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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.
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 Action
Power LED does 1. Check that the MX855 is plugged in.
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.
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.
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.
4. Speakers may be less than 4 Ω.
MX855 does 1. Push MX855 power switch off (out).
not turn off 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 1. Measure the trigger voltage with a volt
work 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.
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).
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.
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.