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Building „The Voice“ into a PHILIPS G7400/Magnavox Odyssey


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Building „The Voice“ into a PHILIPS G7400/Magnavox Odyssey and staying fully compatible

There I was with my PHILIPS G7400 console and a newly acquired „The Voice“ speech-add-on, which was only made for the PHILIPS G7000, not the G7400, and therefore does not fit onto the G7400 housing at all. And which uses an inbuilt speaker, which makes it sounding odd - speech and sound comeing out of two different sources.
Wouldn’t it be nice to put „The Voice’s“ circuitry into the G7400?
  1. Electronically - not all extensions and cartridges are compatible with „The Voice“. It must be possible to switch it off and „remove“ it electronically.
  2. Mechanical - how to fit all those components into the G7400 housing and attach them firmly.
"The Voice" interrupts a few lines of the regular cartridge interface, to control the speech synthesizer's actions and to provide a memory interface for external cartridge speech roms. So far, this has only been used for „SID, the Spellbinder“, but who knows, maybe some future homebrew project will need this too. The memory interface uses lines, that are not used by most of the game cartridges, except i. e. C7010 CHESS and C7420 BASIC. These plugins do not expect „The Voice“ to be sitting on the lines to the G7400 console. Therefore, to stay compatible, it is necessary to reconnect the interrupted lines.
„SID, the spellbinder“-PCB. Cartridge with programme rom and the GI speech rom:
Looking at PCB and schematics, I identified six affected lines:
Leading from G7400 to „The Voice“:
A(!CartWriteEnsble) —> to reset logic IC1 pin 2
B(PlusModeSelect) —> ground
E(ChipSelect) —> not connected
1(T0) —> to SP256 synthesizer chip !LRQ
10(A10) —> not connected
11(!ChipSelect P14) —> to reset logic IC1 pin 1
Leading from „The Voice“ to cartridge port:
A(!CartWriteEnsble) —> memory interface: C2
B(PlusModeSelect) —> memory interface: serial in
E(ChipSelect) —> memory interface: C3
1(T0) —> memory interface: C1
10(A10) —> memory interface: serial out
11(!ChipSelect P14) —> memory interface: rom clock
All the other lines are just fed through.
I decided to use some simple changeover contact relais, which are operated by a mechanical switch turning on and off 12 VDC for the coils.
Mechanically there surely are many possibilities. I decided to shorten the cartridge duct, to gain space inside the housing and to put my switch-device between G7400-PCB and cartridge connector.
Be warned: It is a lot of work and I had to abuse the PCBs quite badly. This might not be an adequate job, if you are doing something like this for the first time. Some practice is helpful. There is a chance to destroy your console :-o.
I wanted the switching-device to consist only of one board and I wanted the whole thing to be plugable, which makes repairs or future changes easier.
I’ll present some pictures, just to give you an impression. I have more. If somebody should have more interest and want to do the same, I can provide more pictures and information. Feel free to PM me anytime.
„The Voice“ as we know it:
The G7400 ripped apart during a test run:
The switch device with the new cartridge connector board:
Changes on the duct:
New cartrige connector attached:
Fom the other side:
The G7400 PCB with removed cartridge connector and new connector cables leading to the switch device:
The speech synthesizers audio line soldered onto G7400-PCB:
„The Voice“. Desoldered cartridge connector and "The Voice" rom board, now connected via cables to gain some space below the cartridge duct:
The Sandwich: connector board, switch device, speech synthesizer and G7400-PCB. Look, how the synthesizer board is attached to the upper housing. It is just pinched between cartridge duct and the middle plastic distance holder. PCB and holder can be adapted a bit with a file:
Everything back into the housing:
That’s what it looks like now. The cartridges are sitting a few centimeters higher, now. With voice on/off switch and a volume knop for speech output. Nice, compact — and working:)
Special thanks all the guys at http://www.videopac.nl and its forum, who are providing excellent information on all aspects of the Videopac/Odyssey related systems. A MUST-website for all friends of the platform! And of course to all the guys on all the other VIDEOPAC related websites, where people posted schematics, service manuals or their own papers, with explanations, how the G7000 works.
Best regards!
Edited by Rolo
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  • 3 weeks later...

Thanks ArcadeJunkie! Great, that you like it. :)

Of course, it's some work, but as long as stuff like that, is a hobby, that's fine. I see no reason, why this should not be possible with a regular odyssey 2. In that regard both systems are quite similar. And the size of the housing is more or less the same.

If you don't have any plans to use special carts like CHESS, BASIC or "SID, the spellbinder", than you could use a simpler T0-switch (->google) and would not need to switch the memory interface.

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  • 1 month later...



Has anyone with an Odyssey2 (or a Videopac—the overseas equivalent) come up with a way to merge BOTH its THE VOICE and Chess System modules into such a console?! How about adding an updated audio/video modification (RCA A/V, RGB comp, or HDMI) along with it?! With all 3 modifcations possible for the Odyssey2 and Videopac, new games may become possible (Ex.: Horse Racing, the Egyptian board game Khet, Bingo, Cribbage, ... ).

How about some newly-designed backlit keyjoypad controllers to go along with it?!?!

Thank You!

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Well, RT12 Productions, I never considered that.

That would be really narrow inside the box. Cables, connectors, switching devices eat up a lot of space, too. As it is now, CHESS and "The Voice" are not running together. The chess program is launching, but hanging somewhere, if "The Voice" is not switched off. As I mentioned above, some cartridge-port lines are abused by both systems in a different way. We would need to built in a switch that is controlled by the game-program. With clever programming it might be possible to switch on "The Voice" only when it is needed and not blocking something.

Or everything built right into a new "FPGA-Odyssey". :)

What's the idea behind the concept? You would like to use the more powerful Z80-clone board as main computing device, too? How would you feed that cpu with your program?

​Maybe a simpler approach would be, to build a cheap microcontroller into a game cartridge, along with the rom, which could do the heavy load and to use the Odyssey as a terminal, just like it is done by CHESS or BASIC. That approach would have the big advantage, that you would stay compatible with all the Odysseys out there, not just a few modded ones.


Concerning the video output. There are solutions out there for generating signals for composite or scart. It's especially easy on the G7400, since the PCB is prepared for that, just not populated by components. I did the scart-mod, too.


What is your idea with the controllers? You want to replace the keyboard? Or controllers like the Intellivision-controllers? Without modding you just have five lines for each joystick.


I'm not sure, if there would be many people, who would do those complicated mods or pay a decent price, especially since the console is quite cheap.

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  • 5 years later...

Hi wilco2009,

it‘s well documented, as far as I remember. I found schematics and a description in the internet. And I took photos. I’m quite sure, I have stored those documents on my PC. I‘m not at home at the moment, but I will have a look, when I‘m back. 
I‘ll tell you.

Best regards, 



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  • 4 weeks later...
On 9/6/2020 at 12:07 PM, Rolo said:

Hi wilco2009,

it‘s well documented, as far as I remember. I found schematics and a description in the internet. And I took photos. I’m quite sure, I have stored those documents on my PC. I‘m not at home at the moment, but I will have a look, when I‘m back. 
I‘ll tell you.

Best regards, 



It could be great.



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