This is a copy of the recreation that used to be hosted at http://projectspeccy.com/projects/ with permission from Steve Smith
I designed a PCB to house several versions of the Spectrum Composite Mod. The PCB simply replaces the existing Modulator PCB. I recommend removing the original carefully and storing it in storage in case you ever wish to re-install it for authenticity.
The PCB itself is straightforward, requiring just a few components to operate. Choose which of the three options you would like to use.
Option 1 is an Inverted Emitter Follower recommended to me by Andrew Gostling in an attempt to get a Dell UltraSharp 2007FP Monitor to work with a 48K Spectrum. Sadly, the monitor is extremely picky about its composite input and is well-documented for it. In this instance, it didn’t work. However, the composite mod works with all the other monitors I have tried it with.
Option 2 is a simple NPN transistor and resistor mod. The NPN Transistor can be any general-purpose device. I have used a BC547 in the past.
Option 3 is a single 100uF capacitor which is seen to be the minimum required.
I have had several conversations about the need for other components about the composite mod. Some say that it is not necessary at all, and others say that if the monitor goes faulty or is very badly designed, it can feed voltage back to the Spectrum. I recommend you do your own research and choose the option that best suits you (including a direct connection and/or suspending the components outside of the modulator box, retaining the original PCB inside the modulator).
All the files necessary for fabricating the Spectrum Composite Mod PCB are available here https://github.com/lostretrotapes/ProjectSpeccy-Sinclair-Spectrum-Composite-Mod-PCB
