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Discussion in 'General Electronics Discussion' started by sax busker, Jun 9, 2011.

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  1. sax busker

    sax busker

    Jun 9, 2011
    Hi -

    I am a Jazz saxophonist and I'm trying to put together an inexpensive, portable busker's amplification system. The goals are portability, light weight, battery longevity and, of course, high quality sound - all at a low price.

    Commercial products are "guitar-centric," meaning that they have no low end and contain guitar effects, which are useless to me (e.g., Roland Cube Street). I basically need a "super boombox" that will faithfully amplify a Jazz piano trio (piano, bass and drums) for backing tracks for me - and I'd like the ability to amplify myself (although this won't usually be necessary).

    The break dancing buskers use car amplifiers and car batteries. I'm taking public transportation, so weight is an issue.

    What I need to know concerns the type of battery needed to run a typical, 75 to 100 watt RMS car amplifier (bridgeable, 2 channel or more). How may amps are needed? And how would one recharge such a battery, and how often would this need to be done? A car sized battery is useless, given the weight.

    So: what are recommendations for batteries? Any rechargeable ones out there?

    Also, the mixer I want to use is AC. What brand-type of small inverter should I get?

    Thanks in advance!

    - Jeff
  2. Resqueline


    Jul 31, 2009
    Lithium batteries will give you a lot more Watthours per weight unit compared to Lead-Acid. Laptop batteries might be sufficient for the power mentioned.
    You'll also want to use a class-D amplifier to conserve power. But what about the run time?
  3. sax busker

    sax busker

    Jun 9, 2011
    Run time needs to be at least four (4) hours, preferably more. If light enough, a spare battery could be brought. Or, commercial units have rechargeable batteries (not AA, C, D, etc. types). Where can I get those? How long do the lithium batteries last, and where can I get them?
  4. davenn

    davenn Moderator

    Sep 5, 2009
    Your other choice is sealed lead acid they are used in portable amplifiers the company I work for sells and I service.

    Most of those amps are in the 50-60W range. bu the time you get up to 100W, your current requirements become pretty excessive and any extended time of operation is going to be very difficult.

    The amps I work on use a pair of sealed lead-acid batteries in series rated at 12V @ 5A/H each ... so 24V @ 5A/H
    They are generally being used to play music or used with microphones, because the output is not being run at full blast nor contineously, they can last for 2 - 3 hours reasonably well.

  5. Resqueline


    Jul 31, 2009
    Lithium batteries (I'm thinking rechargeable types here of course) only comes in assembled packs (due to safety issues).
    You might be able to use laptop batteries as mentioned, but there also exists electric bike batteries with lithium technology.
    Battery Ah value & life will strongly depend on the program material played on the amplifier. If 100% continuous full tilt: 100W / 12V * 4h = 33Ah.
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Another thing is that an increase from 50 to 100 watts will require roughly a doubling of battery capacity for the same battery life. However a doubling of amplifier power is hardly noticeable to listeners. To get an apparent doubling of perceived loudness you would have to go to 500 watts.
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