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RIAA Corrector

2017-11-26 04:34  
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Description

To listen old vinyl LP's in a correct sounding on a sassy with dynamic cartridge you need a circuit, named RIAA corrector. This circuit you can find in old amps, but it isn't embedded in home cinema equipments or amplifiers can be obtained nowadays. Also, if you want to archive your vinyl LP's in your computer it is necessary to use this RIAA corrector. It is good, if this corrector has a little built-in amplifier to drive small control speakers, or earphones. Schematic of circuit  built for this express purpose can be found hier. It has two parts, corrector and amplifier part.

The corrector part contains NE5532 integrated circuit with extreme small noise. Resistors are 1% metal film 0,6W types, condenser's of this corrector section must be 5% or better, 63 - 100 V types. Corrector section has direct output to external amp or computer. Amplifier section contains integrated amp IC LM1877. It deliver to speakers 2W/channel output power with very low distortion. Potentiometer P1 is for control the output power of the amp section.

The whole circuit works from external 12-16 V DC supply. Schematic, photos and PCB layout of the circuitry can be found attached. Short mathematics description of RIAA curve and basics of LP's production also can be found in attached document.

 

Schematic





Download Schematic in PDF format


Parts List



ComponentType  pcs
     
Resistor                 1% MF020727 ohm0,6W2
Resistor                 1% MF02071,1 K0,6W2
Resistor                 1% MF020710K0,6W2
Resistor1% MF020722K0,6W2
Resistor                 1% MF020733K0,6W1
Resistor                 1% MF020747K0,6W2
Resistor                 1% MF0207100K0,6W4
Resistor                 1% MF02071M0,6W6
Potentiometer                                  2 x 50K Log  1
Condenser5% MKT RM21,5 nF63V4
Condenser5% MKT RM23,3nF63V2
Condenser10% MKT RM2100nF63V4
Condenser10% MKT RM2220nF63V2
Condenser10% MKT RM2470nF63V2
ELKO5x11 mm RM11uF50V2
ELKO4x7 mm RM110uF35V4
ELKO5x11 mm RM133uF35V2
ELKO6x11 mm RM1100uF25V1
ELKO10x20 mm RM21000uF25V1
ELKO10x30 mm RM22200uF16V2
ICLM1877N-9  1
ICNE5532  1
ZENERBZX55C9V19,1V0,5W1
RCA PCBconnector, single, red (right channel)2
RCA PCB connector, single, white (left channel)2
PCB power connector 5x2,5 mm1
PCB jack type stereo phone connector1
External power supply 12V/5W min1


PCB









Download Layout in PDF format




Download PCB in PDF format or in Protel format




RIAA Curve



LP's are engraved with reduced bass levels and increased treble levels.

For the same sound level, a low frequency requires a larger groove which gives two drawbacks:

- Less recording time
- Difficulties for the cartridge to follow it and thus, higher distortion

At the other end of the spectrum, the contact between the stylus and the groove makes noise, a high frequency noise. By increasing the high frequencies level during recording we can obtain a better signal/noise ratio as the noise is reduced by the playback curve.

Several other curves did exist before the RIAA but it replaced them completely during the 60'.

Here is the formula to obtain the original RIAA curve:



Where:

N=level in dB
f=frequency
t1=treble time constant, 75uS
t2=medium time constant, 318uS
t3=bass time constant, 3180uS

In 76', IEC introduced a modification of this curve by introducing a new time constant that modifies only the extreme bass. It is known as the RIAA/IEC curve.
This correction has never obtained a big success, the original RIAA curve is still the most widely used.
For information, here is the formula:

Where: t4=extreme bass time constant, 7950uS

The RIAA reproduction curve:
{C}



Hz

RIAA

IEC

20

19.36

16.35

22

19.24

16.62

25

19.04

16.89

28

18.83

17.04

31

18.61

17.09

35

18.29

17.06

39

17.96

16.95

44

17.54

16.73

49

17.12

16.45

55

16.61

16.07

62

16.02

15.59

70

15.37

15.03

79

14.67

14.40

89

13.93

13.72

100

13.18

13.01

110

12.54

12.39

120

11.94

11.82

130

11.38

11.27

150

10.36

10.28

170

9.46

9.40

190

8.67

8.62

210

7.97

7.93

240

7.04

7.01

270

6.25

6.23

300

5.57

5.55

340

4.80

4.79

380

4.16

4.15

430

3.49

3.48

480

2.93

2.92

540

2.38

2.38

610

1.86

1.86

680

1.43

1.43

760

1.02

1.02

850

0.63

0.63

950

0.26

0.26

1100

-0.23

-0.23

1200

-0.52

-0.52

1300

-0.79

-0.79

1500

-1.31

-1.31

1700

-1.80

-1.80

1900

-2.27

-2.27

2100

-2.73

-2.73

2400

-3.39

-3.39

2700

-4.04

-4.04

3000

-4.65

-4.65

3400

-5.43

-5.43

3800

-6.17

-6.17

4300

-7.02

-7.02

4800

-7.82

-7.82

5400

-8.70

-8.70

6100

-9.64

-9.64

6800

-10.50

-10.50

7600

-11.39

-11.39

8500

-12.30

-12.30

9500

-13.22

-13.22

11000

-14.44

-14.44

12000

-15.17

-15.17

13000

-15.85

-15.85

15000

-17.07

-17.07

17000

-18.14

-18.14

19000

-19.09

-19.09

21000

-19.95

-19.95

 

 


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