4 separate rails from a wall wart?

Discussion in 'The Projects Forum' started by guitarguy12387, Nov 7, 2008.

  1. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
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    Hey everyone,

    I'm currently building a mic preamp. I would like to make it somewhat portable and i would like to power it from a wall wart to minimize size and noise.

    Problem is it requires +/- 24v supply, +48v (for phantom power), AND ~12v for relays.

    I have seen this done with a DC-DC converter, but with only three rails... +/-18v, and +48v.

    I'm wondering, first off, if it's even possible to do this. And if so, does anyone know how i might go about it?

    Thanks in advance!
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Can you post a schematic of the circuit, maybe you dont need all these voltages!
     
  3. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
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    Yup! No problem.
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    Well, you can use only a +24 and -24 Volt power supply to power the whole circuit. If the relays are rated 12 volts then power them from the +24 V and use a resistor in series with each one to limit the current to a safe value. What is the 48V phantom voltage you are talking about?
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When I look at the drawing I see J1, the powerplug.
    From left to right the following voltages are expected.
    GND
    + fantom power ( 48 Volts )
    + relais power ( relais voltage )
    GND
    + 24 Volt
    - 24 Volt
    GND

    Take a look how it is is done by behringer, see drawing.

    Greetings,
    Bertus
     
    Last edited: Nov 7, 2008
  6. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
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    Hehe simple enough. Thanks!

    Condenser mics require ~+48v DC to charge the capacitor that is the diaphragm. Often called phantom power.

    Thanks for that, Bertus. I am not really sure what i'm looking at though. What are the inputs to that circuit (x73, x15, etc???). I am not sure how to turn that into what i need, either... bit of a noob haha.

    Thanks again.
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    At X15 there is a adapter of 2 X 18 Volt AC connected.
    pin 1 is top connection, pin 2 is centertap, pin 3 is bottom connection.
    At X73 there is a signal to switch the fantom power on / off.

    Greetings,
    Bertus
     
  8. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
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    Hey,

    Ok that makes sense. Thanks bertus.

    So i would connect x73 directly to its appropriate position in J1 on the preamp?

    So could i use the same circuit for +/-24v with a 24v adapter and run the relays, as mik3 suggested, in parallel off of the 24v source? That is, assuming the adapter will provide adequate current...
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You do not need the circuit round T1 and T2.
    In your schematic S1 switches the fantom on / off.
    You can connect the + 48 Volts directly from the output of IC1 to J1.

    Greetings,
    Bertus
     
  10. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
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    Ohhh ok. Thanks! That makes things easier.

    So will i have to change any circuit values or anything if i use 24v instead of 17?
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    For 24 Volts.
    Take a transformer of 2 X 20 Volts.
    Make R91 and R109 2k2 ( now 1K5 ).

    Greetings,
    Bertus
     
  12. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
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    Hey Bertus,

    Just to clarify...
    ... means use a 20v AC adapter, right?

    Thanks again for the help. It is much appreciated.
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Yes, I mean an AC adapter with 2 X 20 Volts output.
    See drawing.

    Greetings,
    Bertus
     
  14. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
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    Perfect! You have been much help, thanks. I will give this a try and go from there.
     
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