1969 Gibson EB-0 tone control operation?

[Simon Langley]

Curious about the apparent unusual operation of the tone control on my 1969 Gibson Eb-0. When turned from 10 down to 1 the tone gets progressively thinner and the output decreases. It seems that instead of rolling off highs it rolls off lows and volume. Not sure if this is normal or not seeing as how boomy and muddy these basses normally are. The other thing that has me thinking that this is normal is that the difference is very similar to what the "baritone" switch on my 1966 EB-2 does to the tone when activated. Anyone know if this is normal operation or do I have a problem? Have included pictures of the control cavity to show how it is wired up. As far as I know the controls and electronics are OE.



Some strange looking units. Capacitors? Resistors? Inductors?

[rumblethump]

I'm not sure what those 2 parts are, but my 68 EBO is wired normally with a capacitor on the tone control and works normally. I'll try to get a picture up later.

[aquateen]

those two parts don't look like the components that Gibson typically used. could have been rewired at some point.

[SGD Lutherie]

I'm guessing they are inductors, which would roll off the low end.

The EB-2 had a "baritone" switch that did the same thing.

One thing you can do, as long as the parts are in there, is put a cap between the inductors and the tone cap (the green wire). That would act as a varitone type midrange filter. It would roll off some mids, while keeping the lows and highs. (are there any highs?)

The circuit in the Gibson Ripper used a .1µF cap. The EB-2 used a .02µF cap.

If you want a normal tone control, just replace the two inductors with a .047µF capacitor.

[Simon Langley]

Been doing a little research on my own and have decided to rewire the bass as shown in the diagram. Based on their operational characteristic I agree that the units in my bass currently are indeed inductors.

[Stealth]

If so, those might've been acting like a choke circuit - I thought those were common on Gibsons?

[SGD Lutherie]

Originally Posted by Simon Langley

Been doing a little research on my own and have decided to rewire the bass as shown in the diagram. Based on their operational characteristic I agree that the units in my bass currently are indeed inductors.

You might not want the .01µF cap on there, but it was in the original circuit. That rolled off some high end.

[Simon Langley]

The schematic you attached is the one they say is period correct for late 60s to early 70s EB-0 wiring but my volume control is a 500k pot as well as the tone. That is why I decided to go with the older mid 60s setup. I figure I can try it with and without the .01 cap on the volume just to see.

[SGD Lutherie]

Yeah, there's not much difference between the schematics.