Composite mod - which one?

schombi

On all my 16K/48K and Plus Spectrums I use to carry out the "Womble" Composite mod:
http://womblesretrorepairshack.blogspot.de/2008/11/zx-spectrum-composite-video-mod.html

Now I found this one:
http://samsmods.blogspot.co.uk/2011/10/zx-spectrum-48k-composite-video-mod.html

I?m not an electronics engineer, so I wonder which one is better and what does the capacitor actually do?

Macc

Ive done both and to be honest, cant tell the difference

Zorn

A series capacitor removes the somewhat arbitrary DC offset that would otherwise be present on the video signal due to the output buffer circuit in the Spectrum. It's unlikely to make much difference to the picture quality though. Most display devices have such a blocking capacitor in their input circuit anyway, so it isn't usually necessary. However, I prefer to include it.

Of course, a proper composite video signal does have a DC offset (though not the one the Spectrum adds to it), but almost all displays perform DC restoration, so it shouldn't be something to worry about.

opless

TVs do a certain amount of filtering and possibly amplifying (AGC) and make a half decent effort to clean up dodgy signals these days.

The point is, just chop off the power to the modulator, desolder the modulators output and reroute the composite video line directly, remembering to isolate the signal line from the modulator. Which is Wobles method if I remember!

schombi

Thanks for explaining to me. I will try Sams mod, if time allows and check if I can spot a difference. Looks more like a matter of faith :smile:

Fruitcake

If you want the best quality TV picture possible and/or would prefer not to modify the Spectrum then you could opt for the SPECTRA interface which provides a RGB connection via SCART and simply plugs into the expansion slot of the Spectrum. It produces a sharper, brighter and clearer picture than possible using composite video. It eliminates dot crawl and ensures the main display area is centred across the screen, and can also output the Spectrum's sound via the SCART connection to the TV speaker(s).

The SPECTRA interface also provides a joystick socket, RS232 socket, ROM cartridge support and a reset button, and so the need for other peripherals to explicitly provide these facilities can be avoided. It also includes the unique ability to enhance the display output with new attribute colours and resolution, opening the potential for more colourful games!

All of these additional facilities can be disabled using onboard switches and thus the SPECTRA interface can simply function as a SCART interface if desired.

schombi

I already had a look (actually more than one) at the SPECTRA interface. Knowing the quality of your other products, it has to be good. Once time and money allow, I?ll definitely go for one.

ANDREW RYALS

The spectra would be great if it worked with ULA+, just think of all the additional screenmodes which could be use. Yes, I know they are incompatible at the moment, but still how cool what that be!