e001012.pdf

AUDIO & HI-FI

audio DAC 2000

Part 3: practical matters

Readers who have

studied and absorbed

Parts 1 and 2 of this

article will be fully

aware of how the

Audio DAC 2000

works. What remains

to be discussed is the

actual building of the

converter, and this is

done in this third and

final part.

P OWER SUPPLY

Although the summary implies that all

parts of the digital-to-analogue con-

verter (DAC) have been discussed, this

is not entirely true, because the power

supply has not yet been described.

It was seen in Part 2 of this article

that the converter ICs need a symetri-

cal ±5 V supply and that this was

derived via regulators IC13 and IC14

from the ±12 V supply line for the ana-

logue circuits. Since it is important to

keep the supply lines to the converter

ICs as short as possible, the regulators

are housed on the DAC board.

The receiver section and some other

circuits on the DAC board need a sin-

gle +5 V supply and a symmetrical

±12 V supply. These voltages are pro-

duced with the aid of regulators

IC15–IC17, which, together with the

other components of the power sup-

ply, are housed on a separate board,

the PSU board.

The circuit of the power supply is

shown in Figure 5 . Note that the +5 V

line for the digital circuits is isolated

from the ±12 V lines for the analogue

circuits.

The earth lines of the two supplies

are interlinked on the DAC board

between the digital filter and the con-

verter ICs (that is, JP3).

Obviously, the supply consists of

not only regulators, but also bridge rec-

tifiers and smoothing capacitors. Resis-

tors R55, R56, and R58 between the rec-

tifiers and smoothing capacitors limit

the charging current to the capacitors

at power-on, and any resulting inter-

ference.

The secondaries of the relevant

mains transformers are linked to K11

and K13 respectively. The choice of

transformer is up to the constructor,

although some suitable models are

specified in the parts list.

The power supply is conveniently

built on the ‘transformer board’

described elsewhere in this issue. This

board is designed to house all the com-

ponents required for the present power

supply.

Design by T. Giesberts

Elektor Electronics

1/2000

P RINTED - CIRCUIT

BOARDS

As already mentioned in Part 1, the

Audio DAC 2000 is contained on four

individual printed-circuit boards: one

for the ±12 V and +5 V power sup-

plies; one for the digital audio receiver

with display driver; one for a 2-digit

LED display; and one for the

digital/analogue circuits, the digital fil-

ter, the DACs and the analogue output

stage. These boards are sections of the

double-sided PCB shown in Figure 6 .

This high-quality board is available

through our Readers Services. Before

any work is carried out, these four sec-

tions should be separated from one

another along the milled cutting lines,

either by snapping or cutting along the

lines

It is important to construct the var-

ious circuits according to the board lay-

outs and the parts list. It is important

that the orientation of the ICs and the

polarity of the electrolytic capacitors

are strictly observed, since any devia-

tion results unfailingly in a non-work-

ing unit.

The DIP switches, S1–S4, are best

soldered directly to the board. An

exception is S2 if it is foreseen that

processor (that is, software) control

may be used at a later stage. In that

case, the switch may be housed in a

good-quality 8-way IC socket, but even

then the board connector should be

soldered in place at a later stage.

All supply lines are connected to

the boards via terminal blocks that

facilitate the wiring or servicing of the

relevant circuits. The +5 V line for the

digital section is linked to the DAC

board. The receiver board is powered

via the link between K3 and K5. Some

protection against (a too) high supply

voltage is provided by diode D4 on the

DAC board.

The LED display board is linked to

the receiver board via a 10-way flatca-

ble. One end of this cable is connected

permanently to the board via a 10-way

board connector. The other end is ter-

minated into a 10-way socket. Take

good care to use the correct length of

cable. The displays are soldered

directly to the board.

The digital audio receiver, IC1, is

soldered directly to the receiver board.

Take care not to damage this IC by elec-

trostatic discharges. Sockets may be

used for IC4 and IC5. Crystal oscillator

IC3 is also best soldered directly to the

board, since it is then as close as possi-

ble to the ground plane.

Start populating the DAC board by

soldering IC6 to the board — see Fig-

ure 7 . This tiny SMA (surface-mount

assembly) IC is housed in a 28-pin

SSOP case, whose pins are spaced at

only 0.65 mm. This requires extreme

care, a tiny soldering iron tip, and pos-

sibly a magnifying glass to check the

K13

C89

C86

IC17

R58

1 Ω 5

7805

R57

K12

C88

C87

C85

C84

C83

C82

1000µ

25V

100n

10µ

63V

100n

4x 22n

POWER

B80C1500

K11

C81

C78

15V

IC15

R55

3 Ω 3

7812

12V

15V

C76

C74

C72

C70

K10

C80

C79

1000µ

40V

100n

10µ

63V

100n

4x 22n

B80C1500

C77

C75

C73

C71

1000µ

40V

100n

10µ

63V

100n

R56

3 Ω 3

12V

7912

IC16

990059 - 3 - 16

soldering work. Take

good care not to over-

heat the IC: take a pause

between soldering, say,

2 or 3 pins at a time.

Next, solder the converter ICs, IC 7

and IC8, in place. These are housed in a

standard 20-pin SMD case (SOIC), and

are easily soldered. It is best to fit

op amps IC9–IC12 in good-quality IC

sockets.

Capacitors C27–C38 in the analogue

section are 1% close-tolerance types in

a square radial format, with the termi-

nals placed at two opposing corners.

These types are manufactured by

EMZ. Their pitch is standard (7.1 mm),

so they could be replaced by metal-

lized film polystyrene or polypropy-

lene types. It should be borne in mind,

however, that the larger tolerances of

these types may result in significant

changes in the frequency and phase

responses. The EMZ capacitors speci-

fied carry a thin dash that indicates

which terminal is linked to the outer

layer. Make sure that this pin is linked

to ground or to the output of an

opamp: this makes the analogue sec-

tion less sensitive to interference. The

same applies to axial capacitors C25

and C26: place the band on these at the

output side of opamps IC9 and IC11.

The relays are soldered directly to

the board. Do not forget wire bridges

JP2 and JP3: these are permanent links

which may be made in rather thicker

wire than usual.

A final practical hint. To improve

the channel separation at high fre-

quencies, it is advisable to shield the

left- and right-hand sections of the ana-

logue output filter from one another.

Figure 5. Circuit diagram of the power supply for

the Audio DAC 2000. The +5 V line for the digital

circuits is isolated on the board from the ±12 V

line for the analogue section.

13 mm) tin-plate screen between

Re2 and IC12. The screen stretches

from the edge of the board to DIP

switch S4: its position is indicated in

Figure 6 by a dashed line. At the ends,

scratch away some of the lacquer on

the board with a sharp pen knife to

ensure that the screen makes good

contact with the copper area at the top

of the board which functions as

ground plane — soldering the ends of

the screen to the copper is even better.

In the prototype, the addition of the

screen improved the channel separa-

tion by 12 dB at 20 kHz.

E NCLOSURE

When the four boards have been com-

pleted and checked for possible build-

ing or soldering errors, they must be

combined into a complete Audio DAC

2000 and housed in a suitable enclo-

sure. The most suitable enclosure is a

sturdy metal case, which, as far as

appearance is concerned, should

preferably match the audio installation

with which it is to be used.

The prototype is housed in a Mona-

cor Type UC251/SW enclosure. This is

435 mm wide, 230 mm deep, and

44 mm high — see Figure 8 . In some

countries in which Elektor Electronics

appears, Monacor products are sold

under the brand name ‘Monarch’.

The manner in which the boards

are arranged in the enclosure is opti-

mal and constructors are well advised

Elektor Electronics

1/2000

This is best done by placing a small

(86

C76

C74

IC15

12V

C70

C72

RE1

OUT4

OUT5

H14

R45

R48

R49

R40

R42

15V

C73

12V

R44

T 2

C71

R56

IC16

R43

R47

C57

C77

IC10

IC12

C88

C85

IC17

C56

C55

R39

R41

R46

R50

C83

JP2

C84

C82

C66

C86

R57

C68

C28

C31

C34

C37

C11

C1 C2

JP1

C69

C67

C46

C47

C50

IC9

IC11

IC14

C61

C24

C45

C51

IC4

IC1

C43

IC7

IC8

C40

IC5

C14

C15

IC13

OUT2

+5V

C20

C41

C39

C59

C58

C16

C17

S3-1 OW0

-2 OW1

-3 IW0

-4 IW1

-5 I2S

-6 SF0

-7 SF1

-8 SRO

OUT3

R19

R16

R17

R23

R24

R12

MODE

CKO

LRIP

H11

reproduced

at 85% of

actual size

(MD)

(MC)

(ML)

R18

R11

R21

R22

R13

R14

R15

990059-1

LD2

LD1

H16

H10

R20

Figure 6. The double-sided board must be divided into four sub-boards along the fraised lines.

COMPONENTS LIST

radial

C25,C26 = 47pF 1 axial (EMZ )

C27,C33 = 2nF2 1% 1 (EMZ )

C28,C34 = 4nF7 1% 1 (EMZ )

C29,C35 = 330pF 1% 1 (EMZ)

C30,C36 = 1nF 1% 1 (EMZ)

C31,C37 = 1nF5 1% 1 (EMZ)

C32,C38 = 270pF 1% 1 (EMZ)

C55 = 220µF 25V radial

C56 = 1µF 63V radial

C57 = 470µF 25V radial

C76,C77 = 1000µF 40V radial

C78-C81,C86-C89 = 22nF ceramic

C85 = 1000µF 25V radial

grammed, order code 996530-1 ,

see Readers Services pages)

IC6 = DF1704E (Burr-Brown)

IC7,IC8 = PCM1704U (Burr-Brown)

IC9...IC12 = OPA627AP (Burr-Brown)

IC13 = LM317 (TO220)

IC14 = LM337 (TO220)

IC15 = 7812

IC16 = 7912

IC17 = 7805

Resistors:

R1 = 75 Ω

R2 = 220 Ω

R3 = 470 Ω

R4,R50 = 4 Ω 7

R5 = 4-way 10k Ω SIL-array

R6 = 10k Ω

R7-R10 = 22 Ω

R11-R24 = 820 Ω

R25,R26 = 2k Ω 49 1%

R27,R30,R33,R36 = 3k Ω 57 1%

R28,R34 = 4k Ω 12 1%

R29,R35 = 3k Ω 92 1%

R31,R37 = 3k

Miscellaneous:

JP1 = 2-way pinheader + jumper

JP2,JP3 = wire link *

K1,K6,K7 = cinch socket, PCB

mount (Monacor/Monarch type T-709G)

K2 = 10-way boxheader

K4 = 10-way PCB-connector (for flat-

cable)

K3,K5 = 16-way boxheader

K8,K12,K13 = 2-way PCB terminal

block, raster 5 mm

K9,K10,K11 = 3-way PCB terminal

block, raster 5 mm

S1,S2,S4 = 4-way DIP-switch

S3 = 8-way DIP-switch

B1,B2 = B80C1500, rectangular case

Re1,Re2,Re3 = V23042-A2003-B101,

12V/600 Ω (Siemens)

Supply transformers: 2x15 V/4 VA

(e.g. Block FLD4/15; Hahn BVUI

3020165; Monacor FTR-415) , and

2x8(or 9) V/4 VA (e.g.. Block FLD4/8;

Hahn BVUI 3020161; Monacor FTR-49 –

see transformer board elsewhere in this

issue)

PCB, order code 990059-1 , see

Readers Services pages.

65 1%

R32,R38 = 3k Ω 32 1%

R39,R41,R45,R49 = 1M Ω

R40,R42 = 100 Ω

R43,R44,R47,R48 = 150k

Ω

polystyrene/polypropylene

EMZ, Elektromanufaktur Zangenstein

Hanauer GmbH & Co.

Siemensstrasse 1

D-92507 Nabburg

Germany

Tel. +49 9433 898-0

Fax +49 9433 898-188

Ω

R46 = 10 Ω

R51,R53 = 249 Ω 1%

R52,R54 = 750 Ω 1%

R55,R56 = 3

Ω

R57 = 3k Ω 9

R58 = 1 Ω 5

Inductors:

L1-L4 = 47 µH

Capacitors:

C1,C2 = 10nF ceramic

C3 = 68nF

C4,C6,C10,C16,C62-C65,C72,

C73,C83 = 10µF 63V radial

C5,C7 = 47nF ceramic

C8,C9,C11,C12,C15,C17,C46-C53,

C59,C60,C61,C66,C67,C70,C71,

C74,C75,C82,C84 = 100nF ceramic

C13,C14,C23,C24,C44,C45,

C54 = 47µF 25V radial

C18-C21,C39-C42 = 4µF7 63V radial

C22,C43,C58,C68,C69 = 100µF 25V

Semiconductors:

D1 = 1N4001

D2,D3 = 1N4148

D4,D5,D6 = 5V6 1W3 zener diode

D7 = LED, red, high-efficiency

LD1,LD2 = HDN1075O (Siemens)

T1,T2 = BC517

IC1 = CS8414-CS (Crystal)

IC2 = TORX173 (Toshiba)

IC3 = 6.144MHz SG531P (Seiko

Epson)

IC4 = 74HCT32

IC5 = GAL22V10B-25LP (ready-pro-

* see text

Elektor Electronics

1/2000

990059-1

Elektor Electronics

1/2000

Figure 7. Soldering IC6 into place

requires a steady hand, good

eyesight and precision tools.

to use the same arrangement: the DAC

board in one corner, the receiver board

next to it, the supply board in front of

this, and the transformer board in the

remaining corner.

The only items to be fitted on the

front panel are the mains on/off switch

and the display that shows the sam-

pling rate. If desired, power diode D7

may be added to this, but this is not

really necessary since LD1 and LD2

function very well as on/off indicator.

The interwiring may be gleaned

from Figure 8, but is summarized for

convenience’s sake.

• K2 on the receiver board is linked to

K4 on the display board just behind

the front panel via a 10-core flatca-

ble.

• K5 on the DAC board is linked to

K3 on the receiver board via a

16-core flatcable. This link also con-

nects power to the receiver board.

Mind the orientation of pin 1 on the

connectors.

• K12 (+5 V) on the supply board is

linked to K8 on the DAC board via

two cables.

• K10 (±12 V) on the supply board is

linked to K9 on the DAC board via

three cables.

F INALLY

Testing a digital-to-analogue converter

by ear is hardly possible or sensible.

Noticeable differences, such as can be

detected in the case of loudspeakers,

cannot be expected. Nevertheless, a

test audience felt that the DAC 2000

sounded better than a number of other

available types of DAC. They found the

sound cleaner and the stereo image

clearer.

The test results in the box give a fur-

ther judgment of the quality of the

converter. They call for a few com-

ments.

• The bandwidth of sampling fre-

quencies 32 kHz, 44.1 kHz, and

48 kHz, is exactly equal to half the

sampling rate, since at these fre-

quencies the bandwidth of the ana-

logue filter is larger than that of the

steep-skirted digital filter. At

88.2 kHz and 96 kHz, the band-

width is determined by the ana-

logue filter.

• The THD+N at a sampling rate of

96 kHz is measured at a bandwidth

of 22 kHz, because at lower sam-

pling rates the analogue output fil-

ter has a bandwidth of 26 kHz. The

reduction gives a more honest com-

parison of the three measurements.

[990059-3]

Text: S. van Rooij

Figure 8. The completed prototype. The enclosure

used provides more than enough space to house

the various boards in an optimum arrangement.

Elektor Electronics

1/2000

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