from any false triggering or degradation problems associated with other protection schemes. In the event of an actual fault, DC will be blocked at the output until an internal protection fuse blows. This will remove power from the defective channel until repair can be made. In the unlikely event this should happen, disconnect the inputs and speakers from the defective channel and take the amplifier in for service as soon as possible, to prevent any further damage. The Model 1700, due to its higher power rating, employs the same dual power supply scheme, but has a more conventional direct coupled (DC) output circuit. It uses a heavy duty Load Grounding speaker relay for load protection. This has the advantage of connecting the defective channels load to ground for extra protection.
Turn-on/turn-off Muting There will be a three-second muting interval after turn-on. After turn-off, or loss of power for any reason, the amplifier will mute within a quarter of a second. The outputs of all Series One power amplifiers are DC protected and the circuits have no inherent turn-on or turnoff thumps. Protective muting for the Model 1100 is handled by a small relay at the input. The signal does not pass through the relay contacts, but is shunted to ground during the muting interval. Thus any degradation of the relay contacts will only affect the muting, and not the audio quality. The Model 1200, 1400 and 1700 make use of an electronic muting circuit to mute the input of the amplifier. The Model 1700 also makes use of the Load Grounding relay to mute the output of the amplifier by grounding the speaker output.
Input/Output Protection Series One amplifier inputs are isolated by 10K resistors, which are part of the balancedinput circuit. This protects the inputs from burn-out due to extremely high input signals or RF interference. The amplifier output is isolated from capacitive and inductive loads by a high frequency RLC network, which decouples the speaker terminals slightly at frequencies above about 50 kHz. Indicators The green pilot LED indicates AC power, but does not signal status of the muting circuit. After the muting interval is passed, the red clip LEDs will indicate the presence of distortion for each channel. If distortion is heard without clip indication, you should suspect other parts of the system.

3.98 UNWANTED NOISES

Humin this case, defined as a fairly rounded 60-cycle tone. Severe hum usually is caused by broken cables or jacks, with a disconnected ground (shield). This problem can also be caused by corroded connectors, especially 1/4-inch types. For this reason, high-reliability systems should use the XLR or barrier-strip inputs. A milder form of hum, often with a little more tone or harmonic content, is usually the result of ground loops. This problem is caused by 60-cycle magnetic fields, which radiate from power transformers, including the ones in the amplifier. Try re-positioning the cables away from the various components. Note that tape recorder heads, phono cartridges, and electric guitar pick-ups are especially sensitive to this type of interference, and must be kept away from high power electronics. Buzzdefined as a very razzy kind of hum. This is usually caused by interference from solid-state light-dimmer circuits. Follow the same precautions shown above, and make sure the electronics are not connected to an AC outlet which has a dimmer control. Hissdefined as a smooth shhh noise. This is always a problem with sensitive, high-gain electronic inputs, and usually starts at the point of weakest signal. First, check the power amp by unplugging the input cables. Any residual noise (hiss and hum) should be barely audible even with your ear right up to the speaker. Assuming that the amp is OK, you will have to trace the hiss to an earlier part of the system. In a properly designed system, this will be the initial microphone, phono, or tape source. There is a noise floor caused by random atomic vibrations. This limits the signal-to-noise ratio of the original signal; the goal of a proper system is to immediately amplify that signal well above the noise floor so that further degradation does not occur. Gain-staging is a subject in itself, but the principle is to maintain a reasonably constant signal level after leaving the initial pre-amp. The signal must be kept below the point of distortion, and well above the noise floor. To isolate the source of unwanted hiss, start at the amp, and work backwards, reducing and then restoring gains. You should hear a reduction of hiss and audio together at each point, showing that the hiss is coming in earlier. When you find a control which lowers the audio volume, but not the hiss level, you know the hiss is coming in after
that stage. Assuming that the hiss has not always been there, this indicates defective electronics. Certain specialeffects units are rather noisy, so compare with other users. Cracklesdefined as a popcorn noise. If the crackle persists during pauses in the program material, this indicates defective electronics and must be traced down using the above procedures. Crackles which occur during audio peaks or when the electronics are vibrated usually indicate bad connections.

POWER CAPACITY

All speakers have a maximum long-term power limit which is determined by the temperature rise of the voice coil. The speaker can withstand short peaks above this level, since the voice coil takes a little while to overheat. The time lag depends on the size and mass of the voice coil and ranges from a fraction of a second to several seconds. The required speaker rating for a given amplifier power depends on the type of program material. Extreme cases such as lead guitar work may require speaker ratings of twice the RMS power of the amplifier to withstand the full peak power. The average power of signals where some attempt is made to prevent overdrive distortion will be less than the amplifier RMS rating; how much less depends on the dynamic range and headroom allowance. In live-performance situations where feedback and high-energy artists can push the system to its limits, it would probably be wise to match the RMS ratings of the speakers and the amplifiers.

POWER LIMITING

There are several ways to limit the power to safe levels without operator intervention. Some speaker systems have protective circuits, or at least fuses. Fuses can be added which will blow in case of overloads; the problem is to select a fuse with the correct time lag and overload characteristics to match the speaker limitations. The speaker manufacturer is in the best position to specify these values; the following table is presented for rough guidance only. The fuse values shown are calculated for fast-blow fuses, which will carry 135% of their rating for an hour, and which blow within 1 second at 200% current. The RMS power rating shown is correlated to 135% of the fuse current. The fuse voltage is not critical; 32 volt fuses should have the lowest resistance which will avoid loss of damping factor. RMS Power 30w 50w 75w 100w 200w 400w 4-ohm Load 2.0 2.5 3.0 4.0 5.0 7.5 8-ohm Load 1.5 1.6 or 2.0 2.0 or 2.5 2.5 3.0 or 4.0 5.0 16-ohm Load 1.0 1.25 1.5 1.6 or 2.0 2.5 3.0 or 4.0
Table 4.5 Fuse Ratings (values in amps)

SERIES THREE AMPLIFIERS FROM QSC
Series Three has been designed to be the most advanced amplifier line available. It was conceived, engineered, and refined with input from many leading pro audio system designers, operators, and users. Its a combination of advanced features not found elsewhere. Low profile chassis, front-removable channel modules, detented and recessed gain controls, true dual-mono configuration, high efficiency low heat output circuit, and the latest in high-performance/high quality components. The Model 3800 is an ultra high-power amplifier designed explicitly for the most demanding and heavily loaded professional applications. As such, it makes a perfect match with todays new FEATURES I Low Profile Chassis. I 375 watts per channel at 8 ohms. I 600 watts per channel at 4 ohms. I 850 watts per channel at 2 ohms. I Dual-Mono Configuration. I High-Efficiency Output Circuit. I Passive Cooling. I Front-Removable Channel Modules. I Recessed Front Controls.

MODEL 3800

I I I I I I I
high power handling speakers. The Model 3800 is a high current version of our Model 3500 but with a larger power supply, more output devices, and 50% more heatsink area. Its capable of delivering tremendous amounts of power at low impedances. The Model 3800 has an extremely conservative and rugged output section consisting of 20 Large SOA (Safe Operating Area), high-speed, MESA output devices per channel (40 total). This abundant use of costly output devices combined with our patented OUTPUT AVERAGING short-circuit protection assure years of trouble-free service even under the most abusive conditions.
Precision 31-Step Gain Controls. Complete LED Monitoring. Octal Input Socket. Active Balanced Inputs. 1/4" RTS, XLR, and Barrier Inputs. Dual Binding Post Outputs per Channel. Three-Year Warranty

SPECIFICATIONS

OUTPUT POWER (per channel) Continuous Average Output Power Bridged-mono operation. both channels driven 16 ohms, 2020kHz, 0.1% THD 8 ohms, 2020kHz, 0.1% THD kHz, 1% THD 1 kHz, 1% THD ohms, 2020kHz, 0.1% THD 4 ohms, 2020kHz, 0.1% THD kHz, 1% THD 1 kHz, 1% THD ohms, 2020kHz, 0.2% THD 2 ohms, 2020kHz, 0.2% THD kHz, 1% THD 1 kHz, 1% THD 1,100 DISTORTlON (8 ohms) THD: 2020kHz at rated power shall be less than SMPTE-IMD: less than 0.025% at rated power FREQUENCY RESPONSE 2020kHz, 0.1dB 8300kHz, +0/-3dB DAMPING FACTOR DYNAMIC HEADROOM NOISE SENSITlVlTY INPUT IMPEDANCE CONTROLS Greater than 200 2dB at 4 ohms -100dB 2020kHz at rated power 1V RMS for rated power at 8 ohms 20K balanced or 10K unbalanced Front: Recessed detented gain control, AC switch/circuit breaker far each channel. Rear: Mono-bridging and input accessory module switches. Bicolor LED indicating DC power, OK/Protect mode, LED clip indicator, -30dB and -6dB signal level indicators, flashing overtemp indicator. Passive-combined with high-efficiency output stage for 50% reduction in dissipated heat. Unique circuit configuration provides direct-metal mounting of output devices to minimize short-term thermal excursions of power transistors. Fan-assisted cooling recommended for high duty cvcles at 2 ohms. 1,200 1,500 1,700 2,200 0.1%

INDICATORS (per channel) COOLING
AMPLIFIER PROTECTION lndefinite short-circuit* open-circuit, over-temp, ultrasonic and RF protection. Stable into reactive and mismatched loads. Inputs protected from overload *Output Averaging Short Circuit Protection (US Patent 4,321,554) LOAD PROTECTION lndividual channel output relays provide DC Fault, 3 second delayed turn-on (transient protection), and excessive Iowfrequency protection. Instant turn-off, pop suppression and power interrupt protect is also provided. OUTPUT TYPE POWER SUPPLIES Full complementary two-level high efficiency A complete separate power supply for each channel including AC switch/circuit breaker and AC cord. OUTPUT DEVICES (total) 40
POWER REQUIREMENTS 120, 220, or 240V 5060 Hz, 13A (each channel) DIMENSIONS Faceplate 19"x5.25" Depth 17.9" (with rear supports) 15.9 (chassis only) WEIGHT 75 Ib. (Net) 83 Ib. (Shipping) Specifications subject to change without notice.
The amplifier shall contain all solid-state circuitry, using complementary silicon transistors and integrated circuits It shall be capable of operating from 120, 220 or 240V 5060Hz AC mains with internally selectable jumpers. The amplifier shall contain two fully independent channels, with separate AC breaker/switches, power transformers, and protective systems. Each channel shall have independent protective circuitry against open-circuit, short-circuit or mismatched loads; independent thermal warning and shutdown circuits, and independent load protection circuits for turn on/off transients including momentary AC dropouts and DC faults within or preceding the amplifier All protective circuits except AC circuit breaker shall be self-resetting. The remaining channel shall continue to operate, in stereo or bridged-mono mode. Each channel of the amplifier shall be capable of meeting the following performance criteria, with both channels driven simultaneously. Output power into 8 ohms 375 watts, 2020kHz, less than 0.1% THD. Output power into 4 ohms 600 watts, 2020kHz, less than 0.1% THD. Output power into 2 ohms 850 watts, 2020kHz, less than 0.2% THD. Frequency response shall be 2020kHz, with less than 0.1 dB deviation. The voltage gain shall be 34.5dB at full Gain. The power gain (into 8 ohms) shall be 65.5 dB at full gain. The input sensitivity for rated 8-ohm power shall be 1V RMS. Balanced bridging input circuitry shall be standard, and the amplifier shall meet all performance criteria in the balanced or unbalanced mode. Input impedance shall be 20k ohms balanced, or 10k ohms unbalanced. Noise level shall be at least 100dB below rated power, at full Gain. IHF damping factor shall exceed 200. The amplifier shall be passively cooled, with no fans or moving parts. Each channel shall have the following controls, functions, and indicators: 31-detent Gain control, with 1 dB steps over the highest 14dB of adjustment range, with accuracy within 1 dB; Green/Red LED for power/protect indication; Yellow LED signal presence indicators with thresholds 6dB and 30dB below rated power. Red LED clipping indicator for output clipping greater than 0.1%; Flashing red LED indicator for heat sink temperatures within 10C of thermal shutdown. Balanced/Unbalanced input jacks of the inch RTS, female XLR, and barrier strip screw terminal types; Speaker connectors comprising two sets of 5-way bindlng posts on -inch centers and barrier strip screw terminals. Octal socket with DC power for passive and active input accessories. 8-way microswitches for octal socket bypass, mono-bridged mode, channel cross-connection, and XLR input polarity. Each channel shall be front-removable with the amplifier mounted in a rack and without disconnecting the input/output cables. All active components, except AC power transformer, AC breaker/switch, and input/output connectors, shall be mounted on the removable channel module. Module connectors shall be flexible to withstand shocks and vibration for long term integrity. The chassis shall feature permanently attached AC cords, and a ground-lift barrier strip shall permit separation of audio ground from chassis/AC ground. The chassis shall have front and rear rack supports, and shall occupy 3 rack spaces (5.25") Chassis depth, including rear supports, shall be 17.9". Weight shall be 75 Ib. The power amplifier shall be the QSC Audio Products Model 3800.