I'm playing a borrowed Hohner Jack bass, and I've noticed that the D & G strings seem a bit quiet. Is this a function of the pickups, or the tone controls?

And speaking of the tone controls, does anyone know which is supposed to do what? The top knob seems to control volume, the second seems to do nothing, and the third stacked knob doesn't seem to do anything either.

I checked inside and all the wires are still connected. Any ideas?

Sounds as though it's on passive - check there's a battery in it and switch it to active.

if it's anything like my hohner (likely), the controls are volume / volume / bass + treble boost (only), with a switch for active / passive (the boost does nothing in passive mode).

This model doesn't have a switch, I believe it's always in active mode. It has two 9-volt batteries in it which, according to my tongue, have plenty of juice in 'em. ;)

I'll try taking the batteries out entirely and see what I get.

OK, so if I take the batteries out I get: nothing. It's obviously not the active/passive type.

Any other thoughts? Is this common for this bass? Would different humbuckers help? It's got the original EMGs on it.

I have a hohner jack V pro, which is just a 5 string JJ version so I'll assume they're similarly wired.

I was unhappy with the controls; my foggy recollection is that the first volume knob was a master volume and the second did the bridge pickup in a way that meant it could never be louder than the neck pickup. It was weird. And yes, the tone stack only works in active mode.

I rewired it - I found a blend pot and put that in, and removed the preamp altogether. I didn't bother with a tone control at the time and found a bit of black cardboard to go behind the 3 newly created holes (tone stack, preamp LED, preamp switch). A few months later I stumbled across a well priced set of bart's and put them in along with a passive tone control. It was my main gigging bass for a while (in an 80s band!) and is still my main teaching bass.

Ahh just noticed your final post. Maybe you can't just go passive like I did.

As to your other question - the quiet D and G strings are more likely to be the pickups than the tone controls.