I have a great transformer on order from Weber right here http://taweber.powweb.com/store/pdlxfmr.gif (http://taweber.powweb.com/store/pdlxfmr.gif)
Since I have most of the parts already, I designed a nice circuit around it. Note I am planning on having a separate circuit for each winding on the secondary. I expect this should produce some super clean power. 8 of them at 9V DC, and the last one will be 9V AC for my line 6 looper.
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/overkill_circuit.png)
My question about GND is the following. Based on the layout I made, I will have 8 isolated circuits, each pedal should be completely separate. The yellow trace has not been routed so I should be able to print this out as eight separate circuits. However I have a three prong outlet. Should I connect the GND to each circuit to the GND wire on the outlet? It seems like if I do this I'm creating a ground loop. Though without it, I don't really have a GND. What is the correct option?
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/overkill.png)
Oh yeah, the secondaries go to the top holes(11v in) and the jacks connect to the bottom holes(9v out) assume 7809s where you see 7805s
Thanks in advance. If I get it all working I'll post finalized layouts for everyone.
No, they are not connected to Earth and they are not connected together; they float. The only reason that Eagle wants you to connect them is that you are using the "GND" symbol which has special meaning (just like all the other supply parts). The GND symbol ties all points connected to it by using the same Net name. If you went through and renamed each of the GND symbols GND1, GND2, etc, the airwire connecting them would go away. This is because you have renamed the nets to GND1, GND2, etc, just like the symbols.
Yes, I understand why eagle connected them, and I won't. I still don't know what to do with the GND wire from the wall outlet. What do I attach it to? Or do I leave that float as well?
Read up a little more and mains wiring and reply back with where you think it should attach. I am not comfortable advising on mains wiring via a forum, and would prefer to confirm an answer you researched as opposed to tell you and somehow miss something that causes a fire or even worse, you to get hurt. I vaguely remember Steve at Smallbear having a mains powered project on his site where he details some mains wiring considerations, I believe RG also has some on his site (sorry, I haven't verified this, you'll have to look, check his Spyder project) and there are many other pages on the net on the topic. As a hint, where to locate the mains ground is directly related to what material the enclosure is and certain features that are on some power transformers.
As a couple of hints:
There is no true ground but ground - that is, an electrical wire to a metal rod driven into the planet itself. The word "ground" as it's used today in electronics just means "the point I will decide is the source of 0.000000V and a reference against which all other voltages are measured."
In this setup, you do not have multiple grounds. You have - and want, as a matter of fact - only a number of isolated, not-connected voltage sources. You want this to act like individual batteries, right down to not having a ground. Batteries don't have a ground terminal, they only have plus and minus terminals.
I would recommend going back into Eagle and re-naming those things Vminus1, Vminus2, etc.
As to the mains wiring: first, this is NOT a complete nor necessarily accurate description of how to do this safely. You must take responsibility for your own wiring safety. If you do not already know how to wire AC power line wiring safely, I advise you NOT to proceed until you get training or assistance to do it safely.
The ground terminal coming in from the AC power line is a real ground. It's tied through a series of metallic conductors to a rod driven into the dirt of the planet, or is if the wiring you plug into is wired correctly, but that's another story. It's called "safety ground" because it can protect you against electrocution in certain specific conditions. Those conditions are (1) you use a completely enclosing metal box around your circuits (2) that safety ground wire is solidly wired to the metallic enclosure so that any fault currents from the two other AC power wires are shorted to the enclosure. This will blow the AC line fuse. Oh, yeah: (3) there must be an AC line fuse. And (4) the AC power wiring must be wired to meet safety codes.
As an aside, you're missing a diode with anode to output and cathode to input across the voltage regulators. This protects the regulator chip if the input DC to it is shorted. Otherwise, it can die if the filter cap (for instance) shorts.
See the "Spyder" articles and "Power Supplies Basics" at http://www.geofex.com (http://www.geofex.com)
Quote from: R.G. on May 15, 2012, 02:30:25 PM
And (4) the AC power wiring must be wired to meet safety codes.
Funny you say this RG. As a matter of fact, it is common practice in household wiring to connect the Earth grounds and the Neutrals TOGETHER at the main breaker panel.
Great stuff. I appreciate the feedback guys. I'm asking because I know how dangerous mains power is, and I will read up on the sites you recommended.
I know ground is really just a reference. I also knew the mains GND went to the metal enclosure.... but that connects to nothing. I did not understand why, but short protection makes complete sense.
I'll add diodes and a fuse. In fact the voltage drop from the diode will take some of the load off of the regulators, so that is great.
I'm assuming I should size the fuse according to the output(300ma x 8 + 2A = 4.4A) so I'm thinking a 5A fuse should be more than sufficient.
I'll read up, the Spyder looks exactly like what I want to do.
Quote from: aballen on May 15, 2012, 02:53:42 PM
I also knew the mains GND went to the metal enclosure.... but that connects to nothing.
This may be true for your power supply but, what about EFFECTS that are powered by mains? Like the older Flanger, Chorus, and ODs that had the mains run into transformers while the Earth ground was tied to the metal enclosure. The In/Out jacks were tied to the circuit/audio ground AND the earth ground.
The outputs of the power supply end up being referenced to Earth via through the effects pedal, through the connection cables, and into the the amp's input/FX loop jack(s) which are tied to the chassis earth connection either via it's sleeve connection to the chassis or by the amp's internal ground scheme. Going in the other direction, the string ground inside the guitar's body (and you too by way of your fingers) are connected to Earth via the cables and amp internal grounding. This is why people get shocked when the PA and guitar amp are on different outlets with one of them being miswired.
A smaller fuse is better than a larger fuse. By my math, you need something around the 3 to 4 amp range (edit: don't listen to me, listen to RG, apparently I can't do simple algebra today). Being on the primary side, I'd use a slo blo fuse.
Quote from: Govmnt_Lacky on May 15, 2012, 02:43:10 PM
Funny you say this RG. As a matter of fact, it is common practice in household wiring to connect the Earth grounds and the Neutrals TOGETHER at the main breaker panel.
That's true. The low voltage side of the AC power line is grounded at the power pole with a copper wire down the side of the pole to the bottom of the pole itself, then carried into the house on the un-insulated ground wire. The house is supposed to have this re-attached to earth ground by carrying both the pole-ground and a separate earth ground wire to the house's own safety ground wire at the house itself. Both pole-ground and house-ground are attached to neutral at the main breaker box. The idea is that you want the neutral stitched to real, no-fooling earth ground at many places so it doesn't float if one comes loose, and does not float by the voltage caused by any current flowing in the neutral line.
The old two-wire system simply assumed that "neutral" was ground-y enough. We learned better.
I was trying not to get into that with someone who doesn't understand the concept of "ground" in electronics all that well (not to belittle the OP - we've all been there).
Quote from: defaced on May 15, 2012, 03:09:41 PM
The outputs of the power supply end up being referenced to Earth via through the effects pedal, through the connection cables, and into the the amp's input/FX loop jack(s) which are tied to the chassis earth connection either via it's sleeve connection to the chassis or by the amp's internal ground scheme. Going in the other direction, the string ground inside the guitar's body (and you too by way of your fingers) are connected to Earth via the cables and amp internal grounding. This is why people get shocked when the PA and guitar amp are on different outlets with one of them being miswired.
Right!
Quote
A smaller fuse is better than a larger fuse. By my math, you need something around the 3 to 4 amp range. Being on the primary side, I'd use a slo blo fuse.
Correct - smaller is better for fuses as long as it will carry the current and support the start-up inrush surge. Also correct on the slow-blow for inrush.
I'd say something more in the 1/2A range. The current out is eight windings times 11Vac times 300ma, plus 9V times 2.0A. That current is smaller on the primary side by the turns ratio, which gives (11/120)*(8*0.3) + (9/120)*(2) = 0.22A + 0.067A = 0.287A at the primary. Allowing for a 2:1 inrush current and a slow-blow fuse, a 1/2 A woul be where I started.
QuoteI'd say something more in the 1/2A range. The current out is eight windings times 11Vac times 300ma, plus 9V times 2.0A. That current is smaller on the primary side by the turns ratio, which gives (11/120)*(8*0.3) + (9/120)*(2) = 0.22A + 0.067A = 0.287A at the primary. Allowing for a 2:1 inrush current and a slow-blow fuse, a 1/2 A woul be where I started.
Not sure where I screwed up my math, but I re-checked it and agree with RG. Previous post updated.
Ok so I've read up, and here is what I came up with.
- Attach main GND to the metal case
- Added in diodes
- Added a place to mount the fuse, to keep it isolated(and I'll go with 1/2 amp)
What do you think?
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/overkill-2.png)
I'm not familiar with the diode trick, so I'll let RG comment on that. The traces to/from the fuse will need to handle the full load of 0.5 amps, not sure if yours meets that or not. I often like to use IEC sockets with the fuse installed in them. This keeps me from messing up the fuse wiring and generally from having to engineer a bunch of stuff (like trace width). This is the Mouser part number to the last IEC socket like this I bought: 693-6200.2300 There are other mounting and termination styles, this one happens to be a screw in kind with 0.25 inch blade quick disconnects. The datasheet contains the part numbers for the other styles.
Both sides of the fuse must be separated from secondary circuits by at least 8mm in creepage (shortest distance across any surface) and clearance (any 3-dimensional straight line distance). By far the easiest way to handle incoming AC power line fusing and connection is to use an already type-approved and UL/CSA/CE/YADA... marked IEC power inlet with a fuse in a tray.
AC power line wiring gets COMPLICATED.
By now you'll be getting frustrated with me for not just telling you how to do it right. I can't. Even if I tried. A certification lab won't tell you that what you did is safe. They will say instead (if you pass) that they could not find any way they think you didn't meet the safety specifications, which is quite a different thing to say.
I really like that connector. I'll be picking it up and removing the fuse.
The diode seems like overkill to protect a $2 part, but there is space so why not. Also the way i put it in should not create any voltage drop. It appears to be exactly what RG suggested.
RG, not frustrating at all. I appreciate the suggestions, and I get the whole don't wanna be responsible if this guy electrocutes himself thing. I have by the way and I really want to avoid doing it again. Looks like the transformer I'm using is very close to what is listed in the spider tutorial, if not the same one.
So one last question. The 9v ac secondary. Do I just hook those wires directly to a jack to power my line 6 looper?
Quote from: aballen on May 15, 2012, 08:25:04 PM
So one last question. The 9v ac secondary. Do I just hook those wires directly to a jack to power my line 6 looper?
Yes.
However, a 9Vac output will kill 9Vdc pedals dead if you happen to accidentally connect it to them and they use the standard shunt-diode polarity protection. Using the same kind of jack for the 9Vac as the 9Vdc is asking for sudden pedal death if you ever accidentally do this. Cliff tells me that all 9Vac connectors have 2.5mm center prongs, instead of the 2.1mm center prongs on 9Vdc pedals. However, sometimes you can push one in there. Sudden smoke results. Some people have accidentally plugged 9Vac into a daisychain. :icon_eek:
Quote from: defaced on May 15, 2012, 03:09:41 PM
Going in the other direction, the string ground inside the guitar's body (and you too by way of your fingers) are connected to Earth via the cables and amp internal grounding. This is why people get shocked when the PA and guitar amp are on different outlets with one of them being miswired.
Yep. I remember many times as a kid getting shocked on the lips from a mic while I was playing guitar. It's kinda hard to sing while that's happening! One time we were playing a little concert under a gazebo that had a concrete slab. I decided to kick my shoes off (I was a kid) and found that there was a grounding problem. Current was passing through the concrete, through my feet and through my guitar. It was just barely tingly so it took a while to figure out what was happening.
ok I've updated it again, made the layout tighter, added diodes, removed fuse(I'll get one built in to the outlet)
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/overkill-3.png)
and the traces mirrored
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/overkill_layout_mirrored-1.png)
One last question - can you actually get 1000uF caps that fit those spaces on the PCB?
Sorry - it just now struck me that the physical size of the 1000uFs may be too tight.
Oh no way, I was thinking 100 uf and 10 uf. I think I could go to 220uf/100uf, but that about as big as I can fit with this layout.
The datasheet for 780* suggests 1uf and .33 uf
We are just talking 300ma(max) per secondary, so I'm thinking this is enough for ripple protection, am I wrong?
Hey guys I'm back from vacation and getting ready to build this. Still don't understand the 1000uf capacitors though. I've seen them in other places, but not with a good reason, in fact I found an instructable that states they are not needed, but they look cool so he put them in.
Can anyone explain why they are needed? I would hate to omit them if they are really needed, but if there is no good reason for them, I'm not putting them in.
Those caps are there for a few reasons, some not so obvious. The obvious reason is to filter out any noise from the linear regulator, especially the 780x series which don't have very good line/load regulation (meaning they only remove so much ripple on their own). Capacitors placed in the shunt configuration (i.e. a capacitor to ground) act as a filtering element to remove additional ripple that the regulator doesn't squash. While the datasheets typically recommend a relatively minimal value that yields acceptable performance in most applications, we are actually a somewhat specialized application. Modern guitar pedals and amps have a LOT of gain that will amplify any noise introduced from the power supply. The easiest way to buck this noise is at the source which in our case is the power supply. Larger capacitances will filter out more noise which means less crap gets into your pedals. I think I use about 470uF after a linear regulator and my power supply doesn't have any noise problems at all (now my pedals OTOH.. :icon_biggrin:).
The not so obvious reason to use this capacitor is to keep the linear regulator stable. Many regulators will go unstable (oscillation, weird latch-ups, smoke, etc..) without some sort of capacitance at the output. The easy way to stay out of trouble here is to check the datasheet. If they don't specifically say that their device is stable with no input/output capacitors then I assume it isn't and use at least the recommended minimum values (not that it costs much more to go overboard here).
If this helps filtering out noise, and keeps the power clean, well then I want to do it, the whole point of this power supply is that each jack will be isolated and clean.
Looking at other examples here http://www.generalguitargadgets.com/projects/24-power-supplies
The only one that uses the big 1000uf cap is the "ultra clean" power supply, and it appears to only use one on the input side of the regulator.
So should I do two 1000uf caps, instead of the small ones recommended for ripple protection or in addition to them(or just one)?
I never really expected this design of a power supply to be so involved.
Again, really appreciate the feedback.
1000uF really is overkill. I even wrote that in my last post but I guess deleted it before I posted it for whatever reason. After a linear regulator anything above 100uF really isn't noticeable IME.
Power supply design, like all analog design, is a very detail oriented process. You have to understand every part of the system on all levels in order to make the best design choices. Nowadays they make it very easy with ready-to-go power solutions on a chip but things can get hairy quickly when you add multiple output voltages, control circuitry and more power handling.
Of course what we do isn't exactly science and isn't quite art, it's a happy medium that leaves a LOT of room for creativity. I've met guys that I consider real artists when it comes to analog design but it's pretty funny how they are in awe of the cool stuff that we do with analog. Last summer during a coop with some very talented IC designers (guys with many more years of experience than myself), I put a big smile on their faces when I brought a theremin into work, plugged it into a little 5W tube amp I built and let them wail away for a while.
While we're talking about noise contribution from the PS, word has it that using an adjustable (LM317 for example) is much quieter than the standard 78** series. I know that in mic preamps I've built using 317/337 has been quieter to my ears (I don't have the test equipment to back this up though), and they discuss it quite a bit over at diyaudio, where they're looking for super quiet specs.
Not sure if that's something we as musicians should be too concerned about about or if our amp noise swamps any PS noise from our pedals, but it is pretty easy to use the 317s and I don't think there's a much bigger parts count.
There's also the clean up shunt design here: http://www.wenzel.com/documents/finesse.html (http://www.wenzel.com/documents/finesse.html) although there's some debate over how well it works in the real world.
The LM317 series regulators have better line/load regulation, better accuracy and better inherent ripple rejection than the 780x series of regulators. They also have a lower overall noise floor. The 317 really is a better part and is what I use in my pedalboard power supplies. It's not very hard to get the standard circuit built and working quickly and the noise floor of the power supply is definitely good enough for rock and roll!
> don't understand the 1000uf capacitors
We only use the "Peak" of the AC wave. 80% of the time, the load runs on energy stored in the first capacitor.
So it has to be big-enough.
As a _general_ guide, think 1uFd per 1mA, or 1,000uFd per Ampere of load.
In lower-voltage systems, you often want more.
You are hoping to start with 11VAC and regulate to 9V DC. The 11V AC would give 15.5V with perfect rectifiers and infinite capacitor. Real rectifier loses a couple volts. Practical-size caps sag. The 9V rectifier typically needs 3V extra so it can shave-off to 9V exact.
You need a good 12V DC at the end of each half-cycle when the cap has sagged.
Duncan PSD is handy for such predictions. You need some estimate of transformer and capacitor resistance; the defaults are for high-voltage work.
Duncan needs a load. If you need about 12V raw at 0.3A, that's 40 ohms. (Somehow I typed 50 in the simulator so these sims are optimistic.)
(http://i.imgur.com/SdKpy.gif)
The 300uFd cap sags to 9.3V. You can NOT get regulated 9V from that.
The 1,000uFd cap sags to 11.8V.
The 2,000uFd cap sags to 12.3V. This will work.
The 1,000uFd cap "might" work _if_ the "11VAC" runs high or the load is less than 300mA. (But it is bad practice to rely on "if"..... what if you play a gig with low wall voltage? What if you get a new pedal that sucks a full 300mA?)
Hi
+1 for the 1000uF per amp rule (works for power amp supplies as well as pre-regulation).
General comment: It is interesting how terminology causes confusion. Many countries have an Earth wire for AC (which is connected to THE Earth), and Grounds (positive, negative, whatever) for regulated supplies and other stuff (not necessarily connected to the Earth). Simple, descriptive, cost-free and strangely not adopted in some countries. A bit like SI and metric.
cheers
> terminology causes confusion
And it's not a national thing.
There are MANY things we call "ground" (or "earth"). They may even connect. They are not the same!
Offhand:
Safety Ground - ensures your metal case is at a reasonably safe potential.
Garbage Ground - diverts buzz/RFI around sensitive systems
Power Common
Signal Common
Power-Signal Common
On complicated mixed signal board with analog, digital and switching power supplies onboard I usually use at least three separate ground symbols (AGND, DGND, PGND) to help differentiate what components are associated with which part of a circuit. All of them usually connect together either on a dedicated ground layer (four layer boards) or at a single grounding point that is very close to the bulk decoupling capacitors "-" terminal (1-2 layer boards) depending on how many layers are needed and what the project budget looks like.
Then if mains wiring is involved you also have the earth ground to deal with. The proper way to wire an "earth" ground (the green wire from your standard black IEC power cable) is to drill a hole very close to the power inlet, solder the earth ground to a solder lug and securely attach said lug to the chassis. This is what UL and CE labs expects to see anytime they open up and inspect equipment with 3-wire mains power. Lock-tite on the fastening screw isn't a bad idea (this is what most big manufacturers do) but I don't bother, just crank that screw in very securely.
Now that is a great explanation. Thanks guys.
Of course I have another question. If I go with the 2000 uf cap, will that compensate for me going with a 7809? I can go with a 317, but its pretty much back to the drawing board if I do that... and I have never worked with the 317 before.
I'm not sure what you mean about the 2000 uF cap and 9v. According to PRR's calculations (which are reliable - this guy knows his stuff) the 2000uF cap is ideal for 9v.
Using a 317 is almost as easy (and almost the same thing) as using a 7809. The only difference is that you have to set the output voltage with a pair of resistors. Check out this page:
http://www.electronics-lab.com/articles/LM317/ (http://www.electronics-lab.com/articles/LM317/)
In your case, you would replace the 5K pot with a fixed 1.5K resistor and your output should be 9.06V (according to the calculator on the page). You can also bypass the 1.5K resistor with a 10uF or so cap to give even better noise performance. You can keep the input to output diode the way it is.
Ok guys I think I got it... completely reworked. The few additional parts make the layout a little trickier so I made one circuit, which I will duplicate 8 times across my board for eight ultra clean isolated outputs. I'm thinking I can do eight across, or 4 across, stacked if it will save space, and I left room for a heat sink, in case I need it(don't think I will, but just to be safe, there is space).
Here is my circuit, I think I got it all right... 2200 uf cap on the input side, switch to the LM317, two extra resistors, an extra cap on the output side for even more filtering.
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Schematic.png)
Not sure if my cap values are all right, but I think there is room on the board for different values, making space for the 2200uf was key.
Here is the layout
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Layout.png)
It is getting a bit silly, but all of my pedals are DIY, so I want my power to be.... once power is worked out, I'll DIY a nice pedalboard too.
I'm hoping for another round of feedback on the new design... so let me know what you guys think... I'm ready to etch, but I need to order some big caps too, so there is no crazy rush.
Really appreciate all the feedback I'm getting here guys. Great stuff!
Looks pretty good. I'm not sure how far your regulator is going to be from the 2000uF cap at the rectifier. but if they're fairly close I don't think you really need the 100 uF cap on Vin What I would do is throw a .01 - .1uF cap from Vin to ground and Vout to ground. The bigger caps filter out low frequency stuff and smooth out the ripple, and the lower value caps do a better job of filtering out the higher frequency stuff. Some designers even call for 3 sets of caps - 1 for low (big electros) 1 for medium (around 0.1uF) and 1 for high (0.01 or smaller). I think I would probably use something a little higher than 1uF at the output - maybe more like 10uF.
In the schematic just posted, I would swap C2 and C4. Also a 0.1uF right on the pin for Vout is never a bad idea.
Also, some general Eagle advice, you don't need to put junctions on single connections. If you can grab a part and the wire moves with it, you are golden (meaning you have proper connectivity). Junctions can force connectivity but aren't necessary. If a wire isn't grabbing go to "move", click the part and drop it in the same place. The only place you need junctions is where two or more wires connect (wires include pins and such). If you don't place a junction on every wire junction, Eagle's ERC will bitch at you (not a bad thing).
I'm by no means a PS expert, so I'll pose this question to those who have experience and knowledge in that area. Would it be a good idea to have a switch on the "hot" AC leg (as opposed to the neutral leg) and a fuse? Maybe these features are already intended off board.
> if they're fairly close I don't think you really need the 100 uF cap on Vin
Correct. In the old days we sometimes had the raw power in one rack and the regulator in another rack. Then you need a little 100uFd *at* the regulator to steady it. If they are less than a foot apart, one good input cap also steadies the regulator's input side.
Old-old large caps didn't work good for high frequency (and these regulators are high-frequency chips even if we only see 120Hz and DC on them), so we used a small fast part-uFd cap to steady the high-frequencies. With modern large electrolytics (even to 2000uFd), you probably don't need to have a 0.1uFd.
Who knew a simpl question about ground would turn in to this.
Ok so to answer one question, yes I will have a switch off board, with a fuse.
Here are my latest
1) dropped the small cap on the input side to a smaller one
2) added a .01 uf cap on the output side
3) replaced the 1 uf cap with a .1uf cap.
Can I go with film caps on the smaller ones, or do they need to be polarized?
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Schematic-1.png)
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Layout-1.png)
Are we getting there?
Almost, but I'm not sure why you dropped the cap value after the regulator so much. They recommend at least 10uF here IIRC and I prefer closer to 100uF. Remember this capacitor not only filters out supply ripple but also any uncorrelated noise that is added from the regulator itself. Linear regulators use large transistors as either a series (pass) or shunt element which will always have a certain amount of noise associated with it. Take a peek at the datasheet, they even specify a certain noise performance for this device with the recommended capacitances. More capacitance at the output means a lower cutoff frequency for the output filter and better rejection of unwanted noise from the regulator.
I dropped the input cap because I thought you were suggesting that when you said switch C2 and C4. I've bumped it back up to 100uf.
Seems like I'm getting close. Here is the latest.... also, is a non polarized cap ok for the small values. I have tons of film box caps in .1 and .01 and I think I'm going to have a hard time finding a .01 alum electrolytic.
(http://i1200.photobucket.com/albums/bb321/bitracer/Schematic.png)
(http://i1200.photobucket.com/albums/bb321/bitracer/Layout.png)
You misread Cliff's post - he suggested the 100uF cap after the regulator (on Vout). And yes, non electros (flim, ceramic, etc) are fine for the smaller value caps. In fact, non electros usually perform better than electros, it's just very expensive to make non-electoros in large values, plus the physical size gets ridiculous. According to PRR, the small value caps are no longer necessary - I'm assuming that larger value electros are made better today and can filter out higher frequency stuff as well as other caps, but if you want to be on the safe side, just throw a 0.1uF (not 1uF) on either side of the regulator.
I"m all for reducing the part count/footprint... and yeah PRR really seems to know what he is talking about. I'm feeling very dumb right now...
So much input, and I just seem to be going in circles here. Can you answer 3, 4 and 5 for me?
Let me try to sum up what should be done.
1) Drop the 100uf cap on the input side, YES
2) Should I put a .1uf on the input side, ??
3) Should I change the value of C4 or drop it?
4) Should I change the value of C5 or drop it?
5) C3 needs to stay, YES
6) I'm not going to change the packages in the drawing, but I will use film caps for the small values, YES
So close yet so far..... if I am going to make this myself though, I want it to be correct.
1. Yes
2. Probably not necessary, but wouldn't hurt.
3. Change C4 to 10 - 100uF. Cliff (also knowledgeable) suggests and uses 100uF.
4. Probably don't need C5 but wouldn't hurt.
5. Yes
6. Yes - film caps are generally superior to electrolytics (except that you can't get them in large values) so use them where you can
You're doing fine with this ab, and you are wise to be thorough and make sure you have everything right. How's the saying go? Measure twice, cut once. Keep asking questions until you understand everything and then build it.
Just to sum up, without going into a whole lot of detail:
- the rectifier converts the AC to DC
- the DC coming out of the rectifier is pretty crappy and has a lot of noise (a lot of hum at 60Hz)
- the 2000uF cap smooths the DC so that it's not crappy anymore and resembles steady state DC and filters out a lot (hopefully nearly all) of the hum
- the 0.1 uF cap filters out higher frequency noise (but is apparently no longer necessary)
- the LM317 sets the voltage to 9v, but introduces noise of its own
- the 10uF cap (C3) filters out some (hopefully almost all) of that noise
- the 10 - 100uF cap (C4) filters out more (hopefully the rest) of that noise and helps keep the regulator stable
- the 0.1 uF cap C5 filter out some (hopefully most) of that noise (but apparently is no longer necessary)
Way more info about caps than you could ever want to know:
http://www.radio-electronics.com/info/data/capacitor/capacitor_types.php (http://www.radio-electronics.com/info/data/capacitor/capacitor_types.php)
and something a little easier to digest:
http://www.intersil.com/content/dam/Intersil/documents/an13/an1325.pdf (http://www.intersil.com/content/dam/Intersil/documents/an13/an1325.pdf)
Ok, lower parts count, that is good. Here is my latest.
1) Dropped
2) Not necessary, not added
3) C4 now 100uf
4) Not necessary, not added
5) C3 kept it
6) I'll use my np box caps where I can.
So if we are all sure the .1uf caps are not necessary, I'm good to go.
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Schematic-2.png)
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Layout-2.png)
I think I just found another flaw in my design... I was planning on using this transformer(which I already bought)
http://taweber.powweb.com/store/pdlxfmr.gif
But according to PRR... that wont work, because its only putting out 11V on each of the secondaries.... what do I do here? I don't expect to be pulling the full 300 ma on each supply, will the transformer I went with suffice for a simple 40 ma pedal? If not what should I use?
I was planning on making 8 independent power supplies, in a box.... but I don't know if getting 8 separate transformers is practical.
QuoteYou are hoping to start with 11VAC and regulate to 9V DC. The 11V AC would give 15.5V with perfect rectifiers and infinite capacitor.
- PRR
11 VAC = 11 x 1.414(RMS) = 15.5VDC. So it's actually putting out 15VDC on each secondary. This is why you need the bigger cap (because caps are neither perfect nor infinite). If you use a smaller cap, the voltage will sag below 9V between peaks, and be insufficient to power the regulator. The bigger cap prevents this. Re-read his post on that and if you're still unsure, ask again.
I'm not sure what the current draw of each of your pedals is, so I can't comment on the 300mA. I think most analog pedals pull less than 40 though. I know I once measured a bunch of mine and they were all less than 20 mA, but my digital multi-fx pedals are 300 - 500.
As for your previous post, it lookd like you're good to go. The 0.1 uF are a judgement call, and according to PRR are no longer necessary.
Quote from: PRR on June 03, 2012, 10:33:35 PM
You are hoping to start with 11VAC and regulate to 9V DC. The 11V AC would give 15.5V with perfect rectifiers and infinite capacitor. Real rectifier loses a couple volts. Practical-size caps sag. The 9V rectifier typically needs 3V extra so it can shave-off to 9V exact.
You need a good 12V DC at the end of each half-cycle when the cap has sagged.
Tempus, thanks for the explanation... I'm interpreting some things incorrectly, and I appreciate you helping me get some clarity. I really thought he was saying I needed 12V.
It looks like I'm good to go. I'm going to keep the parts count down, I do have to make 8 of these ;)
Time finalize my board, and order some parts, yay! It may be a little time, but I'll post some pictures as I go.
Here we go, all 8, mirrored for etching :D
(http://i1200.photobucket.com/albums/bb321/bitracer/AllTraces.png)
QuoteI really thought he was saying I needed 12V.
He was, and with the 2000uF cap you do. See, what happens is that at the start of the cycle, you've got a solid 15v, but the cap discharges over the course of the cycle. This is the sag he was referring to. If that cap discharges below about 12v (which it will if the cap is only 1000uF unless conditions are ideal - this is demonstrated in the 2nd diagram - notice the pink underlined 11.811? That's what the voltage will be at the lowest part of the cap's sag), the regulator isn't going to have enough voltage to keep regulating. It'll still work, it'll just be unregulated during that part of the cycle, maybe longer if it takes a bit for the regulator to bounce back. In the 3rd diagram, the lowest that the 2000uF cap will allow the voltage to drop to is 12.332. This is because larger caps take longer to discharge. So with a 2000uF cap the voltage at the regulator's input will never dip below 12.332V, and so your regulation will be stable and continuous.
Cool. I was thinking if I started with 11v, there was no way to get a higher voltage out of it. I guess that really depends on the available current/voltage vs the load current/voltage, and the size of the cap.
I should order some parts tonight!
Just thought I would post on my progress. I redrew the circuit, and managed to get 8 of them on a 3x5 board.
This leaves me with one question. For the 2200uf caps, is 16V enough? They should only see 11v from the transformer and the 16v ones I bought are significantly smaller than the 50v ones.
Here is a pic... now a lot of drilling!
(http://i1200.photobucket.com/albums/bb321/bitracer/Snapbucket/3FF0A4BB.jpg)
> thinking if I started with 11v, there was no way to get a higher voltage out of it
> 16V enough? They should only see 11v from the transformer
You are missing the fact that the "11V" is an RMS ("average") reading, and the rectifier/capacitor thing is a PEAK-catching system. Assuming sine-wave power, the Peak is 1.414 times the RMS. 11 Volts (RMS) of AC makes 15.5 Volts DC.
Minus losses. There's always losses.
Plus/minus wall-voltage variation.
Plus transformer un-sag on light load.
> 16V enough?
I'd do one or two 16V caps off 11VAC for experimentation. I've done riskier things (like 36V on 35V caps for years.) But I would not like to build eight barely-sufficient caps into a small box especially for gigging. The transformer's "11V" is probably rated for 115V or 120V walls. I have 125V at my house. I hear of 129V 130V in many many places. (I have plugged-into 160V and not known it: big electro caps make large mushroom clouds.)
I'd prefer to use 25V.
I have 2200uf 50V caps... I'll use them if I can get them to fit... it will be very tight though.
Ok I got the 50v caps in, it was that or 16v. I don't think there should be any harm in using the big caps, other than the space. They are packed pretty damn tight though.
(http://i1200.photobucket.com/albums/bb321/bitracer/Snapbucket/5FC576F5.jpg)
I'm also thinking squeezing this all on a 3x5 board I neglected considering how I'm going to mount this board or the transformer.
I'm thinking I should re-name this thread too, its pretty much a build thread at this point.
Looks great ab (way better than any of my builds that's for sure). Those 50v caps won't cause any problems, so don't worry about that. The extra voltage will give you a little more relability, if anything.
Thanks.
I really appreciate all the feedback I've been getting. Reducing the parts count helped a lot too, no way it would fit on a 3x5 board if there were any additional components.
Now I have to figure out how to box it up. Any suggestions for mounting a board without any space for drilling? I suppose I could use a whole lot of double sided tape, or just go with a plastic box.
Velcro
I don't see what you mean - it looks like there's lots of space to drill a couple of holes there.
I finally got this assembled, and the power is rock solid, but I have a problem. It is putting out 14.7-14.9V. The output is consistent across every supply, so that is good, but the voltage is way to high.
The only variable I see here is the resistors. I'm using a 240 and a 1.5K resistors, which should give me 9.06V
Did I mess up the design somehow? I know a lot of people verified it for me, but it seems in practice something is not correct.
There is no load on the board while I test, not sure if that has an affect... but 14v seems way too high.
How do I trouble shoot this? Any suggestions are appreciated. I really want this working... I even cannibalized my kids Spongebob lunchbox for a makeshift case.
(http://i1200.photobucket.com/albums/bb321/bitracer/3dbc6c25.jpg)
It seems that the +/- tolerance of the resistors shouldn't be enough to cause this. You might want to measure the Vref and use that value when calculating the theoretical Vo or R2.
(http://i1160.photobucket.com/albums/q485/jdansti/7fd33983.jpg)
Unless there's a mistake somewhere, you might just have to temporarily swap a potentiometer for one of the R2s, adjust it until you get the desired voltage, remove the pot without changing the setting, and measure the resistance. Choose a resistor as close as possible to the adjusted resistance of the pot.
EDIT: BTW, what is your AC voltage going into the rectifier?
AC Voltage going in to the rectifier is 11.8V, consistent across all of the secondaries.
Nice, now I need a PDLXFMR-2, lots of time and patience to study mains wiring and a SpongeBob lunchbox... >:(
Thank you all so much for this thread.
FYI, I don't recommend a lunchbox(even if you find a cool one).
It seemed fairly sturdy when closed, and empty, but with the weight of that transformer in it and all the drilled holes it wont hold up. IT will work as a temporary case while I figure out the voltage problem though.
Based on the feedback a few posts ago, is a potentiometer, really the only way to get this working? What value?
I'm concerned something might be off in my design for the voltage to be of by this much.
You've got a 1.5k resistor now. If you have a 2.5k-10k pot lying around that would work. Remember, this is just a temporary swap to see what resistance you need to achieve ~9v. I recommend removing only one of the R2s, and if possible, use alligator clips to temporarily connect the pot to points on the PCB that are common with the R2 connections (for example, you could use any ground point and the + side of C3).
After you remove the pot and measure the resistance, use the same alligator leads to test the selected resistor and see what your voltage is.
Alternately, if you don't have any spare pots, but you have some resistors, you could sub these in starting around 2k and working upwards in resistance, hopefully find a value that works.
> putting out 14.7-14.9V
I think your LM317s may be in backward?
http://www.electronics-lab.com/articles/LM317/
That pinout picture is with the label facing you, the heat-surface away from you.
I'll flip one and test it out.
PRR, did I fry them?....
updated, Well I don't think they are backwards, and even if they were the diode should have protected them.
I flipped one, and got 14.4V, just to be sure I soldered in a new one, but filpped... still got 14v.4
something is definitely wrong.
Are you using this layout? (http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Layout-2.png)
I'm afraid it's incorrect, you have the output and adjust pins switched, the middle pin is the output. You can probably get away with twisting the leads on the regulators to make them fit correctly.
Quote from: slacker on July 14, 2012, 10:16:09 AM
Are you using this layout? (http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Layout-2.png)
I'm afraid it's incorrect, you have the output and adjust pins switched, the middle pin is the output. You can probably get away with twisting the leads on the regulators to make them fit correctly.
(http://i1160.photobucket.com/albums/q485/jdansti/6590b1fc.jpg)
Good catch Slacker. It's easy to assume that the schematic geometry is the same as the physical geometry. I've caught myself making the same mistake.
Slacker! You get the prize... which is not much, just a thank you. It seems the pinout on the part I used in eagle was wrong... Not sure what I chose, bit I found the LM317 part, replaced it, and the error was verifiable right away. I had to do some hand alterations of my board to fix it, but here is the updated schematic... with the correct part... and a photo of my hand re-wired board.
I'm getting rock steady voltage on every output, thought they are not all identical. The voltage varies from 9.14-9.22v, but if one circuit is 9.16 for example, it does not budge from that spot. I'm thinking the variations are from the changes I just made, the heat put in to the 317s by unsoldering re-soldering, inconsistent "traces" if you can call them that.
Time to box it up and plug it all in!
(http://i1200.photobucket.com/albums/bb321/bitracer/Snapbucket/FEE8ACDD.jpg)
(http://i1200.photobucket.com/albums/bb321/bitracer/Snapbucket/056F50ED.jpg)
updated schematic, now verified :D
(http://i1200.photobucket.com/albums/bb321/bitracer/Schematic-1.png)
Quote from: aballen on July 14, 2012, 01:03:54 PM
I'm getting rock steady voltage on every output, thought they are not all identical. The voltage varies from 9.14-9.22v, but if one circuit is 9.16 for example, it does not budge from that spot. I'm thinking the variations are from the changes I just made, the heat put in to the 317s by unsoldering re-soldering, inconsistent "traces" if you can call them that.
I think it's more likely to be a variation of the reference voltage inside the various LM317's and the tolerance of the voltage setting resistors.
The LM317 datasheet from National says the nominally 1.25V reference can actually be from 1.20 to 1.30 and be within tolerance. That's +/- 4%. If your setting resistors are 1% tolerance, then the voltage they would set varies by a bit less than 1% (there's some math to do here to get the real numbers, so I handwaved this) so +/-5% variation is not unreasonable at all for un-trimmed outputs.
You're seeing 9.22/9.14 = 1.00875 or about 0.875% variation from min to max, about +/- 0.435% from min to max. That's incredibly good, and suggests that all your LM317's came from the same wafer, or were otherwise somehow selected.
Nice! I definitely used 1% resistors, and all the LM317s were ordered together. I usually do that because I know its fairly likely all the parts will come from the same lot(or wafer) and reduce variance.
Now I just need to get that 9V ac wired to a jack and I'm good.
When I'm done I'll post up a good quality board for etching so others can make something similar. Can't thank you all enough... I've made a handful of pedals, but I had no idea what I was getting into when I started this power supply project. Switching to the 317 was a learning experience. It should all be worth it.
I have one extra jack on the opposite side puttinh out 9.6V AC, should be up to 2 amps and will power my only non-diy pedal, my line-6 JM-4 looper.
(http://i1200.photobucket.com/albums/bb321/bitracer/Snapbucket/D8E22ADC.jpg)
Quote from: aballen on July 14, 2012, 09:48:25 PM
I have one extra jack on the opposite side puttinh out 9.6V AC, should be up to 2 amps and will power my only non-diy pedal, my line-6 JM-4 looper.
(http://i1200.photobucket.com/albums/bb321/bitracer/Snapbucket/D8E22ADC.jpg)
...and you can pack a bologna sandwich in it when you go to a gig! :)
Ok last stupid question. The center tip in the power supply jacks should be gnd correct? I know wall my pedals are build with "center ground" but before I plug something in, I want to be sure its not - to + here.... I've been using batteries for so long. I wired up all my jacks to be gnd on the tip, which should connect the center on my pedals to gnd. It feels really obvious... but I'm asking anyway.
Also, I really appreciate all the input, so I redrew the board, thinking someone else my want to use it. This layout has four circuits. Etch two side by side for all 8. This is the final, I would consider it verified, though mine was modified by hand. If anyone wants eagle files, I'll be happy to share them. I can upload the files to batchpcb if someone wants to place an order rather than etch them.
(http://i1200.photobucket.com/albums/bb321/bitracer/Layout-1.png)
(http://i1200.photobucket.com/albums/bb321/bitracer/Schematic-2.png)
Thanks again
Depends on the pedal, but most (including Boss etc) are centre negative. I don't know what pedals you've built or the layouts for them, but it wouldn't hurt to check them closer just to be on the safe side.
Quote from: tempus on July 20, 2012, 02:53:56 PM
Depends on the pedal, but most (including Boss etc) are centre negative. I don't know what pedals you've built or the layouts for them, but it wouldn't hurt to check them closer just to be on the safe side.
+1
If the jacks are center negative, then yes, the tips of the jacks would all be "ground". You're using the plastic jacks that insulate both terminals from the case, so you're good.
I assume that you will be using power cables with male plugs on each end that will connect between your new multi power box and your pedals. If the pedals you have are center negative, then you'd want the jacks on your new multi power box to be center negative. However, if you've built or purchased any pedals that are center positive, then you can't plug them straight into the PS box if all of the jacks are center negative.
I recommend clearly labeling the PS jacks showing the polarity. One option if you have one or two positive center pedals would be to make one or two jacks positive center (clearly labeled) or make an adapter cable(s) that turns center negative into center positive. If you do this, make the special cable a different color and label it as a "cross-polarity adapter".
Finally, try to develop a habit of checking your power supply and pedal for compatible polarity before you insert the plug. Even if you know it's the same PS and pedal you've used a thousand times, the habit will save you the one time you have a different PS or pedal (kinda like checking to see if a gun is loaded when someone hands it to you, even though you saw the other person unload it).
just to add that you should keep an eye on different pedals in metal enclosures with mixed polarities and stray unconnected daisy chain dc jacks floating around - you don't want the jacks barrel touching a pedal that's grounded to its case +/- ...does that even make sense?! please forgive the word salad - i'm tired.
anyway the tip i wanted to give was that i use cork stoppers on unused but powered dc jacks to insulate them. you can pick up a bag full cheap at your local arts and craft outlet and they can also be used as make shift knobs for pots and have a nice feel. a drill bit slightly smaller than the shaft/barrel can make for a snug fit.
Sorry for pulling up an old topic, but I seem to get a lot of emails on this one. Since I re-organized my photos, all the links broke so....
The schematic:
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Pedal%20Powerr/Schematic_zps8c486faf.png) (http://s1200.photobucket.com/user/bitracer/media/Pedals/Pedal%20Powerr/Schematic_zps8c486faf.png.html)
The layout:
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Pedal%20Powerr/Power_zps1a58697c.png) (http://s1200.photobucket.com/user/bitracer/media/Pedals/Pedal%20Powerr/Power_zps1a58697c.png.html)
An etch able layout, at 300 DPI, needs to be mirrored:
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Pedal%20Powerr/Layout_zps35959e09.png) (http://s1200.photobucket.com/user/bitracer/media/Pedals/Pedal%20Powerr/Layout_zps35959e09.png.html)
You can order a fabbed one here, its pricey, and since I already provided a single sided one, I recommend you etch, but if you have more $$ than time:
http://www.oshpark.com/profiles/aballen
Also I got it in a proper enclosure. It really is solid now, practically bulletproof. That spongebob lunchbox was awesome, but Viacom sent me a letter about intended use, not sure I understood most of it.... ;)
One side with 8 isolated 9VDC
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Pedal%20Powerr/IMG_3258_zps18e42706.jpg) (http://s1200.photobucket.com/user/bitracer/media/Pedals/Pedal%20Powerr/IMG_3258_zps18e42706.jpg.html)
One side with a lonely 9VAC:
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Pedal%20Powerr/IMG_3259_zps8fca17fe.jpg) (http://s1200.photobucket.com/user/bitracer/media/Pedals/Pedal%20Powerr/IMG_3259_zps8fca17fe.jpg.html)
And the power in:
(http://i1200.photobucket.com/albums/bb321/bitracer/Pedals/Pedal%20Powerr/IMG_3260_zps5dfe28c9.jpg) (http://s1200.photobucket.com/user/bitracer/media/Pedals/Pedal%20Powerr/IMG_3260_zps5dfe28c9.jpg.html)
Of course all the standard disclaimers apply. Mains power is dangerous. You should never even think about building one of these, etc, etc.