Accuphase C 17 Brochure

Page 2

Although the superiority of MC (Moving-
coil) cartridges in their sound quality is
indisputable, their outputs must be am-
plified 20 to 30dB more than MM (Mov-
ing-magnet) cartridges because the out-
put level of an MC cartridge is low.

To provide this extra amplification.
step-up transformers have been tradi-
tionally used. However. recent years
have found the advent of head amplifiers
that realize electronically direct amplifica-
tion of the input signal thanks to the
improvement of semiconductor and cir-
cuit technologies. Although step-up
transformers are still preferred by some
audio enthusiasts. the reason for this is
that the combination of the characteris-
tics of the transformer and cartridge
allows reproduction of unique musical
nuances. Nevertheless. the characteris-
tics of the cartridge are sometimes not
faithfully transmitted and mismatching of
impedances may cause degradation in
the tonal balance.

Accuphase Head Amplifier 0-17 is
constructed with an eye to the faithful
transmission of the unique characteris-
tics of the cartridge. In other words. our
goal was a head amplifier that does not
announce the presence of amplification
system.

All amplification stages of the C-17
employ a cascade push-pull configura-
tion that provides the upper limits of the
frequency characteristics. linearity. and
signal-to-noise ratio. The overall per-
formance of a head amplifier is likely to
be affected by the power supply because
the level of the signal processed by the
head amplifier is extremely low. Conse-
quently. the impedance of the power
supply and noise have a significant in-
fluence on the sound quality.

The 0-17 eliminates almost all the
problems attributable to the power supply
by using mono-construction of power
transformers in which the left and right
power transformers are completely inde-
pendent ol each other.

To accommodate the wide range of
the output voltages and input impe-
dances of MC cartridges. gain can be set
to 26dB or 32dB by selector switches.
Additionally. the input impedance can
also be varied to 10. 30 or 100 ohms by
selector switches.

We are confident that the C-17. which
is designed to be the ultimate head
amplifier. is fully capable of accurately
and faithfully reproducing the unique
sound quality of every type of MC car-
tridge.

ccu Lose (3'17

MC CARTRIDGE HEAD AMPLIFIER

CASCODE PUSH-PULL
AMPLIFICATION REALIZING
IDEAL AMPLIFIER
PERFORMANCE

The circuit diagram or the can is shown in Fig.
1. AS shown. each amplifier circuit stage has
two vertically connected elements that operate
lust as it they were a single element. The
connection of elements is called cascode
connection". which features Iaw feedback at
each element constituting the connection. ex-
tremely small noise. and superb linearity at both
low and high frequencies. The 017 employs
pushpull circuits icrmed in the cascode con-
nection and thereby suppresses the distortion
and noise. The Ideal performance of the 0-17
and an amplifier has thus been realized. These
cascade amplifier circuits are accommodated
into both the right and left aluminum housings
that are independent of each othert thereby
preventing resonances caused by induction
noise and vibration.

COMPLETE LOW-NOISE

DESIGN
Noise. that is, signal-to-nOIse ratio. provides the
most significant clue to determine the pertaini-
once of a head amplifier. Especially. when using
the signal from an MC canndge whose output is
mm or less. how to suppress the restdual
noise of the head amplitier is the most important
theme.

or course. the C-17 employs carefully
selected low-noise crrcutt elements. What is
more. resistance nurse is substantially reduced
by decreasing the impedance of the NFB loop
so that the noise generated in the differential
input circuit is suppressed.

Moreover. to prevent the noise generated in
the DC servo circuit lrom affecting the perform-
ance of the head amplifier. the signal is fed back
to the bases of the Conslantrcurrent transistors
05 and 06 instead of being directly fed back to
the negative side of the differential amplifier
circuit, This feedback method has realized a
signat-to-notse ratio that is virtually the theore-
tlcal upper limit.

TWIN MONO-CONSTRUCTED
INDEPENDENT POWER
TRANSFORMERS; EACH
UNIT AMPLIFIER HAS ITS
EXCLUSIVE REGULATED
POWER SUPPLV

The power supply circuit can be considered a
part oi the amplifier circuit since signals also
pass through it. Therefore. unless its quality
matches that of the amplifier circuit, no improve-
ment in overall sound characteristics can be
realized.

The C-t7 employs twin power transformers
which are both completely independent. electri-
catty and structurally. of each other. One ener-
gizes the ten channel and the other the right
channel. thereby constituting the ideal mono-
cortstructiort. Furthermore. to achieve low impe-
dance over a wide bandwidth. the 0-17 employs
an exclusive oonstant~voltage power supply for
each at the left and right channels. To minlmlze
the wiring route. these constant-voltage power
supplies are accommodated in the same alumi»
num housing where the amplifier circuits are
incorporated.

IMPEDANCE AND GAIN

SELECTORS ENSURE BEST

INPUT MATCHING
The C-t7 I5 provided with excellent input
matching to various MC cartridges which come
in such wide variations of impedances and
output levels. For example. the internal toutput)
impedances of MC cartridges vary all the way
from 2 ohms to about 50 ohms. a difference of
20 or 30 times. Likewise. their output voltage
levels vary from out mV to 0.5 mV. a difference
of 50 times (3MB),

To accommodate this wide variety ot MC
cartridges and preserve line control or sound
quality, the 017 provides three choices of input
impedances and two choices of gains for closer
matching.

The output impedance oi the cartridge need
not be matched as strictly to the input impe-
dance ol the head amplifier as when a step-up
transformer is used.

However. on many occasions. a good r "
will tie obtained it the low output impedanc l
canrldge is matched accordingly to the low input
impedance of the head amplifier

To adapt the input impedance to all kinds oi
MC cartridges so that the sound quality may be
minutely controlled, the 0-17 is provided With
three MC input impedances: it). 30 and 100
ohms. These impedancss are selectable with
selector switches. The io-ohm input impedance
is suitable when using canridges having a load
impedance at about 3 ohms. Similarly. the so
and 100 ohm impedance are for the cartridge
With a load impedances of to ohms or more.
Furthermore. two GAIN selector swttchas (26dB
and 3"dB) are aisc provided to allow use at
tow-output MC cartridges and to obtain a gain of
32dB in addition to the normally used 26-dB
gain. Moreover. the signal received by the head
amplifier is of RIAA recording characteristics,
Thls means that the amplitude decreases at low
trequencies and Increases at high frequencies,
Therefore. a signal of about 20:18 (ten Iimesl is
input to the head amplifier when the frequency
is increased from 1.000HZ to 20,000H2 For this
reason. the maximum input level of the head
amplifier must be at least 50mv. To provide a
wide margin oi the input level. the maximum
value of the Input voltage of the (3-17 IS 150mV
(at a gain at 26dB). thereby realizing a very wide
dynamic range.

INPUT

C-17 Circuit Diagram

+5

OUTPUT

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ACCUPHASE LABDFIATDFYY INC

B865Y

851-0052»00(GZ) PRINTED IN JAPAN