How to get regular mono in both speakers on a New Astro City with 421-8741 sega amp?

[bgwelistyl]

Hi, I have a new astro city with a stock jamma harness that includes this sega amp pictured below. Currently I have it plugged in but I only get sound coming out of my left facing speaker.

I was wondering if any special harness need to be made in order to just get regular sound out of both my speakers?

 

[hrist]

I bet it should work as is, you should have a problem elsewhere with the speaker/amp/cabling

 

[djsheep]

Paging @nipple

 

[nipple]

If you look at my post on how to make a normal cabinet stereo, you should be able to work out where yours is wrong.

Thread 'New Astro City Stereo upgrade how to!'

Nov 19, 2025

Hey guys,

I have recently acquired 3x NAC's

1 was original and had the stereo amp option. So i set about reverse engineering the simple little plug to change from jamma mono to stereo amplified. for my other 2 NAC's

I'm going to try and list the steps below if anyone is keen to have a crack. The best part is you can't drive the amp or jamma at the same time so everything is safe. It's pretty easy.

The way to change between stereo and jamma mono is just done by removing 1x plug from the amp output and then plugging it into the mono speaker plug, it takes about 3 seconds.

1st open...

• nipple
• Replies: 1
• Forum: Sega Hardware Support

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The little loop wires on the plug in the cp may be missing.

Cheeres