speaker volume control

fanuminski

Member
Joined
Dec 26, 2004
Messages
49
Reaction score
0
Location
circle pines, Minnesota
I have a birdie king 2 (and 3) game that I have
a problem with the sound being too loud.

the volume "pot" is turned down all the way
on the board - so I was thinking that if I could
just interupt the wire(s) going to the speaker
with some sort of volume control, that would
be the easiest fix.

Not sure what to use (rheostat or pentiometer?)
or where to get it.

any ideas or help would be greatly appreciated -

thanks,
mike
 
Last edited:
I have a birdie king 2 (and 3) game that I have
a problem with the sound being too loud.

the volume rheostat is turned down all the way
on the board - so I was thinking that if I could
just interupt the wire(s) going to the speaker
with some sort of volume control, that would
be the easiest fix.

Not sure what to use (rheostat or pentiometer)
or where to get it

any ideas or help would be greatly appreciated -
for I can only play one of the two games now because
the other is way too loud!

thanks,
mike

The type on your PCB is commonly called a "potentiometer" or "pot". It's intended for low-power useage, and it's in the circuit before the power amplifier. It is rated for a fraction of a Watt.

If you wish to place one in the output circuit (between the amp and the speaker), it'll need to be what's commonly called a "rheostat", and it should be rated for several Watts. The ones used in early-80s Ataris would be a fine choice.

However, if your PCB volume pot isn't turning down the volume, there's an issue there... because it should. Perhaps the pot is not working correctly, or perhaps there's a short on the PCB, or perhaps a cap has failed. Looks like there are at least 3 electrolytic caps around the amp: a 47µF, a 100µF, and a 470µF. After checking out the pot, I'd probably replace them first, as they cost dimes and a rheostat will code dollars.

My wildass guess is the 100µF cap has gone open, leaving no NFB...
 
Last edited:
thank you for your reply Darren.
Unfortunately, I know little about repair -when I received
this game I just had to repair the trackball.
Repairing PCB's seems a chore above me.
However, I think I could replace the "pot" and even those caps - if it
was just minor soldering.
I have to locate the 3 caps you mentioned - not sure
where they are or even the amp you mentioned.
I do have the schematics to look at -
(that may take me even longer to figure out though)

So where can I buy the volume "pot" and caps -
and would this be a fairly easy job to do?

Mike
PS> if I wanted to put in a rheostat by the speaker itself, where
could I get one of the Atari ones you mentioned?
 
However, I think I could replace the "pot" and even those caps - if it
was just minor soldering. I have to locate the 3 caps you mentioned - not sure
where they are or even the amp you mentioned. I do have the schematics to look at -
(that may take me even longer to figure out though)

So where can I buy the volume "pot" and caps -
and would this be a fairly easy job to do?

Mike
PS> if I wanted to put in a rheostat by the speaker itself, where
could I get one of the Atari ones you mentioned?

If you are comfortable with you skills de-soldering and soldering, then as PCB repairs go, this would be a relatively simple job.

To locate them, look near the volume pot. There you'll find the amplifier (which has 8 pins in a row, and a metal tab), and around it are numerious electrolytic capacitors. They look like tiny little cans. If you choose to replace them, watch how they are marked; this type of capacitor has a positive and negative lead (usually the negative is clearly marked).

If you have the same PDF schematics I found online, look at page 11. In the middle of the left side of the page, you'll see the output amplifier and associated circuitry.

Where to buy things. You could probably find the caps at Radio Shack. I tend to buy that sort of stuff from Jameco, Ed at Great Plains Electronics, and Bob Roberts. Not too sure where to source the Atari rheostat. I seem to remember a thread about them about a year ago, that culminated in a link to a supplier...

bking2.png
 
thanks again Darren -
One last question for you -
can you look at those same schematics to
tell me what the speaker output is (ohm/wattage/volt)
so that, if I decide to, I can get the correct
rheostat to place in line?

However, I will have to look at my volume Pot
to determine what kind and how easy to get at
to replace first.

thanks,
mike
 
One last question for you -
can you look at those same schematics to
tell me what the speaker output is (ohm/wattage/volt)
so that, if I decide to, I can get the correct
rheostat to place in line?

However, I will have to look at my volume Pot
to determine what kind and how easy to get at
to replace first.


BTW, the schems I found were here: http://arcarc.xmission.com/PDF_Arcade_Manuals_and_Schematics/Birdie King 2.pdf

In spite of the fact that the cover says schematics AND WIRING DIAGRAM, there isn't a cabinet wiring diagram, which might indicate details about the original speaker. It's pretty safe to assum an 8ohm speaker. A datasheet for the amplifier (an MB3712) can be found online. It refers to it as a 5.7W amplifer. This would be the peak rated power output, if the sound signal was a full-scale sine wave.

Peak power disappation in a rheostat would occur when its resistance is equal to that of the load (assume 8ohms). If the source is a full 6.75V RMS, then the rheostat would need to disappate about 1.5W. So, I'd suggest a 2W (or greater) rheostat.

But, again, I wouldn't use a rheostat... that's ignoring the problem, and putting a band aid on it. If the output volume isn't changing with the on-board pot, the "proper" solution lies on the PCB.
 
Back
Top Bottom