Wednesday, December 28, 2011

RIAA Corrector

Posted by Teter Doll at 7:30 PM 0 Comments

RIAA Corrector
author: Gabor Toth - tothgszeyahoo.co.uk

 
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


Component Type pcs
Resistor                  1% MF0207 27 ohm 0,6W 2
Resistor                  1% MF0207 1,1 K 0,6W 2
Resistor                  1% MF0207 10K 0,6W 2
Resistor 1% MF0207 22K 0,6W 2
Resistor                  1% MF0207 33K 0,6W 1
Resistor                  1% MF0207 47K 0,6W 2
Resistor                  1% MF0207 100K 0,6W 4
Resistor                  1% MF0207 1M 0,6W 6
Potentiometer                                   2 x 50K Log 1
Condenser 5% MKT RM2 1,5 nF 63V 4
Condenser 5% MKT RM2 3,3nF 63V 2
Condenser 10% MKT RM2 100nF 63V 4
Condenser 10% MKT RM2 220nF 63V 2
Condenser 10% MKT RM2 470nF 63V 2
ELKO 5x11 mm RM1 1uF 50V 2
ELKO 4x7 mm RM1 10uF 35V 4
ELKO 5x11 mm RM1 33uF 35V 2
ELKO 6x11 mm RM1 100uF 25V 1
ELKO 10x20 mm RM2 1000uF 25V 1
ELKO 10x30 mm RM2 2200uF 16V 2
IC LM1877N-9 1
IC NE5532 1
ZENER BZX55C9V1 9,1V 0,5W 1
RCA PCB connector, single, red (right channel) 2
RCA PCB connector, single, white (left channel) 2
PCB power connector 5x2,5 mm 1
PCB jack type stereo phone connector 1
External power supply 12V/5W min 1


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:





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



Download this circuit in PDF
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