Should I remove my back porch video mod when I install a vLA81?

Discussions about Sinclair ZX80 and ZX81 Hardware
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gwpt
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Should I remove my back porch video mod when I install a vLA81?

Post by gwpt »

I have the following back porch video mod in my ZX81 ("3. 555-Based Circuit" in the doc):

http://zx.zigg.net/misc-projects/ZX81_V ... ioning.pdf

and am about to install a vLA81, which also supports back porch video.

So should I:

A) remove my 555 mod (and replace it with the simple transistor mod) and use the uLA81's back porch feature
or
B) leave the 555 mod, and just disable back porch on the vLA81?

Would one be a better option than the other. e.g. better video quality etc?

Thanks :)
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Paul
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Re: Should I remove my back porch video mod when I install a vLA81?

Post by Paul »

Remove the add-on and use output of vla81 directly.
You can't improve it's output.
In theory, there is no difference between theory and practice. But, in practice, there is.
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1024MAK
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Re: Should I remove my back porch video mod when I install a vLA81?

Post by 1024MAK »

I agree with what Paul said.

Mark
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gwpt
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Re: Should I remove my back porch video mod when I install a vLA81?

Post by gwpt »

When you say directly, do you mean wire ula pin 16 directly to the phono jack? Or should I still have the transistor/resistor between them?
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1024MAK
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Re: Should I remove my back porch video mod when I install a vLA81?

Post by 1024MAK »

The vLA81 manual says:
Screenshot_20240701-132001_kindlephoto-4130504655.png
Personally, I would still use a transistor, resistors and capacitors as per the link in my signature below. At the very least, I would use a capacitor.

This is in order to provide at least some protection from the TV/monitor/ external device.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
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gwpt
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Re: Should I remove my back porch video mod when I install a vLA81?

Post by gwpt »

Great, thanks for the help!
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