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RIAA is actual an abbreviation of Record Industry Association of America, an organisation, as the name indicates, has its roots back in the childhood of the gramophone industry.
The necessary RIAA playback equaliser characteristic curve has three frequency references: 50, 500 and 2120 Hz. These frequencies correspond to the time constants 3180, 318 and 75 us respectively. In the figure below is the asymptotic (blue) and real (green) characteristic curve drawn.
Click here to calculate the RIAA network
The picture below is the very well know RIAA reproduction curve.
At 1000Hz there is the 0 dB point which is the reference for all other frequencies: Relative to this point, lower frequencies are amplified (> 0dB) and higher frequencies are attenuated (< 0dB). The mid-band, between 500-2122 Hz is critical since voices are all in this band and our ears are sensitive to these frequencies.
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How to check your existing RIAA filter?
It is relatively simple to examine a RIAA network circuit.
All you nedd is:
- a exact and stable signal generator ( sinewave )
- a good voltmeter ( best the old-fashionable very good pointer instruments )
- a Frequency Meter
- a 2 Chanel Scop( not necessary but handy)
First step: connect your Phonoamplifier as shown in this picture (the Scop isn't necessary ):
The amplifier output voltage should be 1.00 volts @ 1kHz !
Next step: check the output voltages at the frequencies, shown in the table.
| Frecency |
Uout |
| 20 Hz |
9.23 volts (+19.3 dB) |
| 30 Hz |
8.51 volts (+18.6 dB) |
| 40 Hz |
7.76 volts (+17.8 dB) |
| 50 Hz |
7.08 volts (+17.0 dB) |
| 60 Hz |
6.38 volts (+16.1 dB) |
| 80 Hz |
5.31 volts (+14.2 dB) |
| 100 Hz |
4.52 volts (+13.1 dB) |
| 150 Hz |
3.27 volts (+10.3 dB) |
| 200 Hz |
2.57 volts (+8.2 dB) |
| 300 Hz |
1.88 volts (+5.5 dB) |
| 400 Hz |
1.55 volts (+3.8 dB) |
| 500 Hz |
1.35 volts (+2.6 dB) |
| 800 Hz |
1.08 volts (+0.7 dB) |
| 1.00 kHz |
1.00 volts (0.0 dB) |
| 1.50 kHz |
0.85 volts (-1.4 dB) |
| 2.00 kHz |
0.74 volts (-2.6 dB) |
| 3.00 kHz |
0.58 volts (-4.8 dB) |
| 4.00 kHz |
0.47 volts (-6.6 dB) |
| 5.00 kHz |
0.39 volts (-8.2 dB) |
| 6.00 kHz |
0.33 volts (-9.6 dB) |
| 8.00 kHz |
0.25 volts (-12.0 dB) |
| 10.0 kHz |
0.21 volts (-13.6 dB) |
| 15.0 kHz |
0.14 volts (-17.1 dB) |
| 20.0 kHz |
0.105 volts (-19.6 dB) |
If you have a dB scale on your voltmeter,
set the output voltage to 0dB at 1 kHz,
now you are able to read the deviation in dB. |
But there is a second (faster) way to to this:
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Herefor you have to build a correction-network.
This network delivers the complementary signal for the Phono amplifier.
Network circuit:
Important is to used resistors with 0.1% and capacitors with 1% tolerance (or beter).
Take care that the output voltage of the network is 1.00 volts at 1.00 kHz!
The output voltage of you Phono Pre Amplifier should be stable between 20 Hz and 20 kHz.
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more info about RIAA Networks (very technical)
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RIAA measurement