Carvin 505S preamp noise issues

Discussion in 'Pickups & Electronics [BG]' started by BassKick, Apr 14, 2014.


  1. BassKick

    BassKick

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    Dhaka, Bangladesh
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    Hey guys! I got a Carvin 505S 18 volt preamp installed in my bass recently. The treble pot gives off a harsh hiss when in flat position and when completely boosted (+20db). A thing to note is, the noise is not completely audible when played through an amp, even when the horn tweeter is on. However, it is very apparent when I'm recording. The audio interface I have is not faulty. I tested. Also I should mention, the internal cavity, where the preamp is, is not covered by the copper foil which is considered the best remedy for shielding electronics (I think). The pickup cavity is also not copper covered. Instead, both cavities are covered by a black conductive. As my bass is a mass production model ESP LTD B-5E, I doubt the guys were very cautious in shielding the electronics properly. I did check the bridge for shielding issues, and it's properly shielded. Pickups are not noisy as they are hum cancelling Seymour Duncans. I should also mention the noise disappears when I put my hand on the strings, just like it disappears on a passive bass when the tone is boosted. Help I need is: Is the noise occurring due to the missing copper foil in both the cavities? Or are the grounding leads reversed? OR is the preamp broken (I don't think it is as all the controls and EQs work fine)? Thanks in advance :) (The 500k volume pot is a dud.) [​IMG] [​IMG] [​IMG]
  2. Roy Vogt

    Roy Vogt Supporting Member

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    It may be a shielding issue. You could also try reversing the grounding leads. Also, it's possible the trim pot for the gain is too high. Try lowering the level (it's that trim pot with the Phillips head in the blue housing) and see if that helps.
  3. BassKick

    BassKick

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    Thanks for the quick reply :) I actually did trim the gain. It's set to 1 at the moment (that's the lowest I think). The noise doesn't drop though. It's that persistent humming, or rather buzzing in this case, you get on passive basses.
  4. Roy Vogt

    Roy Vogt Supporting Member

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    That sounds like a grounding issue. Are your pickups single or double coil? Does it go away when you use the passive bypass?
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  6. BassKick

    BassKick

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    Pickups are dual coils (Seymour Duncan SSB-5). And yes. The noise is completely gone when I bypass it. It's still very much present in active mode...
  7. Roy Vogt

    Roy Vogt Supporting Member

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    Sep 20, 2000
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    Endorsing Artist: Accuracy, Carvin, Hotwire, Conklin Basses, DNA, Eden
    I'd check the grounding. That sounds like the culprit. If all else fails call Carvin and see if they'll swap out the preamp. They're generally pretty good with customer service.
    I did put a preamp in by myself once and had to have my regular tech clean up my soldering after the fact. I was having all sorts of random pops and hisses from bad cold solder joints, etc. May be worth running it by your bass repair guy if you have one you trust. It may be a $20 tweak.
  8. BassKick

    BassKick

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    Thank you for the suggestion! :) I will do that. I did get the pre installed by a tech guy though. I'll reverse the grounding leads. Will post results if it is fixed. Thanks again for your help! :)
  9. Funkinthetrunk

    Funkinthetrunk Registered User Supporting Member

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    Check all your grounds and really double check the connections on the pots that were removed from the circuit boards and relocated with wires. Make sure there no shorts or any broken traces on the circuit board.
  10. BassKick

    BassKick

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    I'm guessing it's either due to bad grounding or shielding. The noise was present before the pots were removed from the circuit boards. But I will do a double check again just to be sure (The installation was done by a very experienced tech guy). What other issues can cause this? I remember seeing a post in Carvin's forum where someone used the pots to ground the preamp. Should I do that? http://www.carvinbbs.com/viewtopic.php?t=39911&sid=705c23b4c0d2399631801e2d51a3207f The 4th last reply shows the grounding.

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