Voltage "doubler" cables, but are there voltage "splitter" cables???

[azfatboy]

I see a lot of threads with folks using voltage "doubler" cables so they can power an 18V pedal from 2 9V ports. That's great. But my power supplies already have a 12V and an 18V port, and I don't need 'em! Meanwhile, I could really use a couple extra 9V ports! Even worse, those ports are high output (500mA) ports, just sitting there wasted...

So my questions is, is there any way to get:

A converter cable that will convert one 12V (or 18V) port to a 9V port?
-and/or-
A voltage "splitter" cable that will split one 18V output into two 9V outputs?

Especially for the latter, it seems if they can "double" the voltage so easily, in a y-cable with no visible transformers, then they should be able to split it just as easily, no?

 

[David Jayne]

You could make a voltage divider with two resistors. But you'd need to know exactly how much current each device will draw (this can be measured) in order to size the resistors correctly. Or better, use a voltage regulator (adjust ouput by using correct resistors). Either way, you kinda have to know what you're doing. I'm not aware of any off-the-shelf solution but can see it would be handy.

 

[David Jayne]

Voltage Dividers - learn.sparkfun.com

 

[TwinDad]

Yeah, umm... voltage doesn't really split that way. I mean, it can, but you wouldn't want it to, because one of the pedals would be "floating" at a higher ground potential than the other, which might cause some problems.

What you CAN do is get a voltage regulator (here's one for like $2 that I've used on some projects) to bring the 18V down to 9V. You can then divide the 500mA of current amongst however many pedals you can (e.g. one 500mA pedal, 5 100mA pedals, three 100mA and one 200mA, etc.) that add up to 500mA. You can also cook up a regulator circuit "from scratch" using e.g. a LM317 and some resistors and caps or a 7809 and some caps. The $2 regulator is easier and more efficient (and maybe cheaper, depending on where you buy your parts).

Same solution works for the 12V port as well.

Of course the pedals that are sharing an output won't be isolated from each other, so you might (or might not) have some noise issues. Just be careful which ones you pick to share the output.

 

[David Jayne]

To be clear, I wasn't saying a voltage divider could be used to 'split' the voltage to two loads. The divider throws away the unwanted voltage. You'd need one for each pedal.

 

[TwinDad]

To be clear, I wasn't saying a voltage divider could be used to 'split' the voltage to two loads. The divider throws away the unwanted voltage. You'd need one for each pedal.

Oh, I know... I was responding directly to the OP, whose question implied a misunderstanding of how voltage dividing would work. Your response was good

 

[azfatboy]

Yeah, umm... voltage doesn't really split that way. I mean, it can, but you wouldn't want it to, because one of the pedals would be "floating" at a higher ground potential than the other, which might cause some problems.

Ok, I believe you, but I had to ask because if voltage is so easily "doubled" with a simple y-cable, as is evidenced by the voltage-doubler cables available from Voodoo, it seemed like it should be able to split the same way. Guess not.

I was responding directly to the OP, whose question implied a misunderstanding of how voltage dividing would work.

Yep, and I still don't understand... But that's ok...

What you CAN do is get a voltage regulator (here's one for like $2 that I've used on some projects) to bring the 18V down to 9V. Same solution works for the 12V port as well.

To be clear, I wasn't saying a voltage divider could be used to 'split' the voltage to two loads. The divider throws away the unwanted voltage. You'd need one for each pedal.

So, yeah, it sounds like the first option--something that can regulate the voltage from 18V or 12V down to 9V, is at least viable. That works for me.

So, what I want is a cable that will accept the 18/12V input, slice off everything except 9V, and deliver that down the pipe, up to the rated capacity of the port, which in my case is 500mA.

Obviously, my electrical skills are minimal, so designing my own is a pipedream. If I had a list of parts, and simple instructions, I could handle the soldering, but it sounds like what I really wanted, an off-the-shelf part, is also a fantasy...

 

[TwinDad]

Ok, I believe you, but I had to ask because if voltage is so easily "doubled" with a simple y-cable, as is evidenced by the voltage-doubler cables available from Voodoo, it seemed like it should be able to split the same way. Guess not.

Not really. Imagine you have two 9 inch tall boxes and you need to step up 18 inches. You can stack the two boxes on top of each other and get your 18 inches. Now imagine you have one 18 inch tall box and you need to be at 9 inches. You have to cut the box in half, which is a much more difficult task

Voltage, electrically speaking is just like height (both are measures of potential energy, if you want to get all science-y). To get 9V you need to create a point that is halfway between 18V and 0V. You can do this with two equal-value resistors (say 1K-ohm) in series. If you connect the "open" ends of the pair to the battery, the joint between the resistors will be at 9V, since each one will "use up" half of the 18V. Rather like building a 9" tall step that you can step down onto from your 18" height. But the minute you hook a load (your pedal(s)) to that circuit, things get wonky and you won't have exactly 9V because the presence of the load (pedal) changes the amount of current flowing through the resistors. So a simple resistor-divider will work, sort of. You'd just have to tweak the value of the upper resistor to get the right voltage out.

The regulator linked to is an active circuit that gets around these problems by actively producing 9V output (or whatever you dial it to) from a higher input voltage. It is acting like the resistor divider, only it is smart enough to be able to adjust itself to keep a constant output voltage regardless of the load attached (within limits).

You could also use a LM317 or 7809 regulator chip with some R's and C's around it. These chips do the same job but (a) it would be almost as expensive, maybe more by the time you bought parts connectors and stuff, (b) it would be less efficient, and (c) you'd have to assemble it yourself.

Yep, and I still don't understand... But that's ok...

So, yeah, it sounds like the first option--something that can regulate the voltage from 18V or 12V down to 9V, is at least viable. That works for me.

So, what I want is a cable that will accept the 18/12V input, slice off everything except 9V, and deliver that down the pipe, up to the rated capacity of the port, which in my case is 500mA.

Yes, exactly. That is what you want

Obviously, my electrical skills are minimal, so designing my own is a pipedream. If I had a list of parts, and simple instructions, I could handle the soldering, but it sounds like what I really wanted, an off-the-shelf part, is also a fantasy...

Given this I would highly recommend that little regulator I linked to. No soldering, no math, no circuit design. You hook one end to the 18V output of your supply, the other end to your pedal, and dial in 9V on the output. It can handle up to 2A output, so the weak link will still be the 500mA capacity of your power supply. Set it and forget it.

 

[TwinDad]

(YAY! Finally a TalkBass thread I can speak to with some level of experience / authority!)

 

[David Jayne]

Given this I would highly recommend that little regulator I linked to. No soldering, no math, no circuit design. You hook one end to the 18V output of your supply, the other end to your pedal, and dial in 9V on the output. It can handle up to 2A output, so the weak link will still be the 500mA capacity of your power supply. Set it and forget it.

Yup, that's an excellent solution. You'd want to put it in some sort of box. Stick a terminal strip inside to break out to multiple output taps per the OP's desire. Plug it in, put a meter across the output ( I would because I'm fussy) and adjust to 9v. and Bob's your uncle.

 

[TwinDad]

Yup, that's an excellent solution. You'd want to put it in some sort of box. Stick a terminal strip inside to break out to multiple output taps per the OP's desire. Plug it in, put a meter across the output ( I would because I'm fussy) and adjust to 9v. and Bob's your uncle.

You don't even need the meter. The display on the module doubles as a voltmeter and shows (your choice) either the input or output voltage in real time. It's a REALLY nifty little board for the price (or even for quite a bit more)!

 

[David Jayne]

You don't even need the meter. The display on the module doubles as a voltmeter and shows (your choice) either the input or output voltage in real time. It's a REALLY nifty little board for the price (or even for quite a bit more)!

Sure. i edited my post (I'm fussy). I'm sure it's fine. And yeah, I wouldn't make that for two bucks!

 

[Jazz Ad]

Would some of your pedals work at 12 or 18 instead of 9V ? That would be a simpler solution.

 

[TwinDad]

Sure. i edited my post (I'm fussy). I'm sure it's fine. And yeah, I wouldn't make that for two bucks!

Certainly it won't hurt (I would probably double-check it as well)... but the application is probably not precision enough for the OP to go out and buy a meter that would be more accurate than the built in one

 

[azfatboy]

Well, honestly I wish it was a little smaller, but the module does seem like one of the better solutions. And I am happy making a 1:1 exchange on the ports, so I don't think I need an extra terminal strip, I'll just use the existing terminals.

I could sacrifice a couple of my existing cables--just cut em in half and attach each half to one end, then dial in the module for 9V output and bob's your uncle!

Point of clarification: since I am dialing in only the output to be fixed at 9V, and the module will accept variable input voltages, I should be able to make both cables exactly the same way, and use them interchangeably on either a 12V or 18V port, correct?

Since I do have a bench power supply and a multi-meter (which I can use to view the adjustment of the output voltage, right?), could I use this smaller unit without the LED instead?

Also, if I wanted to make this a little more robust, could I use heatshrink tubing? (leaving a little window for the display and button). Maybe I could solder the wires into the terminals? Are there any other strain-relief methods I could use?

 

[TwinDad]

Well, honestly I wish it was a little smaller, but the module does seem like one of the better solutions. And I am happy making a 1:1 exchange on the ports, so I don't think I need an extra terminal strip, I'll just use the existing terminals.

I could sacrifice a couple of my existing cables--just cut em in half and attach each half to one end, then dial in the module for 9V output and bob's your uncle!

Yes, exactly.

Point of clarification: since I am dialing in only the output to be fixed at 9V, and the module will accept variable input voltages, I should be able to make both cables exactly the same way, and use them interchangeably on either a 12V or 18V port, correct?

Yes, exactly.

Also, if I wanted to make this a little more robust, could I use heatshrink tubing? (leaving a little window for the display and button). Maybe I could solder the wires into the terminals? Are there any other strain-relief methods I could use?

Do not solder the terminals. The screw terminals will be plenty sturdy enough, and soldering won't help make a robust mechanical connection.

Heat shrink would be fine. A box would be better.

 

[David Jayne]

The site says it will accept a range of input and create a fixed output so yes, you should be able to use it with either the 12 or 18 volt ports. And yes, wiring as you described is fine. The output is adjusted with a little ten-turn pot. If you shrink wrap the thing you'll want to be sure the pot can't be moved when you're done. Finally, I see that instructions are included regarding calibrating the display, which implies it's not accurate out-of-the box, so you'll need a meter to check that the output is what you want.

 

[azfatboy]

Heat shrink would be fine. A box would be better.

Alright, but the module is already pretty big. A box adds even more bulk (and cost). And all this still has to fit (and be securable) under my dang pedalboard!

NOTE: I also edited my post above to a link with a smaller module with no LED. Since I would have to calibrate it anyway, I am thinking the LED is unnecessarily cumbersome for my application?

 

[ak56]

Just another analogy showing the difference in difficulty between doubling and splitting voltages.

You can stack 6 AA batteries to get 9 volts, but do not try sawing a 9 volt battery into six pieces to get 1.5 volt batteries.

I like the module that @TwinDad linked to.

 

[TwinDad]

Just another analogy showing the difference in difficulty between doubling and splitting voltages.

You can stack 6 AA batteries to get 9 volts, but do not try sawing a 9 volt battery into six pieces to get 1.5 volt batteries.

I like the module that @TwinDad linked to.

LOL technically you could disassemble a 9V battery into its individual 1.5V cells ... but while it's technically possible the likelihood of screwing it up and causing serious injury puts it squarely in the Bad Idea(tm) category.

Certainly don't try to use a saw!