Homemade 9V power - any concerns?

[Greg Ellis]

I have access to a fairly large quantity of 9V DC power adapters, ranging from about 300mA to 1.5A or so. Surplus-type stuff, essentially.

They even have the right jack on the end, the only issue is that they are all positive centre instead of the Boss-style negative centre.

I'm assuming I can just snip the wires, reverse them, solder and tape up with electrical tape or something.

I was even considering making a multi-plug unit, so one wall wart will power several pedals.

I'm assuming I can just twist and solder the wires to a bunch of connectors together to make a multi-jack unit. They must be attached in parallel, rather than serial, otherwise the whole chain would power down by disconnecting just one.

Is there anything I should be concerned about here?

If I understand power supplies correctly, any given pedal will only draw as much current as it needs, so using a larger-than-required supply shouldn't be an issue.

I might even include a 9V battery clip in the power unit, to power my old-school wah pedal (no DC in jack on that sucker).

Any thoughts about all this?

Has anyone else tried this before?

[mhammer]

It's an excellent idea, and one that I recommend to people all the time.

The vast majority of wallwarts, of course, are these black molded boxes (hence the name) that give little indication of the extent of filtering and regulation on board. It might give you an inaudible or negligible amount of AC hum....or it might give you way too much. You can't tell from looking at it or seeing "9VDC 500ma" on the package. Consequently, I find it a recommendable practice to add a little more regulation and smoothing on top of whatever the adaptor itself provides. If the adaptor provides at least 11-12vdc, then you can regulate that down to a stable 9v with an LM7809 3-pin regulator. If it already provides 9vdc, then you can simply add on another smoothing capacitor (1000uf/25v-35v would be good).

Here is where it gets interesting. I advocate use of what I like to call a power distribution box. That is, a separate plastic box you can situate on your pedalboard. The box itself has an input jack for the wallwart, some output jacks to feed the pedals, a status LED to let you know the wallwart is still plugged into the AC outlet, and some additional regulation of some kind. If you wanted to provide several different voltages, that particular magic would be done inside the box. The Smallbear Small-wart is a nice example of how to do that: http://www.smallbearelec.com/Projects/SmWart2/SmallWart2.htm

The nice thing about this arrangement is that you can leave all the pedals and their power wiring in place on the pedalboard, and simply unplug the wallwart from the jack in the power-distribution box, and pack that away separately. It also has the advantage that you can use individual power cables coming out of separate jacks to feed DC to your pedals and the cables can be exactly the length they need to be (man, what will those guys think of next!). So, you can run a cable to your wah with the weird side-jack,, and have an entirely separate cable to connect up your Boss boxes in the back. In short, your power cabling can be convenient.

I know people get antsy around plastic chassis, but since this is not anything you'll be stepping on (I hope to goodness not), plastic is fine, and provides both easy machinability, and a non-grounded chassis (i.e., less risk of shock).

You are correct in assuming that the individual pedals themselves should not draw more current than they require, though not all pedals provide sufficient protection in that regard.

One of the other things you can do with such a box is to provide a "dying battery" output for feeding select fuzzes (Google "dying battery simulator" and you'll find lots of useful links). This would be a separate output from the "healthy battery" output used to feed all other pedals.

Finally, I should point out that many older pedals use mini phone plugs/jacks for external powering. Use of the distribution box lets you run cables with mini phone plugs to them, and barrel plugs to your Boss and similar stuff.

[bagpipe]

Mhammer, thats a really interesting website. Is 200mA enough current to supply a board full of pedals though, as it states on the website? I know that some digital pedals draw a lot more current than the average fuzz or boost pedal, but I'm not sure how much exactly - I know they drain 9V batteries in a couple of hours. I have a One Spot and I looked into how much current it supplies before I bought it - they claim it supplies about 1.5 Amps.

[mhammer]

The M is for Mark, BTW.:smile:

As more and more manufacturers (and players) migrate to digital effects, the current requirements go up. I have a bunch of Line 6 Tone Core pedals, and each of those little buggers wants at least 60-100ma depending on the DSP processing overhead of the particular effect. I checked out a couple of Digitech's pedals and they rate theirs as requiring somewhere around 4W-4.5W of power, (although what that translates into in terms of current I couldn't tell you). Battery life for a 9v in the Multi-Chorus pedal is rated as 4hrs, so I'm guessing it draws on the order of 100-150ma alone. Suffice it to say that if you have one or more digital pedals powered by the same wallwart, it's going to need to supply at least 400-500ma (which is why the One-Spot delivers twice that), to be able to cover off those two to three digital pedals and whatever else you have on your board.

All analog rigs, on the other hand, are more conservative in their power requirements. Occasionally, you'll get the odd power hog that wants 20ma, but the majority can be expected to draw <12ma, and many draw <8ma. So, depending on what style of game you play, analog, digital or both, 200ma CAN be quite sufficient,....or simply not enough.

One option that I have also recommended, along with others much wiser and more knowledgeable than I'll ever be, is an over-sized battery supply. Keep in mind that battery size is approximately proportional to current delivery capability. Stick a 6-pack of D-cells in a holder, and feed their voltage to your pedals, and you have sweet pure DC (no ripple whatsoever) that provides the current equivalent of whatever their volume would amount to in 9v units....which is a lot when you realize how much empty space there is in 9v batteries.

Why would someone power their pedals with batteries from the outside? Good question. When you leave your patch cables plugged in the pedals, the battery remains in circuit unless an adaptor plug is inserted in the external power jack to disable the battery. Using an external battery pack to power your pedals gives the sonic purity (well, the line-noise immunity) of DC, but in a manner that lets you simply hit a switch or pull a master plug and disable your battery power while all your pedals remain connected just the way you like them. There are times when that's a good thing.

[Greg Ellis]

add a little more regulation and smoothing on top of whatever the adaptor itself provides. If the adaptor provides at least 11-12vdc, then you can regulate that down to a stable 9v with an LM7809 3-pin regulator. If it already provides 9vdc, then you can simply add on another smoothing capacitor (1000uf/25v-35v would be good).

Ok, I've tried several of the wallwarts, and they all introduce some pretty terrible hum when compared to a 9V battery.

I'm using the Danelectro Phaser (Pepperoni?) as a test platform.

Output on all of the supplies I tried measures up in the 12-13V range, so clearly I could regulate that down to 9, but I'm not sure how easy it will be to get my hands on that regulator in the short timeframe I've got to work with (2 weeks 'til the jam).

I do have several caps handy, from various projects that never got finished, but I'm not sure they going to be useful here.

Sorry, my cap-fu has gone rusty over the years, hopefully you can read these codes better than me.

Anything useful here?

450v 10uF (2 of these)
450v 22uF
250v 100uF
250v 47uF

bright blue ED2611 R2205K OH SUNG (whatever that is)
orange NPC-EL .0056+/-10% 200 (2 of these)
yellow 562k 400E (3 of these)
red-brown G 2G 103K
red-brown 683J250 NIS Q (2 of these)

How would I add a filter cap (or filter network) outside of the wallwart? Do I just strap a cap between the 9V neg and ground?

Thanks for your help.

[Ripper]

Mhammer has a great idea on the power distribution system for a pedal board. I've been using something similar for years. The only difference is I don't use a traditional wal-wart. I use a power supply from a laptop computer. They are a highly filtered and switched power supply so there is no hum etc. The one I have has an pot inside to adjust the output voltage and it is rated for 6 amps. The nice thing about it is that these power supplies are so slim, they mount perfectly under my boards (my pedal boards are sloped. I then mounted power jacks into the floor of the pedal board and I can tailor the length of my cables accordingly. It works great.

[Wheeman]

... The only difference is I don't use a traditional wal-wart. I use a power supply from a laptop computer. They are a highly filtered and switched power supply so there is no hum etc. ...

I've thought about taking an old PSU from a desktop and re-purposing it like you did. A couple Molex connectors and a pot might do the trick. Just need to find a 'pin-out' guide for one...

[Ripper]

pinout for the molex? Red is 12volt, yellow is 5 volts and the black is ground.
Most have an adjustment inside for voltage adjust. That would make a pretty large power supply, but would power whatever you want it to for sure.

[dwagar]

as an aside, my BCB60 Boss board (for 6 effects) comes with a 1000 mA adaptor.

and you can buy a Boss daisy chain for a few bucks to power up your effects.

[mhammer]

Greg,

The caps you mention are both less than and more than what you need. Operating voltage is suitable for tube amps so you should save them for that. The capacitance values are also insuffucient to do the degree of smoothing you want.

Forgive me if I misjudge the distances, but Markham seems reasonably close to Newmarket. You'll find plenty of electronics distributors in Markham, not the least of which is Electrosonic. You can probably even get what you need in a, ptui!, Source by Circuit City store (s'cuse me while I rinse my mouth out).

Note that a lot of 9v supplies will appear to deliver something higher than 9v when there is no load other than the meter being used to measure it. Use the supply as indicated with pedals, and the output voltage will settle down to what it actually says on the package.

Adding the capacitor is simple. Connect the + lead of the cap to V+ (9v), and the - side to the ground wire. A low-value 1/2w or greater resistor (e.g., 10 ohms) between V+ and the + side of the cap helps the cap to do its work. The voltage going to the pedals is tapped from the junction of the resistor and cap.

You have to think of 60hz hum as a kind of "treble for whales". The filtering on the supply is intended to remove that "treble" so the point where the treble is cut has to be way way waaaaaaayyyyy down. A network formed of 10 ohms and 1000uf provides 6db/oct cut starting around 16hz, which means that any remaining hum at 60hz is attenuated by around 12db below where it presently is. If you used 100 ohms instead of 10 ohms the hum-reduction would be substantially greater, but the resistor limits how much current the wallwart can supply to pedals, so you want to use a low-value resistor.

Hope that makes sense.

[Greg Ellis]

Thanks Mark. Electrosonic is a bit out of the way for me (no wheels), but I might find a shop that's more convenient.

I'm thinking about the notebook power supply idea that Ripper mentioned, too - I bet there's a few of those kicking around at work. Likely 18V or so, though.

[Ripper]

Greg the one I use is from a compaq, it was 18 volt but with the pot inside you can adjust it anywhere from about 8 volts to 20 volts.

[mhammer]

Just one caveat regarding computer-related supplies. One of the reasons that so much current can be packed in such a small unit is that they use a switching supply approach.

Why is that potentially a problem? Because it uses a clock to generate the switching. Any other pedals on your board that also use a high-frequency clock, such as analog chorus, flanger, delays, or any digital pedals, can sometimes produce what is referred to as "heterodyning", when used in conjunction with a switching supply. In "regular-guy-speak" that means that the two or more clocks in the separate devices interact along the power lines and produce the sum and difference of the various clock signals Depending on the actual clock frequencies, the result may be audible...or not. If I have one device that employs a 30khz clock, and another that employs a 40khz clock, their sum (70khz) is clearly inaudible, but their difference (10khz) IS.

What one hears in the forums is sporadic complaints about pedals being very noisy when installed on pedal-boards. At times, there seems to be no rhyme or reason to it, with some folks saying "I use those same pedals and I don't hear it", and others saying the noise is intolerable. .It is sheer speculation on my part, but I suspect that what we are dealing with is small component tolerance differences in the clocking speeds. If I have two DSP-based pedals that each use a 4mhz clock, and an analog flanger that uses a clock varying from 100khz to 1mhz, BUT the clocks on the DSP-based pedals are actually 4.001mhz and 3.997mhz, or something like that (which is certainly close enough to be acceptable in terms of production quality standards for both the crystal used for clocking, and the pedal itself), then their interaction with each other and with the flanger and switching power supply, over the shared power lines, may result in sum/difference byproducts that translate into audible noise. I know that I can plug in a normal non-switching supply to one of my Tone Core pedals and get pristine sound, plug into a different one and get pleasing quiet, but daisy-chaining the supply into both gets me a very unpleasant background hiss.

I suspect that the ideal is to have some sort of RFI/EMI filter separating multiple device and a switching power supply, which starts to get complicated. I can see why many just decide to use individual wallwarts for their digital pedals, or sometimes just give up and go back to analog. Certainly one generally hears little or no complaint from people who use a One-Spot or similar switching supply and an all-analog pedalboard.

Again, it is not that the switching supplies themselves are problematic. Indeed, they provide wonderful efficient power for their size. Rather, the issue is the extent to which the various clock signals running around one's pedalboard are isolated from each other and have a propensity to generate audible byproducts in the first place. Sometimes you get lucky....and sometimes you get noisy.

[Ripper]

I've never had any hum or noise problems on any of the boards I run. My boards are loaded with chorus, flanger and delays of all types and makes dependent on the board. Good quality switching power supplies will have a filter to block out any unwanted interference and any potential ripple issues.

[Greg Ellis]

I found some potentially useful caps in an old broken PC power supply.

2 x 1000uF 10V
1 x 2200uF 16v

I believe (?) if I connect the two 10V caps in parallel, do I get approx 2000uF and effectively a 20V power handling, is that right? And that should work ok for this application, right?

What is the impact of the higher capacitance? It shifts the filter to a lower starting frequency, doesn't it? Any issues there?

I'm sure I've got some 1 watt resistors around, I just need to dig up my colour band reference to figure out what I've got.

[mhammer]

If you stick them in parallel you can add their capacitance but not their voltage rating. If you stick them in series you can add the voltage rating, however the capacitance drops to: 1/C = 1/Ca + 1/Cb...

Rule of thumb is you move one standard rating value up from what you expect to handle. So, with a 9v supply, go with a 16v rating.

And yes, more capacitance = a lower starting point for our power-supply "treble filter" which means greater attenuation when you get out to 60hz and multiples thereof.

[Greg Ellis]

Ah.. ok thanks.

I'll try the 16v 2200uF then.

I found a 10 Ohm 1 watt resistor too.

This is fun!

[Greg Ellis]

Success!!

It looks like something the cat dragged in, but it's working. 500mA and enough plugs to power 4 pedals. And it was all free - rescued parts from various garbage.

As it turned out, the lowest 1 watt resistor I had was about 120 or 130 ohms, so the voltage is down a bit under load - about 8.5V - but it seems to be working well enough with my tuner and the phaser together.

The AC hum is gone. I think my pickups make more buzz than this thing.

Woohoo!

I'm still waiting on a digital delay coming from ebay and a chorus pedal coming as a loaner - those might be a bit more sensitive. I guess we'll see.

Thanks again. Fun project!

[mhammer]

Excellent! Glad that worked out. Don't forget you can always reduce that series resistance by putting resistors in parallel.