Here is some additional information related to the Amiga 1200 audio fix described in my previous posts
This is the PCB audio section with the completed modifications. Note that R325 and R335 are on the bottom side of the board, the other modified components are on the top.
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| A1200 audio opamp and filter section (top) |
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| A1200 audio opamp and filter section (bottom) |
The following oscilloscope images show the audio output at the phono jacks on the rear of the unit after the final Rev 2 board modifications. The Amiga is playing a 1 kHz test tone at maximum volume.
The first image is with the low pass filter disabled (power LED dim). The second image has the low pass filter enabled (power LED bright).
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| Low pass filter disabled |
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| Low pass filter enabled |
The Amiga schematics for each board revision are available online. For reference here are the Rev 2 schematics for the audio section (Paula) with the changes from the Rev 1A board highlighted.
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| A1200 Rev 2 Schematics for audio section |
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