This was a PJ bass guitar, but the same issues can happen in any dual pickup guitar, and electrical problems can hide in any used guitar.
I met the seller at his home. Due to Covid, he brought the guitar out to his carport, plugged it in and proceeded to play a cool riff.
A bit of price haggling ensued (the G string nut slot was too low, causing the string to buzz. The nut would need to be replaced. The strings were corroded and nasty. In fact, the entire guitar was dirty and rather disgusting-looking.
But it was a good brand and model and all the fundamentals seemed good. He got the cash and I got the guitar. I also got screwed a bit because the guitar had a big problem I hadn’t noticed.
I wasn’t keen on getting too close, handling the guitar, etc. due to the pandemic. So I didn’t actually try the guitar myself. (The first piece of advice I give guitar buyers and I ignored it – to my peril!).
The guitar had four knobs – two volume and two tone controls. When I got home and tried it out, it played fine on the P-Bass (neck) pickup, but when I turned that volume down and turned up the bridge (J-Bass) pickup – nada! No sound at all. In fact, turning either volume control all the way off, stopped all sound from either pickup.
Probably a wiring issue, right? I mean, pickups rarely go bad unless someone messes with them or they’re exposed to the elements, etc. But the wiring matched all the standard wiring diagrams for this configuration and all connections were good.
So what’s up???
Some Les Pauls and other models come wired this way. Just imagine two pickups, two volume controls and two tone controls, but wired in this configuration, so that the “Hot” from the output jack runs to lug #2 of each volume pot.
This guitar had originally come with a pc board and a 2-band equalizer and potentiometers meant for active systems. But those pc boards always seem to go bad, so the seller apparently tried to wire up a passive configuration, using the Seymour Duncan wiring diagrams (which are great – and tend to be extremely helpful, but didn’t seem to offer the independent configuration).
It’s almost pointless to have the second volume control in this configuration. The seller probably wasn’t able to figure it out and dumped the guitar off on me. But I don’t mind, since I got a great deal and I know I can fix the problem just by switching the volume connections lugs two and three!
Now there’s a new problem!
What this diagram does not show, yet what is definitely needed is a capacitor to limit “treble bleed”. As you turn down the volume control, you tend to lose way more treble signal than mids or bass. To control that, I soldered a .047uf capacitor between lugs 2 & 3 of each volume control.
Finally, this bass was working properly and sounding fantastic!
So why does the dependent wiring system work so funky? When you roll either volume control to “off”, you’re sending the signal straight to ground rather than going through the pickup. But if the signal (Shall we imagine the electrons as particles or wave? Will we kill any cats* if we observe?)..if the signal can go straight to ground and if electricity always takes the path of least resistance..well, that’s why it doesn’t bother to go through the other pickup.
This is just one of many, many hidden dangers just lurking and waiting to “bite” you when guitar shopping on Craigslist, Marketplace, etc. (I’m omitting Letgo & Offerup since they’ve combined – just what the heck do we call them now? “LetUp”??? “OfferGo”???
*If you don’t “get it”, Google: “Schrodinger’s cat“