Knoll Stereo Amplifier 21K User Manual

21K  
21K Stereo amplifier specifications  
Inputs:  
Input impedance:  
Outputs:  
Output power:  
Ideal impedance:  
Gold RCA jacks with adjustable gain  
50k ohms  
5 way gold insulated binding posts  
90 watts RMS per channel (8 ohms)  
4 – 8 ohms  
Stereo Amplifier  
Installation Instructions v1.1  
Frequency response: 10 Hz – 40 kHz +/- 1dB  
S/N ratio:  
Over 106 dB A weighted (90 watts)  
THD distortion:  
IMD distortion:  
Dimensions:  
Fan noise:  
Power:  
Less than 0.1% 20 Hz to 20 kHz  
Less than 0.01% 60 Hz 7 kHz 4:1 (SMPTE)  
17” x 3.5” x 11.5” (432 x 89 x 292 mm)  
No fan needed  
Maximum 320 watts at 117 VAC 60 Hz  
20 lbs  
Caution: To reduce the risk of electrical shock, do not remove  
the cover (or back). No user serviceable parts inside. Refer to  
qualified service personnel.  
Weight:  
Construction:  
Steel chassis, powder coated; glass epoxy  
printed circuit boards  
Rack version:  
21k-Rack  
Warning: To reduce the risk of fire or electric shock, do not  
expose this appliance to rain or moisture.  
The lightning flash with arrowhead, within an  
equilateral triangle, is intended to alert the user to the  
presence of uninsulated “dangerous voltage” within  
the products that may be of sufficient magnitude to constitute a  
risk of electrical shock to persons.  
Three Year Limited Warranty  
Knoll Systems warrants 21K amplifiers sold in the USA or Canada by authorized  
Knoll dealers to be free from defects in materials and workmanship. This  
warranty extends for three full years from the date of purchase by the  
consumer. Any products returned freight prepaid to Knoll Systems and found to  
be defective by Knoll Systems within the warranty period will be repaired or  
replaced at Knoll Systems option, at no charge. Knoll Systems will not be  
responsible for the actual cost of installation or removal of the product, nor for  
any consequential or incidental damages. Some states do not allow the  
exclusion or limitation of incidental or consequential damages, so the above  
limitation or exclusion may not apply to you. This warranty gives you specific  
legal rights. You may have additional rights, which vary from state-to-state.  
Knoll products sold outside of the USA and Canada may be covered by  
warranties provided by an authorized Knoll distributor. Please contact the  
distributor in the country that the Knoll product was purchased.  
The exclamation point within an equilateral triangle is  
intended to alert the user to the presence of  
important operation maintenance (servicing)  
instructions in the literature accompanying the appliance.  
145 Tyee Drive Point Roberts, WA 98281  
12140 Horseshoe Way Richmond BC V7A 4V5  
Telephone (604) 272 4555, Fax (604) 272 5595  
Made in Canada, © 2005, All Rights Reserved  
 
Do not use this amplifier near water including near a bathtub,  
swimming pool or hot tub.  
Introduction: Thank you for your purchase of a Knoll 21K  
stereo power amplifier and congratulations on your choice. This  
amplifier is specifically designed to be the best sounding  
amplifier available anywhere. Our engineers and designers  
spent years of pain staking research and testing to perfect the  
sound quality. We hope you will appreciate this effort and enjoy  
the amp.  
This unit should be installed so that its location does not  
interfere with proper ventilation. For example, don’t place the  
amplifier on a bed, sofa, rug, or similar surface that may block  
the ventilation openings; or place in a built-in installation such  
as a bookcase or cabinet that may block the flow of air through  
its ventilation openings.  
Unpacking: The carton and packing materials used in shipping  
your new amplifier were specially designed to protect it from the  
shock and vibration of shipping. We suggest that you save the  
carton and packing materials to use if you move, or if the unit  
ever needs to be shipped back to us for any reason. Should you  
discover that your amplifier has been damaged during shipping,  
please contact your dealer or Knoll immediately and request the  
name of the carrier so a written claim can be made.  
The unit should be set away from heat sources such as  
radiators, heat vents, or other devices (including amplifiers)  
that produce heat.  
The unit should be connected to a power supply outlet only of  
the voltage and frequency marked on its rear panel.  
The power supply cord of the unit should be unplugged from the  
wall outlet when it is to be unused for a long period of time.  
The right to a claim against a public carrier can be forfeited if the  
carrier is not notified immediately in writing and if the shipping  
carton and packing materials are not available for inspection by the  
carrier. Save all packing materials until the claim is settled.  
Care should be taken so that objects to not fall, and liquids are  
not spilled, into the enclosure through any openings.  
Placement  
The unit should be serviced by qualified service personnel when:  
During normal home operation the amplifier will become warm.  
However, there are instances during high-level playback into  
low impedance speakers when the amplifier will become much  
warmer than normal. To ensure the amplifier’s trouble-free  
operation, it is necessary to provide adequate ventilation. Your  
amplifier should be kept away from external sources of heat  
such as radiators and hot- air ducts. The amplifier should never  
be placed with other heat-producing components in a cabinet or  
enclosure lacking free airflow. Do not stack other components  
on top of your amplifier.  
The power cord or plug has been damaged; or objects  
have fallen, or liquid has been spilled into the unit.  
The unit has been exposed to rain, or liquids of any kind;  
or the unit does not appear to operate normally, or  
exhibits a marked change in performance.  
The amplifier has been dropped, or the enclosure  
damaged.  
To prevent electric shock, do not use the polarized plug with an  
extension cord, receptacle or other outlet unless the blades can  
be fully inserted to prevent blade exposure.  
Rack mounting  
A rack mount version of the 21K is available. For best operation  
when rack mounting the 21k we suggest it be near the top of  
the rack and have vented blank 1 rack space panels above and  
below the 21k. For multiple 21k amps in one rack we suggest  
spacing the amps 1 rack space apart and inserting a vented  
blank 1-rack space panel between each amp.  
 
Hum and noise  
Troubleshooting  
In most cases, one of the following suggestions should help you  
solve a hum noise in your system. Please try these steps in the  
order shown; proceeding from one step to the next if the prior  
suggestion does not eliminate the problem.  
Your Knoll amplifier is designed from trouble-free operation. If  
you follow the instructions in this manual, you should enjoy  
many years of high-quality listening enjoyment. However, as  
with any sophisticated device, there may be occasional  
problems upon initial installation, or during the life of the amp.  
The items on the list below are a brief guide to the minor  
problems that you may be able to correct yourself. If these  
solutions do not help, or if the problem persists, contact us for  
assistance.  
Potential ground loops in a complex A/V system  
Suggestion #1  
To determine if a cable TV connection is responsible for the  
hum, first turn off all the components. Disconnect the cable TV  
feed to your system at the first place where it connects to your  
components. Alternatively, disconnect the cable TV wire where it  
is connected at the wall outlet. Turn your system back on, and  
listen if the hum has disappeared. If removing the cable TV feed  
has eliminated the hum, you will need to insert a Ground Loop  
Isolator our model GB634) before reconnecting the cable TV  
feed, or contact your cable TV operator to see if they can better  
isolate your cable feed.  
Problem  
Solutions  
Amplifier won’t turn on  
Master power switch turned off (No  
power light LED). Turn on Master Power  
Switch.  
Amplifier won’t turn off  
Remote trigger cable not properly  
connected. Verify connection of trigger  
cable at both ends.  
Amplifier turns on, but no  
audio from one or more  
channels  
Input plugs not connected to proper  
jack or are loose. Check input  
connections.  
Suggestion #2  
Turn off all components in your system, and then disconnect the  
input cables at the amplifier. Turn the amplifier back on to see if  
the hum is still present. If the hum disappears, the fault may be  
in the input cables used. Try replacing them with cables that  
have better shielding, and make certain that the input cables  
are not running on top of any AC power cords. Change the  
cables one at a time to determine if one or all cables are  
responsive. If the hum disappears when the input cables are  
disconnected, but returns after the cables are changed and the  
system reconnected, your source device may be causing the  
problem.  
No audio from one or more  
channels  
Speakers are not connected  
properly. Check speaker connections at  
amp and speaker.  
Audio levels differ  
from source device.  
Improper settings or output levels  
Check the settings on your preamp,  
processor or controller. Also verify  
settings of the rear panel gain controls  
on your amp.  
Audio plays and then cuts off Amplifier may be shorted. Check  
speaker connections for short-circuit at  
amp and speaker.  
 
Input connections  
Connecting the 21K to your source equipment is  
Getting to know the rear panel  
straightforward. Using the high-quality audio interconnect  
cables, match the output channel designations on the rear of  
your source equipment to the input jacks on the rear panel of  
your amplifier that have the same channel name. When making  
connections with RCA type plugs on interconnect cables, make  
certain to gently, but firmly, insert the plug into the jack. Loose  
connections can cause intermittent sound and may damage your  
speakers. Some quality RCA plugs may be very tight, and it is  
important to secure a proper connection between the  
interconnection cable and the input jack.  
A.  
Audio Inputs  
Use the INPUT jacks to connect the outputs of a  
preamplifier, receiver with pre-out connections, CD  
player, or other control devices.  
B.  
C.  
Input Gain Controls  
Use these to adjust the input gain of each channel.  
Product Serial Number  
Write this number in the space provided on page “” for  
future reference.  
Speaker connections  
To ensure that the high quality signals produced by your  
amplifier are carried to your speakers without loss of clarity or  
resolution, Knoll advises that you use high-quality speaker wire.  
Many brands of wire are available — the choice may be  
influenced by the distance between your speakers and the  
amplifier, the type of speakers you use, personal preferences,  
along with other factors.  
D.  
Remote Trigger Input  
Use the REMOTE TRIGGER jack to connect a compatible  
preamplifier, source device, or other product with a  
12VDC output (abut 35mA required).  
E.  
F.  
G.  
Audio Outputs  
This is an unbuffered line level output to other devices  
such as another 21k amplifier.  
Regardless of the brand or type of speaker wire chosen, we  
suggest that you use a wire constructed of fine, multi-strand  
copper with a gauge of 14 or less (the lower the number, the  
thicker the cable). Wire with a gauge of 16 may be used for  
short runs of less than 12 feet. We do not recommend that you  
use any wires with an AWG equivalent of 18 or higher due to  
the power loss and degradation in performance that will occur.  
AC Input  
Use the included power cord to connect your amplifier to  
an AC power source.  
Speaker Outputs  
Use the OUTPUT binding posts to connect the amplifier to  
your speakers: red for positive, black for negative.  
To connect the amplifiers to your speakers, a pair of binding  
posts is provided for each channel output. These posts will  
accept bare wire, spade lugs, or banana type plugs. If bare wire  
is used for the connections, strip approximately 1/2 inch to 3/4  
inch of insulation from the end of each wire and carefully twist  
the strands of each conductor together. Be sure not to cut the  
individual strands or twist them off. All strands must be used for  
optimal performance.  
Connecting your amplifier  
When making connections between any source components and  
the amplifier, or when making connections to any speaker, be  
certain that both the input devices and the amplifier are turned  
off. Unplug all equipment before making any connections so that  
there will be no unwanted signal transients that can damage  
equipment or speakers.  
Correct polarity connections are important to maintain proper  
speaker phasing. When speaker phasing is correct, all speakers  
move in and out at the same time preserving the imaging of the  
program material. Out-of-phase connections mean that some  
 
turn off, check your speakers to verify that they are operating  
properly. If all other potential sources of trouble check out  
properly, contact Knoll for further assistance.  
21k Automatic on  
Make certain that the connection to the controlling device is  
correct. Whenever the controlling device is turned on, the  
amplifier will automatically turn on after a short pause. This  
pause is intentional and it protects your speakers from damage  
while the amplifier stabilizes. You may also hear a relay click  
during start up. This is also normal.  
Knoll Systems service information  
The 21K amplifier does not contain any user serviceable parts  
inside. If you suspect a problem that may require servicing,  
contact us at www.knollsystems.com/contact.html, or by phone  
at 800 566-5579. It is extremely important that only an  
authorized service dealer make any repairs. This will ensure  
proper service and preserve the protection of your warranty.  
Keep your receipt in a safe place so that it will be available to  
verify the purchase date, should you experience a problem  
covered by Knoll System’s warranty.  
To turn off your amplifier, just turn off the device feeding the  
amplifier its audio signals. The amplifier will automatically turn  
off, which takes a few moments.  
Gain controls  
Level adjustments may be made at the rear of the amplifier.  
The circuitry in your new amplifier may be different from your  
previous one. Check the output levels to make sure that the  
control device amplifier and speakers are properly matched.  
Adjust these controls carefully as they operate in conjunction  
with the volume control(s) on your source device. Turn down  
the volume control(s) on the source device before adjusting the  
controls on the amplifier.  
Care, maintenance, and cleaning  
When the 21k amp becomes dirty, wipe it with a clean, dry, soft  
cloth. If necessary, first wipe the surface with a slightly  
dampened soft cloth with mild soapy water, then with a fresh  
cloth dampened with clean water. Wipe dry immediately with a  
dry cloth. NEVER use benzene, thinner, alcohol, or any other  
volatile cleaning agent. Do not use abrasive cleaners, as they  
will damage the finish of the metal parts. Avoid spraying  
insecticide, waxes, polishing agents, or any aerosol product near  
the 21K.  
AC line connector and power cord  
Warning: Under no circumstances should the round third prong on the plug  
be cut, bent or in any other way defeated as this may result in severe shock.  
Always turn off the amplifier and unplug the power cord before making any  
electrical connections.  
Protection circuitry  
Your Knoll amplifier uses an advanced protection circuit. The  
output will be cut off if excessive low frequency (below 10 Hz) is  
present, if the amp over heats or has excessive current  
demands. The amplifier will begin to operate normally after the  
over heating or excessive low frequency. Should this occur,  
check all speaker wire connections, both at the speaker  
terminals on the back of the amplifier to make certain that none  
of the strands from any channel touch another channel, and that  
none of the strands from a “positive” terminal touch strands  
from a “negative” terminal. Even a few stray wires can cause  
the amplifier to go into the protection mode. After checking all  
speaker connections, turn the unit back on. If it continues to  
 
speaker cones will be moving in, while others move out. This  
will cause indistinct or confusing imaging, and muddled and  
cloudy sounds. To avoid incorrect phasing or polarity, be sure to  
use wire that has distinct markings, colors, stripes, wording, or  
grooves on each side of the speaker cable. When making  
connections to the amp and speakers, follow a consistent  
pattern of using one side of the wire to the red terminals and  
the other side to the black. When using cable with markings on  
one side only, standard convention is to consider the marked  
side of the wire as the red, or positive (+) connection, and the  
non-marked side as the black or negative (-) connection.  
Note: While most speaker manufacturers follow industry convention of using  
red terminals for positive connections and black terminals for negative, some  
manufacturers may vary from this configuration. To ensure proper phase  
connections, and optimal performance, consult the identification plate on our  
speaker terminals, or the speaker’s manual to verify polarity. Contact the  
speaker’s manufacturer if you do not know the polarity of your speakers.  
Making rear panel connections  
When connecting the amplifier to your source equipment, match  
the output channel designations on the rear of your source  
equipment to the input jacks on the rear panel of your amplifier  
that have the same channel name. Correct polarity connections  
are important to maintain proper speaker phasing. When  
making connections to the amp and speakers, follow a  
consistent pattern of using one side of the wire to the red  
terminals and the other side to the black terminals.  
Next loosen the knobs of the amplifier’s speaker output  
terminals far enough so that they pass through hole is revealed.  
Follow the proper connection instruction for your system with  
regard to which terminals are used. Once the connections are  
made, twist the cap back so that the connection is secured but  
do not over tighten or use tools, as this may break the delicate  
wire strands and decrease system performance.  
Power control connections  
The 21k amplifier features a built-in remote turn-on system that  
can automatically switch the amplifier on when another device  
in the system is switched on.  
If you are using spade lugs, connect them to the speaker wire  
using the manufacturer’s instructions, and then loosen the caps  
on the speaker terminals. Place lugs between the plastic cap  
and the back of the terminal. Be sure to observe proper polarity.  
Use your fingers to tighten to obtain a positive contact.  
Remote turn-on using products equipped with a low-  
voltage trigger jack: Make sure the 21k front panel power  
switch is in the out of “OFF” position. Use an accessory cable  
with a 3.5mm mono mini-plug on each end to connect the  
trigger output jack on the rear of the source device to the  
trigger input jack on the back panel of the amplifier. The trigger  
needs to be 12 VDC and about 35 mA. When trigger power is  
switched on, the amplifier will automatically turn on at the same  
time.  
When using banana plugs, connections may be made by  
inserting the jack affixed to your speaker wire into the hole  
provided on the rear of the colored screw caps on the binding  
posts. Before using banana –type jacks, make certain that the  
plastic screw caps are firmly tightened down by turning them in  
a clockwise direction until they are snug against the chassis.  
This ensures that the maximum surface area of the plug is in  
contact with the jack. Watch for proper polarity.  
Remote turn-on using external AC to DC power converter:  
If your source device does not have a dedicated trigger jack, it  
is still possible to activate the unit for automatic turn on when a  
Switched Outlet is available on the rear of the source device. To  
control the 21k amplifier this way, you will need a small AC to  
DC power converter like our PS1202, capable of delivering 12  
volts DC and over 35 mA. The DC voltage should terminate in a  
standard 3.5mm type mini plug (this will have to be added to  
the PS1202). This type of converter may be obtained as a power  
adapter from many electronic retailers.  
Run the cables to speaker locations. Do not coil any excess  
cable, as this may become an inductor that creates frequency  
response variations in your system. Lastly, connect the wires to  
the speakers, again being aware of proper polarity. Remember  
to connect the negative, or black wire, to the matching terminal  
on the speaker. The positive or red wire should be connected to  
the matching terminal on the speaker.  
 
-
+
12 VDC 45 mA  
Trigger Input  
Power  
IN OUT  
When installing, make sure the 21k front panel power switch is  
in the out or “OFF” position. Plug the DC adapter into a switched  
outlet on the source device that will be activated when you want  
to have the amplifier turn on. This may be the switched outlet at  
the rear of an AC receiver or other audio equipment. Connect  
the 3.5mm mini-plug from the adapter to the trigger-input jack  
on the back panel of the amplifier. The amplifier now turns on  
and off automatically, based on the status of the controlling  
device.  
Left  
connection.  
Observe  
correct  
L
Speakers  
Right  
High Current  
21KPower Amplifier  
R
voltage.  
Power  
BRIDGE Gain  
(OU T)  
L
R
8
A
2-16 OHM  
SPEAKERS  
120 VAC  
~ 60 Hz  
Bridge switch must be in OUT postion.  
Connect speakers to RED terminals.  
SOURCE  
+
Minimum speaker impedance is  
six (6) ohms.  
-
Power connection  
Bridge Mode  
Once all audio system connections have been made, connect the  
supplied power cord to the amplifier first, and then connect it to  
an AC power source. Please make certain that the amplifier is  
turned off and that the device connected to the remote trigger  
input is off when connecting the power cord and plugging it into  
an AC outlet.  
The 21K can be put into the mono bridge mode to increase the  
power output.  
To do this, first make sure the 21K is powered down or off.  
Speaker damage could occur if it is powered up.  
Connect the source RCA jack to the left input. The left RCA  
source output can be sent to another amplifier input.  
Amplifier operation  
After all connections have been made you are ready for  
operation. First, turn on the source component in your system.  
Make sure the bridge switch is in the out position.  
Connect the speaker (minimum 6 ohms) to the two red speaker  
terminals on the 21K. The left red terminal on the 21K is  
connected to the speaker positive (+) input. The black 21K  
speaker terminals are not connected in the bridge mode.  
It is always a good idea to turn on your amplifier LAST.  
This avoids the possibility of any turn on pops or transients from  
other equipment being amplified and sent to your speakers  
where they may cause damage. Always start with a low volume  
level on your computer or preamp to avoid damage to your  
speakers.  
Turn the Left gain on the 21k all the way down (counter  
clockwise).  
Turn the source on and the power to the 21k and adjust the Left  
gain as desired.  
21k Manual on  
Press the 21k front power switch to the “on” position. There will  
be a short pause from the time the power is turned on until  
power is applied to the speakers. This is intentional and protects  
your speakers from damage while the amplifier stabilizes. The  
red protect lamp will glow and when the amp is ready a blue  
light will switch on. To turn the unit off, press the power button  
again (out position). The amp will turn off in a few seconds.  
Enjoy.  
 

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