Curbow bass electronics problem

[Alexander López]

Help!! My Cort Curbow bass has developed a strange electronics problem. Its output has weakened so much I have to crank up the amps to their limit. Even a passive Epiphone bass has a hotter output.

My Curbow has a passive MightyMite humbucker pickup, soap-bar style; and an active circuit that has volume, Bass, Mid, Treble & a "Slap switch" that engages a different EQ setting. I think it's a Bartolini MK1 circuit.

The instrument's tone is the same, the EQ & slap switch works fine, there's no broken wires, the volume pot works fine and the 9-volt battery is new. What do you think it's happening? Thank you!

[Mike Kolb]

First thing I'd try to rule-out is the 'new battery'.... check the actual voltage as batteries can vary widely, with a long shelf-life, etc. Did the output weaken gradually over time, or was it good one day and bad the next?

One thing to try is to temporarily wire the pickup directly to the jack (bypassing the circuits) and see what kind of results you get there.

The pickup magnets may have deteriorated in strength, maybe exposed to an external magnetic source that weakened the poles. If that's the case, the pickup can be remagnetized (and StewMac has a pretty good article on the procedure).

But double-check the battery first.

[Len Biglin]

Yes Mike is right , you should also check the jack , most systems use a stereo jack where the extra terminal connects the battery negative (black) to the ground of the guitar,so its only "on" when you plug - in.This black wire could be broke near the jack and you won't see that .If you have a m/meter check the 9V red to ground , while plugged in, should read 9V+.If you cant find it after all Mike's ideas as well,the most likely component is the op-amp chip (speaking generically- I don't know the actual preamp) you will need the aid of a tech to remove and try another chip --unless it is a plug in solderless type.

[Rob Mercure]

Mike,

I'm unfamiliar with this particular pickup setup but in almost 40 years of electronics I've neve seen a magnet lose sufficient strength to reduce a signal significantly - in fact winders of "vintage" pickups purposely play tricks on their alnico magnets to reduce to flux to match 40 year old magnets whille ceramic magnets, for all practical purposes, has an infinite flux life. The only things that can really reduce the level of a magnet are extreme heat (which would turn the instrument into charcoal) or extereme electrical current (which would melt the metal parts conducting that much current). Your battery idea has merit, semiconductors do weaken believe it or don't, and any electrolytic capacitor will die as the electrolyte dries up - the typical service life of an e-cap is 15 years or less, often a lot less (and, no, I don't know why some work for 50 years - just chaos I guess).

Rob

[Rob Mercure]

Just to make sure I wasn't off bass in my comments on this I did some quick research on these P/Us and the problem seems to endemic to them. Check out this link - folks might want to use other brands until this problem is corrected.

Rob

http://reviews.harmony-central.com/reviews/Electric+Bass+Pickup/pro...

[Joshua Levin-Epstein]

Rob's link sends us to a review of Asian Bartolini Pick ups, but the bass has a Mighty Mite pickup on it. Perhaps the failings of the Bartolini caused the previous owner to replace them with the M/M. But the question remains "What is the output like when the p/u is connected directly to the amp?" Though the M/M pick up looks like it is sealed, perhaps it has been contaminated by sweat (nothing personal, Alexander. probably the previous owner) and has shorted out internally.

Joshua

[Rob Mercure]

Ooops, my apologies - in my sorry defense I did state that the research was "quick." I use the computers here at the local library and am limited to one hour sessions. So I did my "research" with only seven minutes left to go. A quick google on the bass was what got me there.

I do try to be accurate with my B.S. so if you won't lock me in the cellar again I promise to do better.

Rob