ETI Sound Systems, INC US-1200, US-1800, US-3000, US-4000

THE BEAUTY OF POWER

B-52 US Series Professional Power Amplifiers - Instruction Manual

US SERIES AMPLIFIERS

to the ampliﬁer. Do not block the air vents on

the front and do not block the fans on the rear

 panel.Makesuretheopencellfoamairlters

behind the vents on the front of the ampliﬁer are

clean. If necessary, use a vacuum cleaner to

clean these air ﬁlters.

NOTe: If the air ﬁlter become too dirty, the

ampliﬁer may not operate normally as air

circulating inside the ampliﬁer may become too

hot, thereby triggering the thermal protection.

If you cannot properly clean the air ﬁlters

 externallywithavacuum,removetheairlters

from the ampliﬁer and clean them thoroughly.

 ThisprocedureSHOULDbeperformedBYA

 QUALIFIEDPERSONNELONLY!Disconnectyour

ampliﬁer completely from its power source –

 YOUMUSTPHYSICALLYDISCONNECTTHE

 POWERCORDANDNOTJUSTTURNOFFTHE

 POWERSWITCH!Removetheamplier’stop

cover and locate the plastic brackets, which

house the air ﬁlters. Push the two levers at the top

of these plastic brackets to access the foam

ﬁlters. Remove the foam air ﬁlters, clean them

thoroughly and then place them back into the

ampliﬁer. Secure the ﬁlter by snapping the plastic

brackets back into place.

TRANSFORMeR TheRMAl PROTeCTION: If the

power transformer gets too hot, the thermal switch in-

side the transformer will trigger and will disconnect all

of the secondary power. When this occurs, there will

be no output signals coming from the ampliﬁer and

allLEDs,includingthePROTECTLED,willbeOFF.

Oncethetransformercoolsdown,powertotheampli-

ﬁer will automatically restore. In normal conditions,

the transformer will not overheat. Thermal protection

of the transformer indicates abnormal use, such as

excessiveoperationataverylowimpedanceathigh

signal levels. In this case, check and reconﬁgure your

loudspeakers connection. Reducing the output level

can also help.

NOTe: If the transformer overheats and

the thermal switch disconnects the power from

the ampliﬁer, it will take some time for the trans

former to cool down before power is restored. It

takes much longer for the transformer to cool

down compared to overheated heatsinks.

ShORT CIRCUIT: If the output is shorted because of

faulty wiring, the thermal circuitry will automatically

protect the ampliﬁer and mute the output signals. If

this occurs, the load will disconnect. Check and cor-

rect the short wire condition.

dC VOlTAge PROTeCTION: If an ampliﬁer chan-

nel detects a DC voltage at the loudspeaker output,

the protection circuitry will trigger and the ampliﬁer

will go into protection mode. In normal conditions

there should not be a signiﬁcant DC signal on the am-

pliﬁer outputs. DC on the outputs indicates a serious

problem with the ampliﬁer. In this instance, the ampli-

ﬁer must be referred to qualiﬁed service personnel.

SUBSONIC FReqUeNCy PROTeCTION: Built-in

high-pass subsonic ﬁlters provide subsonic frequency

protection for each channel. This protection prevents

subsonic audio signals, which may sometimes be

present in the music program, from reaching your

loudspeakers. Limiting the subsonic frequencies in

the output signal improves the sound reproduction by

reducingtheexcursionofthetransducer’sconeatlow

frequenciesandpreventsexcessiveheatinginsideof

the ampliﬁer.

NOTe: US-Series ampliﬁers also employ

switchable high-pass ﬁlters (HPF), which limit the

low frequency range to 50Hz when activated.

 TurntheseHPFsONwhenconnectingfullrange

speakers to the ampliﬁer. This will improve the

bass performance of most full range speakers by

 limitinguncontrolledandexcessiveconemotion

due to the lowest of frequencies. Using HPFs with

full range speakers provides more power to the

speaker’s rated range allowing higher SPLs. You

 maywanttoturnOFFtheHPFswhenusingthe

US-Series ampliﬁers with quality subwoofers.

CURReNT lIMITINg PROTeCTION: The output

stage of the ampliﬁer is protected by current-limiting

circuitry. This circuitry is inactive under normal condi-

tions. It activates only when it senses a dangerously

highcurrentthroughtheoutputtransistors,forexam-

ple when a connected load has an impedance that is

too low, or when the output of the ampliﬁer is shorted.

Current limiting protection engages only when it is

needed and is not indicated on the front panel. If

there is a constant over-current condition it will acti-

vatethethermalprotection.Inthiscase,thePROTECT

LEDonthefrontpanelwillilluminate.

ClIP lIMITeRS: US-Series ampliﬁers have built-