Apple twentieth anniversary mac Service Manual

Sound input port input impedance

m > 3.5 kilohms (k

Ω

) nominal, each channel

Input level to video audio input port

Note:  The information in this section applies to the video audio input port next to the S-video port in
the area covered by the port cover plate.

The video audio input port (marked with the ≈ icon, next to the S-video port marked with the æ icon)
has one external sound input mode.

To select the video audio input port for sound input, open the Monitors & Sound control panel, click
the Sound button, and choose TV/CD/Video in the Sound Output pop-up menu. Then open Apple
Video Player, make sure that the Controls window is open, and click the S-Video button in the Video
Source section. Set the volume slider in the S-video window to maximum volume.

m Video audio input connector line level for full-scale output level, with the S-video window’s volume

slider set at maximum in Apple Video Player:  0.1 Vrms

m Video audio input connector line level for full-scale recording level, with the S-video window’s

volume slider set at maximum in Apple Video Player:  90 mVrms

m Video audio input connector input impedance:  10 k

Ω

nominal, each channel

Voltage and impedance for sound output ports

m Front sound output connector output impedance: 32 

Ω

nominal, each channel

m Front sound output full-scale open circuit output voltage: 1 Vrms

m Rear sound output connector output impedance: 32 

Ω

nominal, each channel

m Rear sound output full-scale open circuit output voltage: 1 Vrms

Signal-to-noise ratio (SNR) and frequency response

m SNR:  75 decibels (dB) minimum, 80 dB typical (A-weighted, 2 Vpp output, 1 kHz, digital record and

playback, sound input port to sound output port)

m Frequency response:  20 Hz–18 kHz (–3 dB relative to 1 kHz under the same conditions as the 

SNR measurement)

Appendix D

312