YAVC "Yet Another Volume Control"

**SteveFury** · 09-29-2011, 11:36 PM

I truly love my Bellco AUTOMATIC pachislo machine. However my family has learned to hate... no, loathe it because it's still WAY too loud even when the two switches on the sound board are at minimum. I play to get that bonus, but when I began to reset the machine as soon as its won to keep the peace in the house. It was becoming no fun anymore.

I wanted to make a volume control with these requirements:

* All 3 speakers volume's controlled simultaneously so the correct balance is precisely maintained.
* I didn't want to put 1/8 or 1/4 watt POTS in a circuit drawing several watts for possible burnout failure.
* I needed it to be quiet as a radio set to low at times, and a little louder normally.
* I needed it to be able to be easily set to its factory normal at times.

I'm an electronic experimenter and had an assortment of wire wound resistors at hand and tried several values. I found that 100 ohm on all 3 speakers give me the quiet radio volume, and a 10 ohm resistor on all 3 speakers is still loud, but it definitely removes the offensive "BLAST in your face" effect.

I decided on a 3 position switch to change the resistor arrangements and allow a pathway to its normal manufacturer volume. In order to change all 3 speaker circuits together, the switch would need to be at least the type of a 3-pole 3-position. I found the switch I needed at fry's Electronics, a 4-pole 3-position. I would simply not use the 4th section of the switch. The switch was a bit pricey at almost $7.

http://www.frys.com/product/2598261?...H:MAIN_RSLT_PG

I found what I believe to be the perfect place for the switch, through the plastic frame behind the belly glass, just underneath the fluorescent lamp. I epoxied the resistors one to another to form a resistor block and tie-wrapped them in place to the frame. I kept the wire color the same for each individual speaker circuit to avoid confusion. One top speaker has a brown pair of wires going to the switch/resistors, another speaker has blue and the bottom bass speaker has orange. It kept things simple.

I had to cut one wire to one faston clip for each of the two top speakers. I soldered a long wire from the faston clip down through the harness to the switch/resistor. The wire I cut off of the faston... the one coming from the soundboard I also routed downward through the harness... and of course they are not long enough to reach all the way down around to the switch so I solder-spliced an extension wire to reach, choosing the same color to the correct speaker circuit as I just described above to keep things simple. I heat shrinked the splices for insulation.

The bottom bass speaker connection has a certain white connector. I was not comfortable with cutting wires off the connector so I opened the trace on the back side of the circuit board as illustrated below. Yes, I know the scratching is rather crude but I was too lazy to unsolder the board off the speaker to use a Dremel. I highlighted the trace that I opened up in the photo below for identification.
Note:
Be careful if you solder on these points on the circuit board for your own project. Some of the adjacent connections are very close one to another and if you bridge them, you'll short out your sound board.

It was several hours of work to complete this project but I am extremely satisfied.
I found that I can set my new switch to its minimum volume, and set the two switches on the sound board to the middle and the level simply couldn't be more perfect. It passes the "wife test", and it's still plenty loud to really enjoy it. Although the volume level remains the switched type and not a continuously variable one, I feel the flexibility of 3 switches each providing 3 positions is plenty.

The new volume switch knob is located just next to the bottom bass speaker on the inside of the cabinet as shown below.

If you are kinda rusty with the anatomy of a switch, it can be a bit confusing... especially the one from Fry's with its 16 terminals so I made an animation picture below and I hope it will simplify how the switching works.

YAVC Yet Another Volume Control. Indeed.

**owennewton** · 09-30-2011, 06:02 AM

I just did a wiring job in a guitar with a 4 pole 6 position rotary switch with 29 terminals I don't remember how many pins I had to bridge and how many jumpers I added to it but everything worked the first try. It hooks a 4 conductor humbucker pickup up so depending on the switch position you have coil 1, coil 2 series, series out of phase, parallel and parallel out of phase. It took about 3 hours but it is a kickin mod.