JCM800 Impedance Selector

Dax-The-Ax · Post by **Dax-The-Ax** » Thu Feb 10, 2005 10:04 pm

My Impedance selector is going out and i need to get one from george. Anyone know what the white wire in the center is? I know the white one on the right is the DI, i'm pulling that out.

Flames1950 · Post by **Flames1950** » Thu Feb 10, 2005 10:51 pm

You mean it isn't the common wire that goes to the speaker jacks? Not the color I'm used to seeing, mind you......

Dax · Post by **Dax** » Fri Feb 11, 2005 12:01 am

It does go to the speaker jack, it's the farthest left white wire in the pic, i thought the Brown wire is the common? The White wire attached to the brown goes to a ground, i'm confused.

Dax

Flames1950 · Post by **Flames1950** » Fri Feb 11, 2005 8:33 am

Sorry, bad wording. The brown looks like the OT secondary's common wire. I meant that the white is common for the impedance selector, ie. the one contact that is used no matter what other impedance contact you select, so you have green/white. black/white or yellow/white connections.

Dax · Post by **Dax** » Fri Feb 11, 2005 10:18 am

I was just confused because the center white wire is connected to 2 lugs. I guess if i buy a selector from George, this white will just connect to the center lug like his tech CD shows?

Thanks

Billy Batz · Post by **Billy Batz** » Fri Feb 11, 2005 11:36 am

Its the way rotary switches work. Most of the time a 3 or 4 position rotary switch will have 2 seperate poles. Each pole switches between 3 or 4 positions together with the other. The pole and each position has a lug. Now you can choose to use only one pole in some cases using only the lugs that are going to be in use with that pole or you can attach the wire to both poles so you can use both sets of lugs for convenience sake. The white wire goes to the jacks and is connected to the pole. Each time you click to a different position the pole moves to connect to one of the other lugs which each have a seperate OT tap connected to them. So your choosing between which tap goes to the jacks. Thus you get your impedance selection. Some rotary switches only use one pole. When Im building an amp I prefer the small pot sized switches that mount in pot sized holes like the ones sold by hoffman. Its one pole and very heavy duty.

If you cant tell by looking at the switch which lug is the pole, say if the lugs are in line and unlabeled as they are in your photo, you can simply take a resistance meter and test to see which pole shows 0.00 resistance when measured against all the others in its group. Many switches will have the pole in the center.