jamma (sega st-v) to mvs?

[guiddruid]

Hi guys,

from the recent flurry of emails (well, last week anyway) it would seem
that the mailing list is not dead...

I have a sega st-v motherboard which I would like to use in my neo-geo MVS
wired cab (Super Neo 29).
Everything other than the audio works fine, but the st-v has standard
amplified mono out on the edge-connector, where the MVS cab is expecting
amplified, ground-returned, stereo.
This means that I get out-of-phase mono out of the speakers (and the st-v
amplifier doesn't like the load at all)

What I'd like is a converter board, with an on-board stereo amplifier,
which I can hook up to the st-v's un-amplified stereo output, so swapping
the st-v motherboard in & out would be nice & easy.

Anyone know if such a thing exists (or something near-enough to be
hackable). I'd rather not make it myself unless I really have to.

Cheers,
Simon

__._,_.___
Messages in this topic (1) Reply (via web post) | Start a new topic

 

[eggwheatis]

Hi, I'm fixing up a Taito Space Invaders cocktail for
someone and it needs the following parts:

Coin mech. Mechanical S1 type with metal face plate.
Preferably old 10p but anything considered.

Taito 7900 key, and a Taito 7900/7800 lock found on
the upright also. Someone drilled one of the originals

That's it! Good price paid...I have a Taito part II
cocktail player 2 control panel plate in superb
condition for trade if that helps! I would also do a
really good trade on other stuff I have!

egg

__________________________________________________________
All New Yahoo! Mail – Tired of Vi@gr@! come-ons? Let our SpamGuard protect you. http://uk.docs.yahoo.com/nowyoucan.html

__._,_.___
Messages in this topic (2) Reply (via web post) | Start a new topic

 

[andrewhannay]

How are you connecting it?
To re-cap, the motherboard gives out amplified mono and the cab expects
amplified stereo.
All I would do is connect the mono ground to the stereo ground, and connect
the the mono sound output to the stereo left and right input (or just one of
them like an old fashioned cab). You should not have any problems with that
setup.
Or is there a typo and one of them is not amplified.
Andrew

>

 

[Ordyne]

All you need to do is add a toggle switch so you can turn the MVS speaker
wiring from being left + and right + to speaker - and speaker + for one of
the two speakers..

Cheers,
Craig

>

 

[guiddruid]

> All I would do is connect the mono ground to the stereo ground, and
connect
> the the mono sound output to the stereo left and right input

I think the drive from the st-v is differential, so connecting the -ve
output to ground would be shorting out one side of the driver.

If the ground-return for the speakers in the cab comes back to the edge
connector without connecting to any other grounds, then I might be able to
get mono sound working in that way... I'll have to check the wiring. I
don't want to hack the cab wiring about, as it is all original at the
moment.

the speakers in the cab are 4 ohm, so I would either have to just use one
speaker, or add a series resistor to avoid overloading the amp.

I'd really prefer stereo sound though.

__._,_.___
Messages in this topic (6) Reply (via web post) | Start a new topic

 

[andrewhannay]

I see.
If the speaker returns come to the connector without connecting to other
grounds then that's even better. Make sure both speaker returns are
connected to each other then take st-v +ve out to one speaker and -ve out to
the other speaker, then you will also sort out the 4ohm impedance as both
speakers are now in series giving 8ohm.
It sounds like you have left and right return going to st-v ground and +ve
and -ve output going to each speaker input hence the phase problem you are
having, one speaker is pushing while the other speaker is pulling. If that's
how it is then just disconnect the speaker returns from st-v ground and
connect to each other.
Aaaaah just like the good ol' days isn't it.
Andrew

>

 

[guiddruid]

> the other speaker, then you will also sort out the 4ohm impedance as
both
> speakers are now in series giving 8ohm.

This is what happens now... If you think about the current flow through
the speakers, it means the speakers are 180 degrees out of phase. Sounds a
bit tinny, as you mainly hear the difference signal.
The center-point between the speakers being ground just makes the load
harder to drive.

Simon

__._,_.___
Messages in this topic (8) Reply (via web post) | Start a new topic

 

[andrewhannay]

When you say difference signal do you mean left minus right?
If you do then that means the st-v is giving out stereo.
I use to do this on my old stereo to "fake" surround sound or do voice
cancel, connect left- output to left speaker-, connect right+ output to
right speaker+ and wire left speaker+ to right speaker-.
You shouldn't get a difference signal if you are outputting in mono.
I'm lost.
Have I totally got the wrong end of the stick?
Andrew

>

 

[andrewhannay]

Oh hang on me being stupid, as usual.
Of course, connect +ve output to +ve speaker and -ve output to other +ve
speaker.
I see what you are saying now, they will still be out of phase whether you
connect ground to output ground or not.
OK, mm tricky one in that case.
I guess the speaker returns are connected together.
The only way to do it is in parallel, which means two 4ohm speakers in
parallel is 2ohm.
And you are worried the amp won't be able to drive this impedance.
I see your problem now.
Andrew

>

 

[guiddruid]

> Oh hang on me being stupid, as usual.

well, my explanation was a bit lame too... I was explaining it backwards.

> The only way to do it is in parallel, which means two 4ohm speakers in
> parallel is 2ohm.

that's why craig was suggesting just using the one speaker, or I said I
could add a series resistor.

> I see your problem now.

hehe... so, anyone know where I can get a jamma-adapter type board with a
stereo amp on it?!

Simon

__._,_.___
Messages in this topic (11) Reply (via web post) | Start a new topic