Warranty
Knoll Systems warrants MX855 amplifiers sold in the USA and Canada by
authorized Knoll dealers to be free of defects in materials and manufacturing.
This warranty extends for three full years from the date of purchase by the
original consumer. Any products returned to Knoll Systems and found to be
defective by Knoll Systems within the warranty period will be repaired or
replaced at Knoll Systems decision, at no charge. Knoll Systems will not be
responsible for the actual cost of installation or removal of the product, nor for
any incidental or consequential damages. Some states do not allow the exclusion
or limitation of incidental or consequential damages, so the above limitation may
not apply to you. This warranty gives you specific legal rights. You may have
additional legal rights that vary from state to state.
MX855 Amplifier
Installation Instructions v7.3
8 Channel Amplifier
Warning: To be installed and/or used in accordance with appropriate
electrical codes and regulations.
Description: The MX855 is a member of the long line of Knoll multi-
channel amplifiers. Designed primarily for the custom install industry, it
is used to power speakers with different or similar sources in multiple
rooms. With 8 channels rated at 55 watts per channels at 8 Ω, the
MX855 packs some serious punch. Each channel has a gain control. The
MX855 can be turned on and off via the front panel power switch or via
the 12 VDC trigger. MX855 channels 2-4 can be linked to channel 1
individually using the link switches. MX855 amplifiers designed to meet
the amplifier needs of custom installed systems where high-quality
sound is a specific requirement.
Specifications:
Inputs
8 Gold RCA jacks with adjustable gain
50k Ω
Input impedance
Outputs
detachable plug
Output power
55 watts RMS per channel (8 Ω)
Bridged Power (channel 6) 180 watts RMS (8 Ω only)
Key Features:
Peak output power
Ideal impedance
Frequency response
S/N ratio
100 watts per channel (8 Ω)
4 - 8 Ω
1. Size efficiency. The MX855 consists of a total of 8 power
amplifiers in one 3-1/2” high enclosure. Each power amplifier
channel can deliver 55 watts RMS into an 8-Ω load.
2. Automatic protection circuitry. Each MX855 channel is
individually and fully protected against low impedance,
overheating, overloading, over voltage and under voltage. The
protection circuitry automatically restores the amplifier channel
as soon as its parameter returns to the safe operating area.
3. Individual input gain adjustment. Each channel features
an input gain adjustment pot to adjust each channel for gain
and speaker sensitivity variations.
4. External power on/off. The MX855 can be turned off and
on by external controllers via its 12 VDC trigger jack.
5. Stackable 17" chassis. 19” rack ears available.
6. Link Feature. Certain installations require that some or all of
the stereo channels play the same content. Instead of using Y
cords, the Knoll "link" cascades any or all of channels 2-4 to
channel 1 (L/R).
10 Hz - 40 kHz +/- 1dB (1w)
over 105 dB A weighted (50 watts)
less than 0.1% 20 Hz to 20 kHz
THD distortion
less than 0.01% 60 Hz 7 kHz 4:1
(SMPTE)
IMD distortion
Trigger control
Dimensions
Fan Noise
Power
12 VDC 35mA on 3.5mm mono jack
17" x 3.5" x 11.5" (432 x 89 x 292mm)
quiet 26 dBA
750 watts at 117 VAC or 230 VAC
21 lbs (9.5 kg)
Weight
Note: Specifications subject to change without notice.
Knoll Systems
7. Bridgeable. Channel 4 can be bridged giving 180 watts RMS
into an 8 Ω load for use with subwoofers and speakers that need
more power.
145 Tyee Drive Point Roberts, WA 98281
14-7163 Vantage Way, Delta BC V4G 1N1
Tel: (604) 940 1689, fax (855) 734 3363
Made in Canada/Fabrique au Canada
Knoll Systems service information
The MX855 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.
Installation
Installing the MX855 should be relatively easy. With a bit of
planning, it will give trouble free service for years.
1. The most important consideration when installing the
MX855 is cooling. The MX855 has a lot of power packed into a
small chassis size. When installing it in an equipment stack, it
should be the top component. It needs at least 3"-5" of space
above the amplifier to allow for adequate convection cooling.
2. Amplifiers should always be the top components in the system.
3. If MX855 channels frequently shutdown due to overheating,
install a fan directed up from the MX855 bottom center.
4. Never operate the MX855 on its side, as the cooling potential
drops significantly when operated this way.
5. Connect the MX855 inputs to the source component outputs with
good quality, short as possible RCA jack cables. Connect each
channel individually.
6. Connect the MX855 speaker outputs to speakers using good
quality speaker wire. Minimum 16 gauge copper wire is
recommended with 14 gauge minimum for runs over 30' (10m).
Troubleshooting
If a problem is encountered with the MX855, the most expedient
procedure is to locate the problem and if possible repair it before
requesting service. Be sure to carefully check other system
components such as controllers, CD players, volume controls,
wiring, speakers, etc. that may be at fault.
Problem
Power LED does
not light - no sound 2. Test the AC outlet with a lamp.
3. If remote on/off is used, check that
the trigger voltage is at 12 VDC.
Action
1. Check that the MX855 is plugged in.
4. Check MX855 power button on (in).
Sound cuts out
1. Verify speaker impedance is 4-16 Ω.
Changing speakers may be required.
2. Check if the MX855 feels hot. If it's
hot increase cooling - see Installation.
Note: Ideally the MX855 likes 6-8 Ω loads. Connecting
to 4 Ω loads won't hurt the MX855 but those channels
connected to 4 Ω loads may occasionally shutdown due
to overloading. Never connect to speaker loads less than
4 Ω. Channel 4 bridged mode minimum 8 Ω speaker.
Sound is distorted
1. Turn the volume down.
2. Check speakers for damage.
3. Check inputs for proper levels.
MX855 gain and source output level
may, have to be adjusted.
7. Individually adjust the channel gains as required. Ideally, all
gains are fully on (fully clockwise).
8. Make sure the speakers in each room are connected in phase
with the amplifier + going to the speaker +. Out of phase speakers
give unstable imaging and poor bass response.
9. Connect trigger if being used to a 12 VDC source (about 35mA)
using a 3.5mm mono jack. 5 VDC triggers will not work.
10. Connect the AC power into an outlet that supplies at least
EIGHT amps (1000 watts) dedicated to each MX855.
11. If more power is needed, channel 4 can be mono bridged to
give 180 watts into an 8 Ω load. Minimum impedance for
channel 4 in the bridged mode is 8 Ω. The bridged switch needs
to be in the out position. The bridged input is 4L and the 4L gain pot
adjusts the bridged gain. The speaker is connected to the 4L+ and
4R+ in the bridged mode.
4. Speakers may be less than 4 Ω.
MX855 does
not turn off
1. Push MX855 power switch off (out).
2. If trigger is being used, power switch
needs to be set to off (out) position
or amp is on all the time.
3. Try disconnecting trigger jack.
Trigger does not
work
1. Measure the trigger voltage with a volt
meter. It needs to be 11-15 volts DC
to work (current is about 35mA total
per amp). See page 5 for details.
Speaker pops when 1. Speaker may need resistor placed
amp turned on or off
across terminal. Suggest 2k0 1/4 w.
Discharges speaker internal capacitor.
Caution: Never listen to sound that is distorted. If distorted
sound is heard, turn the volume down immediately or speaker
and/or amplifier damage could occur that is not covered by the
warranty. If this problem persists, contact your dealer.
The trigger is 12 VDC (35mA per MX855) via 3.5mm mono
jack. 5 VDC trigger outputs will not work. To connect the
trigger to a receiver use a 12 VDC power supply (we
suggest Knoll PS1205 power supply with an adaptor). Plug
the power supply into the switched outlet on the rear of
the receiver. Connect the 12 volt wire to a 3.5mm mono
jack. Plug the jack into the rear of the MX855. 12 VDC
polarity is not important. Make sure the MX855 power
switch is off (out). When the receiver is switched on, the
MX855 amplifier is switched on.
User adjustments and service: There are no user
adjustments on the MX855. Your installer may make certain gain
level adjustments on the rear panel.
Caution: The MX855 contains no user serviceable parts, so do
not attempt to open or repair the MX855. Refer servicing to a
qualified technician only or contact the factory for information.
The Link button is normally set to the “in”
position to give all six stereo inputs individual
sources. When the Link button is set to the
“out” position, that input Left/Right is linked or
cascaded (or paralleled) to input #1 (without the use of Y
cords). Any or all combination of linked inputs 2 to inputs
4 are possible. When all inputs are linked to input 1 the
input impedance is about 6000 Ω.
Channel 4 can be mono bridged giving 180 watts into 8
ohms. Never connect speaker loads less than 8 ohms
to channel 4 in the bridged mode. Select the
bridge/stereo switch to the out position for the bridged
mode. The bridged input is 4L. The 4L gain pot adjusts the
bridged gain. The speaker is connected to the 4L+ and
4R+ in the bridged mode.
Caution: NEVER connect the
MX855 to impedances less
than 4 Ω or amplifier
damage not covered by the
warranty may occur.
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