L2500 : Help wanted/buzz in active only

Discussion in 'G&L Bass Forum' started by t c, Jul 23, 2009.

  1. t c

    t c

    Aug 22, 2008
    south florida
    Hi guys, long time lurker, first time poster. I've owned two Tributes and currently own a brand new USA L2000 (awesome) and a slightly used USA L2500 (mostly awesome).

    My problem is a buzzing in active mode only on the newly acquired L2500. While I play the bass mostly in passive mode I would like to keep my gear in working order.

    I have tried the instrument with multiple cabs, amps (no effects pedals) , cables, outlets etc. in an effort to narrow the outside factors. I changed the battery twice and looked at the schematics provided on the Talkbass G&L forum (thanks!) to insure that nothing was apparently loose (including the jack). I've reviewed threads to find similar issues but did not find a specific thread dealing with this exact issue. The bass is out of warranty.

    Any help is greatly appreciated. Thanks in advance!
     
  2. Jimtoonz

    Jimtoonz Supporting Member

    Aug 26, 2007
    Nashville, TN
    Are you near any sources of EMF when you are hearing the buzz? Does it seem to get more loud/faint with movement?

    If the answer to the above is "yes", then you may need a shielding job. One of my "war stories" involves an L-2500 I used to own picking up a radio station during a sound check for a date I played in Nashville.

    If the answer to the above is "no", then I would suggest replacing the chip in the preamp. It should be available from Digikey.
     
  3. t c

    t c

    Aug 22, 2008
    south florida
    Thanks for the reply and the advice, Jimtoonz!

    Yes, I tried it in various locations/positions and the buzz was consistent. Is there a parts# or nomenclature for the preamp chip at Digikey? I used their search function and had no matches.
     
  4. Jimtoonz

    Jimtoonz Supporting Member

    Aug 26, 2007
    Nashville, TN
    There is a thread on here that discusses the chip and its common replacements at length. Look at the one that is currently in the circuit and enter the number on the Digikey web site. It will list any similar parts they have in stock. The part is typically an LF441 or LM4250. Texas Instruments also offers a replacement that is favored by some G&L owners. That part is OPA704. IIRC, it(the TI chip) has a bit better performance as far as slew rate and headroom than the other chips mentioned.

    I have also used an LM741(available at most Radio Shack stores for around 99 cents) in a pinch. Although the 741 likely has inferior specs, my L-2500 sounded fine with it installed until I could order the correct part. All of these should be relatively inexpensive, depending upon your source. If a vendor gets much above $3.00/ea for any of them, look elsewhere.

    Although there is difference between the specifications on the parts mentioned above, I am not sure that most people would know the difference by the sound of the bass when pressed to tell them apart. Your actual mileage may vary.

    One thing I neglected to ask you.... you describe this as a "buzz" - is it a sort of brittle, "midrange-ish" buzz, or is there a lot of low end "roar" present(as in a grounding problem)?
     
  5. t c

    t c

    Aug 22, 2008
    south florida
    Again, thanks for the response. It is a "midrangeish" buzz. It looks like I'm off to Radio Shack for a band - aid while I order a chip from Digikey. i'll post the results.
     
  6. t c

    t c

    Aug 22, 2008
    south florida
    Preamp chip replaced and not only is the buzz gone but the active settings sound BIG! Thanks for the info.
     
  7. Randy S

    Randy S

    Jul 7, 2008
    Western WA
    What was the replacement chip?

    I ended up shielding my L-2500.
     
  8. Jimtoonz

    Jimtoonz Supporting Member

    Aug 26, 2007
    Nashville, TN

    T C -

    Glad to hear you are in business. Enjoy!
     
  9. t c

    t c

    Aug 22, 2008
    south florida
    Randy,
    I used the Radio Shack chip (99 cents) and got a tone identical (to my ear) with my brand new US L2000. I don't anticipate trying another unless the chip goes down.