What an interesting find! I've never seen one of these before. This is an early implementation of the Silent Circuit.
Years ago, I had an exchange with Dudley (Gimpel, now retired MM designer) about this. I was experimenting with something similar (dummy coils on the back of pickups) and asked him if they had tried this approach. Here's what he said:
"The first Silent Circuit we made had stacked single coils, using a vintage style single coil pickup and a thinner hum cancelling coil mounted to the back. This was wound on 1/2 of a Dimarzio stacked humbucker bobbin, as you said. The problem with this approach is that the bottom coil which is only intended to pickup hum, also pickups up the string and when the phase is reversed to cancel the hum, wanted signal is also cancelled. We went to the current design as the coil is positioned to NOT pickup the string and so doesn't cancel out the desired signal, only the hum."
I wouldn't worry about the DCR readings you're getting with everything disconnected. In practice, the Silent Circuit is shorted out in positions 1-4 so the pickups should see ground, and not the 'virtual ground' of the SC.
With the pickguard connected, how does it sound in position 5 (neck)? Does the hum increase when you pull the battery out? That's the better way to know if it's working correctly.
Yes, the hum definitely increases when I pull the battery out. So I guess then that's my answer that silent circuit is working.
Well, the reason I started this post is related to the overall sound of the neck and middle pickup compared to my other
Silhouette Special guitars.
The sound of the neck single coil is my favorite of any guitar but this one sounds nothing good like that.
It is very week and nasally sound in all the positions apart from the position 1 (full humbucker).
I tried raising neck and middle pickup nearly close to the strings, just to see if the overall signal can be boosted.
After doing that, I got slight improvement in the strength of the single coils in the mix but it just doesn't look right.
Even after lowering the humbucker all the way, and raising single coils up, the output level is not balanced.
I'm very close to removing the silent circuit and rewiring everything, using the existing 5 way superswitch...I just need to find the right
schematics and I'll give it a shot.
If that change doesn't make an impact, then I'll install some different single coils and keep the original humbucker as I really like how it sounds.
If you have any cool and versatile schematics for HSS (I'd like to re-use existing switch and pots) please feel free to send me some photos or links.
Regards