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Power Supply
Old 18th November 2009
Gear Head

Power Supply

I want a power supply to power my VU buffer amps with bulbs and some low powered LED's. I found a power supply on the net that I think may work but I'm having trouble finding out if it will do what I want. Essentially I want to have three different voltages that I can send to the components.

Here's what I found. JLM Audio Shop - AC/DC kit

JLM AC/DC Ver. 2 kit is a Linear based universal power supply with can generate 3 voltage rails from a single or dual 15 to 30vac.
It has one pump charge rail for 48vdc, 1 +/- Rails that can be set from +/-2v to 37v by a 25turn trim pot.
All regulators are on one edge for easy heatsink or case mounting.

Can supply maximum 1amp per +/-V rail and 300mA +48vdc. 1amp for +/'-V rails can be boosted to 1.5amp with 4 extra 1N4007 diodes.

Old 18th November 2009
Gear Addict
Minion's Avatar

What 3 voltages do you need ?? LED"s and bulbs can be powered from many different voltages as long as the voltage is at least the minimum needed for the LED/Bulb ..... LED"s in particular can be powerd from much higher voltages than the 1.5v specified by the manufacturer , all you do is add a series resistor to the LED to drop the voltage to what is needed for the LED , the same applies as well with the bulb , as long as you know the current and voltage needed to power it you can calculate the resistor needed to drop the voltage the the desired level .....
Old 18th November 2009
Gear Head

12V for the VU buffers, whatever low powered LED's rquire, and a little less than 12V for the bulbs. Thanks for the help, I love Mr. T.

Old 19th November 2009
Gear Addict
Minion's Avatar

Well then you can run all of this off of the same Voltage , You just need a 12v supply , to power the LED"s you just put a 1.2k resistor in series with the Positive of the PSU to the cathode of the LED (thats for 1.5v 10ma LED"s) , you need a resistor for each LED , as for the bulbs I would need to know there current requirements and exact voltage to tell you the size of the resistor you would need .....

You could probably power all of this with a simple 12vdc wall mart from an old modem or cordless phone or something , you could also easilly build a regulated 12v supply with just a few cheap parts , a 15v Wall mart , 2 capacitors and a lm7812 regulator and some strip board and you got a regulated 12v dc supply , probably do it for under $5 ....

Old 20th November 2009
Gear Head

I currently have a 12VDC power supply that I've been using for the VU buffers and bulbs. I wired from the output of the power supply to the first VU buffer and soldered another wire to that connection to power the bulbs. Then I ran wires from the powered vu buffer/bulb to the next one until all were powered.

I grabbed my multimeter and some alligator clips and checked DC voltage with everything on and it registered 12.08. When I put the resister in place voltage remained the same. Then I tried using a diode in-between the hot and the resistor and I was able to get the voltage down to aprox. 10.3 VDC. Does this sound right?

Now I'm thinking that I'll take another set of wires from the power supply, throw an inductor and resistor to get the desired voltage, and come out with the desired voltage. Does that sound right?

Old 20th November 2009
Lives for gear

What do you want an inductor for in this circuit?
I don't fully understand the description of how you wired this but the 12 volts should go to all VU buffers. You then start again with another wire for the bulbs, if it is bulbs you are using. This 'bulb' wire could have 3 or more diodes in series with it at the power supply end so that the diodes will drop approximately (3 X 0.7) = 2.1 Volts thus giving 10 Volts for the bulbs.
If you are using LEDs then you have 1K5 or thereabouts resistor for EACH LED.
Matt S
Old 20th November 2009
Lives for gear
ulysses's Avatar
How many LEDs do you have?

Rather than running a wire and resistor to each LED and wasting a bunch of wire, resistors, and POWER, why not run the LEDs in series? You have 12V, you probably drop 2V or so across each LED. You should be able to run at least 5 of them in series. Another advantage is they'll all get the same amount of current, and therefore all have about the same brightness. Using a dropping resistor for each LED will give you an arbitrary brightness dependent on variations in the LED voltages.

The elegant solution is to use a resistor and an LM317LZ to make a very simple and easy current source to power the LEDs. You'll lose a couple of volts in the LM317, so you'd probably only be able to string 4 LEDs in series this way - but series/parallel combinations aren't much more complicated.
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