Accuphase T-1100 Gebruikershandleiding - Pagina 2

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The range of available program sources is getting

ever more varied: Compact Discs, analog records,

and net based music distribution, to name but a

few. But the FM tuner still has a special role to

play, since broadcasts cover the entire spectrum

from live performances of time-honored classical

works to the latest hits. The FM band provides a

rich choice of music all day long. In addition,

many local stations have recently come onto

stage using the live broadcast medium to best

advantage.

The T-1100 is a successor model to the highly

praised T-1000. Thanks to a blend of latest RF

circuit design with sophisticated digital signal

processing implemented by a high-speed, high-

precision DSP chip, it has become possible to

move most major functions of the tuner into the

digital domain without sacrificing performance or

sound quality. Audiophiles and music lovers can

now enjoy FM stereo at its best.

The newly developed front end features a double-

tuned circuit that optimizes sensitivity and

selectivity, as well as the revolutionary DDS

(Direct Digital Synthesis) principle for the local

oscillator. All functions after the intermediate

frequency (IF) stage are implemented using digital

signal processing in completely new and

innovative ways. This comprises the variable

bandwidth IF filter, multipath reduction function,

digital

detector

and

demodulator. The result is an FM tuner unlike any

other, offering further enhanced performance and

sound quality. Other attractive features include a

20-station memory, a coaxial output for digital

signal connection, two sets of line and balanced

analog

outputs,

and

supplied

Commander for operation convenience. In sum,

this is a lavishly designed FM tuner that will meet

and surpass even the highest expectations.

Variable Bandwidth IF Filter Improves Interference Performance

The IF BANDWIDTH selector of the T-1100 provides a choice of six settings

(50, 75, 100, 150, 250, 500 kHz). Normally, a wider bandwidth setting is pref-

erable in terms of perform-

ance characteristics, but

by restricting the band-

width, noise can be re-

duced in certain situations,

making it easier to obtain

a good quality signal from

a station affected by inter-

ference from a strong ad-

jacent station.

The variable bandwidth IF

filter is implemented using

a FIR (Finite Impulse Re-

sponse) type digital filter

with perfectly linear phase

characteristics,

thereby

eliminating the phase shift

that can occur with con-

ventional IF bandwidth fil-

ters.

Ideal Digital FM Demodulation Principle

The FM demodulator circuit is a crucial component that has a

significant effect on distortion and noise characteristics of the tuner's

audio output. In the T-1100, the imaginary part of the digitized FM

signal is divided by the real part to extract the tangent of the phase

θ )

angle (

. By calculating the arctangent from this, the phase angle

can be determined. Differentiation is then used to obtain the time

variation resulting in the FM demodulated output (audio output).

Double-Tuned Front End Eliminates Problems With High Input Signal Levels

■An attenuator in the input stage enables the tuner to operate at its optimum

point also when input levels are extremely high, such as in the vicinity of a

broadcast tower or when using a cable network.

■Two-stage double-tuned front end eliminates intermodulation distortion with

strong signals.

■Dual-gate MOS-FETs in the RF amplifier stage ensure excellent third-order

intermodulation characteristics.

■Two-stage double-balanced mixer suppresses undesired signal compo-

nents.

■Revolutionary DDS local oscillator achieves amazing S/N ratio.

FM Antenna

Attenuator

Local/Distance

Selector

The signal from the antenna input is routed to an RF amplifier

and then mixed with the signal from a local oscillator for

DS-DC

stereo

conversion into the intermediate frequency (IF). The local

oscillator here is a highly advanced DDS (Direct Digital

Synthesis) circuit.

● The output of a quartz oscillator is supplied to the frequency

divider to create the timing (namely the sampling frequency)

with which the sine wave data are read out.

● Using this sampling frequency, the sine wave data are read

Remote

in the D/A converter to create the analog waveform output.

● Because there is no feedback loop, the frequency purity of

the D/A converter output can be kept identical to that of the

quartz oscillator.

■ IF bandwidth switchable in 6 stages

Noise or adjacent

broadcast station

Wide IF bandwidth

Narrow IF bandwidth

is susceptible to

reduces interference

degradation by

noise and interference

■ IF bandwidth is selected by turning knob

(with LED indication)

Double-Tuned Circuit

Amplifier

■ Front End Circuit Diagram

DDS （Direct Digital Synthesis）

Multipath Reduction Function (MPR) Minimizes Reflections

Multipath reception refers to a condition where the same broadcast signal

reaches the antenna via several different propagation routes. In the case of

FM, this occurs when the signal travels to the antenna in a straight line, but

is also reflected and therefore slightly delayed by buildings, mountains or

other

tall

obstructions.

When the direct waves and

reflected waves are re-

ceived together, distortion

and noise occur.

The

high-speed,

precision DSP chip in the

T-1100 makes it possible

to perform multipath reduc-

tion (MPR) through signal

processing that effectively

suppresses the harmful re-

flected components. This

technique which is based

on adaptive filtering princi-

ples ensures that only the

desirable direct wave com-

ponents are received, re-

sulting in high-quality audio

output.

Phase Detector

Real

Part

Division

FM Wave Signal

Imaginary

Input

Part

Coils used in double-tuned circuits

AGC

Double-Tuned Circuit

Double

Balanced

Mixer

DDS Local Oscillator

Sine Wave

D/A

Data

Converter

0110

Frequency

Quartz

Divider

Oscillator

■ DDS Block Diagram

■FM Propagation Characteristics

Transmitter

high-

Direct

Wave

Reflected

Wave

Phase

( θ )

Angle

tan θ

Arctangent

Differentiation

（tan

）

■ Digital FM Demodulator

Double

Balanced

IF output

Mixer

Output

Demodulated output