Need some custom pedal power supply help

[Natman]

Hi guys,

I have tried looking into this topic and haven't really found  what I'm looking for. I've been using daisy-chains on 3 wall warts and I want a more tidy, professional solution.     

Do any of you guys build your own power suplies?

I have looked into all of the commercially available products and nothing really does what I need, and furthermore they are expensive! I'm thinking it HAS to be simple enough to DIY one of these.

I have 12 pedals as follows:

8 x 9VDC (not sure of the current requirements btu all pretty typical. 2 of them are digital: Whammy 5 and Ditto X2)

1x12VDC (500 mA Minimum)

2x 18 VDC (one needs 200 mA and happens to be reverse polarity)

You would think that some company must make a power supply for all this but CIOKS Ciocolate is the only one I see that will do it all for sure, and it sure is expensive (and big). I see others which come close but none have the current ratings I need.

I was seriously contemplating a DC Iso Brick, but it uses a wall wart and I would still need one more, so it's not really an advantage besides getting isolated outputs.

There you have it! Fire away 

[Granny Gremlin]

I am interested in this too.  What I have found:

not isolated: http://www.instructables.com/id/Build-A-Power-Supply-For-Your-Guitar-Pedals/

isolated: Geofex took down the technical stuff about their Spyder power supply due to concerns that people would shock themselves trying to build it, but you can still find the info here: http://www.offsetguitars.com/forums/viewtopic.php?f=11&t=15564&start=720#p651703 (pics of completed unit:
http://www.offsetguitars.com/forums/viewtopic.php?f=11&t=15564&start=705#p642118).

There's also this one which looks like there is a PCB available for sale:
https://oshpark.com/profiles/aballen
(scroll down to "Overkill 2"; not sure if it's got isolation for each out or not as I haven't read the build doc yet, but you could add that as an offboard mod probably; you can daisychain boards for more outs - 4 pr board; change out the regulators for diff voltages etc).  Some pics of a build here: http://s1200.photobucket.com/user/bitracer/library/Pedals/Pedal%20Powerr?sort=3&page=1


Lastly, don't go anywhere near such projects if you don't know what you're doing. Unless you have some really whack requirements you are better off getting a premade unit (smaller and you won't die - srsly, it's  hard/impossible to make a more compact unit) - they can be had for as little as $80.  If you do know what you're doing, still be careful; shit happens.

[Natman]

Very good info there Gran!

Still I'd be very surprised if no one has traced their PP2+, Cioks, etc. They apparently use a toroidal transformer, I presume with multiple secondary taps. 

Seems to me like it would be fairly straightforward to get a toroid and build in bridge rectifiers and filters like you would with any tube amp (just smaller)? I see multi-tap toroids all over ebay (they're pricey when new) so I'm pretty sure I can make this for my needs.   

The question is what power (VA) do I need to obtain the min current requirements of my pedals? I did these calculations in unversity but barely understood it all. 

I guess the other question on my mind is: what exactly makes isolated outputs truly isolated?

[Granny Gremlin]

Transformers are the thing that does it in isolated power supplies.  Keeps the loads/grounds off each output from interacting. This can improove noise/hum performance as well as allow for mixing positive and negative ground units on the same power supply (just not the same power output).

You can use a single multitap jobby like you said (expensive) or multiple smaller units (fewer secondaries) in parallel off the mains in like the Geofex Spyder. I also wonder if you could use one mains transformer feeding multiple smaller/cheaper 1:1s (qty = # outputs - 1) - the main tranny to drop voltage into the ballpark and the 1:1s for isolation.

[R.G.]

Still I'd be very surprised if no one has traced their PP2+, Cioks, etc. They apparently use a toroidal transformer, I presume with multiple secondary taps. 

Seems to me like it would be fairly straightforward to get a toroid and build in bridge rectifiers and filters like you would with any tube amp (just smaller)? I see multi-tap toroids all over ebay (they're pricey when new) so I'm pretty sure I can make this for my needs.   

We get a lot of questions like this here. There are a large number of things that seem like on the surface they ought to have simple answers, but the real answers are not simple.

It is really simple to take a transformer, add bridge rectifiers and filter caps and have a DC power supply. In concept, anyway. I wrote up that stuff in a couple of pages at geofex:  "Power Supplies Basics", as noted before.

The problem lies in the details. That kind of DC power supply is too noisy for you to use with most pedals. As many people have found out the hard way, you need a regulator of some kind after it to make it into the smoother DC most pedals need. At a minimum, you're in for a three-terminal regulator chip after the bulk DC supply, and that means having to understand the card and feeding of three-terminal regulators. They're easy, but still some attention is required. And some pedals, typically the heavy power users, don't need as much smoothing and regulation.

Toroids are good, and are no longer ridiculously expensive like they once were. But multi-tap toroids are not what you want. You want multi-winding toroids, which starts to get tricky. See "isolation", below.

The question is what power (VA) do I need to obtain the min current requirements of my pedals? I did these calculations in unversity but barely understood it all. 

That doesn't bode well. You might want to look up Dunning-Krueger.

First, you have to know the DC current requirements of the pedals. This requires reading any published statements about the pedals on line; there are some compendiums of this info on line, and the pedal boxes or info pages on line sometimes tell you a cryptic version. It's simpler to measure the DC current drain by getting out your DMM and some cables and clip leads so you can set the meter up to measure it. Make up a list.

When you have your list of voltages and currents, you have a list of required voltages and currents. That is what has to come out of your power supplies. Inside the power supplies, you will have a regulator on most outputs. The regulator has to supply the necessary current, but it also needs an input DC voltage that is higher than the output voltage by (usually, most regulators, details matter) a couple of volts at least. So the DC you make for the regulator needs to be higher than the DC you get out.

And the DC you provide to the regulators has to be that minimum voltage at the minimum AC wall-socket voltage; that means the typical DC to the regulators is higher than that, and the whole mess has to live with a steady diet of the highest AC wall-socket voltage without overheating or dying of voltage stress. Once you know the minimum/typical/maximum AC wall-socket voltages you're designing for, you can do the computations from "Power Supplies Basics" and arrive at the DC level you need to make for the regulators. This has to also take into account the amount of resistive sag in the transformer that you don't know anything about yet. Oops. Guess, then come back and refine the answer later; so at least two iterations are needed.

When you are done with all that, you know the absolutely perfect transformer voltages you need, and an amount of sag you can't know. You can then estimate the transformer VA needed per winding, and the whole transformer. There is a built-in snag: the transformer VA needed is larger than the DC power it makes by a factor that depends on what kind of rectification you use. For bridge rectifiers, this is usually 1.6 to 1.8.

Once you're through adding all this up, you know a minimum transformer VA. Mother Nature, in the form of economics, is waiting for you here. You might be able to design the perfect transformer to do all this with a couple of tries. But your chances of finding that already made are essentially zero. But you can usually find a bigger, more expensive one than you need, with slightly too-high voltages and currents, so you can forge ahead. It's only money.

When you're done with that, you can go back to thermodynamics. Transformers waste some of their power throughput as heat. So do diodes, capacitors and linear regulators. You now have to figure out what amount of heat dissipation will happen per device, and design a mechanical wrapper that will let the surrounding air wick away the heat. Do this wrong and something dies. Do it subtly wrong, and things die at an unknown time in the future. This usually requires "big".

Getting just the perfect amount of power, rectification, filtering and regulation into a small box that dissipates enough heat without being too big, and is also just the perfect size for your pedal board... well, as the bard said, aye, there's the rub. Doing all that for cheap - well, there are engineers pulling down six figures that do this.

I guess the other question on my mind is: what exactly makes isolated outputs truly isolated?

No galvanic connections. That is, no conductive wire exists between them. In practical terms, this means each DC output has its own transformer winding with no connections to any of the others. That means its own bridge rectifier, filter caps, regulator and output jacks that don't touch the metal chassis for the power supply.

Lastly, we'll turn to an important issue: staying alive. Wiring the AC power side of the transformer(s) is not trivial. It is a technical skill with somewhat arcane requirements. Get it wrong and you can get electrocuted or start a fire. Or electrocute someone else or start a fire some unknown time in the future. This last is why I took down the info on the Spyder at geofex. I kept getting too many questions that betrayed that the asker had no clue how much they didn't know about AC power safety. It really is a question of life or death.

[Natman]

 

I wish we had the hand-clapping emoji on this forum. That was just fantastic, RG. I'm rather stunned actually it's probably the best answer to any question I've posted online ever! Thank you for putting the time into writing that dissertation for me, I am seriously grateful and you've gone above and beyond. 

I have a glancing understanding of everything you wrote, a little more than the average hack. I'm a metallurgical engineer and had to take the mandatory electrical machinery course. Being taught 3-phase power for motors and what not, I was sitting in class thinking: guitars, amps, pedals, etc. But I digress.

I'm a hopeless DIYer and I think I'm going to dabble in this because I simply can not find a power supply that does what I want except for the Cioks Ciokolate. 

So the one thing I'd like to know is this:

Could I use a  toroid with 2 center-tapped ~40V secondaries to get FOUR separate 18V outs (or less) with regulators?

Or does the center tap mean that the outs are all linked galvanically as you said? 

[R.G.]

I wish we had the hand-clapping emoji on this forum. That was just fantastic, RG. I'm rather stunned actually it's probably the best answer to any question I've posted online ever! Thank you for putting the time into writing that dissertation for me, I am seriously grateful and you've gone above and beyond. 

You're welcome to any help I can provide. I'm still paying back the folks that taught me stuff. Probably always will be.

I have a glancing understanding of everything you wrote, a little more than the average hack. I'm a metallurgical engineer and had to take the mandatory electrical machinery course. Being taught 3-phase power for motors and what not, I was sitting in class thinking: guitars, amps, pedals, etc. But I digress.

Yeah - I'm an EE, specialized in control systems, but I had to take the motors and transformer course too. Funny that - my first job was designing power supplies, and over the years that motors and transformer course has been more use than figuring out where the poles go in the state space.

I'm a hopeless DIYer and I think I'm going to dabble in this because I simply can not find a power supply that does what I want except for the Cioks Ciokolate. 

Go for it. The big issue is probably the mechanical one - space to put the various power supplies. I'm not familar with the Cioks, but you said it is "big". That makes a lot of things easy. If you have a pedalboard, make the pedalboard under side all be space for your power supply. With lots of room, things get simple. My current day job is with a pedal manufacturer, and we just released a multi-output pedalboard power supply, so the issues are fresh to me.

As an engineer, you're familiar with having to get all the requirements right, and in a way that customers will both buy and be happy with - which are different requirements!  The trick in our power supply was not getting enough power in it (or out if it) but in making it both small enough to fit under common pedalboards and having room for the output jacks and such in an easy to use package. Every engineering solution is a compromise. It took me a long time to learn the full implications of that.

So the one thing I'd like to know is this:
Could I use a  toroid with 2 center-tapped ~40V secondaries to get FOUR separate 18V outs (or less) with regulators?

Or does the center tap mean that the outs are all linked galvanically as you said?

No, you can't. "Center tap" means that there are two sections of winding connected in the middle. This can be used to make a +V and a -V power supply, but they will share a ground at that center tap. A toroid with two center tapped secondaries can give you four power supply voltages (or more, there are ways), but everything running from one center tapped winding will be connected together. You can only get two independent, isolated power supplies from that.

The bottom line is that one transformer winding (CT or not) gives one isolated power supply, period and end. If you need many isolated power supplies, you need many isolated windings.

There is a big "if" lurking in there that doesn't get much notice. It's this: "if you need many isolated power supplies...". That is by no means a necessity. Many-output power supplies have become all the rage for pedalboards, and the makers of these things love to tell you horror stories of how not having isolated power supplies will make your crops fail and bring drought and pestilence on the land.

The real truth is that there are only a very few situations where you need an isolated power supply. They do happen sometimes, but those are the exception, not the rule.

I have real world experience with this, as the company I work for has sold a single pedal power supply for many years, and there are literally tens of thousands of setups with this one NON-isolated power supply running huge, complicated pedalboards on daisy-chains without problems. These things are inexpensive, easy to find, and reliable. I find it moderately hilarious that a guitarist will think that if one good non-isolated power supply won't meet some special condition, the next step is a multi-hundred-dollar, multi-output power supply, when for 1/10 the price they could use a second good power supply to get their one isolation need met. But that's just me. 

[Granny Gremlin]

Could I use a  toroid with 2 center-tapped ~40V secondaries to get FOUR separate 18V outs (or less) with regulators?

Or does the center tap mean that the outs are all linked galvanically as you said?

Nope.  What you mentioned in that second sentence there is one of the reasons why, yes, but I don't think that would even work as expected (vs just not being isolated). A center tap is a line into a single coil; you need multiple coils.  You could use it to get 2 isolated daisy chains though.

You need this (you can ignore the dual primaries, but many power transformers have them for flexibility):



Vs this (centre tap on the secondary):

[Natman]

Again THANKS guys!

cough*trutone?*cough

I've had 3 wall warts daisy chaining my pedals for years. It works, but I wanted to streamline and I do hear some pops and noise from pedals interacting. Not dramatic but I want a more pro setup.

OK so I'm going to have to sit down and figure this out. My big issue is mostly 2 pedals: Kingsley Jouster (needs 12 VDC @ 500 mA) and a Memory Lane 2 (18 VDC @ 250mA). Eveything else is pretty standard. I want to go DIY because I don't have much disposable income and even $200 is too rich for my blood.

I might just get the MXR Iso Brick because it covers most of what I need, it's small and reasonably priced. The C12 is almost there but it won't do the 12V 500 mA and I'd need a Y-cable for the Memory Lane...

Back to work!

[Granny Gremlin]

Even my original (non Iso) DC brick would handle all your needs aside from the 12VDC (and isolation; but you don't need that per se if you're mostly OK with 3 daisy chains now); 2 plugs is still better than 3. Or look at the Joyo (not isolated, despite the claim, but handles 9, 12 and 18V pedals and is very cheap).

I am only looking at power supply DIY because I've built so many pedals I have outgrown my board (it was small) and figure it would be an easier to sell it off with the DC brick installed (I could be wrong).  I also have replaced one of my 18V pedals and the other will be replaced by a project I will be getting to soon so I no longer need the 18V outs (all straight up 9Vers now) but I do need more than 8 x 9V outs and some isolation (it may be something else but some of my pedals don't seem to be playing well together, but that could be due to an unrelated issue I am having) - like 3-4 isolated outs as a minimum, with 1 or 2 (depending on current draw limits) I can run a daisy chain off of. Nothing premade seems to do this and only this (my current DC brick is so small, I can't bear to 'upgrade to something 4x larger with 12 and 18V outs I don't need).

Checking just now I realise that the Fame - DCT-200 power supply is isolated (at that price I just assumed it wasn't).  Just not available in North America but cheap as shit in the Eurozone; maybe a cousin could order it for me and send it over with the next family member who crosses the pond. Gonna have to go read a few reviews because at that price I am a little skeptical of quality but the gut shots look good (does 12V AC or DC, but not 18 unless you sum 2 x 9V outputs; special cables are available... so it could work for you too):





It's a bit big still, but don't think I can do much better for less than 40 euros, if it lives up to the hype.

[bluebunny]

cough*trutone?*cough

cough *yes* cough   

R.G. is too much of a gentleman to advertise, so I'll do it.  (I have no shame!)  Let's just say my 1Spot is one of the best buys (in any shopping category) I ever made.  And I've been happy to recommend it to others, who have made the same purchase and had the same good* experience.  If you really, really need isolation, buy two. 

* This is a lame adjective.  I apologise.  I really need some tabloid-style hyperbole here!

[Granny Gremlin]

1Spots are OK for most people most of the time, yeah, but it can't help you with 12V, not sure if it can do 18 safely (Y cable off 2 outputs) and if you have any weird pedals (AC, +ve ground, abnormally high current draw etc) it won't go so well. So it is just not an option for the OP.  Personally I don't find the form factor very convenient either (all the guitards in both my current bands use them).  Only one has some issues (weird pedal - it's fine when he takes it out of the chain).

Anyway, seems RG isn't so bashfull here and makes a compelling case: http://www.diystompboxes.com/smfforum/index.php?topic=53030.10;wap2

Like I said, I am not one of those 'gotta be isolated' dudes (I did exclicitly mention that isolation is not required above), but I am having trouble with my non-isolated supply when I add this one specific pedal, and who knows what I will acquire in the future, so...

[tubegeek]

Could I use a  toroid with 2 center-tapped ~40V secondaries to get FOUR separate 18V outs (or less) with regulators?

A center tap is a line into a single coil; you need multiple coils.

In theory that is true but - especially with toroids - you may find it easy to dig down below the insulation and separate the center tap connections into two leads leading to the half-secondaries. In other words, the three wire leads are USUALLY connected to four secondary ends and the two you'd like to split apart may be possible to disconnect and access independently without a lot of actual trouble. When they wind them, they don't make a "tee" connection into the middle of a coil, they just wind a bunch of coils and connect colored leads to the ends as appropriate.

Since the outer tape is usually clear, you MAY be able to see what's going on before any destructive exploration.

If you're curious, carefully remove the clear tape wound around the exterior and see what you can find. Put it back carefully when you are done.

Also - the primary is usually wound first next to the core so the secondary windings are usually quite accessible on the top.

All toroids of a certain volt-amp rating need the same primary windings, then the secondary arrangements are what differ from one model to another. So I guess they just wind all the primaries and put 'em on a shelf until it comes time to fill a particular order for a particular secondary arrangement. The safety concerns also lead to putting the AC line connection down deep.

[Natman]

I'm going for it.

I might be a little nuts, but I feel like I have to try.

Here's where I'm at:

1) I scoured the Net for a multi-tap xformer to suit my voltage requirements. I found this R-core for cheap and it shipped from China (of course). It took a month to get to me but not complaining for the price, it looks like high quality and not too big:

2 x 115 V Primaries
5 x Secondaries:
18V-0-18V (500 mA each)
9V 300 mA
9V 300 mA
9V 300 mA

Ya, I know the 18V secondaries are really a center-tapped 36V, but that's as close as I could get.

Here's my plan:

One 18V will be regulated for 18 V supply and the other for 12 V. They will share a ground and therefore not isolated but too bad. Each of these will only feed exactly 1 pedal and the potential for noise is only when those 2 pedals are used at the same time. 2 of the 9V jacks will be daisy-chained because they don't use much current and I use those pedals sparingly. One 9V jack will be dedicated to my Whammy pedal which needs about 235 mA.

Since the above are RMS voltages,  I have to multiply by 1.41 to obtain peak V and I will have enough overvoltage for the regulators to do their job. I expect the 12 V regulator to get hot, so I ordered a high current model (3A) and will add a heat sink to it.   

2) Components: I am planning to use 50V electrolytics, 470 and 0.1 uF. If I got this right, a larger cap after the rectifier delivers a longer discharge time and therefore smoother DC. Post-regulator, the smaller cap will dischagre fast, cleaning up the noise somewhat. Maybe you can school me if I'm wrong? I'm going to use perfboard and standoffs, can't be bothered with PCB.   

3) I need to find a suitable enclosure. At the moment, there is only a narrow space on my pedalboard where this can fit, but I'm confident I can make it work. I won't limit myself to Hammond enclosures. This is going to be a permanent fixture on my board with a removable IEC power cord.

That's it for now, will post pics when I get all the parts and find time to build it (likely Christmas holidays). When all is said and done, I will have a custom power supply for about $80. Nothing on the market comes close!

[PRR]

> If I got this right, a larger cap after the rectifier

Rough-guess 1uFd per mA.

As most of your windings are 300mA AC, you can't happily suck even 300mA of DC without sag/heat. Even your 500mA AC winding may not be good for over 300mA of DC. (Your 235mA load is just about right.)

That pencils as 300uFd.

In low-volt work, round up generously. (At high volt, >300V, less than 1uFd/mA can work and is often done.)

If the cost difference from one size to the next is small, round-up more generously.

_I_ would shop for 1,000uFd. Popular size, and good for many things (thus I might get a 10-pack for a few percent off of each).

However if you have 470uFd in-hand or coming on a boat, that should be fine.

18V AC should peak-catch to about 25V DC. Regulate to 12V, you throw-away 13V. If the current is say 235mA or 0.235A, then the heat is 13V*0.235A= 3.055 Watts.

With this quite-large drop from raw to regulated, a less-large filter cap will deliver less DCV at high current which will reduce the heat in the regulator. However if you cut this too close it will fall out of regulation if load surges or wall-voltage sags (I have seen a lot of sag).

A naked TO-220 package is good for about a Watt. If you polish and grease it, bolt it to an old VW head and run a blower on it, about 19 Watts (maybe 39W). For (round up) 4 Watts, a 2 inch by 2 inch flat plate exposed both sides will be adequate. Length/thickness should not be over 7, so 1/8" aluminum is ample (I have used thinner and got away with it). A chunk of pedal-box may be fine. If you use the actual box (grounded), you either need an insulator kit or source the fully-insulated TO-220 package.

[Natman]

That's really helpful PRR -thanks!

[R.G.]

What Paul said, but more.

A transformer winding is rated for the RMS current it puts out, and the simple calculations assume a resistor load. If you rectify that with full wave bridge and filter it, the actual loading on the winding is about 1.6 to 1.8 times the DC current out of the filters. I use the mental arithmetic that transformers need rough twice the RMS current rating that I want DC.

You might want to bone up on power supply technology with a very quick, light overview. There is one such at geofex: http://www.geofex.com/Article_Folders/Power-supplies/powersup.htm

As long as you're buying stuff at Mouser, they sell the Wakefield 274 heat sink for $0.23 each. This will get a TO220 up to a few watts safely. I keep a bag of them on the bench. Don't forget to get some kind of heat sink goo or rubber thermal washers, too. No heat sink will help much if there isn't some heat sink interface to let the heat through the micro-pockets of air caused by surface roughness on the sink and the transistor.

[Natman]

Super cool RG, I already read that

I've got these heat sinks on order:
http://www.digikey.ca/scripts/DkSearch/dksus.dll?Detail&itemSeq=185141139&uq=635848251954166738

It's rated 38^o C/W thermal reistance vs 28^o C/W for your Wakefield. Is less or more better?

Last thing I need is to run into trouble with the 12V supply. I swapped the 470 uF caps for 1000 uF BTW.   

[cherler]

Here's a supply I built when I knew even less than I do now about power electronics. It's just 8 secondaries into a rectifier, smoothing cap and regulator. I went way overboard on the smoothing caps, didn't leave enough room for thermal concerns with the regulators and managed to hit myself with mains twice before I finally enclosed it, but at least it has pretty blue led's!! And my house hasn't burned down, that too.

[R.G.]

I've got these heat sinks on order:
It's rated 38^o C/W thermal reistance vs 28^o C/W for your Wakefield. Is less or more better?

Heat sink thermal resistance is an approximation to Ohm's law for heat. If you think of temperature as voltage and watts flowing through something as current, then thermal resistance tells you how many degrees of temperature have to rise to get that many watts to flow through the resistance.

If you make 1W flow through a thermal resistance of 38C/W, the device heating the sink has to get 38C hotter than the air around it to make the 1Watt flow. A 28C/W sink will demand a "voltage" of only 28C, so for the same power, a 28C/W sink will keep the thing being cooled 10C cooler.

However, there are a lot of gotchas in that. the thermal resistance of a sink depends critically on exactly how the local air flows over it, and how un-impeded that air flow is. It's orientation sensitive, and since it relies on the chimney effect of hot air rising away from the sink, it's sensitive to what's around it. You also have to goop the interface between the transistor and sink with something so they stay in intimate contact. Heat sink goo is expensive, but critical. You can sometimes get little several-grams syringes at computer places for mounting CPUs to heatinks (!) for a few bucks. One of these is enough for maybe a dozen transistors, as you want only the thinnest film of goo that fills all the air spaces. No heat sink goo and a 10C/W sink can become a 50C/W sink.