Filter capacitor question

Discussion in 'Amps and Cabs [BG]' started by Gimli, Jun 21, 2001.

  1. My main bass amplifier is a Carvin ST2472 head manufactured in 1973. I have been experiencing weird static like crackle and hiss sometimes when I play through it (this happens mostly when the electricity is dimming or when the lights go out completely). Anyway, mostly it hasn't been too serious so I haven't thought much of it, but this morning I decided to e-mail Carvin about it. A customer service representative e-mailed me back and told me that I likely had a power filter problem and that the capacitors, being old, were probably failing. He said that since it is such an old model the parts are obsolete and didn't give me much hope as to repairing it. This is my main amp and I really like it so I was wondering if perhaps I could find new capacitors which would be good replacements for the old parts even if they're not the exact model and whether such repairs will be costly. Thanks.
  2. Nightbass


    May 1, 2001
    Seattle, WA
    In a nutshell, no, it wouldn't be too hard to replace them. The three main things you need to match in an electrolytic capacitor is the voltage rating (volts), capacitance (mfd), and the physical size of the cap. Any competent electronics tech would be able to help you. Cost? $10-20 for the caps. I usually get them from surplus stores.

  3. And the incompetent ones will let you find out the hard way about discharging caps before you work on them. If you don't know your way around a high voltage amplifier, leave it for somebody who does. There is a time for do-it-yourself, and this ain't it.
  4. Um...unfortunately it looks like it has to be a do-it-yourself project. Has anyone ever completed a major operation such as this one before? Also, I have another question. Since my brother knows a thing or two about electronics and also because it is an older amplifioer we decidced a few weeks back to open up the chassis and see if there was any dust or oxidation building up inside. Unfortunately it seemed that the front of the chassis was firmly attched to the casing in some way and I am quite unsure how to open the thing up without ruining the casing. I really don't know what is holding it in place, it could just be stuck. Does anyone have any suggestions, aside from letting techies take care of it?
  5. MikeyD


    Sep 9, 2000
    As mentioned in this thread, if you are working near power supply electronics, you HAVE to know what you are doing - unless you like the idea of being injured or killed.

    You must ensure the equipment is unplugged and that the capacitors have been discharged before you get near them. You must get the properly rated replacements (if indeed these are the faulty components), and you must wire them correctly. You must also ensure that they are mounted securely.

    If you are not familiar with how to do the above, you are taking a big risk, IMO. In this case, bringing the amp to a qualified technician is highly recommended.

    - Mike
  6. Thank you a whole lot for giving me hgelp in this matter. I must admit that the whole affair came as something of a shock.... although I guess with an amp this old it is to be expected. I'm also happy that all of you are providing me with safety tips (albeit sometimes sarcastically... but nontheless providing them). One more thing though, is it a possibility that the guy at Carvin was wrong? I've been reading about this sort of problem on the Net and using the search function and crackling does not seem to be a symptom mentioned in conection with failing capacitors. My amp does not exhibit any of the other symptoms (i.e. muffled sound, funny vibrato effect, ghost notes, or changing volume)... is it possible that there is another problem here?
  7. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    You are talking about a 30-year-old amp. Of course it is possible that there is something else wrong with it. It sure does sound as if the problem is related to the power supply in some form. I would suggest having a technician look at it. Not only does he have the knowledge, he also has the testing equipment to aid in diagnosing the problem.

  8. pkr2


    Apr 28, 2000
    coastal N.C.
    I think it would be very unlikely that your problem was diagnosed properly. I've known and worked with some scary good techs that couldn't make a long distance diagnosis with only a description of the symptoms.

    A power supply cap will either create a bad 60 cycle hum through the speaker or blow the power supply fuse when it craps out.

    The fastest way to determine if it's a filter cap problem is to carefully bridge a known good cap across each filter cap and see if the problem clears up with the new cap in the circuit.

    This is definitely not a do it yourself project.

    Carry your amp to a good tech and get it done properly.