Digital Frequency Dividing Network

DF-75

Accuphase Laboratory, Inc.

The DF-75 is a frequency-dividing network for a multiamplifier system, dividing the music signal into multiple
frequency bands.
In 1999, Accuphase launched the DF-35, a digitalfrequency dividing network that utilizes digital signal
processing for implementing filters.
Subsequent model changes include the DF-45, DF-55,and DF-65. The DF-75 is the fifth-generation digitalfrequency dividing network.
Technical highlights of DF-75;• The performance of the A/D and D/A conversion
circuits has been improved• Adoption of 64-bit floating-point arithmetic• The cutoff frequency of the filter has been increased
to 3101 points
1Appearance• Functionally organized front panel• Aluminum hairline finished top panel• Natural wood grain finished side panel

Top panelSide panel

New feature
Display off switch

Accuphase Laboratory, Inc.

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The design of the front panel has not changed
significantly from the previous DF-65 model, but a new"display off switch" has been added as a feature.
This switch turns off all indications except for theAccuphase logo. In addition, all switches except thedisplay off switch will no longer function.

2Rearview• Various types of input/output terminals
Digital outputs

Analog outputs

Digital inputs

Analog inputs

Accuphase Laboratory, Inc.

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The DF-75 has multiple inputs and outputs as follows:• Analog input
Balanced / Line
• Digital input
HS-LINK / Coaxial / Optical• Analog output
Balanced / Line × 4 channel• Digital output ※for cascade connection
HS-LINK

HS-LINK: Accuphase original digital interface for audio
signal3

Internal View
• Isolated layout of analog and digital circuits
A/D converter circuit
Filter amplifiercircuit
DSP circuit

Power supply forthe digital circuits

Power supply forthe analog circuits

D/A converter circuit

Accuphase Laboratory, Inc.

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The DF-75 utilizes a layout that isolates analog anddigital circuits.
The placement of each circuit block is designed to create
the shortest signal path possible.

4Filter settings• Filter characteristics can be set precisely and flexibly– Cutoff frequency: 3101 points, 10Hz ~ 50kHz– Slope characteristics: 6dB/oct, 12dB/oct, 18dB/oct, 24dB/oct,48dB/oct, 96dB/oct– Absolute phase: Normal/Reverse, Independent setting for left andright channels– Level control: +12dB ~ -40dB, 0.1dB step
– Delay: -3000cm ~ +3000cm, 0.5cm step

• Delay compensator function
Accuphase Laboratory, Inc.

5The DF-75 can precisely and flexibly set filter
characteristics.
In particular, the cutoff frequency has been greatly
increased from 59 points for the previous model DF-65 to3101 points.
The "Delay compensator function” compensates for thedelay when a signal passes through the filter, and theamount of delay is automatically set based on the filter
characteristics.

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High-precision filter engine• High-precision filter engine using Analog Devices' DSPADSP-21565– 64-bit floating-point arithmetic when Fs =< 192kHz– 40-bit floating-point arithmetic when Fs > 192kHz

Accuphase Laboratory, Inc.

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The DF-75 is equipped with Analog Devices' DSP ADSP21565 for high-precision computation.
For signal processing, 64-bit floating-point arithmetic isused for sampling frequencies Fs of 192 kHz or lower,
while 40-bit floating-point arithmetic is used for Fs above
192 kHz.

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Electrical performances• Guaranteed specifications have evolved from the former
model DF-65
Guaranteed specification

Specification*
DF-65
DF-75
S/N ratio
116dB
117dB
THD+Noise
0.0007% 0.0006%
Channel separation**
108dB
110dB
* All specifications are measured with analog input - analog output** 20Hz - 20kHz

Accuphase Laboratory, Inc.

7Analog performance is significant since the channel
divider is usually connected between the preamplifier
and the power amplifier.
The DF-75 has improved the electrical performance ofthe analog circuit section over the previous model byevolving the A/D and D/A conversion circuits.

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High-performance A/D converter circuit• 4 A/D converters per channel in parallel operation• Ultra-low noise and distortion technology ANCC*• Fully balanced configuration• Featured Asahi Kasei Microdevices AK5578* Refer appendix

Accuphase Laboratory, Inc.

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The A/D converter section is a fully balanced
configuration, with four ADCs connected in parallel foreach channel. Furthermore, ANCC, a noise anddistortion canceling technology, is incorporated.
The A/D converter chip is Asahi Kasei MicrodevicesAK5578.

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High-performance D/A converter circuit• 4 D/A converters per channel in parallel operation• DACs parallel technique MDS+* circuit• Ultra-low noise and distortion technology ANCC*• Fully balanced configuration• Featured ESS Technology ES9028PRO* Refer appendix

Accuphase Laboratory, Inc.

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The D/A converter section is a fully balanced
configuration, employing Accuphase's proprietary MDS+
conversion principle, with four DACs connected inparallel for each channel. It also features ANCC, a noiseand distortion cancellation technology.
The D/A converter chip is ESS Technology ES9028PRO.

9Furthermore• Fully functional system backup• Simple setting mode, Independent setting mode
• Cascade connection to increase the number of channels
Cascade connection

DF-75

DF-75

PreampPower
amp

Power
amp

Power
amp

Power
amp

Power
amp

Power
amp

Power
amp

Power
amp

Accuphase Laboratory, Inc.

10DF-75 offers a fully functional backup feature, allowing
users to save all memories and basic setting parameters
for restoration as needed.
While users can simultaneously set both the channel’slevel and delay values in simple setting mode, they canput the values for each channel separately using theindependent setting mode.
DF-75 opens up possibilities with its cascade connection
capability through HS-LINK. The signal from thepreamplifier can be effortlessly distributed to another DF75, creating a multi-amplified system with more than 4ways.

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Appendix “ANCC”• ANCC: Accuphase Noise and distortion Canceling Circuit– To detect and cancel the noise and distortion at the input stage ofamplifier
I-V converter
R

Current input

Voltage output

Injects the cancelingcurrent

Detection amp

ANCC

Detects noise anddistortion components

Accuphase Laboratory, Inc.

11ANCC: “Accuphase Noise and distortion CancelingCircuit”
ANCC is a circuit technology that cancels noise anddistortion by detecting noise and distortion
components in the amplifier input and then injecting acancellation current that inverts the polarity of thecomponents.

11Appendix “MDS+”• MDS+: Multiple Delta-Sigma+– Technique to make D/A converter parallel operation– The root of the number of parallels improves performance+

Digital input signal

DAC1

I-V
Converter

Analog output +I-V
Converter

Analog output --

DAC2
Level
Shifter

DAC3

DAC4

Accuphase Laboratory, Inc.

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The MDS+ is a technique to make DACs parallel.
The same digital signal is supplied to each converter,and the output of each DAC is summed before being
sent to subsequent stages.
The audio signal values are added, canceling theconversion error and the noise. The ratio between thesignal and conversion errors increases, so theconverter performance is improved.
The improvement degree works by a square root of
the number of DACs.
In the DF-75, all performances are improved by afactor of two.

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