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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Newb power supply questions
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regularjackson



Joined: Apr 12, 2012
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PostPosted: Thu Apr 19, 2012 5:10 pm    Post subject: Newb power supply questions Reply with quote  Mark this post and the followings unread

First post here which I will preface with the fact that I am a total newb to electronics in general. I recently successfully put together a MFOS WSG and a number of different effects pedals and such from various kits. I decided I would like to take the next step and put together a sound lab mini-synth plus and would like to get away from batteries with this one. I was looking at Rays design for the bi-polar power supply, but I've been scared off by all of the warnings, and I really don't know what I'm doing. I've looked around a bit for a bipolar supply that I could buy that's prebuilt, but I don't really know what I'm looking for. Does anybody have any suggestion for a reasonably cheap power supply? Thanks.
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marvkaye



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PostPosted: Thu Apr 19, 2012 7:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Do a search on Ebay for "HAA15".... it's a bipolar PS from Condor / Power One that should meet your needs.

<marv>
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prgdeltablues



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PostPosted: Fri Apr 20, 2012 1:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Or you could go with Ray's wall-wart based bipolar power supply. !2V AC wall-warts should be fairly easy to source, and then you don't have mains power anywhere near your cabinet to worry about. It's a very easy build - the only thing to be aware of is that the outer casings of the positive and negative regulators are at different potentials, so they mustn't touch (nor obviously must their respective heatsinks if you need them).
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dylar



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PostPosted: Fri Apr 20, 2012 6:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

I second that. Ray's wall-wart power supply is super easy to build. I built two from the stripboard design on these forums. It's a bit different than Ray's design, but works great. If you already built a WSG then the power supply will be no problem. Just make sure to get an AC wall wart (Ray links to them)
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regularjackson



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PostPosted: Sun Apr 22, 2012 12:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the advice. I imagine the mfos bi polar supply isn't too hard to put together, I was just a little nervous about the warnings and such. Maybe I'll try it out, thanks!
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loydb



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PostPosted: Mon Apr 23, 2012 6:08 am    Post subject: Reply with quote  Mark this post and the followings unread

I've put together a few of the MFOS power supplies, they're a very easy build.
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drakfluga



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PostPosted: Sat May 12, 2012 2:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

I want to build a wall wart supply like the one on MFOS.com. I'm looking to make it +/- 15V for my DIY stuff, and I'm wondering about Ray's design specs. He says on the site that a 15V supply should use a 15V AC wall wart. Now, it's been years since I took my electronics course in college, but I remember distinctly learning that voltage regulators require a higher voltage than they provide. Checking the specs on the 7815:s I could find at my local supplier, they say the expected input voltage for a reg with 15V output is 23V. Am I missing something? I want to make sure I know what I'm doing before I start building this thing.

Also, if I choose to go with a higher voltage wall wart, will I need to redesign the circuit at all, i.e. change the rating on the caps etc?

Still trying to relearn all I've forgotten from my younger days, as well as learn a lot of stuff I never learned back then.

Cheers!
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Blue Hell
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PostPosted: Sat May 12, 2012 3:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

http://electro-music.com/forum/topic-51694.html sums it all up nicely - I'll sticky that one.
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drakfluga



Joined: May 09, 2012
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PostPosted: Wed May 16, 2012 8:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
http://electro-music.com/forum/topic-51694.html sums it all up nicely - I'll sticky that one.


Thanks! Great thread, however, it doesn't answer my question. It discusses current rating. I was asking about voltages, mainly for the wall wart and filter caps in Ray's design.
Still, that was a highly worthwhile read. Cheers! Wink
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Blue Hell
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PostPosted: Thu May 17, 2012 7:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, that was a bit too quick, sorry.

drakfluga wrote:
I want to build a wall wart supply like the one on MFOS.com. I'm looking to make it +/- 15V for my DIY stuff, and I'm wondering about Ray's design specs. He says on the site that a 15V supply should use a 15V AC wall wart. Now, it's been years since I took my electronics course in college, but I remember distinctly learning that voltage regulators require a higher voltage than they provide. Checking the specs on the 7815:s I could find at my local supplier, they say the expected input voltage for a reg with 15V output is 23V. Am I missing something? I want to make sure I know what I'm doing before I start building this thing.

Also, if I choose to go with a higher voltage wall wart, will I need to redesign the circuit at all, i.e. change the rating on the caps etc?

Still trying to relearn all I've forgotten from my younger days, as well as learn a lot of stuff I never learned back then.

Cheers!


You'll want a minimum of about 3 Volts over the regulator for it to keep regulating properly, and you want the voltage over it to be not too much higher for the regulator will run warmer then.

Peak voltage from a transformer is about 1.4 times the specified voltage, but that transformer voltage usually is specified for some load (so dont be surprised you measure more on an unloaded transformer).

Subtract the diode drop from that peak voltage, and that'll be what you see over your filter capacitors. The working voltage of those capacitors should be chosen to be a good bit higher, as electrolytics live longer when over dimensioned.

Also calculate with some tolerance, see what happens when your mains voltage is 10% lower or higher (which can happen).

The value of the filter caps comes from the amount of ripple voltage you can tolerate - the peak voltage minus the maximum ripple should still leave the 3 Volts the regulator wants, so when you scale the voltage up you could likely use somewhat smaller filter capacitors, or make them larger when you scale the voltage down.

Hope that helps better?

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drakfluga



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PostPosted: Thu May 17, 2012 8:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Ok, that was a bit too quick, sorry.


No worries! Wink

For the capacitance, I just want as much as possible? Ray has specced his +/-12V example schematic with 3300uF caps. If I go to 15V that should still do fine, right?
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Blue Hell
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PostPosted: Thu May 17, 2012 8:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, but your regulators will run hotter of course ... (which has not much to do with the capacitors).
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drakfluga



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PostPosted: Thu May 17, 2012 9:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Yes, but your regulators will run hotter of course ... (which has not much to do with the capacitors).


Right. I'll fit some heatsinks on those as well, of course.
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regularjackson



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PostPosted: Fri May 18, 2012 10:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay, so I ended up ordering the mfos wall wart supply. I would like to house it in it's own independent enclosure, as I would like to use it to power a couple of different things I have built. I was hoping to get some advice on how to go about this. Can I run the plus, minus and ground to to banana plugs and power the soundlab that way? Is that a bad idea? Thanks for any help in advance!
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regularjackson



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PostPosted: Tue May 22, 2012 3:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry to bombard with questions, but I have one more. I ended up putting the mfos wall wart supply into the case with the sound lab, and now that I finished everything up, of course it isn't working, so I have some troubleshooting to do. My question now is in regards to the danger of power supplies. what are the dangers exactly with handling it? I think I understand that if I touch the leads of the capacitors I could be in for a large shock. Is that the main danger? Anything else I should know about this? Thanks in advance!
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