Accuphase C-3850 User Manual
● Revolutionary low-noise "Balanced AAVA Volume Control" ● High-rigidity,
high-accuracy volume knob sensor mechanism ● Separate high-efficiency
toroidal power transformers for left and right channels ● Selectable preamp
gain ● Fully modular construction with separate left/right units for each amplifier
stage ● Logic-controlled relays for shortest signal paths ● Independent phase
selection for each input position ● Printed circuit boards made from glass cloth
fluorocarbon resin ● Massive wood cabi net with natural grain finish
The Ultimate Analog Preamplifier — Balanced AAVA, the supreme volume control
system from Accuphase, provides incredible smoothness and complete mastery over the
music reproduction process. Outstanding signal/noise ratio prepares the stage for the
source to emerge with breathtaking realism, conveying a wealth of acoustic detail such
as hardly ever experienced before. The C-3850 represents the pinnacle of 45 years of
Accuphase excellence in analog preamplifiers.
Having been founded in 1972, Accuphase commemorated
its 40th anniversary by releasing a next-generation beacon
model, the Precision Stereo Preamplifier C-3800. It marked
a major milestone and was highly lauded by audiophiles
around the world as a tour de force in technological
excellence, performance, and sound quality. The new
Precision Stereo Preamplifier C-3850 continues the
challenge and raises the bar even further, bringing
together the entire wealth of preamplifier know-how gained
by Accuphase over the years. In construction as well as
circuit design, it incorporates latest technology realized
with components selected through a thorough review
process including extended listening tests. The result is an
audio instrument that admits no compromise in the pursuit
of peerless performance for musical mastery.
Conventional volume controls attenuate the input signal by
Balanced AAVA (Accuphase Analog Vari-gain Amplifier) Volume Control
High Voltage
Current Feedback
Amplifier
Conversion into current
with 16 weighting
stages (1/2 - 1/2
V- I Converter
1
−
2
1
−
2
2
1
−
8
2
1
−
15
2
1
−
16
2
16
)
4-parallel
2-parallel
16 current switches
16
2
= 65,536
possible combinations
introducing a resistance (either using a rotary variable
resistor or fixed resistors) in the signal path, and then
amplifying the result. This makes it inevitable that–along
with attenuation–information will be lost and noise will
increase at the lower volume level settings that are
normally used. By contrast, AAVA does not "turn down" the
volume in the ordinary sense. Rather, it switches a
combination of V-I amplifiers as required in order to directly
change the amplifier gain and thereby achieve the desired
volume. This revolutionary approach eliminates impedance
changes as well as adverse effects from noise and other
factors. Because there is almost no increase in noise, S/N
ratio does not suffer at any listening level including the
important moderate volume settings. Frequency response
remains uniform and sound quality always maintains its full
excellence. The C-3850 features a further evolved version
Operation Principle of
Balanced AAVA in C-3850
I-V Converter
Reconversion of current into voltage
＋
Current values
are added
LEVEL DISPLAY
+ OUTPUT+ INPUT
The musi c signa l is converted into 16 types of weighted current by V-I
(voltage-to-current) converting amplifiers, as shown in the illustration below.
The 16 currents are turned on or off by 16 current switches, and the
combination of switch settings determines the overall current. The resulting
current forms a variable gain circuit that adjusts the volume of the music signal.
The respective currents are combined and converted back into a voltage by an
I-V (current-to-voltage) converter before being sent to the subsequent stage.
Current
ratio
of this principle, called "Balanced AAVA", with two AAVA
circuits driven in a parallel balanced configuration. This
results in ideal volume control behavior from balanced
input to balanced output. In addition, the volume knob and
sensor mechanism fashioned with utmost precision from a
single highly rigid aluminum block provides silky smooth
operation with excellent tactile feel, and also improves the
quietness of motor-driven operation. The entire path for all
signals from the input connectors to the outputs is fully
balanced, and signal purity is further elevated by the use of
ultimate-quality parts and materials, ensuring electrical
characteristics and sonic excellence of the highest order.
With its no-holds-barred use of resources, and its bold
realization of latest circuit design, the C-3850 is an analog
preamplifier that redefines the state of the art and points
the way towards the future.
AAVA Operation Principle
0.5
Graphic representation of 16 types of V-I
converter amplifiers and resulting currents
0.4
0.3
0.2
Balanced
Input
–
INPUT
High Voltage
Current Feedback
Amplifier
CPU controls current on/off
switches so that volum e
level matches knob position
V- I Converter
1
−
16
2
1
−
15
2
1
−
8
2
1
−
2
2
2-parallel
1
−
2
4-parallel
CPU
VOLUME
Volume knob is turned and volume
level position is detected
Current values
are added
＋
I-V Converter
Reconversion of current
into voltage
Balanced
Output
–
OUTPUT
0.1
0
1
1
−
−
2
2
2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
The se V -I con ver ter s h and lin g m inu te
cur rent le vel s e nab le ext rem ely
del icat e v olu me con tro l.
1
1
1
1
1
1
1
−
−
−
−
3
4
5
6
2
2
2
2
1
−
−
−
−
7
8
9
10
2
2
2
2
1
1
1
1
1
−
−
11
12
2
2
1
−
−
−
−
13
14
15
16
2
2
2
16 types of V-I
converters
2
–Extruded from solid aluminum block –
High-rigidity volume sensor construction
ATTENUATORBALANCE
★Cut away mode l of vol ume sens or m echa nism
■
Upper two V-I converter amplifiers feature a special
configuration, with 4-parallel operation for the topmost and
2-parallel operation for the second level, resulting in lower
impedance and an amazing S/N ratio improvement of 2 dB.
■
No more left/right tracking differences or crosstalk.
■
Amplifier display shows accurate gain as numeric
indication.
■
High S/N ratio, low distortion, uniform frequency response
and optimal sound quality maintained at any volume setting.
■
Attenuator and balance control also implemented by AAVA,
eliminating additional circuitry.
■High-resolution volume control: Combination of V-I con-
verter amplifiers gives 65,536 possible volume steps.
The amplification circuitry of C-3850 consists of a total of 18 unit amplifiers,
including I-V assembly, AAVA circuitry, balanced input and balanced
output amplifiers.
Turning the volume knob on the front
panel causes the actual volume level
position to be detected. The corresponding signal is se nt to a CPU
which in turn contr ols the current
switches and thereby the gain of the
AAVA ci rcuitry. The massive knob
extruded from a solid aluminum block
and mounted on large-diameter shaft
has exactly the rig ht amount of
inertia. Together with the low-friction
internal mechanism this provides a
silky smooth operation feel and also
allows extremely quiet motor-driven
operation.
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