What switch do I need?

[hembryguitars]

I am building a doubleneck for a customer. P-Bass on top, Tele on bottom. Two output jacks, one going to each amp. I would like a single three way switch on-on-on. 1=top neck 2=both necks 3=bottom neck but I am worried that when both necks are on that the signals will be crossed and both signals will be sent to both jacks. I am familiar with DPDT switches, is that all I need?

[StratLover]

If in position 2, both pickup sets are hot I would think that there would be interference from one or the other unless there were a split between the two.
In this plan, is there going to be seperate volume and tone controls or will there be a single set for both pickup sets?
If two are going to be used, the interference should be eliminated by nullifying the volume on the unused pickup set, but the question still remains. Will you still pick up interference in the other amplifier? (POSSIBLY)
Another fix could possibly be a push/push switch for each, thus eliminating the twisting motion alltogather, giving you the use of one tone and volume, or whatever configuration this client should choose.

This is an interesting inquery.

Is my knowlege of this correct or am I missing something here. Check out this members site for yourself and help out a fellow Nut.

[JohnH]

If Im understanding it correctly, and if it is basically two separate circuits, ie not sharing common tone/volume controls, then I think that DPDT on-on-on will work, without interferance.

The two poles of the DPDT would not connect, its just like two single pole on-on-on, which happen to be ganged together. Put the output of the bass to one pole and of the guitar to the other. take the output from the guitar from one side and the bass from the other side of the other switch. Actually, its easier to draw it.......



The black dots indicate the central position

regards John

[hembryguitars]

Thanks for the answers. The schematic is what I was thinking in my head, but just couldn't be sure.
Thanks again all.

[JohnH]

I've been thinking some more, and without wishing to confuse, there is another way that may be slightly better. It is to use a DPDT on-off-on switch. This will properly ground the hot wire of whichever instrument is switched off, instead of leaving it floating. It may be slightly quieter since it would pick up less RF noise. Anyone have views on which is best?



John

[RJB]

A floating input is more prone to noise. However a hard short to ground will probaly produce a noticable thump when switched to that posistion. I would use a 2uF cap to ground instead. The impedence should be low enough to shunt the audio, but the time constant near DC should be slow enough to prevent a thump.

[JohnH]

I did a test with a jumper lead, to try the effect of grounding the output to see if there was a thump. I didn't get one, just nice quiet silence. I suppose the existence of any dc offset would depend on the amp. None found on my solid-state Marshall. So I still believe my second diagram above.

[hembryguitars]

I think you're right John, Thanks!