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It's not a matter of amplification. As you pointed out, jamma RGB signals are generally at high levels. So why use a video amplifier IC?

To place the video circuitry of the arcade board under adequate load. It is designed to drive high level signals.

To buffer the video and have a cheap point of failure between your expensive arcade board and monitor.

To output at 75 Ohm impedance.

HAS supergun has been doing things right for 4ish years now. It's not really a new concept, but one not many people adopted. We owe RGB some thanks for steering us all in the right direction.

I believe that 8 DIN VGA breakout cable would work but haven't looked closely into it. Mind you, if people want to run two video outputs simultaneously we'd be better off using the THS7374, which is capable of driving two separate outputs.
 
Correct me if I'm wrong. I understand THS7316 / THS7374 RGB amps work as video buffers in this setup, making impedance matching for 75 ohm expected by SCART (Arcade monitor have a 1k-10k impedance). The voltage is reduced from 2.2Vpp to 0.7Vpp, and the Sync signal attenuated to ~350-500mV.

I use this circuit and it works great with several kind of boards and CRT TV sets:

arcade-scart-video-driver.png

A good reason to include 1k trimpots instead of resistors is that you can correct color balance without the need to manipulate CRT TVs. One trimpot for sync is useful to adjust signal for more picky TV sets.
 
Correct me if I'm wrong. I understand THS7316 / THS7374 RGB amps work as video buffers in this setup, making impedance matching for 75 ohm expected by SCART (Arcade monitor have a 1k-10k impedance). The voltage is reduced from 2.2Vpp to 0.7Vpp, and the Sync signal attenuated to ~350-500mV.

I use this circuit and it works great with several kind of boards and CRT TV sets:

arcade-scart-video-driver.png

A good reason to include 1k trimpots instead of resistors is that you can correct color balance without the need to manipulate CRT TVs. One trimpot for sync is useful to adjust signal for more picky TV sets.
I prefer RGB pots too, but thought it best to keep it simple. Fixed resistors will never need adjusting and will be suitable for 90% of arcade boards.

I agree re the sync pot, and am comfortable with it for my own personal use. But for the general public, how do you safeguard against someone misadjusting it and sending too high a voltage down the sync line?
 
I'm branching this off into two separate projects.

A basic PCB and an advanced PCB.

The basic PCB is what's currently being shown. Through hole components with a video circuit revolved around the THS7316, DC coupled output. This PCB is currently in fabrication and will be shipped express, so I should have something to show in a week or so.

The advanced PCB is very similar to the basic version however it utilises an AC coupled THS7374 circuit and utilises mostly surface mount components. Sync is passed through the THS7374 and trimpots are used to calibrate RGB levels as opposed to fixed resistors.

Next step will be releasing the Easy EDA project files, Gerber files and drawing up schematics. This will happen once I have assembled PCBs in hand and everything has been tried and tested.
 
Could you give more detail on how are you handling the audio part?

An interesting option may be a switch to drive the audio through the Minidin / minijack or directly to speakers. But I suppose that may defeat the concept of "Mini" supergun... fortunately it's Open Source so everyone can modify it to their needs :)
 
The 3.5mm jack is switched, meaning that audio is passed through the DIN unless a cable is inserted into the 3.5mm jack, in which case audio is no longer passed to the DIN and is only output through the 3.5mm jack.
 
That's a very nice feature.

Is Speaker - connected to ground, or does it follow a schematic similar to this one? this page says it's the typical circuit that it's fine, it has two capacitors and four resistors for the audio section.

Apart from that, is it possible to damage the tv speakers if the volume is set up too high on the board or there is some kind protection?
 
Same schematic as you linked to. Audio is attenuated via a voltage divider, DC blocked via a capacitor and the jamma audio pins are never grounded making it safe.
 
Nice! Why the mix of SMD and through-hole for caps and resistors?
 
I'd prefer to keep radial caps as through hole. More variety of brands and easy to solder.

I can change the audio resistors and the THS power cap to surface mount.

I may add a surface mount power LED too and see if I can squeeze in stereo output, just on the advanced PCB.
 
Almost ready to wrap this up. Going with two versions, COMPACT & ADVANCED.

Both 2 layer PCB's. COMPACT is 110 x 40mm while ADVANCED is 110 x 50mm.

COMPACT utilizes a THS7316 with through hole components. Low overall cost, quick & easy to assemble.

ADVANCED utilizes a THS7374 with surface mount components (aside from radial caps), and adds a switched 3.5mm audio output jack.

Choose whichever one suits your needs.

I should be ready to release the source files within a week or so.

MiniGun-Comp-Top.png
MiniGun-Comp-Bottom.png
MiniGun-Adv-Top.png
MiniGun-Adv-Bottom.png
 
It looks great! :thumbup: I also prefer through-hole electrolytics since they have been more tested and SMD ones are a pain to remove and they can explode using hot air.

Shouldn't a 0.1uF ceramic capacitor be placed before the THS7374 input of Sync signal for AC coupling? Since this signal is buffered by the THS7374 shouldn't have more sense to use a 75 ohm resistor at the output instead of 470?

I'm looking for the connectors, I think these ones are right but I'm not 100% sure:

Female:

https://www.mouser.es/ProductDetail/490-MD-80SG
https://www.ebay.es/itm/5-piezas-reemplazables-S-Video-8-pin-Mini-Din-tomas-JCP-montado/153043703939

Male:

https://www.mouser.es/ProductDetail/Kycon/KMDAX-8P?
qs=sGAEpiMZZMvlX3nhDDO4AN7yze9pKzO9oYJhP0fv%252BtM%3D
 
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Looks good! Will you be offering pre-made superguns for purchase (I can't remember if this was discussed in this thread or not)?
 
The prototype pictured above works great. It's probably my favourite version, so looks like there will be three editions.

The compact which is the smallest and lacks the 3.5mm audio output..

The basic, pictured above which is the same as the compact but adds the 3.5mm audio output.

Advanced which utilises SMD and the THS7374.

I needed to change the 43Rs to 220Rs on the RGB input voltage divider. Long and boring story on how I botched that. I'm reading 0.7V p-p for RGB and 0.6V p-p for sync. Perfect.
 
Did you:
  1. Use solder paste and a rework station, or
  2. Have some fabricator bake the prototype for you, or
  3. Are you a virtuoso at hand soldering?
Because between that proto and the sync pulse generator you posted, the solder work looks fantastic for prototyping stuff.
 
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