A different attenuation circuit

[MKL]

Sanwa makes a Jamma RGB to NTSC converter to help recording videos from a cab. It's called VC-J and also has an audio attenuation circuit with volume adjustment that works fine even with those boards (Cave SH-3, etc.) that have issues with the other attenuation circuit the people here know and use.

http://img229.imageshack.us/img229/6005/vcjgw6.jpg
(scroll the pic to the right for a scheme)

Here's a pic of the circuit in a supergun I've recently built:

http://img231.imageshack.us/img231/7171/s2022927gc4.jpg
(tip: wire the pot so that it raises the volume when turned clockwise)

 

[Xian Xi]

So the basic difference is the caps, so how do you like it?

 

[Hewitson]

MKL I'm unhappy with the quality of the sound with the 10k/1k attenuation circuit so I'm wondering what your opinions are of this one. Does it sound better?

 

[werejag]

need a pcb made of this stereo/mono switch and this circuit twice

 

[Hewitson]

Buy a prototype board and do it yourself, its not difficult.

 

[norton9478]

School me in electronics schematics...

is teh ) on the cap Neg or Pos?

Also, where does the Inside of the jack go after it goes through the cap?

 

[Hewitson]

The flat line is the positive, if a resistor is shown with an arrow nearby that means its a variable resistor (potentiometer) and the arrow is the wiper (centre terminal).

 

[norton9478]

Duhh, that makes sense.

Also for MKL...

Any idea of a good nominal value for the Pot?

In case we just want to use resistors instead of the pot.

 

[werejag]

Buy a prototype board and do it yourself, its not difficult.

im well aware of how to prototype im working on a pcb soon for my own needs

 

[Hewitson]

Why say you need a pcb then?

 

[norton9478]

Why say you need a pcb then?

Think he meant "Need to make a PCB".

 

[Hewitson]

Also for MKL...

Any idea of a good nominal value for the Pot?

In case we just want to use resistors instead of the pot.

bump

 

[Hewitson]

Is anyone able to explain to me why theres issues with the Cave boards with the circuit that uses a 10k resistor, yet this circuit uses a 47k resistor plus a pot and they work fine?

Edit: The only explanation I can come up with is that for some reason the audio circuit on the Cave PCB's requires a higher ground resistance than 1k in order to work.

I'm going to measure the resistance on a car speaker's negative terminal tomorrow and see what reading I get.

 

[Xian Xi]

What kind of problems does the Cave boards have with the 10k circuit? Too loud? Too soft?

 

[Hewitson]

I have not seen it for myself but I believe they do not output any sound at all.

 

[Xian Xi]

So has anyone made one to see how much better it is in a supergun instead of the 10k circuit one?

 

[Kyuusaku]

Here the 47K loads the input, the first cap and pot together make a negligible high pass filter, the pot is also a voltage divider and the second cap just blocks DC. If you rearrange the circuit for clarity, you can simplify it to just a really big pot configured as a voltage divider.

 

[Hewitson]

I still don't get it. That 47k resistor should attenuate the signal more than enough to make the pot unnecessary.

Im working on the sound section of my supergun ATM and need an attenuator (without a pot) that'll work on all boards, including Cave.

 

[Xian Xi]

I built the 47k circuit but haven't installed it yet to test it.

 

[Hewitson]

This site has some interesting information on audio attenuating, if we can work out the average voltage outputted by a arcade PCB's amp we should be able to design the ultimate supergun attenuator.

http://www.termpro.com/articles/faders.html

 

[Gwyrgyn Blood]

I have not seen it for myself but I believe they do not output any sound at all.

Yup, that's what happens. I had a supergun with an attenuation circuit in it and I couldn't get sound at all from my Galuda 2 PCB. After I took it out it worked just fine.

Im working on the sound section of my supergun ATM and need an attenuator (without a pot) that'll work on all boards, including Cave.

Can you make a switch to select output without any attenuation? That'd be the easiest way to make sure Cave games work.

 

[Xian Xi]

This site has some interesting information on audio attenuating, if we can work out the average voltage outputted by a arcade PCB's amp we should be able to design the ultimate supergun attenuator.

http://www.termpro.com/articles/faders.html

Nice site. The line-level adapter comes out to be the same 10k and 1k circuit. So I guess it would be better to make an adjustable one.

What is the output voltage for the audio on a Cave board, 12v? It's probably 10v which is why the 10k circuit doesn't work with it. Maybe if you build one with a 1.2k resistor instead of 1k it should work.

 

[Kyuusaku]

I still don't get it. That 47k resistor should attenuate the signal more than enough to make the pot unnecessary.

Im working on the sound section of my supergun ATM and need an attenuator (without a pot) that'll work on all boards, including Cave.

The resistance out of an amplifier is supposed to be very low, so a 47k load won't attenuate anything, that's the point of a big load. The pot in the circuit is not used as a variable resistor but a "variable attenuator". You can't have a static resistor work in all cases since different boards will have different powered amplifiers. Some games will use 5V single supply, some will use +-5V split supply, some will use 12V single supply. The goal is to get 1.2Vrms which is line level out of the attenuator, so for most games you'll need to attenuate between 4x-10x. There could always be exceptions though such as games which output line level expecting the cabinet to amplify or <=5V games which preamp the audio.

BTW, whether Cave games have 10V or 12Vrms output wouldn't matter because you could just turn up the volume. Also as newer games, I don't think they'll use split supplies.

If you put a huge load (like 47k) and use a pot as a voltage divider, you're good to go on any game, and if you do that, just use a big pot to save a big resistor..

 

[Xian Xi]

So in your opinion, how good is this circuit?

 

[Hewitson]

Thanks for the explanation Kyuusaku although I still don't quite understand why a 47k doesn't attenuate the signal yet a 10k does.

What I'm trying to achieve here is to build an attenuator that does not need adjusting, yet works on every game. Is this possible in your opinion? I'm thinking if we can work out the average voltage outputted to the speaker + from a number of games including Cave ones it could be done.