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 cabinet 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

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

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.

Balanced AAVA (Accuphase Analog Vari-gain Amplifier) Volume Control

				Operation Principle of
	Conversion into current	16 current switches		Balanced AAVA in C-3850
	with 16 weighting	216 = 65,536
	stages (1/2 - 1/216)	possible combinations
	V-I Converter
	1
	−
	2
High Voltage	4-parallel
Current Feedback	1
Amplifier	−2			I-V Converter
	2
	2-parallel			Reconversion of current into voltage
	1		Current values
	−8
	2
			are added
	1
	−15
	2
	1			LEVEL DISPLAY
	−16
	2
+ INPUT					+ OUTPUT
Balanced	CPU controls current on/off		CPU		Balanced
	switches so that	volume
Input					Output
	level matches knob position
				VOLUME
				Volume knob is turned and volume
– INPUT	V-I Converter			level position is detected	– OUTPUT
	1
	−16
	2
	1
	−15
	2
				BALANCE ATTENUATOR
	2			Current values
	1			are added
	−8
				I-V Converter
High Voltage	1			Reconversion of current
	−2			into voltage
Current Feedback	2
Amplifier	2-parallel
	1
	−
	2
	4-parallel

AAVA Operation Principle

The music signal 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.

0.5

Graphic representation of 16 types of V-I converter amplifiers and resulting currents

0.4

0.3

Current ratio

0.2

0.1

These V-I converters handling minute current levels enable extremely delicate volume control.

0

1	1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
− −2		−3	−4	−5	−6	−7	−8	−9	−10	−11	−12	−13	−14	−15	−16	16 types of V-I
2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2
1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	converters

– Extruded from solid aluminum block –

High-rigidity volume sensor construction

Turning the volume knob on the front panel causes the actual volume level position to be detected. The corresponding signal is sent to a CPU which in turn controls the current switches and thereby the gain of the AAVA circuitry. The massive knob extruded from a solid aluminum block and mounted on large-diameter shaft has exactly the right 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.

Cutaway model of volume sensor mechanism

■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 converter 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.