newb power supply projects

[fogwolf]

So I was reading the what matters and what doesn't thread and someone suggested a power supply is a good 1st or 2nd project, so I've decided I'd like to give that a shot. I was wondering if someone could either recommend one with PCB, wiring diagram, etc... and/or give me some guidance on one I've found at tonepad - http://tonepad.com/project.asp?id=59.

I can't figure out where the input power connection goes exactly. I'm assuming that since there's a transformer on the circuit board I'm wiring this to AC mains? How do I do that? Would I just attach a power cord and 3-prong plug like I might find on a guitar amplifier or something? If so, how would I do that? The project page says "An external 12V AC wall wart can be used to avoid the risk of working with 120v wiring. Use extreme care with wiring." - so a) why would we need the wall wart when there's a transformer on the circuit and would it cause any problems to have them both and b) where and how would I connect a wall wart to this power supply? I don't see anything specifying how I would connect either a jack for an AC wall wart or how to wire the supply for mains.

Also, it says it's adjustable/variable voltage - how is that controlled? Can I basically just hook anything up to it that requires between 7-12V and it will get the correct voltage? If so, how does that work?

My last question is would it be possible to make this variable between 7-15V? If so, would I do I only need to substitute a 15VAC transformer for the 12VAC one? Would there be any other safety or component changes to take into account to do this?

Thanks!!

[mdh]

These are exactly the sorts of questions that will elicit the answer, "If you're asking these questions, step away from the soldering iron and learn a whole lot more about safety and working with mains power!"  That's not to say that you can't build a power supply, but you should almost certainly go the wall-wart route if you're going to do it with your current level of knowledge.  In any case, you should go read Power Supply Basics for Effects on Geofex.com.

1. The AC input to the pcb in the Tonepad project is connected to the two blue square pads on the layout labeled "12V AC".  This is emphatically *NOT* mains AC.  It would come from the secondary of a 120V to 12V (or 240V to 12V, depending on the mains power where you live) step-down transformer.  If you used a 12V AC wall wart, this is where the two conductors from the output of the wall wart would connect.  There is no transformer on the pcb, just a rectifier, some filter capacitors, a voltage regulator and its supporting components, plus the output jacks.

2. The voltage adjustment is made via the 1k trimmer.  You have to set it so that you get the desired voltage at the outputs.  This is practically the datasheet application circuit for the LM317 voltage regulator.

[fogwolf]

Thanks. Yes, the wall wart route sounds much safer. Will read up more on power supplies before I start this one as well. Thanks for clearing that up.

What about if I wanted this supply to be variable between 7-15V - is this possible?

Thanks!

These are exactly the sorts of questions that will elicit the answer, "If you're asking these questions, step away from the soldering iron and learn a whole lot more about safety and working with mains power!"  That's not to say that you can't build a power supply, but you should almost certainly go the wall-wart route if you're going to do it with your current level of knowledge.  In any case, you should go read Power Supply Basics for Effects on Geofex.com.

1. The AC input to the pcb in the Tonepad project is connected to the two blue square pads on the layout labeled "12V AC".  This is emphatically *NOT* mains AC.  It would come from the secondary of a 120V to 12V (or 240V to 12V, depending on the mains power where you live) step-down transformer.  If you used a 12V AC wall wart, this is where the two conductors from the output of the wall wart would connect.  There is no transformer on the pcb, just a rectifier, some filter capacitors, a voltage regulator and its supporting components, plus the output jacks.

2. The voltage adjustment is made via the 1k trimmer.  You have to set it so that you get the desired voltage at the outputs.  This is practically the datasheet application circuit for the LM317 voltage regulator.

[mdh]

What about if I wanted this supply to be variable between 7-15V - is this possible?

You would first of all need to have a larger input voltage from your wall wart.  18V AC should get you in the right ballpark.  You need to have something like 2V DC greater than your maximum desired voltage at the input of the regulator (i.e., the output of the rectifier).  Then of course you need to make sure all of your capacitors have a high enough voltage rating to handle the full voltage of the wall wart you wind up using (and don't skimp here, there's really no point).  Finally, using a higher voltage might affect the minimum voltage within the range of adjustment, so you may not get down to 7V.  This last detail can probably be worked out from the data sheet, or one of the ubiquitous LM317 calculators floating around on teh interwebz.

[fogwolf]

So forgive me if this is a dumb question, but to make sure I get capacitors with high enough voltage ratings, I don't simply get them higher than 18V for an 18V wall wart - would I actually apply Ohm's law to figure that out? Thanks.

What about if I wanted this supply to be variable between 7-15V - is this possible?

You would first of all need to have a larger input voltage from your wall wart.  18V AC should get you in the right ballpark.  You need to have something like 2V DC greater than your maximum desired voltage at the input of the regulator (i.e., the output of the rectifier).  Then of course you need to make sure all of your capacitors have a high enough voltage rating to handle the full voltage of the wall wart you wind up using (and don't skimp here, there's really no point).  Finally, using a higher voltage might affect the minimum voltage within the range of adjustment, so you may not get down to 7V.  This last detail can probably be worked out from the data sheet, or one of the ubiquitous LM317 calculators floating around on teh interwebz.

[Morocotopo]

You need caps rated AT LEAST for the same voltage you put through them. Better to have some safety margin, so you use higher rated ones. The next standard value is 25V, so you use those or higher. Higher voltage rating is no problem, lower is.
It looks like you are not really ready for a power supply build, you need to read / learn more. you could electrocute yourself if you work with 120/240V, this is no joke, or at least damage your pedals / equipment.
You could build it but before applying power, have someone with the knowledge check it out.
This is not to scare you, but to help you learn.
good luck!

Morocotopo

[fogwolf]

Not taken the wrong way at all - totally understand and plan to take it very carefully with this one - just starting to think about building it. Will do more reading and building before attempting this though. Thanks!

You need caps rated AT LEAST for the same voltage you put through them. Better to have some safety margin, so you use higher rated ones. The next standard value is 25V, so you use those or higher. Higher voltage rating is no problem, lower is.
It looks like you are not really ready for a power supply build, you need to read / learn more. you could electrocute yourself if you work with 120/240V, this is no joke, or at least damage your pedals / equipment.
You could build it but before applying power, have someone with the knowledge check it out.
This is not to scare you, but to help you learn.
good luck!

Morocotopo

[fogwolf]

One more question actually (ok, actually 2).

1) On the tonepad wiring diagram it states if using metal standoffs you can use those to ground the enclosure. If I use plastic standoffs how could I ground the enclosure?

2) mdh, you said "The AC input to the pcb in the Tonepad project is connected to the two blue square pads on the layout labeled "12V AC".  If you used a 12V AC wall wart, this is where the two conductors from the output of the wall wart would connect." How is this done exactly? In other words, I've only ever seen wall warts with a socket on the end for plugging into a jack on your effect. Is there a special jack that you could solder to these two blue square pads that would take something like this:

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=121216

If so, how would I find one of these jacks? Searched on Mouser for an AC jack but didn't find anything.

Thanks again.

You need caps rated AT LEAST for the same voltage you put through them. Better to have some safety margin, so you use higher rated ones. The next standard value is 25V, so you use those or higher. Higher voltage rating is no problem, lower is.
It looks like you are not really ready for a power supply build, you need to read / learn more. you could electrocute yourself if you work with 120/240V, this is no joke, or at least damage your pedals / equipment.
You could build it but before applying power, have someone with the knowledge check it out.
This is not to scare you, but to help you learn.
good luck!

Morocotopo

[mdh]

1) On the tonepad wiring diagram it states if using metal standoffs you can use those to ground the enclosure. If I use plastic standoffs how could I ground the enclosure?

If you wanted to ground the enclosure (which isn't strictly speaking necessary if you're using a wall wart to supply the power) and you don't use metal standoffs, you could solder one end of a wire to the ground pad on the pcb, and wrap the other end around a machine screw securely fastened through a hole in the enclosure.  Using a wall wart for power, though, there's really no reason to do this (and let me once again emphasize that this is the only safe way to go given your current level of knowledge).  I usually use a plastic box for this type of circuit.

2) mdh, you said "The AC input to the pcb in the Tonepad project is connected to the two blue square pads on the layout labeled "12V AC".  If you used a 12V AC wall wart, this is where the two conductors from the output of the wall wart would connect." How is this done exactly? In other words, I've only ever seen wall warts with a socket on the end for plugging into a jack on your effect. Is there a special jack that you could solder to these two blue square pads that would take something like this:

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=121216

If so, how would I find one of these jacks? Searched on Mouser for an AC jack but didn't find anything.

Most wall warts have a barrel connector on the end like the one you linked.  These connectors are typically used for DC supplies, but even AC wall warts tend to use the same kind of connector.  So you'll want to get a jack that matches the connector on whatever wall wart you plan on using.  Where things start getting a little dicey here is that your wall wart might "match" the DC jacks on your pedals, and you want to make sure that you never plug your AC wall wart into your pedals that expect 9V DC, and that you don't plug your AC wall wart into one of the output jacks of your power supply.  One way to avoid that is to intentionally buy a wall wart with a plug that is mechanically incompatible with the things you don't want to plug it into.

In any case, since the board isn't designed to accomodate a board-mounted input jack, you would either have to redesign the board, or use a chassis-mounted jack for your power input.  The next dicey detail is that the jack needs to be isolated from the rest of the circuit -- that is to say, if you have a metal jack and a metal enclosure, the outer shell of the jack (which connects to the outer barrel of the plug) is electrically connected to the enclosure, unless you take measures to make sure it isn't.  This means either using a plastic jack or a plastic enclosure.  You would then solder wires between the jack and the 12V AC pads on the board, making sure that you use the correct connectors on the jack (polarity doesn't matter, but often there will be 3 lugs on the jack to accomodate switching between battery power and external power).

A lot of this stuff is hard to explain in words, which is why we have all these diagrams.  I see that you have a few "newb..." threads going today.  I suggest that unless you're really burning to build a power supply, you build a few battery-powered projects to get your bearings before you do the power supply.

[fogwolf]

Thanks again. Yeah, I'm on my 2nd project and like I said, just saw that in the "what matters what doesn't" thread that someone suggested a power supply as a first or second project, but I'm going to wait on it while I try to learn more about it.

A couple more questions:

1) "You would then solder wires between the jack and the 12V AC pads on the board, making sure that you use the correct connectors on the jack (polarity doesn't matter, but often there will be 3 lugs on the jack to accomodate switching between battery power and external power)." - So, if one were to use a DC jack, what is the correct way to connect to the 2 pads? When connecting with a batter supply in my other project the positive connection went to the top 2 connectors and the ground to the bottom - so in this case would I use just 1 of the top connectors and the bottom one? Does it matter which goes to which pad on this power supply?

2) Looking at this power supply project - http://www.musicfromouterspace.com/analogsynth/WALLWARTSUPPLY/WALLWARTSUPPLY.php it looks from the photo as though they suggest cutting off the barrel connector and soldering each conductor to the board, but that isn't detailed - is that something that is sometimes done as well?

Thanks again.

1) On the tonepad wiring diagram it states if using metal standoffs you can use those to ground the enclosure. If I use plastic standoffs how could I ground the enclosure?

If you wanted to ground the enclosure (which isn't strictly speaking necessary if you're using a wall wart to supply the power) and you don't use metal standoffs, you could solder one end of a wire to the ground pad on the pcb, and wrap the other end around a machine screw securely fastened through a hole in the enclosure.  Using a wall wart for power, though, there's really no reason to do this (and let me once again emphasize that this is the only safe way to go given your current level of knowledge).  I usually use a plastic box for this type of circuit.

2) mdh, you said "The AC input to the pcb in the Tonepad project is connected to the two blue square pads on the layout labeled "12V AC".  If you used a 12V AC wall wart, this is where the two conductors from the output of the wall wart would connect." How is this done exactly? In other words, I've only ever seen wall warts with a socket on the end for plugging into a jack on your effect. Is there a special jack that you could solder to these two blue square pads that would take something like this:

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=121216

If so, how would I find one of these jacks? Searched on Mouser for an AC jack but didn't find anything.

Most wall warts have a barrel connector on the end like the one you linked.  These connectors are typically used for DC supplies, but even AC wall warts tend to use the same kind of connector.  So you'll want to get a jack that matches the connector on whatever wall wart you plan on using.  Where things start getting a little dicey here is that your wall wart might "match" the DC jacks on your pedals, and you want to make sure that you never plug your AC wall wart into your pedals that expect 9V DC, and that you don't plug your AC wall wart into one of the output jacks of your power supply.  One way to avoid that is to intentionally buy a wall wart with a plug that is mechanically incompatible with the things you don't want to plug it into.

In any case, since the board isn't designed to accomodate a board-mounted input jack, you would either have to redesign the board, or use a chassis-mounted jack for your power input.  The next dicey detail is that the jack needs to be isolated from the rest of the circuit -- that is to say, if you have a metal jack and a metal enclosure, the outer shell of the jack (which connects to the outer barrel of the plug) is electrically connected to the enclosure, unless you take measures to make sure it isn't.  This means either using a plastic jack or a plastic enclosure.  You would then solder wires between the jack and the 12V AC pads on the board, making sure that you use the correct connectors on the jack (polarity doesn't matter, but often there will be 3 lugs on the jack to accomodate switching between battery power and external power).

A lot of this stuff is hard to explain in words, which is why we have all these diagrams.  I see that you have a few "newb..." threads going today.  I suggest that unless you're really burning to build a power supply, you build a few battery-powered projects to get your bearings before you do the power supply.

[mdh]

1) "You would then solder wires between the jack and the 12V AC pads on the board, making sure that you use the correct connectors on the jack (polarity doesn't matter, but often there will be 3 lugs on the jack to accomodate switching between battery power and external power)." - So, if one were to use a DC jack, what is the correct way to connect to the 2 pads? When connecting with a batter supply in my other project the positive connection went to the top 2 connectors and the ground to the bottom - so in this case would I use just 1 of the top connectors and the bottom one? Does it matter which goes to which pad on this power supply?

Well, the exact way that you connect the pads to the jack depends on the jack.  I don't claim to know the pinouts of all jacks, so if I have a jack in my hands and I want to know how it's pinned out, I either look at the data sheet or I use my DMM to figure out what's connected to what.  The thing to be careful of is that you're using the correct one of what you're describing as the "top 2 connectors", because one of those connectors is connected to the plug when the plug is in the jack and the other one is not.  The one that's not connected when a plug is in the jack is the one that the battery would be connected to in your other projects, assuming you wired them correctly.  Once you have identified the two connectors that are actually connected to the plug when it's in the jack, wire one to one of the 12V AC pads and the other to the other one.  It doesn't matter which one is which, because it's AC.

2) Looking at this power supply project - http://www.musicfromouterspace.com/analogsynth/WALLWARTSUPPLY/WALLWARTSUPPLY.php it looks from the photo as though they suggest cutting off the barrel connector and soldering each conductor to the board, but that isn't detailed - is that something that is sometimes done as well?

Yes, you could do that as well.  The thing to watch out for there is that you have sufficient strain relief and a smooth-edged hole in the enclosure so that the cord from the wall wart doesn't get yanked out or cut open.  All that really matters is that there is a secure electrical connection between the output of the wall wart and the input of the rectifier/regulator board, and that everything is mechanically well-supported so that points that shouldn't be electrically connected can't come into contact.

[fogwolf]

Thanks again for all the information.

1) "You would then solder wires between the jack and the 12V AC pads on the board, making sure that you use the correct connectors on the jack (polarity doesn't matter, but often there will be 3 lugs on the jack to accomodate switching between battery power and external power)." - So, if one were to use a DC jack, what is the correct way to connect to the 2 pads? When connecting with a batter supply in my other project the positive connection went to the top 2 connectors and the ground to the bottom - so in this case would I use just 1 of the top connectors and the bottom one? Does it matter which goes to which pad on this power supply?

Well, the exact way that you connect the pads to the jack depends on the jack.  I don't claim to know the pinouts of all jacks, so if I have a jack in my hands and I want to know how it's pinned out, I either look at the data sheet or I use my DMM to figure out what's connected to what.  The thing to be careful of is that you're using the correct one of what you're describing as the "top 2 connectors", because one of those connectors is connected to the plug when the plug is in the jack and the other one is not.  The one that's not connected when a plug is in the jack is the one that the battery would be connected to in your other projects, assuming you wired them correctly.  Once you have identified the two connectors that are actually connected to the plug when it's in the jack, wire one to one of the 12V AC pads and the other to the other one.  It doesn't matter which one is which, because it's AC.

2) Looking at this power supply project - http://www.musicfromouterspace.com/analogsynth/WALLWARTSUPPLY/WALLWARTSUPPLY.php it looks from the photo as though they suggest cutting off the barrel connector and soldering each conductor to the board, but that isn't detailed - is that something that is sometimes done as well?

Yes, you could do that as well.  The thing to watch out for there is that you have sufficient strain relief and a smooth-edged hole in the enclosure so that the cord from the wall wart doesn't get yanked out or cut open.  All that really matters is that there is a secure electrical connection between the output of the wall wart and the input of the rectifier/regulator board, and that everything is mechanically well-supported so that points that shouldn't be electrically connected can't come into contact.