- Oct 13, 2002
- Internment Explorer sp3
Ok - So I have a Line 6 FM 4. I've just burned my second power supply for it. apparently I'm not the only person on the internet to do this. While I was looking for a replacement I came across this:
I'd like to try this out as I'm pretty sure my power supply has 12v DC on it. I don't want to try it without running it by a few people first as those pedals aren't all that cheap.The DL-4, as designed, expects a 9VAC signal, which is non-polarized at the jack. At the power input of the DL-4 is a rectifier/filter that turns the 9VAC into 6VDC. That 6VDC line is tapped to the battery line, which is 4 D batteries (4 * 1.5VDC per battery = 6VDC). That 6VDC is used to generate all the operating voltages within the unit (6VDC, 3.3VDC, 6.6VDC, and 5VDC). Notice that what makes the DL4 REALLY work are all DC voltages.
Now wouldnt it be nice if we could use a DC supply from our VDL Pedal Power to bypass that rectifier circuit? Pay attention.
Diode rectifier/filter circuits CAN accept a DC signal with no damage to the circuit. The rectifier circuit will just simply pass the DC signal (with a voltage drop because of the forward drop of the rectifier diodes). It will rectify an already-rectified signal. Because of the diode voltage drop, you have to feed it a slightly higher DC voltage to get the same output as you would with an AC voltage. That's why the VDL PP has a dip switch to up the DC voltage from 9V to something higher (12-14VDC, lets just say 12VDC for this argument). But because you are using a DC supply now, polarity matters! And in the case of this circuit, it must be center-positive to prevent from reverse biasing the semiconductors and blowing them up.
As far as current draw goes, a circuit will only draw what it needs. So most ratings are given as a maximum expected current draw times some safety factor (usually 50%). So in a worst case scenario, a circuit will draw 100mA, so a designer may recommend a 150mA rated adapter.
That said, you have 2 ways to power a DL4: 9VAC or 12VDC. Remember, AC and DC power draws are measured differently. Straight DC voltage is able to supply more current than an equivalent VAC supply. So at 12VDC, it may only require a max of 200mA, but at 9VAC it may require 1200mA. That's why the VDL guy and the DL4 guy give you different current draw ratings. Also, they both may be assuming 2 different safety factors!