Audio pot is 10 watts for arcade games

[vanwatson]

Why is the audio pot rated at 10 watts for the audio board?  any reason why it's a 10 watts pot?

[lilshawn]

any reason it shouldn't be?

maybe they adjust the audio level by adding additional resistance to the speaker line.

maybe they just had a bunch left over and used them any way?

maybe you mean "10k ohm"

[vanwatson]

It's on most schematics in the manuals of 80's arcade games, the pot is 10watts it says

[Ken Layton]

Why is the audio pot rated at 10 watts for the audio board?  Any reason why it's a 10 watts pot?

Games like Atari "Asteroids" and "Pole Position" use a 10 watt rheostat not a pot. The reason for this is that the audio to the speaker comes out of the game board at full blast volume. Atari inserts a 100 ohm (or on some games a 50 ohm) @ 10 watt Mallory brand rheostat to cut the volume down to the speaker. They did this because then the "volume control" could be placed conveniently right inside next to the coin door for easy adjustment.

[vanwatson]

10 watt Mallory brand rheostat

But what kind of amplifier or amplifiers is going to the Rheostat? what kind of amplifier is this called when using a rheostat like this?

The Rheostat is wipe does to the speaker terminal
The Rheostat Right side terminal goes to the right channel Op amp amplifier
The Rheostat Left side terminal goes to the left channel Op amp amplifier

So the Rheostat is on the output of the power amplifier?




 

[ed12]

yes as i have been pointing out to u
and as ken say's it was way easier to place a control at the coin door
then going into the back and turning it up/down


ed

[vanwatson]

yes as i have been pointing out to u
and as ken say's it was way easier to place a control at the coin door
then going into the back and turning it up/down

But can't you just run wires from the preamps volume pot to the coin door? or that will pickup to much noises and will be amplifying the noises?

Is that why they used a volume pot in the power amplifier? to not amplify noises

[Ken Layton]

But can't you just run wires from the preamps volume pot to the coin door? Or that will pickup too much noise and will be amplifying the noises?

To do it that way you would have to use shielded wire (which costs a lot more) and you'd have to be very careful on how the wire is routed through the cabinet so it wouldn't pick up AC power hum in the sound.

By using a rheostat you can use ordinary wire and not be so particular about cable placement.

[vanwatson]

Yes true the wire would pickup weird noises and hum from the high voltages of the monitor and other boards

The audio amplifiers it not a complementary amplifier, but it's "bridged together" and not complementary

[ed12]

it comes down to $$ verus $$
if u use sheilded wire the cost is way up there
plus u must watch routing etc etc
just some good ol 16ga-18ga wire will do the job just fine
and add to the fact we are using the final's is a +
no noise to worrie about etc etc

ed

[jennifer]

   They must be using shielded cable somewhere however.... Every time I dig in my scrap wire room, I always wind up tossing a handful off to the side.

[ed12]

older game board's ran shieled to the monitor
rgb/gnd/sync/sheild

ed

[vanwatson]

The Syncs do need to be shielded because if the syncs get to much noise it's hard for the monitor circuit to lock up the vertical and horizontal , so you can get a garbage display

[vanwatson]

Mostly the volume pot is just a normal voltage divider after the Mixing stage. The volume pot is inbetween the mixing stage and the Left and Right output stages.

Flow Chart:
The Sound chip outputs a signal, then there is a DAC circuit, mixing circuit, VOLUME POT, output amplifier circuit, Speaker

[SavannahLion]

So... are you trying to be Nick Burns now or...?

[lilshawn]

inb4 PBJ psudo account.