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speaker box switching?

Discussion in 'Amps and Cabs [BG]' started by mench, Mar 29, 2003.


  1. hey - I don't post here much (obviously by the post count) but I was wondering if you guys could help me with something.

    I've got a Hartke 3500 head which I usually run through a Yorkville 410 box, but I also have an old JBL 15" from the early 70s/late 60s which I sometimes use to get the oldschool funk sound happening.

    Now usually I'm content to just run one or the other for a gig - there's no point in running both cos the 15 actually has less bottom end than the 410, and is much less efficient. But my band's cd launch is coming up soon and I was thinking of building a switchbox so I could switch between the boxes mid-song.

    Is this likely to be damaging to the amp? They both the same resistance (8ohms), but have pretty different ratings - although the JBL's isn't stated cos it's so old (the 410's is 500W)

    James
     
  2. A JBL E140 is rated for 200 watts. The previous model K140 is rated for 150 watts.

    Both JBL are very efficient drivers. The E140 is 1.5dB more sensitive, plus it handles more power. Neither JBL will give you much bottom end. They are designed for efficiency and punch, not for bottom. I much prefer the E145 in JBL 15" drivers.

    The switch box would have to designed to handle the amperage produced by your amp. I would double whatever estimate you come up with, just to be safe. An over-engineered switch is better than one that is marginal for the requirements. I'd look for one that handles at least 10 amps.
     
  3. Whappo Grande

    Whappo Grande

    Feb 9, 2002
    Santa Clara, CA.
    Manager: AccuGroove Speakers
    I agree with bgavin.

    In addition, if your Hartke head will pull a 4 Ohm load, why not run them both? (Two 8 Ohm cabs = a 4 Ohm load)
     
  4. I wouldn't switch in mid-note...Also, make sure the switch is a break-before-make, some rotary switches for example are make-before-break whitch means momentarily both would be engaged as you switch. Oops, now I read that both cabs are 8 ohms, so even if they are both on, that would be a 4 ohm load, no problem, so scratch the break-before-make requirement. So you could conceivably get a 3 position switch and do A or B or A+B in parallel....

    hmmm...actually make-before-break would be a benefit as it would help the "thump" you might hear while switching....

    :meh:
     
  5. Whappo Grande

    Whappo Grande

    Feb 9, 2002
    Santa Clara, CA.
    Manager: AccuGroove Speakers
    A 3-Way toggle switch properly wired would be another option.
     
  6. thanks for your help guys

    bgavin - when you speak of amperage, do you mean that most switchboxes have a fuse or just that the circuitry needs to be able to handle that kind of current?

    and I don't want to run both boxes cos I want to switch between them for different sounds, and get the sound guy to mic both boxes so his bass feed will change without him having to do anything to it - I don't want to rely on him to change the sound at the right time. Also, I want to hear the difference on stage.

    James
     
  7. A switching device makes and breaks physical contact points. These points have to have sufficient metal to carry the amount of current your amp provides, plus a generous additional amount of extra current for safety reasons.

    Making and breaking contacts under power will cause an arc as the connection is broken. What this will do to your amp output circuits is unknown to me, but is sure isn't anything I would do to my equipment.

    The make-then-break switch type avoids this by keeping an uninterrupted load on the amp while the speakers are switched. This type of switch is arc-less, also. But it will subject your amp to half the impedance load during the make-wipe-break cycle. I doubt this is an issue, as it is momentary. Amp circuits are not my thing, so this is better answered by Bob Lee, or somebody else with engineering expertise in output circuits.