Software Support > GroovyMAME
Testing Composite Blending from PC – VideoAMP + Antonio Villena VGA → Composite/
Zebidee:
--- Quote from: Rion on September 04, 2025, 10:06:19 am ---Just to clear this up 🙂
The standard versions (v1–v4 and the normal v5) can only run one output at a time so it's either SCART or VGA passthrough. The reason you’ve seen me running both SCART and VGA together is because I have one of the very few v5 Pro units, which supports true dual output. That version was never released widely and only a handful were built, and mine came out of some specific testing and feedback discussions with njz3.
...
I only mention this because it helps explain why my setup doesn’t match what you’d normally expect from a stock VideoAMP since only the Pro model will do SCART + VGA simultaneously.
--- End quote ---
Thank you. This explains a lot. The question about whether VideoAMP supports multiple outputs has been kicked around on BYOAC before, but never really answered properly.
I bought a VideoAMP v3.3 a couple of years ago, mostly for the EDID feature (forcing the GPU into 240p). However, I never got around testing for various reasons/excuses, including: my available PCs already run CRT_emulator so no driving need, GreenAntz transcoder development, TV repair/modding, and serious injury.
Anyway, I think VideoAMP is a great thing, and dual output widens it's appeal and usefulness.
Right now I have two CRT TVs, a component TV (Sony flat 20") and a modded dual RGB SCART/VGA input TV (JVC curved 20"). I'd love to be able to test them with VideoAMP, both running the same output simultaneously. I've added a pic below as a teaser.
--- Quote ---Over time I also suggested a few smaller things that ended up being useful for everyone:
• Adding a DIP switch to convert RGBHV → RGBS, so you don’t need an external sync combiner.
--- End quote ---
This is also a very good feature.
I have managed to get GreenAntz auto-detecting composite sync input. It works great when csync is the only input. No need for a switch.
However CRT_emulator, when generating composite sync, does not switch off the vertical sync output! These "ghost" signals overwhelm the XNOR logic, creating an inverted vertical sync pulse. This problem affects all the transcoders I have tested it with (not just GreenAntz), it seems to affect all XNOR-based logic Csync. So the vertical sync still needs to be "blanked" when using CRT_emudriver Csync, thus a manual switch is still useful.
This might just be a problem with my setup (Win7, HD6450), so interested if this problem (vertical sync still output when in csync mode) is universal or just affecting me. I posted about it here, but only heard crickets chirping. Maybe I should just ask Calamity directly.
--- Quote --- • Writing a wiki page for the VideoAMP when using CRT EmuDriver setup to make it easier for new users.
--- End quote ---
Great idea. Link?
--- Quote ---I also don’t think njz3 or Bandicoot would be against making more Pro units if someone really needed that functionality. It never became the standard model, but asking them directly might be all it takes.
--- End quote ---
IMO these features should be in the standard model. Is there some reason to exclude them, like cost?
--- Quote ---Over the years I shared info, demo videos, and wiki links with Bob from RetroRGB, hoping he or one of his contributors might give it a look.
We talked about:
• How the VideoAMP acts like a “UMSA on steroids” with SCART, VGA passthrough, audio input, sync filtering, and even GunCon support.
• The usefulness of features like the built-in RGBHV to RGBS switch and the dual-output on the small Pro run.
• How it connects to the wider CRT PC workflow, including CRT EmuDrivers, GroovyMAME, and other CRT focused distributions.
Bob was always polite and said he was really busy, and even mentioned passing it along to his Linux and MAME contact Dan who could better cover it.
So it is not that there was disinterest, but more that it never quite fit into his usual coverage focus, which makes sense given how niche CRT and PC setups can be.
I only bring this up to underline that I did try to push the VideoAMP into more mainstream visibility, but at the end of the day it mostly remains something shared within the PC CRT setups.
--- End quote ---
Thanks again. I agree with these points and none of it really surprises me. VideoAMP is great, but you need to have a driving reason to use it. He gave some valuable feedback though, and all those points you listed are good ones. Partly mirroring Bob's comments, I feel that:
* The Csync switch is essential.
* Boosting video output to support two outputs simultaneously would greatly improve the appeal and "need" for VideoAMP.
* A better understanding of how people would likely use VideoAMP in their PC/CRT/arcade/retrogaming setups is a good thing.
I have a few ideas and insights that could help njz3 and Bandicoot with their development. For example, how to boost the THS7375 outputs, and/or tweaking the outputs for different situations (e.g. output to two arcade monitors vs to just one TV). I might also be able to help with the Csync.
Calamity:
--- Quote from: Zebidee on September 04, 2025, 10:43:35 pm ---This might just be a problem with my setup (Win7, HD6450), so interested if this problem (vertical sync still output when in csync mode) is universal or just affecting me. I posted about it here, but only heard crickets chirping. Maybe I should just ask Calamity directly.
--- End quote ---
Sorry, I probably missed that or got me in the middle of some extra busy period. AMD's native c-sync is barely used by a few users as far as I know. I found it problematic to setup. E.g. if things don't go well it's hard to tell if the lack of sync is caused by c-sync or something else. If things break eventually and you need to do some configuration, you'll be back to separated sync without the proper wires. If you want to dual boot on Linux, no c-sync there. Etc. That's why I find a much better solution to handle c-sync externally.
Anyway, it's interesting what you mention of vertical sync not being turn off. I didn't know that. That's probably because it was assumed that v-sync wouldn't be wired. In fact that's how I connect it to my BVM, leaving the vertical bnc disconnected.
These are things worth investigating, having the right equipment, skills and time.
Calamity:
--- Quote from: Rion on September 04, 2025, 10:06:19 am ---I only bring this up to underline that I did try to push the VideoAMP into more mainstream visibility, but at the end of the day it mostly remains something shared within the PC CRT setups.
--- End quote ---
I think VideoAMP is fantastic as it solves several issues at once that no other device combines: amplification + detection + edid emulation.
The only thing I missed in the test unit that njz3 gently sent me is amplification for the vga passthrough. I don't know if this was included in later versions, but looked like great addition for my use case.
The usefulness of hardware EDID emulation as an alternative to software based custom video is way more questionable, but that's another topic.
It was also suggested to provide support for VideoAMP through Switchres, which I really would like, if only I had the time.
njz3:
Hi,
Rion ping me to jump to this topic and answer about the simultaneous output feature.
The "standard" board has only a single THS7375 (gain ~x5) and there are 3 pots directly placed on the RGB lines of the amplifier.
Then, we added different impedances to the traces routed to each respective type of output (VGA, Scart, or RGBS) so that the final output amplitude match what is expected by the load.
For example, the VGA and Scart outputs have ~200ohm so that, when you plugged a 75ohm load, the final amplitude of the output signal is matching the expected 0 .. 0.7V range (you can actually boost a little bit the output signal to 110% of the input, sometime that can help).
If you plugged VGA and Scart outputs simultaneously, they will share the same video smplifier THS7375+3x pots, but then you have 2x75ohm load, dividing the output amplitude by 2x.
The "Pro" board has 3x THS7375, each output type has its own amplifier and get a separate output impedance.
I kept the 3 RGB pots only to tune the gains for the RGBS output (arcade monitor). VGA and Scart outputs have fixed impedance to get 1:1 amplitude with the VGA input.
Because it adds 2x THS7375, I cannot maintain the same price as the standard board (each chip already add ~2€ to the BOM + increased manufacturing costs/time).
At the end, the board price would be globally more expensive (+10€) while not everybody is interested by having simultaneous outputs.
I did a small batch of "Pro" boards, so if people wants they can ask me to get one.
Lately, I spent most of my time finalizing the jamma low-latency add-on for the videoamp (JammaMia board), so the VideoAMP design is almost frozen since a year or more.
We still welcome request for changes, provided they are simple enough to not "revolutionize" the board.
Zebidee:
Hi njz3 8)
--- Quote from: njz3 on September 05, 2025, 07:55:01 am ---The "standard" board has only a single THS7375 (gain ~x5) and there are 3 pots directly placed on the RGB lines of the amplifier.
Then, we added different impedances to the traces routed to each respective type of output (VGA, Scart, or RGBS) so that the final output amplitude match what is expected by the load.
For example, the VGA and Scart outputs have ~200ohm so that, when you plugged a 75ohm load, the final amplitude of the output signal is matching the expected 0 .. 0.7V range (you can actually boost a little bit the output signal to 110% of the input, sometime that can help).
If you plugged VGA and Scart outputs simultaneously, they will share the same video smplifier THS7375+3x pots, but then you have 2x75ohm load, dividing the output amplitude by 2x.
--- End quote ---
A reasonable approach to sharing a single amp - but your impedance matching is gone and still only one output at a time.
--- Quote ---The "Pro" board has 3x THS7375, each output type has its own amplifier and get a separate output impedance.
I kept the 3 RGB pots only to tune the gains for the RGBS output (arcade monitor). VGA and Scart outputs have fixed impedance to get 1:1 amplitude with the VGA input.
Because it adds 2x THS7375, I cannot maintain the same price as the standard board (each chip already add ~2€ to the BOM + increased manufacturing costs/time).
At the end, the board price would be globally more expensive (+10€) while not everybody is interested by having simultaneous outputs.
I did a small batch of "Pro" boards, so if people wants they can ask me to get one.
--- End quote ---
I imagine that the video output quality is improved as well, even for a single output - I'd pay a little extra for that alone. So I may just have to get one from you!
--- Quote ---Lately, I spent most of my time finalizing the jamma low-latency add-on for the videoamp (JammaMia board), so the VideoAMP design is almost frozen since a year or more.
We still welcome request for changes, provided they are simple enough to not "revolutionize" the board.
--- End quote ---
I know just how you feel ::) Regardless, here are my suggestions (a little long, sorry).
I believe you can reduce the number of THS7375 amps required. Maybe just two are needed. The datasheet states in many places that the THS7375 can support two 75R outputs simultaneously. You'll just need a few more caps and resistors.
[REDACTED]
Hope this help(ed). Make a local copy if you think this may be useful. I am aware of sensitivities and may delete all this in a week or two to save it being "harvested" by unwelcome players.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version