INTRODUCING
THE
H
‐
1500
II
PLUS
PHONO
STAGE
The
H
‐
1500
II
PLUS
is
Allnic
Audio’s
mid
‐
line
phono
stage
model,
just
under
the
top
of
the
line
H
‐
3000.
Like
all
Allnic
Audio
products,
it
uses
Permalloy
(iron
and
nickel
alloy)
for
its
transformer
cores.
Allnic
is
grateful
to
Mr.
G.W.
Elmen
of
Western
Electric
for
inventing
Permalloy
for
transformer
core
use,
and
in
so
doing,
providing
an
enormous
service
to
recorded
music
listeners
everywhere.
The
H
‐
1500
II
PLUS
has
the
following
features:
•
LCR
TYPE
RIAA
EQUALIZATION:
RIAA
equalization
is
a
specification
for
the
correct
playback
of
vinyl
records,
established
by
the
Recording
Industry
Association
of
America.
The
purpose
of
the
equalization
is
to
permit
longer
playback
times
and
improve
sound
quality.
RIAA
equalization
is
a
form
of
establishing
a
flat
frequency
response
for
the
playback
of
recorded
music.
The
necessity
for
this
equalization
process
arises
from
mechanical
difficulties
inherent
in
record
production.
In
order
to
prevent
the
cutting
needle
from
over
‐
cutting
into
the
next
record
groove
in
the
bass,
as
a
record
is
cut,
some
bass
frequencies
are
attenuated.
In
the
treble
region,
in
order
for
high
frequency
sounds
not
to
be
masked
by
the
noise
inherent
in
moving
a
stylus
over
and
through
a
modulated
vinyl
surface,
some
treble
frequencies
are
boosted.
With
the
application
of
the
correct
filtering
techniques
on
playback,
the
result
is
a
flat
frequency
response
with
better
signal
to
noise
ratios.
There
are
four
de
‐
emphasis
methods
that
can
be
applied
at
playback:
A.
Active
filters
(Negative
feedback
types):
Different
quantities
of
negative
feedback
are
applied,
with
deeper
feedback
to
the
high
frequencies
and
shallower
to
the
low
frequencies.
The
benefits
of
this
method
are
improved
signal
to
noise
ratios,
low
cost
and
consistent
operation.
Some
of
the
shortfalls
are
looser
bass
reproduction
and
possibly
a
pinched
and
compressed
high
frequency
playback
due
to
excess
feedback
ratios.
B.
Passive
filters
(CR
type):
‐
The
frequencies
are
filtered
to
fit
the
RIAA
specification
by
varying
the
amount
of
attenuation
at
different
frequencies
through
a
complex
capacitor
‐
resistor
network.
This
technique
results
in
no
voltage
overload,
purer
reproduction
(because
there
is
no
feedback),
and
more
accurate
RIAA
compensation.
However,
there
are
problems
because
the
system
provides
no
gain,
and
insertion
loss
and
impedance
matching
issues
arise.
C.
Hybrid
filters
(use
of
both
CR
and
negative
feedback
types):
In
this
method,
both
types
of
filters
applied
separately;
an
active
filter
is
applied
to
the
low
frequencies
and
a
passive
filter
to
the
high
frequencies.
Unfortunately,
both
the
advantages
and
disadvantages
of
each
of
these
two
types
of
filters,
already
discussed,
affect
the
playback
system
at
the
same
time.
D.
LCR
filters,
which
are
used
in
the
H
‐
1500
II
PLUS:
Two
pieces
of
a
linear
reactor
(a
kind
of
choke
coil)
comprise
the
main
part
of
these
filters,
assisted
by
precise
CR
filters,
in
order
to
lower
impedances
and
insertion
loss.
In
vacuum
tube
circuits,
active
and
passive
filters
usually
are
operated
on
one
hundred
plus
kilo
ohms
of
impedance.
An
LCR
RIAA
filter's
impedance
is
a
constant
600
ohms.
Furthermore,
an
LCR
RIAA
filter's
series
resistance
is
less
than
13
ohms
(as
a
comparative,
some
famous
ones
are
31
ohms).
The
lower
the
impedance,
the
more
dynamic
is
the
sound
reproduction,
with
better
bass
response
and
speed.
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