SPLITTER FOR S/PDIF COAX/OPTICAL OUTPUT - WebHTB

1<br />

<strong>SPLITTER</strong> <strong>FOR</strong> S/<strong>PDIF</strong> <strong>COAX</strong>/<strong>OPTICAL</strong> <strong>OUTPUT</strong><br />

THIS circuit was originally designed to enable<br />

one S/<strong>PDIF</strong> output on a CD player to<br />

drive several inputs. The circuit acts as a 3-way<br />

splitter or format converter for S/<strong>PDIF</strong> (‘digital’)<br />

or optical signals. The function of the circuit<br />

is determined with the aid of two jumpers,<br />

as follows:<br />

JP 1 JP 2 Function<br />

O O optical input to optical and coax output<br />

O A optical input to optical (buffered)<br />

and coax output<br />

C O optical input to optical output,<br />

coax input to coax output<br />

C A coax input to optical and coax output<br />

In the selections available, JP 1 has priority.<br />

The third option indicates that the circuit is capable<br />

of splitting two sources separately, while<br />

retaining their formats. It is not possible to<br />

make cross connections because it is not usually<br />

required to convert from coax to optical.<br />

The other way around, though, is far more<br />

usual, and available with the other three options.<br />

The optical inputs and outputs consist of<br />

Toshiba ‘Toslink’ modules, which are TTL compatible.<br />

The coax inputs and outputs are formed<br />

by RCA-style ‘phono’ sockets. Both the Toslink<br />

modules and the phono sockets are accommodated<br />

on the printed circuit board.<br />

A digital (coax) input signal is first amplified<br />

by IC 1a . Resistor R 4 lightly loads the gate<br />

to prevent it from oscillating if no input signal<br />

is connected. In some cases, a resistor with a<br />

slightly lower value may be required in this position.<br />

Next, jumper JP 1 allows the output of<br />

the amplifier (position ‘C’), or that of Toslink<br />

receiver IC 2 (position ‘O’), to be selected. The<br />

Toslink signal is superimposed on a half-supply<br />

bias created by R 5 and R 6 , and then applied to<br />

IC 1b . The half-supply bias corresponds to the<br />

switching threshold of IC 1b. This allows Toslink<br />

transmitters IC 3 , IC 4 and IC 5 , to be driven<br />

from the output of receiver IC 2 , or from the output<br />

of IC 1b . Remember, the signal supplied by<br />

the latter is cleaned and amplified. Simply select<br />

the option which gives the best results.<br />

The buffer formed by the four parallel-connected<br />

inverters has sufficient drive capacity<br />

to match the low impedance of the primary of<br />

transformer Tr 1 . The transformer actually<br />

forms the heart of the circuit. The three digital<br />

outputs are electrically isolated from the input,<br />

although the r.f. signals ‘see’ the ground level<br />

through capacitors C 4 , C 5 and C 6 . Matching<br />

resistors R 9 , R 11 and R 13 prevent reflections<br />

at the relevant output from exceeding the ×1<br />

level. Resistors R 8 , R 10 and R 12 similarly damp<br />

the ringing effects which occur on the non-used<br />

secondary windings. The drawing shows the practical<br />

construction of the transformer, which is<br />

based on a type G2.3-FT12 ferrite ring core.<br />

This type was chosen because of its high bandwidth<br />

and coupling factor, factors which allow<br />

the primary winding of 15 turns to occupy only<br />

IC2<br />

TORX173<br />

K1<br />

5V<br />

14<br />

L1<br />

IC1<br />

7<br />

270µH<br />

2 4<br />

75Ω<br />

C7<br />

100n<br />

5 6<br />

R1<br />

1<br />

3<br />

C8<br />

1µ<br />

63V<br />

IC1 = 74HCU04<br />

C9<br />

100n<br />

C1 R2<br />

100Ω<br />

10n<br />

5V<br />

L2<br />

47µH<br />

1<br />

5V<br />

R3<br />

10k<br />

IC1a<br />

1<br />

5V<br />

R5<br />

1M<br />

10k<br />

4Ω7<br />

R4<br />

R14<br />

8k2<br />

C10<br />

R15<br />

100n<br />

5V<br />

2<br />

4Ω7<br />

R16<br />

8k2<br />

C11<br />

R17<br />

100n<br />

5V<br />

4Ω7<br />

R18<br />

8k2<br />

C12<br />

R19<br />

100n<br />

C2<br />

O 1<br />

JP1<br />

C<br />

1n<br />

R6<br />

1M<br />

3<br />

JP2<br />

3<br />

2<br />

4<br />

3<br />

2<br />

4<br />

3<br />

2<br />

4<br />

O A<br />

A<br />

IC3<br />

TOTX173<br />

1<br />

IC4<br />

TOTX173<br />

1<br />

IC5<br />

TOTX173<br />

1<br />

5<br />

9<br />

11<br />

IC1c<br />

1<br />

IC1d<br />

1<br />

IC1e<br />

1<br />

R7<br />

IC1b 4<br />

13 IC1f<br />

220Ω<br />

1<br />

1<br />

K5<br />

Tr2<br />

9V<br />

1VA2<br />

B1<br />

6<br />

8<br />

10<br />

12<br />

B80C1500<br />

zie tekst<br />

*<br />

see text<br />

*<br />

siehe Text<br />

*<br />

voir texte<br />

*<br />

C3<br />

100n 1<br />

C16<br />

470µ<br />

25V<br />

Tr1<br />

*<br />

(15)<br />

2<br />

C15<br />

100n<br />

3<br />

(3)<br />

4<br />

5<br />

(3)<br />

6<br />

7<br />

(3)<br />

8<br />

IC6<br />

7805<br />

ELEKTOR ELECTRONICS JULY/AUGUST 1995<br />

220Ω<br />

220Ω<br />

220Ω<br />

R9<br />

75Ω<br />

R8<br />

R11<br />

75Ω<br />

R10<br />

R13<br />

75Ω<br />

R12<br />

C14<br />

10µ<br />

63V<br />

C13<br />

K2<br />

K3<br />

C5<br />

47n<br />

K4<br />

100n<br />

C4<br />

47n<br />

C6<br />

47n<br />

5V<br />

954045 - 11

---

about half the core, while the secondary<br />

windings of three turns each are distributed<br />

over the remainder. All windings<br />

are made from 0.5-mm dia (24 SWG)<br />

enamelled copper wire.<br />

The power supply is conventional and<br />

‘on board’, consisting mainly of a 1.2-VA<br />

mains transformer, a bridge rectifier and<br />

a 7805 three-pin voltage regulator. All ICs<br />

on the board have individual supply decoupling<br />

parts. Current consumption of<br />

the circuit is of the order of 70 mA. We<br />

regret that the printed circuit board shown<br />

is not available ready-made.<br />

Parts list<br />

Resistors:<br />

R 1 ;R 9 ;R 11 ;R 13 = 75Ω<br />

R 2 = 100Ω<br />

R 3 ;R 4 = 10kΩ<br />

R 5 ;R 6 = 1MΩ<br />

R 7 ;R 8 ;R 10 ;R 12 = 220Ω<br />

R 14 ;R 16 ;R 18 = 4Ω7<br />

R 15 ;R 17 ;R 19 = 8kΩ2<br />

Capacitors:<br />

C 1 = 10nF ceramic<br />

C 2 = 1nF ceramic<br />

C 3 ;C 7 ;C 9 -C 13 ;C 15 = 100nF ceramic<br />

C 4 ;C 5 ;C 6 = 47nF ceramic<br />

C 8 = 1µF 63V radial<br />

C 14 = 10µF 63V radial<br />

C 16 = 470µF 25V radial<br />

Inductors:<br />

L 1 = 270µH choke<br />

L 2 = 47µH choke<br />

Semiconductors:<br />

IC 1 = 74HCU04<br />

IC 2 = TORX173 (Toshiba)<br />

IC 3;IC 4;IC 5 = TOTX173 (Toshiba)<br />

IC 6 = 7805<br />

Miscellaneous:<br />

JP 1 ;JP 2 = 3-way pin header, w. jumper.<br />

K 1 -K 4 = RCA style PCB mount socket,<br />

Monacor T709G.<br />

K 5 = 2-way PCB terminal block, pitch<br />

7.5mm.<br />

B 1 = B80C1500<br />

Tr 1 = G2.3-FT12 ferrite ring core;<br />

primary 15 turns 0.5mm dia. ecw,<br />

secondary 3×3 turns 0.5mm dia.<br />

ecw.<br />

Tr 2 = 9V/1.2VA transformer, e.g, Hahn<br />

BV EI 302 0376; Velleman<br />

1090012M; Monacor VTR1109<br />

(1.5VA); Block VR1109 (1.5VA).<br />

Design by T. Giesberts<br />

[954045]<br />

ELEKTOR ELECTRONICS JULY/AUGUST 1995<br />

954045-1<br />

~<br />

~<br />

954045-1<br />

R14<br />

K5<br />

C10 C11 C12<br />

R15<br />

R16<br />

TR2<br />

R17<br />

R18<br />

IC3 IC4 IC5<br />

8<br />

1<br />

7<br />

R19<br />

B1<br />

<strong>SPLITTER</strong> <strong>FOR</strong> S/<strong>PDIF</strong> <strong>COAX</strong>/<strong>OPTICAL</strong> <strong>OUTPUT</strong><br />

C15<br />

C9<br />

IC2<br />

L2<br />

C16<br />

6 5<br />

C13 C7<br />

L1<br />

C8<br />

C14<br />

IC6<br />

JP2<br />

A<br />

O<br />

R1<br />

C1<br />

C2<br />

R2<br />

R3<br />

R4<br />

R5<br />

R6<br />

R9<br />

R8<br />

4<br />

954045 - 12<br />

2<br />

3<br />

IC1<br />

C<br />

A<br />

O<br />

R7<br />

C3<br />

JP1<br />

C4 C5 C6<br />

R11<br />

R10<br />

K1 K2 K3 K4<br />

R13<br />

R12<br />

TR1<br />

954045-1