Coverting Alesis Mixer to run on Battery

Discussion in 'The Projects Forum' started by NYCBill, Oct 22, 2013.

  1. NYCBill

    Thread Starter New Member

    Oct 22, 2013
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    I have an Alesis MultiMix 8 mixer that I would like to run off a battery. Ideally off the 12V DC battery I have that runs my Crate Limo amp. The Alesis has an 3-pin screw-on connector. The unit is labeled 18VAC, 500ma x2.

    Q1. Would the build be easier to connect the mixer to the 12V source or is it easier to build a new 18VAC powersupply? (I suspect the latter)

    Q2. I have 18V batteries from my tools. Can I just use an inverter? Do need 2 different inverters, one for each pin? Where might one purchase such inverters and anything else I might need.

    TIA!

    Bill
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Anything wrong with getting a 12VDC to 120VAC inverter and just plugging the mixer into that? No "hacks" necessary at all.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Your mixer has the rectifier inside if it is using 18VAC. A rectified 18VAC output will likely be 24 volts DC inside your mixer. You may have additional voltage regulators that bring the voltage down from there with good regulation.

    It might help to find a schematic of your mixer and post, OR it may be helpful to explain why you want a battery power supply and we might be able to help you more.
     
    #12 likes this.
  4. #12

    Expert

    Nov 30, 2010
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    The power supply is out of stock at Alesis. $36 if available. 2 x 18 RMS @ 1/2 A each

    The block diagram shows lots of op-amps, which normally usually use +/- 15DC in audio products, which is readily obtainable from 18VDC, so I think asking for 18VAC (25.4 Vp) means there is more going on than dual 15V op-amps. This is going to need AC.
     
  5. cornishlad

    Member

    Jul 31, 2013
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    A diagram I saw a while ago showed the 2 x 18vac going straight to separate bridge rectifiers and 78/7915 regulators. In which case feeding in about 20 volts dc to each rectifier should be ok. I don't remember how the phantom power supply voltage was generated thou.
    The trouble with using dc to dc inverters, Chinese types available on.Ebay for peanuts, is that I haven't yet found one with isolated outputs, so running two off a common battery is a no no.
     
    Last edited: Oct 23, 2013
  6. cornishlad

    Member

    Jul 31, 2013
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    I should have added that the diagram I saw was for a 16 input mixer. You should not try feeding in dc until you have determined that the mx8 is the same. You should be able to see if you open it up and trace the ac input.
     
  7. rogs

    Active Member

    Aug 28, 2009
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    Looks like a centre tapped +/- 9VAC supply. 2 x 12V batteries should do the job...although at 500mA they're going to need to be SLAs....
     
  8. #12

    Expert

    Nov 30, 2010
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    If this is a center tapped supply instead of just (2) 18 VAC supplies, it would be 36 RMS center tapped.

    The existence of a phantom supply helps explain. A phantom supply starts with 48 VDC. 36 root 2 is 50.9V
     
  9. cornishlad

    Member

    Jul 31, 2013
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    I have eventually found the diagram for the Alesis mx16 I had seen some time ago. My memory had let me down so I've uploaded it here. It's quite likely the mx8 is similar but no guarantee.

    The external transformer gives 36vac centre tapped. Goes to one bridge rectifier and two regulators for +/- 15v. The other rectifier is blocked from dc by capacitors and is the phantom power circuit.

    I think you might be able to feed in -20-0 +20 dc but the phantom power is never going to work. Basically, without major surgery it's not a practical idea.
     
    Last edited: Oct 24, 2013
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