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RGB amp (VGA to JAMMA)

RealMFnG said:
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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That would be awesome. I haven't been very active for the past year or so due to real-life stuff, but getting more into the hobby again recently. I'm eager to try out the new revision should you get around to it :)

Wanna explain which part of the circuit is incorrect? Kinda curious about it, I looked at it with @PascalP and we didn't spot any major issues back then comparing it to Arthrimus's schematic.
 
Yeah man, I feel ya. I was MIA for a good bit too. Weird how life in the pandemic has me home 100% of the time, but strangely have made no time for the hobby.

Download Diptrace and open up JAMMAizer's Diptrace file in there. It becomes immediately apparent. Also, Arthrimus installed test points for ohm'ing out/tuning the RGB pots which is a nice touch that should be implemented too.
 
I checked my PM's, the only schematic I received from @Arthrimus was in PDF and that's also the one I shared with you. I don't think he actually shared the updated gerbers in the JAMMAizer topic did he? Still curious.. :)
 
I need to send all of my bits to a friend to assemble for me. I'm not the best at SMD work.
 
Starting to understand this a bit better now.

1673159920702.png


Still learning Diptrace though.
 
Taking another stab at this as I understand things a tiny bit better (not an engineer):

1680726378255.png


  • Will have jumpers for combining H/V sync
    • For MAME users
  • Will have jumpers for turning on/off the low pass filter
  • Will have jumpers for disabling the 0.1uF capacitor from VCC to GND
    • I find that produces noise
  • Will have test points for calibrating resistance on the 1k variable resistors
  • Micro USB or JST PH for sourcing +5vdc power
  • Will have separate planes for video ground
  • DB15 Male connector so it plus right into the video source
    • Naomi or PC
Everything is based upon @Arthrimus's JAMMAizer video circuitry
 
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Starting to take shape:

1680755866763.png


From the datasheet, THS7375's LPF (low pass filter) is OFF if connected to +5vdc and ON if grounded. A 3 position jumper will allow the user to select what they desire. A 2nd jumper combines H and V sync into CSync for MAME users. JST NH connector for the monitor connection.

Fun little ditty. Just gotta make sure I route the traces correctly at this point. Form factor is in place (keeping it as small as possible). All componets but the JST power connector (for Naomi users) are in .
 
RealMFnG said:
Starting to take shape:

1680755866763.png


From the datasheet, THS7375's LPF (low pass filter) is OFF if connected to +5vdc and ON if grounded. A 3 position jumper will allow the user to select what they desire. A 2nd jumper combines H and V sync into CSync for MAME users. JST NH connector for the monitor connection.

Fun little ditty. Just gotta make sure I route the traces correctly at this point. Form factor is in place (keeping it as small as possible). All componets but the JST power connector (for Naomi users) are in .
Click to expand...

Dang, some timing! I was just thinking about making one of these for a Naomi I recently picked up.

If you need any assistance, let me know! I have a fair bit of experience with KiCAD and board design.
 
It is done and ready to go (I think). Double checked the routing. Seems legit. Just need to order up some PCB's now.

Let me ask you guys, should I put a female VGA right angle connector on the side going into the monitor (right side of this pic) as well? That way you'd have the flexibility to use both an DSUB15 RGB connector and the 5 pint JST NH connector.

1680840604172.png
 
RealMFnG said:
Let me ask you guys, should I put a female VGA right angle connector on the side going into the monitor (right side of this pic) as well? That way you'd have the flexibility to use both an DSUB15 RGB connector and the 5 pint JST NH connector.
1680840604172.png
Click to expand...

Looking good bud! And a big YES for the VGA connector :)
 
Sp33dFr34k said:
Looking good bud! And a big YES for the VGA connector :)
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You got it!
invzim said:
Nice!

A couple of pointers

1680860885469.png


Combining H/V by just 'shorting' them together with a jumper is not the way to go, output signal will not be TTL and you could damage the source.
This article gives you a couple of options, https://www.hdretrovision.com/blog/2019/10/10/engineering-csync-part-2-falling-short


PC and Naomi should output very clean RGB, to save space/reduce complexity I would remove the LPF option.
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The guidance for CRT Emu users would be to set CSync to be outputted on both pin 13 and 14. If CSync is enabled in CRT Emu, there is no need to do any jumpering. In lieu of CRT Emu users not enabling CSync, they can jumper H/V sync. I've been doing that for years with MAME and haven't had issues. I also don't want to raise the cost complexity for Naomi user. Let me think it through.

LPF is a curiosity for me. I want to see how it looks going both ways. It doesn't take up much room.

Question about VGnd. Can I have VGnd be its own copper pour? Or does VGnd need to connected to common ground?
 
@invzim, the XOR gate used in JAMMAizer, it is it correctly producing TTL sync? I might as well put it in if that is proper.
 
Ok, All nets check out and I am pretty sure I have the routing correct this time around. Also, I feel I can read a schematic much better now. Should help with future projects.
  • Thanks to @invzim's suggestion, I used the passive sync combiner circuit found here which leverages a 2N3904 transistor (sadly, Digikey doesn't sell the SMD version). Has a jumper to switch from RGBHV or RGBS input. RGBS input just connects input from pin 13 to output on pin 13/JST header. RGBHV input assumes you are feeding an RGBHV signal in and passes the combined sync signal outputted from the sync combiner circuit to pin 13 on the output/JST header.
  • If you are always going to input RGBS, you can use the solder blob jumper and can skip installing the sync combiner circuit. If you are always going to enable or disable the LPF, you can use the solder blob jumper. Otherwise, you can use the jumper header on both or install slide switches.
  • 5V power input can come from either micro USB or JST NH header. No need to install both depending on your situation. Though both can be installed at the same time.
  • MAME users are behooved to install the USB connection
    • USB connection's shield is not grounded
  • NAOMI users are behooved to install the JST connector
  • Connection to your monitor is either via HD15/VGA female or JST NH depending on your situation.
    • Only one connection or the other can be installed
  • Connection to your source is via HD15/VGA male and should plug right into your source's VGA connection
  • Test points are provided for each RGB line to ensure matched output impedance
    • JAMMAizer's default output impedance is 475Ω and should be the default setting
  • Video ground and common ground have their own separate copper planes. I am not sure if that works. I suppose I will find out. There is a jumper that connects both planes together.
Let me know if I missed anything.

1680941288590.png


1680940116707.png
 
RealMFnG said:
  • Video ground and common ground have their own separate copper planes. I am not sure if that works. I suppose I will find out. There is a jumper that connects both planes together.
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I would keep it simple, all my stuff has common ground for everything and with video gnd=gnd.
 
Thanks @invzim. I wasn't sure. I have pins 5-8 and 10 along with HD15 shield connector touching VGND on their own copper plane. And added a via jumper to connect VGND to GND if it doesn't work out that VGND can exist on its own ground. I'll find out I suppose; FOR SCIENCE!

1680997363434.png


I just ordered up some PCB and will test this out very soon. Getting a MAME PC up and running now. Have a fingerboard and will show what the video looks like unamped to an MS9. Then compare that to the video after it is wired through the amp.
 
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