There is many a web page or YouTube video devoted to video outputs on retro computers and gaming consoles. Mostly these deal with the somewhat later computing or console incarnations such as the Sega Mega Drive, Nintendo NES or Commodore 64s. There are some excellent write ups on the subject, and you can't go past RetroRGB.com for some solid information well beyond the scope of this article. The ZX81s video demands though are rather less unassuming than most, requiring only the display of a (hopefully) clear black and white image.
What kind of perfection are we after? I say video perfection, this is a perhaps a little misleading, as what I'm really after is a video experience, an experience that captures the heart of ZX81 usage. This is of course a rather esoteric requirement, if perhaps partially at the heart of using the real deal instead of a emulator to start with.
Below are some of the variations on a theme I've tried, this is not an extensive list of every possible configuration available. So this is not a guide, more of a primer before launching your own quest down the rabbit hole of ZX81 monitor selection.
To CRT or LCD?
Back in the 80s the best monitor for a stock ZX81 was a black and white television. The perfect monitor for a ZX81 with a composite mod in 2017 is probably a black and white monitor with composite inputs. Simply put, the ZX81 does not output a chomiance (colour) signal, only a luminance (black and white) signal, any colour induced into the picture is by pure accident. There are not a great deal of black and white monitors available these days, so what easily available monitor options are available in 2017 and beyond?
There are a whole host of options available these days, from old CRTs to video converter boxes and new LCD televisions. The choice is only limited user preferences and in some cases by the constraints of the ZX81s video signal and it's interaction with modern devices. My personal preference varies, on the whole though I'm rather taken by Sony Broadcast monitors as these induce that all important retro feeling.
Option 1: An LCD TV
|ZX81 with LCD television as monitor.|
At this point, If you're happy with LCD displays you can stop right here, your never going to get a clearer display out of a ZX81, still there are minor issues with the display, and your personal preferences play a part in the ultimate monitor selection.
It's difficult to find an LCD TV with a 4:3 aspect ratio, meaning that text and therefor the underlying pixels are always going to look elongated. This may or many not be a worry, certainly the enhanced video quality more than makes up for the distortion. Then again anyone after retro video purity may well take some offence at lack of near squareness in the aspect ratio. Of course an LCD monitor may already fall into the abyss of impure horrors for those with high retro tastes.
I have found that some LCD televisions play up a little when loading tape, loading from the ZXpand or going into fast mode. Anytime the Sync signal is dropped by the ZX81 an LCD televisions may revert to a blue or black screen momentarily, where most CRT monitors will retain the greyish background or display the loading bars normally associated with a ZX81.
Option 2: The CRT Colour TV
|Late model TV with the ZX81 using RF out.|
Refresh rate is probably misleading here as technically speaking all PAL TVs and monitors are refreshed at 50htz. This may really be a phosphor persistence rating problem. The rating of particular coating thi inside particular model seems to be just high enough to mostly maintain an image between refresh cycles. Doubtlessly this is not the only reason for this units headache producing flaws.
On the positive side, the TV has AV inputs for a very clear image, though more interestingly it also has no issues in picking up a ZX81s RF signal, producing one of the clearest images I think I've ever seen RF wise. So if you're not keen on modifying a ZX81 for composite out a late model CRT TV might be the best video output option.
Regardless of the positives, using a standard TV as a computer monitor in 2017 is just plain awful, even if you're after that retro CRT experience. Sitting up close to a standard flickering television is underwhelming, did we really do this 30 years ago?
Option 3: A Professional / Broadcast CRT Video Monitors
|Sony 9inch PVMs|
Presently being discarded by the TV industry, PVMs and BVMs are highly coveted by many a serious retro gamer. Sought after PVMs are typically 20 inches plus, with extensive features including Composite, S-Video, RGB and YCbCr inputs. All this providing an expansive, high quality retro gaming experience suitable for most retro consoles. Of course a ZX81 in no way needs all the higher end features, we're just after a clear picture.
A ZX81 isn't going to be used from the couch or armchair, most likely it'll be desk based, so clarity is probably the foremost factor in choosing the monitor. Sizes over 14 inches aren't going to add much to experience, and RGB and YCbCr are nice to haves but not important unless using you're also planning on using the monitor with more advanced micros.
Nicely I have 2 Sony PVM monitors, a PVM-9040ME a PAL only monitor that has S-Video and Composite ports and a PVM-9042QM monitor with a full spectrum of video inputs available. Both monitors have screen sizes of 9inchs, a small size by today's standards but not so tiny by the standards of the day. These monitors provide a beautiful viewing experience.
Option 4: Video Upscalers and Converter Boxes
The ZX81s video output, even with a ZXCCB installed is dependent on the version of ULA inside. While the signal can be corrected for missing back porch, the underlay signal generation may not be exactly to PAL standards. I'm not am expert on the subject, but given the lack lustre results using various converter boxes which for all intensive purposes work fine other conversion duties I'd guess this is the cause of the problems I've encountered.
The best converter box I've found is a rather ancient one, an Aver Media TV Box 5. It's unfortunate that the maximum resolution this will pump out is 1024x800, somewhat below the capabilities current generation LCD VGA monitors. For this the TV Box suffers, as monitors perform best at their own native resolutions and the resulting image is a little blurry.
I've put up a little video that highlights the problems or successes of various converter boxes at my disposal. The best I can say is buy one at your own risk, and at the end of the day a cheap LCD television seems by far a better option.