CHAPTER 5
Opamps for Low Voltages
High Fidelity From Low Voltages
Nowadays there is considerable interest in audio circuitry that can run from +5 V, typically obtained from a USB port. It is expected that reasonable quality will be obtained: what might be called five-volt fidelity. Since there is only a single +5 V rail available, the maximum possible peak voltage is clearly ±2.5 V, equivalent to 1.77 Vrms or +7.16 dBu. (This calculation obviously ignores opamp output saturation voltages.) A slew rate of only 0.31 V/μs is enough to give this maximum output at 20 kHz.
When the usual ±17 V rails are used, you get a maximum level of 12.02 Vrms or +23.81 dBu. Five-volt audio gives a maximum level that is 16.6 dB less, so the dynamic range is reduced ...
