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RGB amp (VGA to JAMMA)

Sp33dFr34k

Sp33dFr34k

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I needed an RGB amp for upping the voltage levels from VGA to jamma spec. More specifically, I'd like to use it for my Naomi.

Been searching for this thing for quite some time. Fortunately, @Arthrimus used a similar amp in his awesome JAMMAizer and he was willing to share his schematic for the amp part.

I asked @RealMFnG for help, he created the PCB based on this schematic, which is really awesome!

This is the rev 1.0 of the RGB AMP:

Z5EoeKSl.jpg


Features:

- Plug in solution
- Can be used with a Naomi and PC
- 5V power can be drawn from pin 9 or via a microUSB connection, Solder blob selectable
- Solder blob for jumpering H/V sync if needed
- Solder blob for jumpering CSync to pins 13 & 14

I am not sure how much need there is for such a solution, but I will be describing my progress here as I go and release the files.

1. Ordering the PCB and parts
2. Testing
3. Gerber + BOM will be released once successfully tested

Once again huge thanks go out to @RealMFnG & @Arthrimus!! :thumbsup:
 
Last edited:
Sp33dFr34k said:
Been searching for this thing for quite some time, stumbled upon the Ultimarc RGB amp, but that one supports AC only, whilst I needed DC so that didn't work.
Click to expand...
Can you please tell what you mean by this?
 
brad808 said:
Sp33dFr34k said:
Been searching for this thing for quite some time, stumbled upon the Ultimarc RGB amp, but that one supports AC only, whilst I needed DC so that didn't work.
Click to expand...
Can you please tell what you mean by this?
Click to expand...
Edited out that part, I was incorrect. In any case the Ultimarc video amp didn't work for me, here's what Andy from Ultimarc had to say about it:

"The issue would be the video output and input is AC coupled which causes a DC voltage to build up which swamps the video signal. The amp will only work with DC coupled video which is produced from standard game boards and video cards."

Arthrimus mentioned he used his circuit to amp Dreamcast VGA output to his NNC monitor with great success, so hopefully it works for my Naomi setup as well :)
 
Sp33dFr34k said:
I am not sure how much need there is for such a solution, but I will be describing my progress here as I go and release the files.
Click to expand...
I am a MAME-graduated arcade snob. In my travels, I run into ppl all the time that have gutted US woodie cabs that want the MAME treatment (I'll only touch generic Dynamo's). Being that the cabs are gutted, an alternative is needed for the J-Pac. While Ultimarc's Amp would work, I fell out of love with the image it renders long ago and much prefer the image that TI's THS series amps produces. So this standalone amp would work very nicely for that application. Coupled with cheap Chinese USB controller PCB's, wiring a MAME PC to a cab would be a very economical solution over the J-Pac.

So there is the other need that would suit this solution.
 
The ultimarc rgb amp doesn't change the image quality, just the brightness.

The confusing point I think he (Andy) was making is that the amp require a 5v DC power supply. Most graphics cards already provide this so no external PSU is needed. Some sources don't so you need to solder an external 5v dc psu to it for those consoles or PCBs.

It's definitely a lazy product because it's made with the assumption that you always need to boost 1v to 5v. In reality, each monitor and rgb source is a little different.

My PCs work fine on my tri-sync monitors without the amp. Their 1v rgb is more than bright enough. My PS2 only puts out around .7v so I use the amp (or it looks dull even when maxed out). But, when boosted the PS2 signal to 5v it's too much for my monitor and the image looks washed out. So, I had to install pots on the RGB lines to drop the voltage (to around 3v).

The amp really should have come with pots given the wide range of arcade monitors and source material.
 
My interest in arcades started with MAME before I graduated to real arcade hardware. I am well versed in Ultimarc products. I can say in my opinion, the Ultimarc RGB amp is pretty horrible at contrast. It is the same amp in the J-Pac. I find the THS-series amps produce an image that has much more dimension. I've talked about this before in other threads. Here is one instance.

In any case, this site is about projects. It is always fun to tinker.
 
I've tried PC's and rPi's before with good results without an amp, straight into the MS9. However I found the Naomi to be lacking in brightness and thought at first the Ultimarc amp was going to fix that, I fed it 5V but that made it overly bright to the point where it only showed a completely white image...

Still haven't had the time to tinker with this one, life's busy and the little one is consuming a lot of time, I have some other stuff to deal with first and then I hope I can give this a try soon.
 
RealMFnG said:
My interest in arcades started with MAME before I graduated to real arcade hardware. I am well versed in Ultimarc products. I can say in my opinion, the Ultimarc RGB amp is pretty horrible at contrast. It is the same amp in the J-Pac. I find the THS-series amps produce an image that has much more dimension. I've talked about this before in other threads. Here is one instance.

In any case, this site is about projects. It is always fun to tinker.
Click to expand...

Again, the Ultimarc amp doesn't change the image quality. If your contrast is effected it's because the amp converts all 0.7-1v rgb to 5v and 5v might be too much for your monitor. The specs on arcade monitors typically state a range like 3v-5v.

If the monitor is a tri-sync then the amp might not be needed at all. Using one would also result in a washed out image in that scenario. If there is a .75ohm / 1kohm switch, it needs to be set to 1kohm if using an amp.

Typically, you can adjust the contrast and brightness pots down on the monitor to compensate for excess voltage but if you can't, then you'd need to add additional resistors (ideally pots) to the RGB lines.

Whether an Ultimarc amp is used or a diy amp or another brand, the above issue would be the same. I.e. All monitors are slightly different so sometimes adjustments might be necessary.
 
Zebra said:
Again, the Ultimarc amp doesn't change the image quality. If your contrast is effected it's because the amp converts all 0.7-1v rgb to 5v and 5v might be too much for your monitor. The specs on arcade monitors typically state a range like 3v-5v.

If the monitor is a tri-sync then the amp might not be needed at all. Using one would also result in a washed out image in that scenario. If there is a .75ohm / 1kohm switch, it needs to be set to 1kohm if using an amp.

Typically, you can adjust the contrast and brightness pots down on the monitor to compensate for excess voltage but if you can't, then you'd need to add additional resistors (ideally pots) to the RGB lines.

Whether an Ultimarc amp is used or a diy amp or another brand, the above issue would be the same. I.e. All monitors are slightly different so sometimes adjustments might be necessary.
Click to expand...

Again, I know all of this. It is an RGB amp, not a signal processor. I get that. I've been using the Ultimarc amp for 15+ years. I've also encountered numerous monitors for which you cannot calibrate out the crushed whites (contrast) that the Ultimarc amp produces. That is why this DIY amp has pots on the RGB lines.

Ok, back on topic please.
 
Is the amp chip going to be a THS7375? I'm using a 7374 amp right now and while it's much better than without, I still think the output isn't high enough. Thinking of trying two 7374s in a row with pots, since I can't find any 7375 shipped quickly here.
 
rememberizer said:
Is the amp chip going to be a THS7375? I'm using a 7374 amp right now and while it's much better than without, I still think the output isn't high enough. Thinking of trying two 7374s in a row with pots, since I can't find any 7375 shipped quickly here.
Click to expand...
This one's designed with a THS7316 in mind, you can see on the gerber it has 8 pins as opposed to the 14 the THS7375 has.. :)
 
@Sp33dFr34k @RealMFnG istead of:

- Solder blob for jumpering H/V sync if needed
- Solder blob for jumpering CSync to pins 13 & 14

Can you revise it to be removable 2 pin jumper caps?
 
@Sp33dFr34k
Any update on this topic ?

Trying to find a good way to connect VGA to jamma...
The best amp is used so far is the one from the Capcom Converter (used to connect Naomi or Exa-Arcadia to jamma cabinet)
 
@zombiz no update from me unfortunately, I have assembled one and tried a lot of stuff with my Naomi, but couldn't get it to look any better than without the amp. So for my use case it didn't have the desired effect. I've sent the files over to @tonyt76 as he wanted to test one as well, but I don't think he ever got around to it. Maybe you can chime in, should you have an update Tony?
 
Sp33dFr34k said:
@zombiz no update from me unfortunately, I have assembled one and tried a lot of stuff with my Naomi, but couldn't get it to look any better than without the amp. So for my use case it didn't have the desired effect. I've sent the files over to @tonyt76 as he wanted to test one as well, but I don't think he ever got around to it. Maybe you can chime in, should you have an update Tony?
Click to expand...
I am going to take another whack at it soon. I've been studying Arthrimus's JAMMAizer in Diptrace and know I've built the circuit incorrectly. The hurdle now is to learn Diptrace. I only know how to use EasyEDA, sadly.
 
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