Audio Circuit (Atari Jaguar)
The audio on the Atari Jaguar is fairly straight forward. The sound is generated digitally from the Jerry DSP, sent through a DAC then an amplifier, and out to the back AV connector.
The digital sound is generated via the Jerry DSP chip (U15), as digital audio 16-bit words, one for each channel (left and right) out of SCK (bit clock), WS (high = left audio, low = right) and TXD (16 bit audio data).
These go into a DAC chip (U5 TLDA545A). This converts the digital signals to analog audio.
The digital audio data comes from Jerry TXD (16 bit word audio data, pin 60), into the data pin of the DAC (pin 3).
During periods of silence the data pin is ground.
This data gets clocked on every pulse of the bit clock (DAC pin 1 / Jerry SCK pin 58).
The bit clock runs permanent, but changes frequency. On the BIOS screen it is typically 665 kHz, and on the game it is usually 1.662MHz.
If the Word Select pin (Jerry pin 59 / DAC pin 2) is high, it is left audio data, if it is low it is right audio data.
The IREF (pin 7) should be a DC around 0.9V for the current used in the DAC.
VCC (pin 5) should be 5V (from the REG1), and Ground (pin 4) should have continuity to ground.
The DAC then outputs analog audio from pins (left pin 6 / right pin 8), which is then amplified via a stereo Class-AB amplifier (U4 TDA1308).
You cannot really see any audio out on the oscilloscope due to the feedback loop on the amplifier stage, so it is better to measure the output of the TDA1308 amplifier (left out pin 7 / right out pin 1).
Run your oscilloscope at 5ms to 200ms time division for the easiest visual, without any trigger.
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