#1
hey everyone, i have a 9 volt power supply(6 gang) for my pedals but one of my pedals needs 18v to run so i was wondering rather than having to get a separate supply needing another plug socket could i just use two of the ports in my 9 volt supply and wire them up in series like the picture below


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would that work or am i missing something vital.

cheers

Nath
Last edited by 2841981 at Jun 24, 2010,
#2
You're missing the fact that they're 9V taps in parallel on a single rail run off of a single transformer tap, which supplies 9V. That would be like running two 9V batteries in parallel and trying to achieve 18V by tapping the 9V line twice.
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#3
Quote by Mike-T93
You're missing the fact that they're 9V taps in parallel on a single rail run off of a single transformer tap, which supplies 9V. That would be like running two 9V batteries in parallel and trying to achieve 18V by tapping the 9V line twice.

this..

it won't work unless you have a power supply with isolated outputs, but most ps's you can buy won't be isolated, they'll just be all in parallel like Mike was saying
#5
What you can do is use a boost converter (charge pump) chip to double the voltage. This is a very efficient way to do this, but the problem you are going to run into is switching frequency. If the frequency is in the audible range you may have it picked up by a pedal.

Boost converters work by switching a MosFET on and off fast enough, as well as having an inductive or capacitive element in the circuit, so that the output voltage is higher than the input voltage. It will cause the pedal to draw more current though, so you will have to be careful of that.

The Max IC on the other page Blandguitar posted is a boost converter chip. You will want to make sure that you put a filter capacitor on the output, a filter capacitor between Vcc and Ground for the boost converter chip and then maybe even a capacitor on the input to the chip to keep noise issues out.

This is a lot more work than just taping two lines, unless the power supply has isolated outputs. What model is the power supply that you have?
#7
Quote by Invader Jim
you just love charge pumps dont you


Part of my day job involves analysis and design of switch mode power supplies so I do like them quite a bit :p
#9
I'm just saying it's the easiest way to get an equal voltage but opposite polarity. Also TS, the larger cap you use the more current you take from the charge pump, as well as better noise filtering; though the V+ on an IC shouldn't take too much current. The MAX1044 allows you to send the switching far above the audio range.

edit: Damn, I took too long to type that.
#11
Quote by Invader Jim
connecting pin 1 of that chip eliminates the whine by increasing it to above the audible range.


Its switching frequency does increase, but you can always have other switching noise going on in the chip as well. As an example, at work one of our chargers uses a chip that has a switching frequency of 132Khz, but it can still be clearly audible at times, due to other transistors in the chip. I've never worked with that exact chip, but i've never found a boost converter that has no noise at all.

But its a great way to get the voltage you need

Find its data sheet Jim, you'll see it then.
Last edited by XgamerGt04 at Jun 24, 2010,
#13
Jim, +9, 0, and -9 it allows him to not even bother with a Vb to reference the op amps, just stick a resistor to ground.

edit: Jim, a 10uF cap would do it, I'd probably use higher though, low voltage high capacitance caps are cheap.
Last edited by blandguitar at Jun 24, 2010,