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My supergun prototypes

pacoarcade

pacoarcade

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Initially when I made this post it was called Machinegun Supergun and the design was simpler, but it has evolved into Pacogun.

It pretends to be a simple, safe and cost-effective way to connect JAMMA boards to SCART TVs and audio amplifiers or speakers, with a focus on audio and video quality, reliability and electrical correctness. This means that I'm continuously looking to improve it in this regard, looking for new video amps, audio components, etc. Suggestions are welcomed.

This design is inspired by other projects:
It also has some unique characteristics:
  • DC-coupled RGB output for signal integrity using a THS7373 video buffer
  • Connector to plug a CSYNC processor circuit in form of "hat"
  • Isolation transformer with polypropylene capacitors and a jumper to remove ground loops when using minijack output
  • Color calibration pots and, at the same time, brightness control using one knob
  • Direct speakers output selectable by an accesible switch and a two pin molex connector
Photos

pacogun2dash-3.jpg


pacogun2dash-5.jpg


Features
  • Voltmeter that can be disabled, set to +5V/+12V selectable by a jumper
  • Heavy gold plated KEL connector made in Japan
  • Buffered and 75Ω impedance matched R,G,B video signals
  • TTL or 75Ω ~400mV buffered CSYNC selectable by a jumper
  • Individual pots to adjust R,G,B to achieve perfect color balance in any TV set
  • +5V and GND footprint between the joystick connectors
  • SPK+, GND and SPK- footprint for direct speakers with MVS Stereo or Konami Stereo games
  • Switch to select Line Level audio or direct speaker output
  • Molex Mini Fit PSU connector with the same pinout than Minigun
  • 2x DB15 connectors following Undamned pinout
  • Extended JAMMA Buttons 4 & 5 support via switch (thanks to plasia)
  • Buttons 4, 5 and 6 through JST Kick harness
  • Mini DIN-8 AV connector with the same pinout as Minigun / HAS / XRGB Mini
  • Audio atenuation featuring galvanic isolation with high-pass filter using polypropylene capacitors
  • 3.5mm Mini jack audio output that disables audio through Mini DIN 8 when used
  • AUX connector with DC coupled R,G,B, raw CSYNC, attenuated audio, +5V and GND
  • Four CSYNC modes: Schmitt, THS7374, Raw and external trough AUX connector
 
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I like it.

I particularly like how we are starting to establish a standard with superguns re power / controller / kick / video connectors.

P.s. I'm going to announce yet another new supergun; the...

Rocket Launcher Bazooka Nuclear Missile Cat Shooter Hyper Induced Mega Blaster Ring Stinging Sailor Butt Slut SUUUUUUPPPPPEEERGUUUUUNNN.

Beat that. :D
 
This looks really nice.

Regarding:
  • Galvanic isolation with high-pass filter using polypropylene capacitors and voltage divider for line level audio
I'm curious about this circuit.
I assume the transformer has two windings, and you use one per audio channel?

How do you calculate the specs of the polypropylene capacitors to get the filter that you desire? Any pointers to how to do this?

My existing knowledge of audio circuitry is basically none, but when I've been doing dumb superguns for myself, I've just copied this circuit:
http://hacks.slashdirt.org/hw/supergun/
where the thinking is stated as "Note: there’s no AC coupling (no capacitor on the signal path) because I didn’t think it was necessary: on the input side, JAMMA boards’ output should be clean enough. They’re driving a 8Ω speaker, any significant DC bias would destroy it, much more than such (reduced thanks to the higher load) bias would destroy the transformers. On the output side, measurements show that secondary DC bias is negligible, as expected. Also, 1/4W resistors are just fine. Given the load, they won’t see half that much power, and if something goes wrong, they’ll be nice little fuses."

Do you get noticeable better audio with the caps?
 
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Level 1: MVS needs K4 on Jamma. (You are here)
Level 2: Atomiswave needs K5 on Jamma. (Personally I like switchable up to this)
Level 3: Chamma stuff needs k4-6 on Jamma. (Booo Chamma!)

:) Looks nice. As Frank said, cool that we've got some real standards going. Now we can make a standard RGB->YPbPr converter, power adapters etc...!
 
@buffi my Supergun is Mono, so there's only one audio channel. However, I use SPK+ and SPK- terminals. They go to one side of the transformer and I get the sound from the other side, so the audio circuit of the arcade board is electrically isolated.

I'm using a 1:1 transformer, the formula for the cutoff frequency is fc = 1 / (2 * PI * R * C). I place the voltage divider before the audio transformer. These links have all the information you need, check out the chapter "Subsonic protection" that explains the convenience of using a high pass filter:

https://sound-au.com/articles/audio-xfmrs.htm
https://electronics.stackexchange.com/questions/344651/attenuate-75w-speaker-to-line-in

The Supergun sounds very nice, anyway I've only tested them with some cheap pc speakers and TV speakers so I've not made comparisons with different capacitors. I prefer to use the direct speaker connection when possible.

Thanks for the suggestion @plasia , that's an interesting feature. I've not included it because I don't plan to have that hardware, but that option would make the Supergun more versatile, so I take note.
 
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rsignal said:
@buffi my Supergun is Mono, so there's only one audio channel. However, I use SPK+ and SPK- terminals. They go to one side of the transformer and I get the sound from the other side, so the audio circuit of the arcade board is electrically isolated.

I'm using a 1:1 transformer, the formula for the cutoff frequency is fc = 1 / (2 * PI * R * C). I place the voltage divider before the audio transformer. These links have all the information you need, check out the chapter "Subsonic protection" that explains the convenience of using a high pass filter:

https://sound-au.com/articles/audio-xfmrs.htm
https://electronics.stackexchange.com/questions/344651/attenuate-75w-speaker-to-line-in

The Supergun sounds fine, anyway I've only tested them with some cheap pc speakers and TV speakers so I've not made comparisons with different capacitors. I prefer to use the direct speaker connection when possible. Polypropylene caps are more reliable than electrolytics, that's a reason why I've chosen them.

Thanks for the suggestion @plasia , that's an interesting feature. I've not included it because I don't plan to have that hardware, but that option would make the Supergun more useful, so I take note.
Click to expand...
Thanks for the pointers.
The reason I'm asking is that I'm constructing a Jamma A/V splitter which has a pretty similar circuit (see bottom of schematic: https://i.imgur.com/8RFPc2n.png)
It is also using a 1:1 transformer after a voltage divider from SPK+ and SPK-.

I don't however use any caps whatsoever for my circuit (since the place I took that part from (hacks.slashdirt.org/hw/supergun/) didn't seem to think it was needed.

Now I'm sortof curious, and think I'll try caps in the circuit and see if I can hear a difference. If not, then I can just bridge the connections I guess.

Your supergun looks real nice. Basically a Minigun ADV beefed up with isolated mono audio. I like it!
 
Before reading that article I tested my circuit without caps and I didn't notice any difference in sound quality. Anyway, the subsonic protection filter seems the way to go to make the circuit more reliable so I keep them.
 
The isolation transformer is a TY-250P (datasheet) featuring 20Hz - 20KHz frequency response.
 
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Ok, so the resistors divides the voltage difference by about 5. Any particular reason for picking that number?

Seems reasonable to me, but I've been dividing it by more (10) for my current circuits, which is maybe not needed :|
 
This way the volume output is not annoyingly low. Assuming you're not setting your board and TV volume to 100% it should be safe in this regard.

I recommend starting with low volume, this way there won't be any problem.
 
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Looks cool! Are you going to be selling these?

Also, why mono only? That part I don't understand.
 
Thanks! initially I planned to offer 5 of these boards as experimental prototypes to cover some costs but I'm waiting for a new revision and I want to do more testing, so I prefer to wait.


I'm looking for an alternative DB15 part without screws from a reputable distributor. In order to avoid touching the metal case and the pins is to use a bottom and top case as the HAS does. Since these are the firsts prototypes, this will come later than sooner.
 
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Not sure if it helps, but if you check my BOM of the Minigun there's digikey db15s listed that don't have those protruding screws attached.
 
Thanks, but the problem is all that metallic shell, not only the screws. I can't avoid touching them when inserting the board.

I think the way to go is to use a case. Even isolating that shell to ground it's not difficult to touch the pins.
 
I hear you. Seems like a lot of effort to have to paint all those parts, and likely the paint will wear off with use defeating the purpose of your efforts.

I'd say case it or leave them non-grounded.
 
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