5
Operating Manual - MFA-8000 and MFA-6000 Power Amplifier
peaking at the clipping level, the following AC line cur-
rent capacities are recommended for system design pur-
poses:
Load
MFA-6000
MFA-8000
Idle
1 Amp
1.2 Amps
8
Ω × 2
7.5 Amps
10 Amps
4
Ω × 2
10 Amps
15 Amps
2
Ω × 2
15 Amps
20 Amps
Table 3.1: Recommended AC line current capacity
Both MFA amplifiers consume less than 12 amps
when operating at 1/8 power into 2
Ω
loads. This condi-
tion satisfies the UL, CSA and building electrical code
requirements for a piece of audio equipment not to con-
sume more than 80% of the current available when plugged
into a grounded 15 amp outlet and operated at 1/8 of maxi-
mum power.
3.3
AC Grounding Requirements
To reduce the risk of ground loop hum, all system
ground references should originate at the same point in
your AC power distribution. Never remove the amplifier’s
ground pin as it is both unlawful and dangerous, creating
a potential shock hazard.
4.
CABLE REQUIREMENTS
4.1
Input Cables
Be sure to use shielded cable whether balanced
or unbalanced. Shielding which is properly grounded will
protect the signal from outside electrical interference such
as RF, fluorescent lighting, even computer noise. As a
general rule, unbalanced or single-ended (tip-sleeve) lines
of less than 10 feet are satisfactory, but greater distances
may require a balanced signal. Avoid running input lines
in close proximity or parallel to long speaker lines, AC
power cables, or power transformers, as this may gener-
ate hum or oscillation.
4.2
Output Cables
The MFA amplifiers are capable of delivering
high levels of output current, therefore the wire gauge used
for speaker cables is particularly important. Inadequate
wire gauge adds significant resistance to the speaker’s own
impedance, reducing the power which is actually deliv-
ered to the speaker. It will also result in a decrease in the
damping factor and possible fire hazard.
Since power at the speaker load is a primary con-
cern in system design, we have included a table to best
determine appropriate wire gauge for your application.
Table 4.1 lists the percentage of the speaker load power
which would be lost in an arbitrary 100 ft run of 2-con-
ductor cable. This table expresses the power loss as a per-
centage of the load’s power rather than the total amplifier
output power, so that you can use this table to accurately
determine power loss at other cable lengths. For example,
if you plan to deliver 100 watts to an 8
Ω
load through 50
ft of 14 ga. cable, the power loss in the cable would be
3.2%
÷
2 = 1.6% of 100 watts or 1.6 watts lost in the cable.
Wire Gauge
Ω/
100ft
8
Ω
load
4
Ω
load
2
Ω
load
8
.0605
Ω
0.8%
1.5%
3.0%
10
.1018
Ω
1.3%
2.5%
5.1%
12
.1619
Ω
2.0%
4.0%
8.1%
14
.2575
Ω
3.2%
6.4%
12.9%
16
.4094
Ω
5.1%
10.2%
20.5%
18
.6510
Ω
8.1%
16.3%
32.6%
Table 4.1: Percentage of speaker load power lost in 100
foot run of 2-conductor cable.
5.
RACK-MOUNTING REQUIREMENTS
5.1
Mechanical
All Ashly amps are designed to fit in standard 19-
inch racks. The front panel rack-mount ears are suffi-
ciently strong for most applications. If you desire further
integrity for mobile racks, we recommend using the four
additional holes in the back of the chassis for supplemen-
tal rear-mounting (see dimensional drawings).
5.2
Cooling
Be certain that both the front and back of the rack
have unhindered access to free air flow. Fan direction is
from front to back. It is not necessary to leave empty space
above or below the amplifier for cooling purposes. Ther-
mal output of the amp is measured in max BTU/hour for
typical audio program material when both channels are
just peaking at the clipping level.
Load
MFA-6000
MFA-8000
Idle
420
500
8
Ω
1900
2420
4
Ω
2300
3450
2
Ω
4140
4830
Table 5.1: Maximum BTU/hour
