Opinion on possible wiring

[DaveyM69]

Hi,

I have never used coil switching/shunting before so I've been kicking around a few different ideas. I want to keep everything humbucking so I am not interested in single coils (although I can achieve this by using the blend if I wish).

How does this look, and is it a useful setup in your opinion?

 

[line6man]

Don't use a 250k pot after a preamp. The signal impedance is too low for it to work properly. It will behave as an on/off switch.

I can't tell what the 4P4T switch does. Do you have a diagram that labels the pin layout, to show the switching scheme?

 

[DaveyM69]

Don't use a 250k pot after a preamp. The signal impedance is too low for it to work properly. It will behave as an on/off switch.

This is how it is in the existing wiring (pre is Bartolini 5.4 A/P) and it works fine in both active and passive modes.

I can't tell what the 4P4T switch does. Do you have a diagram that labels the pin layout, to show the switching scheme?

It is just how I've drawn a 4 pole, 4 position rotary - 4 of the image attached but the [DEL]poles[/DEL] positions flattened out.

 

[Lo-E]

Don't use a 250k pot after a preamp. The signal impedance is too low for it to work properly.

Agreed. Might want to put the volume before the preamp so it will work well in active or passive. Might also consider adding a passive tone control - not necessary, but nice to have.
Otherwise, what you have drawn looks pretty reasonable if not a bit busy.

 

[DaveyM69]

Might also consider adding a passive tone control.

That's what R2 and C1 are

Otherwise, what you have drawn looks pretty reasonable...

Cool - good to know!

 

[line6man]

This is how it is in the existing wiring (pre is Bartolini 5.4 A/P) and it works fine in both active and passive modes.



It is just how I've drawn a 4 pole, 4 position rotary - 4 of the image attached but the [DEL]poles[/DEL] positions flattened out.

The preamp must have a high output impedance then. Either way, it is better for the volume pot to see the same impedance in both modes.

The issue I see with the wiring is that you are shunting the unused coils in inner and outer coil mode to the signal, when they should be shunted to ground. Pickups have a lot of wire on them, so when you short one out and connect in to the signal from another pickup, that opens the door to a lot of extra hum, because the coil is unshielded.

 

[Lo-E]

That's what R2 and C1 are

Oh. You mean that passive tone control you've got there? Yeah... you should have one of those!

I was so busy looking at switching, I missed the tone altogether.

Line6Man makes a good point; a shunted coil is, essentially, an antenna.

 

[Steve Dallman]

Usually, with two humbuckers, shunting the two inside, or the two outside coils, leaves two coils that will work as a humbucking pair (inside or outside) when both pickups are used and equal volume. This usually requires shunting one coil to ground and the other to hot to keep opposing coils. I've done this in a dozen guitars and basses and it works well.

 

[DaveyM69]

Thanks for the comments.

Re the coil shunting; I've seen many diagrams where one coil shunts to cold/ground or the other coil shunts to hot which is why I drew it that way. How much of an issue is possible noise when done that way? I would have thought so long as it was shorted and not just left open at one end it should be OK but I'm open to your experience!

The only way I can think of grounding the not needed upper coil (neck in inner mode, bridge in outer mode) is to use a 6P4T switch, something like the attached. The unused coil on the neck pickup in inner or outer mode will still be shorted to hot if the main series/parallel switch is set to series but, as far as I can tell, that is unavoidable.

Ignore the master volume for now - it works fine with the NTMB so I'm not sure whether I'll change it or not...

 

[line6man]

Thanks for the comments.

Re the coil shunting; I've seen many diagrams where one coil shunts to cold/ground or the other coil shunts to hot which is why I drew it that way. How much of an issue is possible noise when done that way? I would have thought so long as it was shorted and not just left open at one end it should be OK but I'm open to your experience!

The only way I can think of grounding the not needed upper coil (neck in inner mode, bridge in outer mode) is to use a 6P4T switch, something like the attached. The unused coil on the neck pickup in inner or outer mode will still be shorted to hot if the main series/parallel switch is set to series but, as far as I can tell, that is unavoidable.

Ignore the master volume for now - it works fine with the NTMB so I'm not sure whether I'll change it or not...

As a previous poster stated, a shunted coil connected to the signal path is basically an unshielded antenna. It is not desirable to do that, when you have the option to wire it properly. All you have to do is leave the unused coils disconnected when not used, and shunt to ground, when appropriate. There is nothing you can do about the neck pickup's north coil, in inner coil mode, but at least avoid shorting it out, so that the resistance in the coil is greater.

 

[DaveyM69]

Thanks line6man.
If I understand correctly: using a 6P4T I can remove the unused north coils from the circuit completely, the bridge south coil can be connected on the ground side only in inner mode - all good
This leaves the neck south coil in outer mode. If I leave it's + disconnected then it will be 'hanging' to the signal path if the master S/P is in series. Would you suggest this is better than shorting it?

 

[Lo-E]

I would think it would act as an antenna either way.
RE: your question "How much of an issue is possible noise...", provided your control cavity is well shielded, you might be fine. This would allow you to stick with a 4T4P switch.
The advantages of a 4T6P are cool; you can get the switching you describe, plus other options. You can even get it to handle some of the series/parallel duties. You should be able to get it to shunt and ground all unused coils as well, although I haven't put a huge amount of thought into it.
The drawback is that it's hard to find one that'll fit in a control cavity. The third deck on an Electrocraft switch, for instance, makes it pretty darn tall.

 

[DaveyM69]

I've just purchased this.

I'll post here when they arrive and I've assessed the quality. 5 6P4T switches inc shipping from Taiwan to UK for just over £9 seems like good value to me! If it doesn't fit or is garbage then I haven't lost much

All the other parts ordered from BestBassGear so I don't have to drill any new holes and I have a chance of fitting everything in!