Musical Fidelity M250 User manual

M250 Amplifier Instructions for Use Page 1 of 8
Issue 4: May 2002
O PERATE PO W ER
MUSICALFIDELITY
M250
MONOBLOC AMPLIFIER
INSTRUCTIONS FOR USE
Thank you for purchasing the Musical Fidelity M250 monobloc power amplifier.
Used properly and carefully, it should give you many years of outstanding
musical reproduction.
Dust regularly with a soft duster or soft brush, but be careful when using
cleaning or polishing agents - they may harm the surface finish.
If you have any questions about your audio system,
please consult your dealer who is there to help and advise.

M250 Amplifier Instructions for Use Page 2 of 8
Issue 4: May 2002
SAFETY INFORMATION
IMPORTANT! (U.K. only)
This unit is supplied in the U.K. with a mains lead fitted with a moulded 13 amp plug.
If, for any reason, you need to cut off this plug, please remove the fuse holder and dispose of
the plug safely, out of reach of children. It must not be plugged into a mains outlet.
The wires in the mains lead supplied with this appliance are coloured in accordance
with the following code:
Green and yellow..............Earth
Blue...............................Neutral
Brown................................Live
WARNING - This appliance must be earthed
As the colours of the wires of the mains lead of this appliance may not correspond with the
coloured markings identifying the terminals in your plug, proceed as follows:
The wire which is coloured green-and-yellow must be connected to the terminal in the plug
which is marked with the letter E or coloured green or green-and-yellow, or by the earth
symbol:
The wire which is coloured brown must be connected to the terminal which is marked with the
letter L or coloured red.
The wire which is coloured blue must be connected to the terminal which is marked with the
letter N or coloured black.
If connecting to a BS1363 plug, a 13 amp fuse must be used.
WARNING:
The M250 is a powerful amplifier and must necessarily supply high voltages
through the loudspeaker terminals. Therefore, to avoid any possibility of an
electric shock DO NOT TOUCH THE SPEAKER TERMINALS when the unit is
being used.
To comply with BSEN60065 safety regulations, the 4mm “banana” plug holes have
been fitted with plastic blanking pieces. Removal of these will invalidate any elec-
trical safety approval of this product.
WARNING:
Any modifications to this product not expressly approved by Musical Fidelity who
is the party responsible for standards compliance could void the user’s authority to
operate this equipment.

M250 Amplifier Instructions for Use Page 3 of 8
Issue 4: May 2002
GENERAL ADVICE
INSTALLATION PRECAUTIONS and USER INFORMATION
Your new M250 power amplifier is designed and built to provide trouble-free performance, but
as with all electronic devices it is necessary to observe a few precautions:
Heed all warnings shown on the back of the product.
Only connect the M250 amplifier to a mains outlet having the same voltage as marked at the
back of the unit.
Always ensure that when disconnecting and reconnecting your audio equipment the mains
supply is switched off.
Position the mains lead and signal interconnects where they are not likely to be walked on or
trapped by items placed on them.
Do not use near water, or place water-filled containers on the amplifier, for example, flower
vases or potted plants. If water does spill into the player, immediately pull out the mains plug
from the wall socket and inform your dealer, who should then check the unit before further
use. Entry of liquid into the amplifier is dangerous, and may cause electric shock or fire
hazard.
Do not place the unit near heat sources such as radiators, direct sunlight or other equipment.
The case of this amplifier can run at high temperatures - operate the unit in a well ventilated
area, and do not touch the side heatsink fins after periods of use at high output power.
Do not remove covers or try to gain access to the inside. There are no internal user adjust-
ments. Refer all service work to an authorised Musical Fidelity agent.
NOTE: Unauthorised opening of the equipment will invalidate any warranty claims.
There are fuses inside the M250 Amplifier. In the unlikely event that one blows, refer the unit to
your audio dealer. Do NOT try to replace the fuse yourself as this will invalidate the warranty.
Dust regularly with a soft duster or soft brush, but be careful when using cleaning or polishing
agents - they may harm the surface finish.
The electronics in modern hi-fi equipment is complex and may, therefore, be adversely affected
or damaged by lightning. For protection of your audio system during electrical storms, remove
the mains plugs and disconnect any aerial lead.
If after-sales service is required, to help your dealer identify the M250 please quote the serial
number located on the rear panel of the unit.
RADIO FREQUENCY INTERFERENCE (R.F.I)
This product has been tested to ensure that its operation is not adversely affected by normal
background levels of R.F.I., and that it does not itself generate excessive amounts of interfer-
ence. However, if a problem persists, please contact your Musical Fidelity agent.

M250 Amplifier Instructions for Use Page 4 of 8
Issue 4: May 2002
CONNECTIONS AND FACILITIES
MADEIN EN G LA N D BY MUSICALFIDELITY
POWER CONSUMPTION 400W
SERIALNUMBER
50/60H z
PO W ER
UNITS 15-17 OLYMPIC TRAD ING ESTATE
FU LTO N RO AD W EM BLEY MID D LESEX HA9 O TF EN G LA N D
IMPORTANT
SPEAKER
OUTPUTS
+CAU TIO N
DO NOTREMOVESC REW S
ORC O VERS UN DER AN Y
CIRC U M STAN C ES.
NO USERSERVICEABLE
COMPONENTSINSIDE.
REFER SE RV ICING TO
QUALIFIED EN G IN EER.
LINE
INPUT
LOOP
OUTPUT
ON
OFF
TRIGGER
IN
TRIGGER
OUT
34 56
Front panel layout
1OPERATE indicator LED (blue)
2 Power status button (see page 6)
3POWER-on indicator LED (orange)
Back panel layout
3 Speaker output (see page 5)
4 Speaker output (see page 5)
5 Power switch
6 IEC type mains inlet socket
7 Trigger output (see pages 5 and 6)
8 Audio loop output (see page 5)
9 Audio line input
10 Trigger input (see pages 5 and 6)
O PERATE PO W ER
MUSICALFIDELITY
12 3
78 910

M250 Amplifier Instructions for Use Page 5 of 8
Issue 4: May 2002
CONNECTIONS
Taking the left channel connections, the
pre-amp’s left output is connected to the-
first M250’s LINE INPUT (used for the
woofer, or low frequencies), and then the
first M250’s LOOP OUTPUT is connect-
ed to the LINE INPUT of the second
M250 (used for the tweeter, or high fre-
quencies).
Repeat this process for the right channel.
If you are in any doubt about bi-amping,
please contact your dealer, who will be
able to advise.
TRIGGER CONNECTIONS
Two 3.5mm jack sockets on the rear panel
marked TRIGGER IN and TRIGGER
OUT are provided for electronically
switching the “audio sense” mode - see
page 6. These are directly linked together
inside the amplifier, to enable onward con-
nection to a further unit, such as another
M250.
OUTPUT CONNECTIONS
Connect your loudspeaker to the terminals
marked SPEAKER OUTPUTS.
Two sets are provided for parallel opera-
tion or “bi-wiring”, but note that the
combined load impedance must not be
less than 4 ohms.
BEFORE SWITCHING ON. . . . .
Plug the accessory IEC mains lead into the
rear panel socket, then the other end into a
wall outlet.
Turn the volume control on your preampli-
fier to minimum, and switch on its power.
All input, output and power connections
should be made with the mains power
switched OFF.
INPUT CONNECTIONS
As the M250 is a mono power amplifier,
two are required for stereo operation, and
further units can be used for multi-channel
surround systems or bi-amplification etc.
The M250 can be used with a preamplifier
or any audio line level source which has a
volume control.
Connect your pre-amplifier or other line
level source to the RCA socket on the
back panel marked LINE INPUT.
For the best results we recommend either
Musical Fidelity X-LINX "no-nonsense"
cables for this connection or the highly
rated Nu-Vista leads with integral RFI
suppression. Various lengths are available
in the Nu-Vista interconnect range. Please
contact your local dealer for more infor-
mation.
BI-AMPLIFICATION
The M250 has a LOOP OUTPUT socket
to allow “bi-amping” of a speaker with
suitable active or passive crossover net-
works. This socket is directly linked
inside the amplifier to the LINE INPUT
socket to enable onward connection to a
further unit, such as another M250.
In this arrangement, typically one M250 is
used to drive the “tweeter” (high frequen-
cies), and one to drive the “woofer” (low
frequencies) of each loudspeaker enclo-
sure. Thus, four M250s would be needed
for a stereo pair.

M250 Amplifier Instructions for Use Page 6 of 8
OPERATION
Issue 4: May 2002
OPERATION
Press the POWER rocker switch on the
rear panel - the orange POWER LED on
the front panel will light confirming that
the unit is ready for use.
Audio Sense Mode
The M250 is now in “audio sense” mode,
and will turn on when an input signal is
detected.
When an audio signal is received the
amplifier will turn on, and the blue OPER-
ATE LED will be lit. If there has been no
audio input for about 15 minutes the
amplifier will turn off and the OPERATE
LED will go out.
The M250 may be turned on or off manu-
ally by pressing the power status button on
the front panel.
When the amplifier has been turned on
manually by the front button it will revert
to “audio sense” mode if there has been no
audio input for about 15 minutes.
When the amplifier has been turned off
manually by the button it will stay off,
even if audio input is present, until there
has been no audio for about 15 minutes,
when it will revert to “audio sense” mode.
If there is an audio input signal present
when mains power is applied to the M250,
it will turn on immediately with the
OPERATE LED lit.
Trigger Mode
The M250 responds to a “trigger on” con-
trol voltage of between 5 and 12 volts posi-
tive or negative, received via the 3.5mm
TRIGGER IN socket on the rear panel.
The first trigger pulse received after apply-
ing mains power will turn the amplifier on,
and cancel the “audio sense” mode.
When the amplifier senses a “trigger off”
pulse (return to zero voltage), the amplifier
will turn off.
The M250 may be turned on or off manual-
ly with the front panel button at any time.
When the amplifier has been turned on
manually by the button, it will turn off if it
receives a “trigger on” signal followed by a
“trigger off” pulse.
If the amplifier has been turned off manual-
ly by the button, it will turn on if it receives
a “trigger off” signal followed by a “trigger
on” pulse.
To cancel trigger mode and revert to audio
sense mode, first remove the trigger source.
Then, using the mains switch at the rear of
the unit, turn mains power off and after a
few seconds, back on again.
Audio Adjustment
Select the required audio input source on
your pre-amplifier, and advance the volume
control to obtain the preferred sound level.

M250 Amplifier Instructions for Use Page 7 of 8
Issue 4: May 2002
TROUBLESHOOTING
Basic problem-solving with an amplifier is similar to troubleshooting any other electrical or
electronic equipment. Always check the most obvious possible causes first. To give you a few
ideas of what to look for, check the following:
If none of these actions effect a cure, please contact your dealer, or an authorised Musical
Fidelity service agent. Remember, never open the case of the M250 power amplifier yourself,
as this will invalidate the guarantee.
Problem Possible Cause Remedy
No power when MAINS Mains plug not inserted Plug in securely
POWER switch is operated fully into rear socket
No sound Tape monitor function has Switch off tape monitor
been selected on the pre- at the pre-amplifier
amplifier
Wrong connections between Check audio input lead
pre-amplifier and the M250 connections
Speakers not connected, or Check speaker cables
incorrectly wired
In multi-channel use, the Speakers are connected out of Ensure speakers are
sound is not precise, and phase connected correctly
lacking bass and stereo
image

M250 Amplifier Instructions for Use Page 8 of 8
Issue 4: May 2002
SPECIFICATIONS :
Output voltage, RMS 45 Volts 20Hz to 20kHz
peak 127 Volts
Power output 250 Watts into 8 Ohms (24dBW)
450 Watts into 4 Ohms
Peak-to-peak output current 72 Amps
Damping factor 180
Output devices per channel 6
Total Harmonic Distortion + noise 0.006% at 1kHz up to 90% power, into 4 or 8 Ohms
Intermodulation distortion 0.004% at 12.5 Watts into 8 Ohms
Frequency response 20Hz to 20kHz ±0dB
10Hz to 100kHz +0 / -1.5dB
Audio gain 30dB (31.5 times) nominal
Input impedance 31K Ohm
Input sensitivity for full power output into 8 Ohms 1.42 Volts
Signal / noise ratio, reference full power output > 115dB “A”- weighted
Input 1 RCA connector
Outputs 1 amplifier channel via 2 pairs of speaker binding posts
1 RCA loop output socket
Power requirements 100 / 115 / 230V AC, 50 / 60Hz (factory preset)
1000 Watts maximum into 8 Ohms load
70 Watts idle
Dimensions 192 mm, 7.6 inches wide
125 mm, 4.9 inches high including feet
460 mm, 18.1 inches deep including terminals
Weight 12 kg, 26.4 lbs unit only, unboxed
14 kg, 30.8 lbs in shipping carton
Standard accessories IEC type mains lead
Musical Fidelity reserves the right to make improvements which may result in specification or feature changes without notice.
M250
Monobloc Amplifier