Tonepad Power Supply question

[studiostud]

Hey everyone,

I put together the tonepad board for the power supply and I'm wondering if I can just bypass the use of a transformer if I use a 12.6V wall wart adapter?  If that is the case, then my next question is that the power supply I have has a negative and positive lead, but the PCB has a point for ground and two points for positive because the transformer has three leads on the secondary power side.  So how would I hook it up?  Would I split the positive lead threads and put them to the two points?

The main reason I'm asking this is because I'm having trouble getting the transformer to work.  I tested the primary side and registered 116-118VAC, and I switched the multi-meter to ~20VDC, but I can't seem to get anything from the secondary side.  Everything goes to 0V... what am I doing wrong?  Thanks in advance for any help.

Jeff

[luke691]

12.6v AC wall adaptor will be fine....

Transformer does not rectify current... you should be measuring voltage on the secondary side of the transformer using the AC scale on your multimeter...

The four diodes on the power supply board form a bridge rectifier, the voltage on the secondary side of these diodes will be dc..

[studiostud]

Thanks!  One more quick question.  I have one positive ground pedal (fuzz face) that I would like to keep positive.  I would like to put it in a single box with a couple other effects that are negative ground.  I realize that you can't put it on the same daisy chain, but can they both be run off the same surge protector as long as I am using different AC adaptors?  I just wasn't sure how far you had to go to separate the two. 

[studiostud]

Ok.  So I hooked up the AC/DC adapter which, even though it is a 12VDC output, actually fed about 17V into the PCB.  The problem now is that when I test the DC jacks on the PCB, they have the center pin as ground.  Is there a simple explanation for this?  Maybe a component I soldered backwards?  Maybe this is correct?  I didn't want to test it with a circuit and risk sending reverse polarized voltage to it.

[studiostud]

bump.  anyone got some feedback?  I just want to make sure I'm not going to fry something on either the PS PCB or any of the others...

[zyxwyvu]

Thanks!  One more quick question.  I have one positive ground pedal (fuzz face) that I would like to keep positive.  I would like to put it in a single box with a couple other effects that are negative ground.  I realize that you can't put it on the same daisy chain, but can they both be run off the same surge protector as long as I am using different AC adaptors?  I just wasn't sure how far you had to go to separate the two. 

Yes, they can be run off the same surge protector. Different adapters should work fine. Another option is to use a MAX1044 charge pump IC to reverse the voltage, as shown here: http://www.geofex.com/circuits/+9_to_-9.htm.

Ok.  So I hooked up the AC/DC adapter which, even though it is a 12VDC output, actually fed about 17V into the PCB.  The problem now is that when I test the DC jacks on the PCB, they have the center pin as ground.  Is there a simple explanation for this?  Maybe a component I soldered backwards?  Maybe this is correct?  I didn't want to test it with a circuit and risk sending reverse polarized voltage to it.

The center should be ground for standard negative ground effects. This is to allow proper power switching using our power supply jacks. If you're worried about reverse voltage damage, put a diode in series with your (presumed) positive lead like this: PS+---|>----effect+. If you get no power, it is reversed. If that works, you've got them right.

The 17V I assume was measured with the adapter unloaded? That means the adapter is unregulated (just a transformer, rectifier, and capacitor), and will settle down to around 12V once connected to a load.

[scondon]

Thanks!  One more quick question.  I have one positive ground pedal (fuzz face) that I would like to keep positive.  I would like to put it in a single box with a couple other effects that are negative ground.  I realize that you can't put it on the same daisy chain, but can they both be run off the same surge protector as long as I am using different AC adaptors?  I just wasn't sure how far you had to go to separate the two. 

You don't need separate AC sources.  However, I don't think it's a good idea to put a positive-ground effect in the same box as negative ground effects - you'll need to run separate grounds, separate power jacks, and which ground will you use for the input-output jacks? Seems like a royal PITA and not worth the trouble.  If you really want to do this I'd recommend searching the forum for others' experiences. for example, here's a relevant post: http://www.diystompboxes.com/smfforum/index.php?topic=68954.0

Ok.  So I hooked up the AC/DC adapter which, even though it is a 12VDC output, actually fed about 17V into the PCB.  The problem now is that when I test the DC jacks on the PCB, they have the center pin as ground.  Is there a simple explanation for this?  Maybe a component I soldered backwards?  Maybe this is correct?  I didn't want to test it with a circuit and risk sending reverse polarized voltage to it.

If you're looking for help with a project, it's best to provide a link to the specific schematic/project page. If you don't, people won't know exactly what you're talking about.  http://www.diystompboxes.com/smfforum/index.php?topic=29816.0   This seems like the kind of question you could answer yourself with a little searching, but yes, most stompboxes use center-negative power supplies.

on preview: zyxwyvu beat me to it