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UNDERSTANDING THE INDICATORS ON THE A 21

AC Present Indication 

When the A 21 is plugged into a live AC outlet, a soft blue halo glows behind its 

On-Off

 button 

and  its  red  “P”  Badge  glows  faintly.  These  indicate  that  the  unit  is  plugged  into  a  live  AC 

outlet, even when it is turned off.

On, Off and Fault/Protection Status Indicators

    

 

 

 

 

 

Whenever  the A  21  is  turned  on,  the  soft  blue  glow  behind  its  On-Off  button  will  change  to 

red  for  about  five  seconds  as  its  internal  circuits  stabilize. Then  the  red  glow  is  replaced 

by  a  brighter  blue  glow  to  indicate  normal  operation.  If  the  glow  remains  red  after 

turn  on  or  while  the  amp  is  playing,  it  indicates  activation  of  the  A  21’s  protection 

circuits  and  no  sound  will  be  heard  from  the  speaker. The A  21  protects  itself  from  external 

conditions  such  as  excessive  heat,  load  impedance  that  is  too  low,  or  a  short-circuited 

speaker  connection  or  wire.  After  you  correct  the  fault,  the  A  21  will  resume  operation.  If 

the  A  21  remains  “in  protection”  after  it  has  cooled  down  and  you’ve  confirmed  there 

are  no  external  faults,  it  could  indicate  an  internal  problem.  Please  contact  Parasound’s 

Technical Service Department.

Left and Right Channel Status Indicators

These are two small round indicators in the center of the recess in the front panel. The indicator 

on  the  left  displays  the  status  of  the  left  channel  and  the  indicator  on  the  right  displays  the 

status of the right channel. 

Both Illuminated

When both channels are operating normally, these both glow blue.

No Illumination: 

When the A 21 is turned off, these indicators are off.

High-Temp Indicator

This  indicator  is  near  the  right  side  of  the  panel  recess.  It  will  glow  red  if  either  channel 

overheats. The On-Off button will also glow red if the A 21 overheats. 

Gain Control Knobs

These  adjust  the  gain  (level)  of  the  A  21.  We  recommend  that  you  rotate  the 

Left  and  Right  Gain 

controls  to  their  maximum  clockwise  positions,  marked 

THX  Reference.

 

Refer to 

Gain Controls

 in 

Technically Speaking

 for more information about these adjustments.

Ground Switch 

The 

Ground 

switch  can  assist  in  reducing  audible  hum  caused  by  ground  loops  in  your 

system. This switch should be in its 

Normal 

(down) position. If you hear hum you can move 

it  to  its 

Lift 

(up)  position  to  eliminate  it.  Refer  to  the 

Technically  Speaking 

section  for  more 

information about ground loops.

10

A

B

E

C

D

A 2

F

G

F

G

A

&

B

C

&

D

B

E

F

C

&

D

C

&

D

Содержание Halo A 21

Страница 1: ...A 21 Amplifier Owner s Guide...

Страница 2: ...u are unpacking your new amplifier inspect it thoroughly for possible shipping damage If you see any contact your Parasound dealer right away Be sure to save and store both the inner and outer cartons...

Страница 3: ...NAL DC SOURCE FOR A 21 AUTOMATIC TURN ON OFF _________________________________________________________________________________ CONNECTING THE A 21 TO TRIGGER ANOTHER COMPONENT ________________________...

Страница 4: ...rackets provided With its four feet removed the A 21 chassis and front panel height occupies four rack spaces 7 or 176 mm When mounting equipment below the A 21 you will also need to allow about 1 8 b...

Страница 5: ...that you connect them to these inputs Refer to the Balanced and Unbalanced Lines in the Technically Speaking section for additional information about why we recommend using balanced lines What You ll...

Страница 6: ...e Ground switch is in its Normal down position To Connect Plug one end of the cable into the Unbalanced Right Channel Input jack on the A 21 Plug the other end of this cable into the unbalanced right...

Страница 7: ...ed or stretched once they are connected To Connect Plug one end of the cable to the right channel Loop Out jack on the A 21 Plug the other end of this cable to the right channel input jack on the othe...

Страница 8: ...lack Right negative speaker terminal on the A 21 Insert the other end of the wire with the ridge or other marking into the red right positive terminal on the speaker Insert the wire without the ridge...

Страница 9: ...th an impedance of 8 or higher Before Connecting Remove power to all the components in your audio system Set the A 21 Stereo Mono Bridge Switch to its Mono up position To Connect From the Source Plug...

Страница 10: ...ou need to first select the Manual On Off option by placing the Auto Turn On switch on the rear panel to its middle Man Manual position Connecting an Active Audio Source for Automatic On Off If you wa...

Страница 11: ...utomatically turn on and off the A 21 with an external DC voltage choose the DC Triggering option by moving the Auto Turn On switch on the rear panel to its lower 12V position What You ll Need A cable...

Страница 12: ...matically there is 12 Vdc present at its own DC Trigger Out jack so it can trigger additional amplifiers or other components on and off What You ll Need A cable with a 2 5 mm sub mini plug on each end...

Страница 13: ...oblem Please contact Parasound s Technical Service Department Left and Right Channel Status Indicators These are two small round indicators in the center of the recess in the front panel The indicator...

Страница 14: ...oltage for your unit is marked on its carton Changing the A 21 s operating voltage involves rewiring internal connections for both its main power transformer and standby power transformer plus changin...

Страница 15: ...able parts inside To avoid the risk of electric shock do not remove its top cover The amplifier s exterior can easily be cleaned with a soft cloth pre moistened only with a few drops of water or glass...

Страница 16: ...Mono Bridge switch is in the Mono bridged position Damaged speaker Move to the correct position for the jack in use Balanced Unbalanced Input switch is in the incorrect position Not enough ventilation...

Страница 17: ...cept any of the following Units with collect shipping charges Units without a valid RA number Units without a suitable shipping carton Units for which we see or hear evidence of improper packing For a...

Страница 18: ...ive signals For example when a 1 Volt signal arrives at a balanced input stage the differential input sees a positive 1 Volt minus a negative 1 Volt or 2 Volts total External hum and noise that someho...

Страница 19: ...This separates the A 21 s signal input ground from its chassis ground to isolate unwanted voltage in the ground shield of the unbalanced RCA input cable Be sure your system installation is finished b...

Страница 20: ...o drive the MOSFET drivers in the following stage Circuit designed by John Curl Parasound design consultant John Curl has been a legend among audiophiles and electronic engineers for decades He pionee...

Страница 21: ...these fuses halt operation to minimize damage to additional parts The Driver Stage The driver stage provides critical amplification for which we employ a complementary matched pair of MOSFETs selected...

Страница 22: ...ced 66 k Input Sensitivity for 28 28 V Output into 8 Unbalanced 1 V Balanced 1 V per leg Features and specifications subject to change without notice Loop Output Level Same as input level S N Ratio 11...

Страница 23: ...Parasound Products Inc 950 Battery Street San Francisco CA 94111 415 397 7100 Fax 415 397 0144 www parasound com...

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