Schematic for a *working* PCE rgb amp with 7314?

Using a digital gate to buffer sync only works if the signal is at a logic level. I personally don't know where to find digital sync, but I strongly suspect it's available somewhere. If the sync you're using is not digital/it's attenuated, then using the 4 ch amplifier is a better option since it can handle the lower sync level and is easier to build than 2 chips. Digital gates have better performance, but only when they can be used.

 

thanks, it seems the digital gate solution won't work at this case.... tried both points already (directly from Hu6260 and from expansion port...) will give it a shot with a 2nd 7314 and see what happens :victorious:

Calpis, when you have some time can you read on this thread here ? Basically user micro came up with this schematic:



Doesn't it do the same thing as the solution I followed? I measured the RGB lines on my current setup and before they go into the 7314 they are 0.97~1.23v (yeah I doubt those reistors are only 5%)

 

Yeah it's basically the same. There's a slightly different bias point, but the datasheet says 5.1 M for 5 V supply so you're good.

 

Thanks Calpis
I have made a thread here and in nfggames about a logic level c-sync point, hopefully someone will know more
In case I try the 4-channel 7374 I assume the pullup part is the same, correct?

 

You can probably use the same cap/pullup for sync, but it really depends on the signal the PCE puts out; if the PCE puts out a nice signal then it's fine, but really both sync and RGB need to be measured to know the correct bias point for both. That probably won't happen any time soon.

 

By measuring you mean using an oscilloscope, right?

 

I got this info in my search for a suitable c-sync point:

 

Yes using an oscilloscope.

It's good to know that there isn't a digital sync source, but I don't think who you consulted actually measured the signal (or fully understood my sync buffer circuit). It could be approx. 300 mV, or not, since the composite video circuit uses non-equal-weighted averaging and an imprecise (inverting IIRC) amplifier to sum the components. Besides "300 mV" isn't entirely enough information to construct a nice DC-coupled amplifier, the DC offset is needed as well as a rough understanding of how the DAC is implemented (can be figured out with resistor loads).

When you build your circuit using the 4 ch amplifier, I think you can use the same 5.1 M pullup, the bias + internal offset is sufficient so that even if the sync signal is 600 mV it shouldn't clip. Provided the 4 ch amp works, and the signals aren't clipping, you have a pretty high quality amplifier now. The only ways to improve it are to use faster amplifiers without built-in filters, and DC-couple the whole amplifier, which requires signal measurement and a much more complicated circuit. Honestly it's not worth pursuing since the PCE has such low resolution video you won't see a difference on a low-resolution CRT or fixed-pixel display. Hopefully the topic is put to rest now lol

 

Thanks for the extra info Calpis!

I am determined to make this work, I have already invested my time (and yours) on that , it will bug me lots if it does not perform satisfactory
Hopefully Bad_Ad84 will send me some 7374 amps, I will test in the meantime with a 2nd 7314 and see how that goes

 

The THS7374 worked well for me with a Turbo Booster. I was able to feed the RGB and CSYNC from the expansion connector on the booster to the 7374 and got a solid image on both my PVM-2030 and XRGB-mini.

 

Just wanted to bump this as I tried the above schematic on my TG-16 tonight; the image looks incredible and building the amp was no problem at all, I'd highly recommend this to anyone who wants to RGB mod their TG-16/PCE! I should also add that I used composite video for sync and didn't encounter the checkboarding problem that keropi ran into.