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Old 7th September 2012, 11:11 AM   #1
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Default RIAA Question - Power

Hello guys.
I just want to know if I put a say 1V rms signal in front of the RIAA equalization, I know that I loose 10x of the signal at output. So I get 100mV at output. My logic tells me that I also loose 10x power of the signal or???

Thanks.

Last edited by DIYspaceW; 7th September 2012 at 11:25 AM.
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Old 7th September 2012, 11:40 AM   #2
oshifis is offline oshifis  Hungary
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Impedance matching is not used at signal gain stages, therefore power loss is not important. More important is preserving signal to noise ratio. A RIAA equalizer attenuates high frequency signal and also noise more than low frequency. This also applies to record surface noise and noise generated by previous gain stages. So the there is ultimately an increase in S/N.
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Old 7th September 2012, 11:49 AM   #3
sreten is offline sreten  United Kingdom
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Hi,

x10 change in voltage is a x100 change in power (at fixed impedance level).

x10 voltage = 20dB gain*. The RIAA curve is +/- 20dB with 1kHz being 0dB.

A passive RIAA stage does output 1/10 the input voltage at 1kHz.

rgds, sreten.

* Gain in decibels is standardised to reflect power.
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Old 7th September 2012, 12:57 PM   #4
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Hi!

As others have stated already, power loss is not relevant in a preamp.

Note that the 20dB loss is purely due to the EQ curve. Depending on the implementation of the filter you will also have some insertion loss. This is typically between 3-6dB. This depends on the ratio of the output impedance of the driving stage and the input impedance of your RIAA network.

Best regards

Thomas
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Old 7th September 2012, 02:20 PM   #5
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Thank you all for the comments... So if I understand your statements correct the answer to my question is YES, the power is also lost. (1/100 aprox.)
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Old 7th September 2012, 04:26 PM   #6
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Hi!

Yes, but as mentioned it is not relevant. This has nothing to do with the power you will actually get from the system to the speakers, if that is what you are thinking about.

Thomas
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Old 7th September 2012, 04:53 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

If it was a passive RIAA EQ designed to work at 600 ohm in and
600 ohms out, then yes, the power loss is x100 or 20dB at 1KHz.

However its simple to build an active RIAA stage that with 3mV input
outputs a nominal 300mV at 1KHz, i.e. the gain at 1KHz is 40dB.

40dB is x10,000. (20log[Vout/Vin]). Thinking about the voltage
gain in power gained or lost terms doesn't really help much.

They are just relative ratio's, not absolutes.

rgds, sreten.
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