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4 separate rails from a wall wart?

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Thread Starter

guitarguy12387

Joined Apr 10, 2008
359
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!
 
mik3

mik3

Joined Feb 4, 2008
4,843
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?
 
bertus

bertus

Joined Apr 5, 2008
22,944
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
 

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G

Thread Starter

guitarguy12387

Joined Apr 10, 2008
359
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.
Click to expand...
Hehe simple enough. Thanks!

What is the 48V phantom voltage you are talking about?
Click to expand...
Condenser mics require ~+48v DC to charge the capacitor that is the diaphragm. Often called phantom power.

Take a look how it is is done by behringer, see drawing.
Click to expand...
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.
 
bertus

bertus

Joined Apr 5, 2008
22,944
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
 
G

Thread Starter

guitarguy12387

Joined Apr 10, 2008
359
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...
 
bertus

bertus

Joined Apr 5, 2008
22,944
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
 
G

Thread Starter

guitarguy12387

Joined Apr 10, 2008
359
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.
Click to expand...
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?
 
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