What's new

invzim

Champion
Joined
Apr 9, 2016
Messages
1,058
Reaction score
2,503
Location
Oslo, Norway
View attachment 1406
View attachment 1407
View attachment 1408

So researching this a bit, and analog stuff is not my strong side. Took a look at what the namco, konami and riverservice jvs 2 jamma boards do when it comes to audio attenuation.

Observations:
The namco board obviously has some kind of error in mono mode.
All have electrolytic capacitors in-line in some variation, with values corresponding to a resistor.
Using only speaker+ seems ok.

I was planning on doing plain voltage division, but seems all these boards use caps for some filtering stuff. Anyone good with RC circuits/filters that can explain what's going on?
 

Attachments

  • konami-audio.png
    konami-audio.png
    32.3 KB · Views: 651
  • namco-audio.png
    namco-audio.png
    38.3 KB · Views: 621
  • rs-audio.png
    rs-audio.png
    36.1 KB · Views: 485
Last edited:
Not a technical help, but I find hi low converters (line out converters) work great. I use one hooked to speaker + and - for jamma games in my net city.

Basically both positive inputs on the converter go to spkr+ and both negatives to spkr-. As a bonus the attenuation is adjustable and they're very inexpensive.
 
Can you snap a picture of the inside of one of those converters?

Looking at the schematics, the one by Konami by far seem the cleanest, a cap and a simple voltage divider..

I'm also tempted to drop support for amplified stereo input as it would mean another connector, added user complexity and a pretty limited audience?
 
Can you snap a picture of the inside of one of those converters?

Looking at the schematics, the one by Konami by far seem the cleanest, a cap and a simple voltage divider..

I'm also tempted to drop support for amplified stereo input as it would mean another connector, added user complexity and a pretty limited audience?
Sure, I'll see if I can pop one open non-destructively. I'd agree that input for amplified stereo isn't really a huge deal. Most of the time I'm using amplified mono from a jamma edge, or line level stereo.

The one I use is similar to this, minus the remote turn on wire
http://www.bcae1.com/images/jpegs/IMG_8088b.jpg
 
Some nice people told me what the caps were for, and I learned a little in the process :)

The caps are there to remove DC offset/DC components of the audio signal - or said in another way, removes signals with 0hz frequency (like a DC offset).

skate323k137: no need to open it.. I saw some circuits with transformers, but not going to get into those variants.
 
The power amplifier on some boards, like for example CPS2 and NAMCO SYSTEM 11/12 use a "H-BRIDGE" configuration where both poles of the speaker are connected to the amplifier instead of just one side, meaning each speaker wire will have a opposing power potential.

In monaural mode they will cancel each other as they're generated from the same signal (one of the wires will have the opposite/inverted voltage potential than that of the other wire).

But then the point is moot as those have RCA pins for audio outputs. (exception being System 11)
 
Back
Top