Tuesday, 8 May 2012

Commodore 64c Mssiah Mods

My Commodore 64c internally modded for use with Mssiah.

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.


Composite Video Out
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 motherboard. Connections described in more detail here.

Audio Out Jacks for SID#1 and SID#2
Audio Out for SID#1 soldered to rearside of motherboard.
Audio Out for SID#2 wired as described in Mssiah pdf. Both Audio outs go through 1uf capacitors +side to SID -ve side to jack.

DPDT Switch to ground audio ins or send audio ins to Feedback pots.
This is wired using AlphaA's excellent schematics. 
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.

4 pots with InactiveX's no-dead-spot-calibration circuit
Pots are wired with Inactive X's schematic below. Link to thread here.

DPDT to cut lines to port 2 when using Mouse in Sequencer
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!

Wired as described in Mssiah pdf however I removed r8 and added an Audio In cable to SID#2. Audio in cable is wired to DPDT switch as outlined above.

SID#1, SID#2 and Video Out in progress.

Audio Out SID#1 and SID#2 jacks almost finished showing 1uf capacitors. 
Blue cable is SID#2 Audio in, white cable is SID#1 Audio in.
Yellow RCA is Composite Video Out (with Purpley Blue wire)
I ended up using a screened and grounded cable for the Audio IN and OUT run across the circuit board in an attempt to stop unwanted noise.

Rearside of Pot board showing sticky fixers to keep it in place

Rearside of motherboard showing Pot solder points

Top view of motherboard in progress

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.

Rearside of motherboard showing connections for SID#1 audio out, GND, and Video Out. Audio out is Orange, Audio in is White, Video Out is Purpley Blue.

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