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Old 4th December 2010, 02:28 PM   #1
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Default RIAA curve question?

Where does the RIAA curve cross the 0dB line? Is it somewhere around 1060Hz?

Does every phono amp design to cross the 0dB at/approx the same frequency?

Thanks

Last edited by Sunsun22; 4th December 2010 at 02:32 PM.
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Old 4th December 2010, 02:35 PM   #2
Salas is offline Salas  Greece
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This is textbook Riaa.
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Old 4th December 2010, 02:53 PM   #3
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Every phono preamp should have the same frequency response curve.
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Old 4th December 2010, 03:08 PM   #4
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Thank you for the information.
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Old 4th December 2010, 04:14 PM   #5
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Quote:
Originally Posted by Sunsun22 View Post
Where does the RIAA curve cross the 0dB line? Is it somewhere around 1060Hz?

Does every phono amp design to cross the 0dB at/approx the same frequency?

Thanks
It's all relative (really!). If you take the 1000Hz point as reference, 0dB, the curve gives you the attenuation or gain at other frequencies relative to the gain at 1000Hz. (See Salas' table).

If you have a preamp with a gain of say 40dB (100x), that means that the gain at 1000Hz is 100x. So there is no '0dB' crossing' as such. From the table you can see that in the situation of a 40db gain preamp, the attenuation at 20kHz, which is the largest in the audio band, is about 20dB. That means there is still 40-20=20dB gain left at 20kHz.
If your preamp had a design gain of 20dB at 1kHz, than at 20kHz the gain would be down to 20-20=0dB. That *could* be considered '0 crossing' but it is a meaningless thing, because, you see, it's all relative

jan didden
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Old 4th December 2010, 04:20 PM   #6
Salas is offline Salas  Greece
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Indeed. The chart also says ''relative to'' for a good reason. Everything is relative. Hey even Jan and I are relatives. He is a Greek in a bathtub!
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Old 5th December 2010, 02:40 PM   #7
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Quote:
Originally Posted by Sunsun22 View Post
Where does the RIAA curve cross the 0dB line? Is it somewhere around 1060Hz?

Does every phono amp design to cross the 0dB at/approx the same frequency?

Thanks
The 0 db point of the RIAA cruve is arbitrary. It is only the shape which matters. The concept is that it should be an exact compliment to the curve used in the recording process. The RIAA curve standard is only one FR curve in the chain that must be taken into consideration. Optimal complex impedence of the electrical load the cartridge terminates in including tonearm wiring is another. Unless all of them are correctly "equalized" the FR between the input to the recording cutting head amplifier and the output of the playback preamplifier will not be flat.
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Old 8th December 2010, 05:52 AM   #8
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The curve shape is defined by the poles at 3180us and 75us and a zero at 318us.
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Old 8th December 2010, 06:05 AM   #9
sreten is offline sreten  United Kingdom
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Hi,

The standard curve is 0dB at 1kHz, but most stages are +20dB at 1kHz.

rgds, sreten.
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Old 8th December 2010, 07:08 AM   #10
Calvin is offline Calvin  Germany
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Hi,

the original RIAA curve is defined by the 3 time constants 3180s (pole), 318s (zero) and 75s (pole). These time constants can be represented by the frequencies 50Hz, 500Hz and 2122Hz. Later a second zero at 7950s (zero) was added. This is the so called RIAA/IEC variant.
Since this preequalization curve raises till infinite with rising frequencies and since this is non practical with reallife cutterheads the company Neumann introduced a variant with an additional zero at ~3.18s. The amplitude response of the preequalization curve levels out above 50kHz. This is called the RIAA-Neumann variant, which afaik has never become a official standard.
In playback RIAA and RIAA/IEC differ in that the IEC-variant adds a subsonic-lowpass filter at 20Hz. The Neumann variant differs to the RIAA-standards in that its bandwidth limit raises from app. 20kHz to higher values.
For a sufficient description of the curve a reference point in frequency and level is needed. Usually 1kHz and anormalized-to-0dB-level is taken. But it could as well be taken from 20Hz or 20kHz or whereever You want and at any reference level you want.

jauu
Calvin

ps. sreten, could You explain what you mean? To me it doesnt make sense

Last edited by Calvin; 8th December 2010 at 07:19 AM.
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