Problem with 3band EQ

[metalli-guy]

Hai there. I've got my hands on a Stony "Sound of Rock Power" bass with a single active Musicman pickup with a 3-band eq. It's got a decent feel neck, nice hardware and an adorable flamed top.

BUT, the sound is messed up. It works without a battery, but tone controls have no effect.
I got this preowned, therefore it's safe to assume someone messed with the wiring before, and I can't seem to get it working right.

The pickup has no markings, only thing I know about it is that it has only two wires coming out (hot and shield)
The 3-band eq is a stp-001_amp-1 from Sung Jin Industrial Co.

Can anyone point the direction of a wiring diagram I could use?
Or do any of you guys have any pointers for me?

Thanks in advance.

 

[40Hz]

Unless your preamp specifically has a passive tone control provision, you're probably stuck with just a volume control with the preamp switched off. There are a lot of preamps that don't have a passive tone control feature, including some of the more expensive ones.

Odds are pretty good your preamp and wiring are ok. You just don't have a passive tone option.

 

[ddnidd1]

The tone controls are part of the preamp circuit and require a battery to function.

 

[Peter Wagstaff]

7 years later lol. I'm assuming it just needed a new battery, but I'll add anyway.

My international series Peavey Fury II has the same circuit board and preamp controls but with a Peavey branded active pickup. I have never tried to wire the pickup bypassing the preamp. It was also pre-owned, and I've always had a bad time because of their wiring. My problems have mostly been with the battery connector and the output jack. In my case, I think they just rewired the TRS stereo jack to the battery, so if you unplug the instrument cable it disconnects the circuit and saves the battery. This way I have never been able to play without a battery, but maybe it would be as you describe (sounds okay but only volume control). I need to replace that jack and their wiring anyway, so I might test it when I have the time.

As for a wiring diagram, it doesn't look like a very complicated circuit board (062D IC, all through hole components, and a nice connector), so if someone had the time they may be able to trace the connections and draw one. I doubt there is any fault in the board or the components, but you could replace a component if needed. The IC is probably just an opamp for some active filters, but those are harder to replace and easier to damage without an IC socket. Like I said it could be repaired or replicated, but then you may as well look into buying a new preamp circuit.

 

[MoireBass]

The OP didn't say how the preamp operated with a battery.
It's not impossible that the circuit could pass some audio without power but the controls not do anything. Most preamps use a device called an op amp (operational amplifier). There are two main configurations used for op amp circuits, called the inverting and the non-inverting configurations. The inverting configuration can pass audio around the non-powered op amp with only a small amount of loss. The non-inverting config doesn't.

 

[kgbeast]

It is not uncommon for a passive pickup, active bass to play without a battery. But yes, in that case there will be no tone control functionality. If you put the battery in, the tone should work and sound should be better and louder as well.