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Old 2nd December 2008, 02:50 AM   #1
ashlar is offline ashlar  United States
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Default Preamp output voltage limit

In car audio, why is the output voltage of preamp processors only limited to 9.5 volts and no higher?
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Old 2nd December 2008, 04:02 AM   #2
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Op-amps have a limited power supply range. The 'absolute maximum' supply voltage is generally 18v. Most designers choose to operate them below the absolute maximum and run them at 15v.

Most op-amps can't swing the output voltage to the rails so the output is somewhat less than 15v (peak voltage). Most lose at least 1v. This would give you an output of 14v peak which is equal to ~10v RMS. Most lose more than 1v so the maximum unclipped output is actually nearer 9v.


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Old 2nd December 2008, 12:41 PM   #3
Eva is offline Eva  Spain
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Since ADCs and DACs usually work with a limited voltage range like 5Vp-p, high preamp voltages are a double edged sword when digital processing is involved. Applying gain to the output of a DAC results in noise being amplified too. Then, applying attenuation in the digital domain before the DAC reduces the useable resolution by several bits in most cases.
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