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Current Ratings
The wide dynamic range of audio signals normally causes
a high peak-to-RMS ratio in an amplifier's DC supply
currents. The HM-1 has internal storage circuits to minimize
the peak-to-average ratio, which
• reduces the peak power rating required by the
supply;
• allows efficient use of switched-mode power
supplies which have similar peak and continuous
ratings.
The following table lists the current and power draw for
a single HM-1 at light, moderate, and maximum operating
levels.
C
r u
e r
t n
a
n
d
P
o
R
M
S
O
p
r e
t a
n i
g
L
e
v
l e
C
r u
e r
t n
L
g i
t h
1
5 .
A
n (
o
i l
m
t i
n i
) g
R
M
S
M
o
d
e
a r
e t
2
0 .
A
o (
c c
s a
o i
a n
i l l
m
t i
n i
) g
R
M
S
M
a
i x
m
u
m
3
0 .
A
(
o c
t n
n i
u
o
s u
i l
m
t i
n i
) g
R
M
S
Each HM-1 draws 0.4 ADC, 20 W in a quiescent state.
The RMS current is measured over a 500 ms integration
time. The peak current is measured over a 10 ms integration
time.
Each HM-1 can drive a slaved Meyer subwoofer from a
connection on the amplifier panel. Adding the subwoofer
increases the amplifier's output current, which increases
the power supply current. The current and power ratings
for an HM-1 and a subwoofer are listed in the following
table at light, moderate, and maximum operating levels.
C
r u
e r
t n
a
n
d
P
o
w
r e
D
a r
R
M
S
O
p
r e
t a
n i
g
L
e
v
l e
C
r u
e r
t n
L
g i
t h
2
0 .
A
n (
o
i l
m
t i
n i
) g
R
M
S
M
o
d
e
a r
e t
2
5 .
A
o (
c c
s a
o i
a n
i l l
m
t i
n i
) g
R
M
S
M
a
i x
m
u
m
3
5 .
A
(
o c
t n
n i
u
o
s u
i l
m
t i
n i
) g
R
M
S
An HM-1 with subwoofer draws 0.4 ADC, 20 W in a
quiescent state.
4
w
r e
D
a r
w
f
r o
1
H
M
1 -
P
e
a
k
R
M
S
P
e
C
r u
e r
t n
P
o
w
r e
P
o
2
0 .
A
7
2
W
9
6
P
E
A
K
R
M
S
3
5 .
A
9
6
W
1
6
8
P
E
A
K
R
M
S
5
0 .
A
1
4
4
W
2
4
0
P
E
A
K
R
M
S
w
f
r o
1
H
M
1 -
w
i
h t
S
u
b
w
o
f o
P
e
a
k
R
M
S
P
e
C
r u
e r
t n
P
o
w
r e
P
o
2
5 .
A
9
6
W
1
2
0
P
E
A
K
R
M
S
4
0 .
A
1
2
0
W
1
9
2
P
E
A
K
R
M
S
6
0 .
A
1
6
8
W
2
8
8
P
E
A
K
R
M
S
Voltage Ratings
The voltage operating range for the HM-1 is 48 VDC
nominal, 52 VDC absolute maximum, and 35 VDC
minimum without shutoff.
Allowing operation down to 35 VDC provides two
benefits. First, a moderate voltage drop (up to 8 V) for
long DC power cables has a minimal impact on audio
performance, enabling the use of light-gauge cables for
most installations.
Second, since some switched-mode power supplies
slowly foldback the voltage if they experience current-
limit, power supplies with lower power (current) ratings
can be used efficiently. Since supplies with lower power
ratings typically experience current-limit when the HM-1
is at continuous limiting, some voltage drop and loss of
headroom is acceptable provided the voltage does not
a
k
drop below 35 VDC. At 35 V, the maximum current draw
w
r e
is 25% lower than the values stated in the preceding
tables.
W
P
E
A
K
NOTE: If the HM-1 will not be driven at continuous limiting,
a power supply that satisfies the moderate specifications
W
P
E
A
K
for voltage and current can be used safely without risk of
sonic degradation or interruption.
W
P
E
A
K
It is important to understand how the selected power
supply responds to current-limit, particularly for
switched-mode supplies. Some supplies trip off and must
be reset manually, while others remain off for a period of
time and reset automatically. In both cases, the HM-1
suffers audio interruption. In the third, and preferable
case, supplies that feature voltage foldback allow brief
periods of current-limit without audio interruption; for
this reason, we recommend using such supplies.
The HM-1 does not require tight voltage regulation and
operates down to 35 V although peak SPL values are
reduced. This operating voltage flexibility allows for
wiring loss and voltage foldback without interruption
r e
or degradation of the audio signal.
a
k
Many high power industrial supplies (1–5 kWatt) are
w
r e
available for 19" EIA racks that are suitable for large
installations with equipment rooms. Distribution panels
W
P
E
A
K
with branch circuits can be used economically with up
to 8 HM-1s on a branch. Contact Meyer Sound for
W
information on tested and approved supplies.
P
E
A
K
W
P
E
A
K
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