Preamp output voltage limit

ashlar · 2nd December 2008, 01:50 AM

In car audio, why is the output voltage of preamp processors only limited to 9.5 volts and no higher?

Perry Babin · 2nd December 2008, 03:02 AM

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.

Eva · 2nd December 2008, 11:41 AM

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.

2nd December 2008, 01:50 AM	#1
ashlar diyAudio Member Join Date: Nov 2008	Preamp output voltage limit In car audio, why is the output voltage of preamp processors only limited to 9.5 volts and no higher?

2nd December 2008, 03:02 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	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. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

2nd December 2008, 11:41 AM	#3
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	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. __________________ I use to feel like the small child in The Emperor's New Clothes tale

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