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What is Jamma pin L (speaker -) for?


Frank_fjs
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What is Jamma pin L (speaker -) for?

 

Jamma pin 10, speaker +, is the positive audio output which is grounded to the general ground pins.

 

I know Neo-Geo utilises pin 10 & L as positive left/right speaker output for stereo sound, outside of this does pin L ever have any other use in a standard monoaural Jamma game board?

 

This really has me stumped. I'd love to know the purpose of pin L (speaker -).

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It’s the inverting pin for connecting to a speaker. Where speaker + and - actually go differs between boards depending on the amplifier design. But gnenerally you just connect a speaker across + and - pins. Some boards may have one of the pins tied to ground, depends on what amp chip is used.
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It’s the inverting pin for connecting to a speaker. Where speaker + and - actually go differs between boards depending on the amplifier design. But gnenerally you just connect a speaker across + and - pins. Some boards may have one of the pins tied to ground, depends on what amp chip is used.

 

Womble is 100% correct. We learnt this the hard way recently!!!

 

Usually, you would connect speaker + to one side of your speaker and the other speaker terminal to ground. (this is how we used to wire Hankin tables)

 

I strongly suggest NOT to wire cabinets this way.

 

In our example, the 60in1 board manufacturer was using an output amplifier chip that worked perfectly when the speaker was wired with one side to ground as above.

 

BUT, without advising us, they changed the amp chip on the PCB to a type that has BOTH speaker output terminals floating and grounding one side of the speaker BLOWS UP the amp chip on the PCB.

 

So stick to the "two wires to the speaker" approach (spkr+ & spkr-) and you will be safe no matter how the board is manufactured.

 

For general info, these two wires are usually white.

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Thank you gentleman.

 

I'm still confused however. I was under the impression that speaker- isn't an actual ground point for speakers, as unintuitive as that sounds.

 

I'm designing a supergun PCB. I'm not interested in supporting Neo-Geo stereo sound, I only want to be able to safely and reliably support standard mono audio. The audio will be routed to a consumer TV so I want to attenuate the amplified audio to a safe level.

 

My research suggests that the attached picture is the best way to handle this. Would grounding speaker- as shown protect the amp chip in your scenario Mike?

26175686_10159860848585602_2142542700_n.jpg

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Thank you gentleman.

 

I'm still confused however. I was under the impression that speaker- isn't an actual ground point for speakers, as unintuitive as that sounds.

 

I'm designing a supergun PCB. I'm not interested in supporting Neo-Geo stereo sound, I only want to be able to safely and reliably support standard mono audio. The audio will be routed to a consumer TV so I want to attenuate the amplified audio to a safe level.

 

My research suggests that the attached picture is the best way to handle this. Would grounding speaker- as shown protect the amp chip in your scenario Mike?

 

That wiring as shown in the diagram would protect the PCB as it has a capacitor in each of the lines, the SPKR+ and the SPKR-. The SPKR- isn't DC grounded and that's what matters.

 

The capacitor (in this case a non-polarised electrolytic or "NP") blocks the DC voltage and only allows the AC signal through thus protecting the amp no matter how it is wired on the game board.

 

If the amp used by the manufacturer requires one side to be connected directly to ground then they will do that on the actual game board. Wiring the way you suggest will work fine and protect the PCB no matter which way it is wired.

 

In short (pun intended:D) ALL GOOD!

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Thank you gentleman.

 

I'm still confused however. I was under the impression that speaker- isn't an actual ground point for speakers, as unintuitive as that sounds.

 

I'm designing a supergun PCB. I'm not interested in supporting Neo-Geo stereo sound, I only want to be able to safely and reliably support standard mono audio. The audio will be routed to a consumer TV so I want to attenuate the amplified audio to a safe level.

 

My research suggests that the attached picture is the best way to handle this. Would grounding speaker- as shown protect the amp chip in your scenario Mike?

 

That must be converting amplified audio out down to signal audio in.

 

Whoever did the diagram could have just linked all the ground to one termination point.

ie. The Arcade PCB ground & TV Termination ground need to be connected to ensure signal reference.

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That must be converting amplified audio out down to signal audio in.

 

Whoever did the diagram could have just linked all the ground to one termination point.

ie. The Arcade PCB ground & TV Termination ground need to be connected to ensure signal reference.

 

That method doesn't address the SPKR- connection. Your suggestion would work on boards that use a single ended audio amp but would be flaky on boards that use a non-grounded output design.

 

The diagram as shown addresses all possible situations safely and still connects the grounds of the game board and TV together without risking blowing up the amp chip on the game board.

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Thanks everyone!

 

Have connected everything accordingly and included a toggle switch to route speaker negative to either audio output or ground. This is to cater to stereo only Neo-Geo motherboards. Sound won't be output as stereo, rather dual mono, but this means that at least both audio channels will come through. I've had to do it this way due to using an 8 DIN connector for video/audio output, in conjunction with standard Neo-Geo RGB scart cables (which only cater to mono audio).

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That method doesn't address the SPKR- connection. Your suggestion would work on boards that use a single ended audio amp but would be flaky on boards that use a non-grounded output design.

 

The diagram as shown addresses all possible situations safely and still connects the grounds of the game board and TV together without risking blowing up the amp chip on the game board.

 

Still address the SPKR- connection but show the diagram like this.

[ATTACH=CONFIG]121776[/ATTACH]

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I guess not but they are quite descriptive showing that indeed, these points are grounded.

 

Actually the OP diagram could be wired up badly because it doesn't indicate that the Arcade PCB and TV input need to be THE SAME ground referenced to ensure Red, Green, Blue & Sync signals are properly handled.

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Actually the OP diagram could be wired up badly because it doesn't indicate that the Arcade PCB and TV input need to be THE SAME ground referenced to ensure Red, Green, Blue & Sync signals are properly handled.

 

It is accepted that the same downward arrow is a common ground point. When there are differing grounds, usually a different symbol is used for them. You had better not read any of my schematics then if this way of indicating ground concerns you :lol

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It is accepted that the same downward arrow is a common ground point. When there are differing grounds, usually a different symbol is used for them. You had better not read any of my schematics then if this way of indicating ground concerns you :lol

 

I would take it that they are common (As I have in the updated revision).

But someone with minimal electrical/electronics experience may not.......?

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What if someone has a stereo only Neo-Geo multi MVS board? With only sp+ connected they would only hear one channel of audio. To accommodate this I've added a jumper to run both sp+ and sp- to audio output.

 

I think there may be some other rare/unique cases where certain boards utilised sp-

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When you want to hook up JAMMA boards to a TV, the SP- is simply NOT used. That's ALL you need to know.

 

A good attenuation system is the following:

 

[ATTACH=CONFIG]122080[/ATTACH]

 

This is not correct for EVERY JAMMA board. There are many different outputs from JAMMA audio.

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What if someone has a stereo only Neo-Geo multi MVS board? With only sp+ connected they would only hear one channel of audio. To accommodate this I've added a jumper to run both sp+ and sp- to audio output.

 

MVS multislots don't follow the jamma pinout so if you want your device to be compatible with them too you need to make something to accomodate that. For a connection to a scart TV, for instance, sp+ ® goes to scart 6 and sp+ (L) goes to scart 2. When using a standard jamma board on the same setup you will have dual mono.

 

I think there may be some other rare/unique cases where certain boards utilised sp-

 

ALL jamma boards use bridged amplifiers where sp- is never ground and need not be used at all and if you really want to use it you use it in the same way as sp+ for dual mono.

 

- - - Updated - - -

 

This is not correct for EVERY JAMMA board. There are many different outputs from JAMMA audio.

 

In fact they're all the same but I'm all ears if you want to make examples.

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In fact they're all the same but I'm all ears if you want to make examples.

 

I am running my factory in China building (amongst other things) JAMMA based games and believe me - they are most certainly NOT as you assume. Sorry if you are not aware of the dozens of differing JAMMA audio connections.

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Ok, thanks.

 

I'm restricted to mono audio by design as the supergun pcb I've developed uses a DIN 8 connector of the same pin spacing as a Neo-Geo AES. Therefore, I'll be using a standard wired AES RGB scart cable which only accomodates mono audio.

 

I'm not terribly fussed with stereo output for now as 1) A majority of games don't utilise it and 2) Games which are stereo typically have some form of external (to the Jamma harness) connection for stereo output.

 

Regarding sp- I've grounded it by default with a jumper to connect it to audio output (in conjunction with sp+) if ever needed - still mono output for reasons described above however at least both audio channels will be output.

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Ok, thanks.

 

I'm restricted to mono audio by design as the supergun pcb I've developed uses a DIN 8 connector of the same pin spacing as a Neo-Geo AES. Therefore, I'll be using a standard wired AES RGB scart cable which only accomodates mono audio.

 

I'm not terribly fussed with stereo output for now as 1) A majority of games don't utilise it and 2) Games which are stereo typically have some form of external (to the Jamma harness) connection for stereo output.

 

Regarding sp- I've grounded it by default with a jumper to connect it to audio output (in conjunction with sp+) if ever needed - still mono output for reasons described above however at least both audio channels will be output.

 

Be aware that by grounding the spkr- you potentially risk blowing up the audio amp on the JAMMA board "IF that's how the amp in on that particular board is wired"

 

I had to re-call about 30 Hankin tables for EXACTLY this issue when the PCB manufacturer changed output amps from a "grounded" spkr- to a "floating" BOTH spkr outputs.

 

Be careful please.

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I am running my factory in China building (amongst other things) JAMMA based games and believe me - they are most certainly NOT as you assume. Sorry if you are not aware of the dozens of differing JAMMA audio connections.

 

Thanks for coming back to me with actual examples of jamma boards that need audio connected differently and not with a snobbish reply.

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I've grounded via a decoupling cap, am I safe?

 

The schematic I posted a fair few posts above is how I have wired it, which I thought was safe from your description below that particular post.

 

Yes, if you have "-" grounded via the decoupling cap you should be safe.

[ATTACH=CONFIG]121776[/ATTACH]

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I've grounded via a decoupling cap, am I safe?

 

The schematic I posted a fair few posts above is how I have wired it, which I thought was safe from your description below that particular post.

 

Yes because you haven't DC grounded it

 

- - - Updated - - -

 

Thanks for coming back to me with actual examples of jamma boards that need audio connected differently and not with a snobbish reply.

 

Stop being a wanker. I wasnt being "snobbish" just factual.

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