iMac (Flat Panel), Power Mac G4 (Digital Audio) and (QuickSilver): Sound Output Ports

Headphone Sound Output Port

A 3.5 mm sound output port is located on the back of the computer. It is suitable for connecting a pair of headphones or amplified external speakers. By plugging headphones or amplified speakers into the headphone port, the internal speaker and the Apple Speaker sound output port will no longer emit sound. Sound will return when the plug is removed from the headphone port.

Sound output through this port has the following electrical characteristics:

• output level 2.0 V peak-to-peak (0.7 V RMS)
• impedance suitable for driving standard 32 Ω headphones
• signal-to-noise (SNR) 90 dB
• unweighted (typical) total harmonic distortion (THD) 0.03 percent or less.

Apple Speaker Sound Output Port

The Apple Speaker sound output port is a 2.5 mm stereo mini jack. It has a smaller diameter than the headphone sound output port to avoid inadvertently plugging headphones into it. By plugging speakers into the Apple speaker sound output port, the internal speaker will no longer emit sound.

Computers that have the Apple speaker sound output port:

• Power Mac G4 (Digital Audio)
• Power Mac G4 (QuickSilver)
• Power Mac G4 (QuickSilver 2002)
• Power Mac G4 (Mirrored Drive Doors)
• Power Mac G4 (FW 800)

• iMac (Flat Panel)
• iMac (17-inch Flat Panel)
• iMac (1GHz Flat Panel)
• iMac (USB 2.0)

Warning:

Some types of headphones and other audio devices have a 2.5 mm plug. You should not to plug such devices into the Apple Speaker sound output port. Doing so could damage the devices. The Apple Speakers include an internal ROM that enables the computer to identify the speakers. Speakers other than the Apple Speakers should not be connected to the Apple Speaker sound output port.

USB speakers

USB speakers work with these computers.

Sound Circuitry

Power Mac G4

The Power Mac G4 computer has sound circuitry that is connected to the KeyLargo integrated circuit (IC) by a standard I2 S bus. The KeyLargo IC provides DB-DMA (descriptor-based direct memory access) support for the I2 S port.

The sound circuitry includes a signal processing IC that handles the equalization and volume control functions, a codec IC that performs analog-to-digital and digital-to-analog conversion, and a digital power amplifier that drives the Apple Speaker sound output port.

All audio is handled digitally inside the computer. The custom audio circuitry performs digital-to-analog conversion for the audio signals to the internal speaker and the headphone sound output port.

iMac (Flat Panel)

The iMac (Flat Panel) has sound circuitry that is connected to the Pangea integrated circuit (IC) over a standard I2S bus and receives commands from the Pangea IC over an I2C bus. The Pangea IC provides DB-DMA (descriptor-based direct memory access) support for the I2S bus.

The custom sound circuitry includes a signal processing IC for equalization and volume control functions and a codec IC for A/D (analog to digital) and D/A (digital to analog) conversion.

The sound circuitry performs analog-to-digital conversion for the internal microphone and also performs digital-to-analog conversion for the audio signals it sends to the internal speaker and the headphone sound output port. A dedicated 18 watt internal digital amplifier drives the internal speaker and the Apple Speaker sound output port.