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DIY combo build, turning a behringer BLX 1200 into something useful

Discussion in 'Amps and Cabs [BG]' started by Red Man, Apr 10, 2014.

  1. Red Man

    Red Man

    Feb 15, 2011
    Hey all

    I've just recently started doing research on my latest wacky idea, my own lightweight combo. I've got an Behringer BLX1200 ultrabass as my starter. My idea is to completely gut it, just so I'm left with an amp chassis and a carpet box.

    Silicon chip magazine designed a 250w in 8 ohm class d power amp which I intend on building 2 of and bridging, giving me 500w of power into 8 ohms.

    With the speaker I intend on replacing the 12" aluminum cone driver with an 8 ohm lightweight neodymium speaker that can handle atleast 500 watts rms.

    At this stage I'm unsure what to do in regards to preamps and what bass driver I should use.

    Feel free to follow me on my journey.
  2. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Cool, and very ambitious. Personally, I'd make sure the cab/driver matching is well sussed before I did anything else. ;)

    Is there an online link to the power amp design? Tube or solid state for the preamp section?
  3. WesW

    WesW <><

    Jul 25, 2002
    Lynn Haven, FL
    Cool idea!

  4. Red Man

    Red Man

    Feb 15, 2011
    What do you mean about cab/driver matching, becides making sure that I get a powerful enough speaker with the right ohmage what else do I need to worry about?

    Also here is a link to the amp design: http://archive.siliconchip.com.au/cms/A_112975/article.html

    I have no idea at all what to do in regards to the preamp. I guess I could buy a preamp pedal and just run it into the power amp?
  5. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    You need to match the driver to the internal volume of the cab, and tune the porting (if any) appropriately to both the cab and your particular tonal needs and tastes. In the Amps FAQ sticky at the top of the page you'll find many resources to help you do this. Often times experienced Talkbassers will chip in a bit to help your get there too, but the more you've already done your homework, the more likely it is that people will want to help you.;)

    I found the public portion of that article and had a look at the Altronics kit, which I assume is what you're going to use? I can't read the whole article, does Mr. Clarke include a power supply design or recommend an existing one as well?

    That power amp requires a pretty strong signal to drive it fully. Some pedals may do it, but many may come up a little short. Also, I didn't see a limiter or soft clipping circuit mentioned, and for a bass instrument application you're probably going to need that for best results.

    Take a look at Rod Elliot's site, http://sound.westhost.com/, for a couple of viable preamp designs. He sells circuit boards for them and I've posted DIY preamp build threads in the past that used his stuff. Those builds are in the FAQ as well.
  6. What Passingwind said.................

    There is a lot more to cab design then sticking a speaker in a box.
  7. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    +1001 to the two posts above. You must include the speaker enclosure details in the choice of a suitable driver. This work can be done before doing any of the electronics work. Once you have a good working speaker cabinet then you can build the electronics and you'll already know what the speaker system sounds like. Makes it easier to get a feel for what the amplifier is doing.
  8. CL400Peavey

    CL400Peavey Supporting Member

    Nov 7, 2011
    Grand Rapids Michigan
    Personally, if you have the gumption to build the amp, then you should just skip the combo in general and build a better cab as well.
  9. In addition to the above posts I would recommend either getting or building a different cab with more speakers or keeping that cab but adding an extension cab. 500 watts into a single 12 won't yield you much more volume than 250 watts. 250 watts each into two separate 12s will double the volume.
  10. Red Man

    Red Man

    Feb 15, 2011
    This is where I'm confused, the behringer combo ( http://www.bazaar-world.com/uploads/amp/46/180294140464-6.jpg) which I'm using as the box for the combo currently contains a 12" aluminum cone speaker. It is rear ported. Becides ensuring there is enough air in the box for the speaker to work effectively (im assuming that behringer did that when they designed the box) what else do I need to look out for?
  11. Every speaker has different specs which require different cabinet volumes. Some are designed for sealed enclosures, others for ported/vented enclosures. If you do replace the speaker, you need to check the specs on the one you are thinking of to assure it will perform properly in your application.
  12. Red Man

    Red Man

    Feb 15, 2011
    The amp module is built. I've just hit another snag, I'm trying to find a power supply that will deliver 500 watts at +/- 50 v that'll fit in the Behringer chassis. So far I've come up empty handed and I dont want to get a toroidal transformer. Once I get the power supply sorted then I'll go ahead and do research on the perfect speaker for the job.

    This is the finished amp module:
    https://www.dropbox.com/s/afgvdqja3gmc6rn/2014-04-16 00.11.59.jpg
  13. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    How much room to you have left in there? You're looking for a switch-mode supply, I take it?