commodore 64c

Description: All modifications were sourced through the Mssiah forum, with appreciation extended to all contributors. Credit has been given to those responsible, and photographs of the build have been included for reference. RCA connections are soldered to the ground and the rear side of the motherboard. A ground bus was created to join the video output and the two audio jacks using black wire connected to the rear side of the motherboard. Further connections are described in detail. The double-pole double-throw (DPDT) switch either routes both audio inputs to ground through a 1 µF capacitor and a 100 kΩ resistor or through a 1 µF capacitor to a 470 kΩ linear potentiometer connected to the audio outputs to create feedback loops. An additional 1 kΩ resistor was added in series with the 470 kΩ potentiometer as a precaution against sending sound directly back into the SID chips, although its necessity is uncertain. The DPDT switch disconnects lines 7 and 8 to port two; while it may not be necessary to cut both, the use of a DPDT switch was intended to prevent any potential conflicts. The SID2SID connection is installed, and a small hole was drilled for the blue audio out cable to exit from the top side of the board. The audio output from SID#2 is soldered to pin 26 of SID#2 on the rear side.

The electronic schematic involves several key components and connections that facilitate audio processing and routing within the system. The RCA connectors serve as the interface for audio input and output, ensuring a reliable connection to external devices. The grounding system is crucial for minimizing noise and interference, with a dedicated ground bus that connects various components, enhancing overall signal integrity.

The DPDT switch plays a pivotal role in the audio routing scheme, allowing for flexible signal management. When engaged, it can direct audio signals to ground, effectively silencing them, or route them through the specified capacitors and resistors to manage feedback and signal levels. The 1 µF capacitors act as coupling capacitors, blocking DC while allowing AC signals to pass, which is essential for audio applications. The resistors, particularly the 100 kΩ and 470 kΩ, are chosen to set appropriate signal levels and impedance matching, critical for optimal performance and preventing distortion.

The inclusion of the 1 kΩ resistor in series with the potentiometer serves as a safeguard, limiting the feedback level to the SID chips, which can be sensitive to excessive input levels. The decision to cut lines 7 and 8 to port two demonstrates a proactive approach to avoiding potential conflicts in signal routing, ensuring the system operates smoothly without unintended interactions between components.

The physical modifications, such as drilling a hole for the audio out cable, reflect practical considerations in the design process, ensuring that the system remains functional and user-friendly. The careful soldering of the audio output to pin 26 of SID#2 further emphasizes the attention to detail required in such builds, ensuring reliable connections that will withstand use over time. Overall, the schematic embodies a thoughtful integration of components aimed at enhancing audio performance while maintaining system integrity.All the mods were sourced through the Mssiah forum, so thanks to all for sharing. I`ve tried to credit all those responsible, and to help anyone else wanted to do the same I`ve also added a few photos of my build. RCA soldered to GND and rearside of motherboard. I ran a GND bus joining video out, and the two audio jacks in BK wire to rearside of m otherboard. Connections described in more detail here. The DPDT either sends both Audio In`s to GND through 1uf cap and 100k r, or through 1uf cap to 470k linear pot connected to Audio Outs to create feedback loops. I also added a 1k r in series with the 470k pot as I was wary of sending sound directly back into the SID`s- not sure if this is necessary though.

DPDT cuts lines 7 and 8 to port two. Not sure it`s necesary to cut both but I only had a DPDT switch so I thought why not be double sure of preventing any conflicts! SID2SID installed. I drilled a small hole for the Blue Audio out cable to run out of the topside of the board. SID#2 Audio out is soldered to pin 26 of SID#2 on the rearside.