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is there something wrong with my amp?

Discussion in 'Amps and Cabs [BG]' started by P bass guy, Jun 9, 2014.


  1. I'm afraid this is impossible to answer, but it's bugging me so I have to try.

    I'm just getting back into playing after years of inactivity, but I was never very knowledgeable or good with gear.

    For weeks, if not the months I've been playing I've felt there was something "off" or not quite right with my bass tone. I have trouble describing it. Closest I can come is that it's not quite as clean or as smooth as it should be. My guitarist, drummer, and my son don't hear it but I do. I thought it was my bass, maybe pre amp, tried changing the battery, sounded the same. Tried another bass that is a dead silent passive P bass. Same thing.

    A possible clue, or possible "red herring" - One time recently while jamming I completely lost sound suddenly. I couldn't find the reason. Randomly flipped switches, unplugged the bass going to try another battery knowing it was basically new, but it didn't make sense so plugged in for one more try, and sound was back. I told myself I must have stepped on the cord and been unplugged, but I was using a 90 degree end cable tucked behind my strap and into a side mount input jack. I really can't see how I came unplugged. It was super hot in the room that night and wondered if I overheated and it had time to cool down?

    Another possible clue / possible read herring - I blew out speakers on my cab. I posted up a thread about that and chocked it up to playing too loud for a 2x10 - but I think I overstated how loud we were and I swear I've played that cab that loud before without incident. I wasn't pushing much low EQ really.

    A played a different cab and hoped it had all been the speakers for the past several weeks. Basically a mint condition brand new 1x15 and I didn't push it. Still heard that tiny bit "off" and not perfectly clean sound. Very minor low mid / high mid EQ bump. Tried EQ flat, still heard that weird quality to my tone. Sounds almost like clipping, but no clip light and per gain is low.

    My son said it's an "only you can hear that thing". It's minor not an obvious thing, but I swear there is something.

    The amp is a Trace Elliott AH250 and I believe it's about 30 years old. I've owned it nearly ten years. It lived in my basement the last several years and was played regularly by my sons band. When I moved recently I realized everything in that basement was much dirtier than I was really comfortable with, so it had been exposed to dust and dirt and moisture, possible mold and mildew if not directly. It stayed safely atop speaker cabs and didn't get wet the six times the basement flooded.

    I just hear this tiny bit of "not right" in my tone. I'm intimidated to take the head apart to clean inside "just because". I can't even prove there's anything wrong with my sound.

    Is there some sort of dummies guide to checking amplifier function. Am I losing my mind? Any advise?
     
    Last edited: Jun 9, 2014
  2. Hi.

    Edited: as well, misunderstood the wording on the op.

    The process of elimination is the best one I've found.
    ONE AT A TIME ;).

    First is always fresh cords, both the instrument and the speaker, another instrument and another cab.
    Second is a patch cord on the FX loop.
    The third is to try the pre- and the power amp separately by plugging an another amp to the pre-out (or FX out/send) and the instrument directly into the power amp in (FX in/return).


    If all this fails to remedy the symptoms, the problem usually lies deeper in the circuit.

    With an old amp, the power supply capacitors is usually the first suspect in the event of odd behaviour, as are worn out/dirty potentiometers and oxidized contacts.
    On some designs (most older SWR's, some Ampegs), the bias can drift over time causing an unpleasant distortion.

    The power supply capacitors are usually easy to replace, and should be replaced IME on any amp over 15 years old as a default.

    People claim miraculous success stories by just spraying some deoxit onto a scratchy potentiometer, IME the only way to really clean a potentiometer is to dis-assemble it. Just as it's the case with the contact points.
    No amount of "business-oil" is going to replenish the worn out track or dimple ;).

    Adjusting the bias on SS amps is sometimes really tricky, You HAVE TO know ecxactly what you're doing and HAVE TO get it right the first time, there usually isn't a chance for a second try.
    Not with the same output devices anyway :(.

    Good luck.

    Regards
    Sam
     
    Last edited: Jun 9, 2014
  3. Sorry I didn't phrase that well (since edited). I meant to say it was very hot in the room that night. Wondered if that may have contributed when I lost sound.

    I will follow some of your suggestions. I have already tried a different bass and a different cab, and different instrument cable. I hadn't thought to try a different speaker cable. I'll do that and also try a patch cable in the effects loop. Unfortunately I don't have another amp to try pre / power amp separately.
     
  4. Never heard of putting a patch cord on the fx loop, what would you accomplish by doing that?
     
  5. Go to guitar center and try one of there amps and cabs with your bass and one of their basses. Or combo amps. If you can still hear it with both then it is just you. If you can still here it with only your bass it is the bass. If you can no longer hear it, it is your amp.
     
  6. Hi.

    AFAIK almost all series connected and some parallel FX loops have switch(es) in the jacks that perform different duties.
    If and when the duty is to defeat a part of the circuit when a jack is inserted, and that switch either stucks open or closed when it's not supposed to the signal flow is interrupted. If the contacts are just oxidized, the sound suffers because of the added resistance.

    A patch cord eliminates those switches from the signal chain and routes the signal by a "clean" path.

    Usually IME the switches CAN NOT be cleaned permanently just by squirting some "business oil" into the jack and then working the plug a few times in and out.
    It can work a while, but the permanent fix is to open the amp up and to clean the contacts with the aid of a strip of paper or cloth soaked in the liquid of Your choice.
    The business side of emery paper/cloth will destroy the plating on the contacts in a split second and should NEVER BE USED when cleaning metal contacts of any kind.
    The cloth backing OTOH works very well IME when soaked.

    Regards
    Sam
     
  7. MrLenny1

    MrLenny1

    Jan 17, 2009
    N.H.
    You plugged in another battery & you had sound.
    Battery cable/connector could be bad.
     
  8. Bassmec

    Bassmec

    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    It bypasses the in jack socket switches which can become corroded and fail to make a proper contact.:)
     
  9. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    This might help explain the issue with effect loop (and other) jacks.

    When nothing is plugged into the jack, the signal is sent though a shunt switch on the jack. If that tiny contact has oxidation on it, the signal is degraded. It can kill your signal completely or it can act as a resistor in the circuit reducing your signal level. When cleaning these contacts, it isn't good enough just to apply some Deoxit or whatever product is being used. You need to open the contact and scrub to clean it properly.

    Inserting a patch cable bypasses the shunt switches and the signal is routed from the effect send to the receive jack. It can help but if the shunt has oxidation, chances are ¼" plug tip contacts on the jack do as well. All contacts should be periodically cleaned. Don't forget the jack on your bass as well.


    [​IMG]
     
    Last edited: Jun 9, 2014
  10. Thanks for the explanation. I'm not quite sure though if you mean plugging the bass into the fx return or a patch cord from send to return.
     
  11. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Patch cord or instrument cable from effects sent to return.

    If the jacks have an issue because they are not clean, this test can help because it bypasses the shunt switch.
     
  12. samson3382

    samson3382

    Apr 26, 2009
    Boise, Idaho
    Are you using quality speakon end speaker cables?
    I recently was getting a weird fuzz randomly, and could not figure it out. I finally discovered I was able to consistently reproduce it by twisting the 1/4" speaker cable. I tried re-bending the tab inside the jack, didn't help. I ordered about $15 worth of stuff from parts express and switched everything over to speakon. (Amp already had it) Problem solved. My not be the problem in your case, but wouldn't be a bad thing either way.
     
  13. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If given the choice between speakons or ¼" connectors, I'll take speakons in a heartbeat. The contacts are better and the connection is solid.
     
  14. will33

    will33

    May 22, 2006
    austin,tx
    You're getting advice from real techs here OP. I'll just say start with the simple, easy stuff and go from there. Pulling the amp from its case and removing the top cover is just operating a screwdriver, you can do that. Clean all the old dust and gunk out of it. Don't forget to do the cooling fan blades. Can use denatures alcohol and an old soft-bristle toothbrush to get any mold/mildew off of stuff.

    You don't have to be an electronics major to just look around for any parts that are obviously burned, deformed/mishapen, or have come loose.

    Your amp won't have the dangerous voltages in it tube amps do unless it's running a preamp tube full-on. Those can be around 300 volts, so check that.
     

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