In need of a Power Supply for a Alesis Multimix 8 USB (18V) (Will pay)

Discussion in 'Tech Talk - Electronic Repair Modifications DIY' started by bass_and_art, Apr 4, 2013.

  1. Boswell

    Boswell Moderator Well-Known Member

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    OK, that's fine. Just take care, that's all!
     
  2. alebro

    alebro Active Member

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    The official adapter has the following readings

    3 & 2 = 20.6 V
    3 & 1 = 41.6 V
    2 & 1 = 20.6 V

    The custom built adapter has the following

    3 & 2 = 10.6 V
    3 & 1 = 21.7 V
    2 & 1 = 10.6 V

    So the custom adapter is putting out half the expected voltages. It ran the mixer for years but there is this fault with the clip light and I'm fairly sure there is more background hum using this than using the official adatper.

    When the official adapter is used the clip light is on for a moment when the mixer is first turned on. I guess the unofficial adapter never puts out enough to fully satisfy the expected power to the circuits and so the clip light remains on.

    I haven't seen inside the official adapter but the label on it states it has two outputs, each is 18 V. If I'm understanding correctly this likely means there are two 18 V windings in there. The unofficial transformer on the other hand has two 9 V windings, half the rating and this is why the readings on the pins are half the voltages.

    You might ask why I care about the unofficial adapter if I have one that works fine, it's because I have 2 of the same mixer. They are actually really good mixers for the price imho. It would be great to get the lower powered adapter working correctly but I suppose it's not actually possible as I am guessing the two transformers are rated differently.
     
  3. Boswell

    Boswell Moderator Well-Known Member

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    I think you have summed up your situation very well.

    You are unlikely to find a low-cost 18-0-18VAC adaptor, but you could get another single 18V a.c. unit and use the two of them to power your second mixer!
     
    kmetal likes this.
  4. Lee2020

    Lee2020 Active Member

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    So if I'm reading all this right is not to try and power it using a laptop power pack so what is the solution. As the original power pack is expensive am i able to buy a replacement transformer to wire up.
     
  5. Boswell

    Boswell Moderator Well-Known Member

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    Possibly. I'll do a search and let you know.
     
  6. Boswell

    Boswell Moderator Well-Known Member

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    I've can't find any wall-wart type of transformer with a UK plug and an 18-0-18 secondary, but there are plenty of open-frame or encapsulated units. Try starting with Farnell Components. As an example, they have an encapsulated series with power ratings from 4VA up to 52VA.

    To get a rough required VA rating, look at the rating plate on your official 18-0-18 transformer and multiply its maximum output current in Amps by 40. If it's specified in Watts, use the Watts figure plus 15%.
     
  7. alebro

    alebro Active Member

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    That's very useful information for the Multimix 12, and I might use it so thank you. I think some wires have been crossed though.

    @Lee2020 is looking for a power supply for Multimix 6 FX, which reportedly is specced as 18.5 VAC at 700 mA (see this post)

    Looking at the power supply that ended up being used for a Multimix 8 FX I suspect the same supply wired up as described would work for the Multimix 6 FC even though it's not quite a match. Parts of that post quoted here -

     
  8. Lee2020

    Lee2020 Active Member

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    The more i thought about it though i know the original transformer has two 9v feeds from it but if i wired up a 18v laptop power pack and bridged the right two connections that go into back of mixer then it should work or would it pop the mixer
     
  9. alebro

    alebro Active Member

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    Have you measured it? Does it have 9 V on 2 pins and 0 V on the other?
     
  10. Boswell

    Boswell Moderator Well-Known Member

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    I think we're getting confused between the Multimix 8 and the Multimix 6FX power adaptors. They are both dealt with in this thread.

    According to the user manuals, the Multimix 6FX needs a single 17.5V AC input at 700mA (18V AC would be OK). This is probably used inside the mixer with one lead taken to chassis ground and the other serving two half-wave rectifiers for the internal + and - rails.

    The Multimix 8 USB FX needs two separate 18V AC inputs, each at 320mA. It doesn't say in the manual, but Alebro's meter measurements in post #22 shows that these are used as 18-0-18. These probably feed a bridge rectifier to get the + and - rails with the input centre tap (0V) taken to chassis ground.

    The implication of these figures is that, with a single 18VAC supply, the 6FX is likely to work, but the 8 USB FX is unlikely to work in an acceptable fashion, even if a centre-tap were wired or artificially created. A pair of 18V AC wall-wart supplies could be used to make an 18-0-18 V AC supply, provided they were wired so that the phasing on the secondaries was correct.
     
    kmetal likes this.
  11. alebro

    alebro Active Member

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    Just to confirm, my readings were for the adaptor for Multimix 12, which uses a transformer of 2 18 V 1000mA windings with a total output of 36 VA

    Someone used this 18v 9VA AC/AC for Multimix 8 - link (details are in the post here), seems it would also work for Multimix 6 but using a 18 V DC is not ever going to be a good way of doing it.
     
  12. Lee2020

    Lee2020 Active Member

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    So will the laptop adapter work on my 6 fx mixer
     
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