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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
PSU instead of batteries?
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Sprak



Joined: Oct 19, 2005
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PostPosted: Mon Dec 26, 2005 5:03 am    Post subject: PSU instead of batteries? Reply with quote  Mark this post and the followings unread

Hey all, was wondering.. what kind of modifications would I have to do to power my Soundlab with a 9V power supply adapter instead of batteries? Just spent half an hour trying to find out why my prototype wasn't sounding anymore, looking for shorts etc., before figuring out that the batteries had gone dry....
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Uncle Krunkus
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PostPosted: Mon Dec 26, 2005 5:49 am    Post subject: Reply with quote  Mark this post and the followings unread

The problem is to make it a +/- 9V power supply. This you will probably not find off the shelf. I'm setting mine up to run off a +/-12V PSU which I custom built.
There is a way of deriving a +/- supply off one battery, but it almost certainly will not deliver the goods as far as running a Soundlab goes.
Have a look at this if you want to experiment: -
http://www.geofex.com/circuits/+9_to_-9.htm

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Macaba



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PostPosted: Mon Dec 26, 2005 7:13 am    Post subject: Reply with quote  Mark this post and the followings unread

You could in theory set up a 18V power supply to function as a +/- 9V supply. This would fulfil your aspirations. To get an efficent power supply from 18V (using resistors would be quite inefficent I think) you'd use lots of diodes in series (each diode has a typical drop of 0.7V) or EVEN better, use a 9.1V zener diode. If you need more information on how this is setup, reply with such a request.
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Sprak



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PostPosted: Mon Dec 26, 2005 7:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Macaba, please teach me how Smile I have a bunch of 9.1v zener diodes lying around.
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Macaba



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PostPosted: Mon Dec 26, 2005 7:53 am    Post subject: Reply with quote  Mark this post and the followings unread

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If somebody can see a reason why this wouldn't work, feel free to criticise. Sprak- breadboard it and feedback how nicely it works.

(Credit must go to http://www.kpsec.freeuk.com/powersup.htm for the original diagram that I butchered up)
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mosc
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PostPosted: Mon Dec 26, 2005 8:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Be careful using systems like this. If you are careful it will work, but now you have two grounds which are 9 volts appart. This could be dangerous. You probably won't kill yourself but sooner or later you'll blow something up.

IMHO, if you need a +/- 9 volts power supply, then get a good one, don't kludge something like this just to use up parts you already have or to save a little bit of money.

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Macaba



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PostPosted: Mon Dec 26, 2005 8:20 am    Post subject: Reply with quote  Mark this post and the followings unread

The circuit shown is the basic principle of a voltage regulator anyways. The issue with two grounds is the same in any PSU, you have a ground before and after the transformer. So basically, you just never hook anything up to the battery ground, always being careful to hook it upto the voltage regulator ground. So its not an issue really?
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Pehr



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PostPosted: Mon Dec 26, 2005 8:49 am    Post subject: Reply with quote  Mark this post and the followings unread

I use two 9V adapters (battery eliminators Confused ) for my SL Embarassed connected exactly as the batteries...
At the time I started building my first SL it was the easiest way...it was before I knew about that +/-12V PSU... Razz

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Wild Zebra



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PostPosted: Mon Dec 26, 2005 9:47 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm sure you have your reasons for a power supply, but one of the awesome things about this synth is that it runs off batteries. I put some duracels in mine about 3 or 4 months ago and there is no sign of slowing this puppy down.
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Macaba



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PostPosted: Mon Dec 26, 2005 9:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Wild Zebra- theres a point:

Two 9V batteries should last AGES. Sprak- Are you sure you've got low power consumption components? If you used exactly the same components as Ray specified, then it should last ages. If it doesn't last a reasonable amount of time, check for a short. It seems worth it to stay with batteries, because you get FAR less mains interference, a cleaner sound.
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mosc
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PostPosted: Mon Dec 26, 2005 10:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Macaba wrote:
The circuit shown is the basic principle of a voltage regulator anyways. The issue with two grounds is the same in any PSU, you have a ground before and after the transformer. So basically, you just never hook anything up to the battery ground, always being careful to hook it upto the voltage regulator ground. So its not an issue really?


I assume the 18v supply is a DC supply. Never connect anything else up to it if you connect your SoundLab with such a power supply circuit. If the 18v supply is connected to the mains ground, then you are running your SL at a different ground. Never connect the SL to anything else: an external mixer, preamp, amplifier or other synth if you use such a circuit.

What you have is a very basic +9v Zener diode voltage regulator. These work OK for supplying voltages for LEDs, lamps and such, but they are not great for audio circuits. To top that off, you are kludging it to a +-9V regulator by coming up with a derived ground. That's where the prolem comes in.

You have a lot of time invested in your DIY circuits. Give them the respect they deserve and use a well designed power supply.

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Wild Zebra



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PostPosted: Mon Dec 26, 2005 10:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Also I used cheap Alkalines from my local "dollarstore", and these were not lasting very long. Then I said F-it and got some good name brands. Haven't had a problem yet.
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Macaba



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PostPosted: Mon Dec 26, 2005 10:52 am    Post subject: Reply with quote  Mark this post and the followings unread

mosc wrote:

I assume the 18v supply is a DC supply. Never connect anything else up to it if you connect your SoundLab with such a power supply circuit. If the 18v supply is connected to the mains ground, then you are running your SL at a different ground. Never connect the SL to anything else: an external mixer, preamp, amplifier or other synth if you use such a circuit.

What you have is a very basic +9v Zener diode voltage regulator. These work OK for supplying voltages for LEDs, lamps and such, but they are not great for audio circuits. To top that off, you are kludging it to a +-9V regulator by coming up with a derived ground. That's where the prolem comes in.

You have a lot of time invested in your DIY circuits. Give them the respect they deserve and use a well designed power supply.


Ah yes, that seems to check out apart from a few things you could possibly explain. 0V is the point with 0 potential difference. So if you wire a soundlab using my PSU to an external amplifier, connecting the grounds, they are still the points with 0V's, the amplifier circuit won't "see" 9.1V above ground? Especially as the amplifer is likely to be powered off the mains, which brings up another point:
You can have many different rectifying configurations such as the half-bridge and the full-bridge which result in essentially different ground configurations (center tapped, and not) and there isn't a problem?

I'm eager to learn about this, thanks for taking the time mosc to educate me. Smile
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Uncle Krunkus
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PostPosted: Mon Dec 26, 2005 5:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

You tell 'em Mosc! Wink
Yes, big problems when you deviate from PSU convention.
The problem with a derived 0V is that back in the PSU the earthing will end up on the -ve rail. When you connect an output to an amp, etc it's shield on the amp side will be 9V below the sheild from the SL (because your earth is 9V above)
It sounds complicated, but it's really just relativity!!
At the very best, you'll short the -ve side of your SL (and everything that entails) If there are other circuits, synths, effects units etc. in the loop which have their earth's commoned (through shielding connections usually) you'll get a special kind of earth loop hum,..... well it's more of an earth loop bang!! And all that very expensive smoke will escape from vital components. (it's really hard trying to get it back in!!!) Laughing

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mosc
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PostPosted: Tue Dec 27, 2005 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Macaba,

If you look at your power supply circuit, you have labeled one end of a wire 0 V and the other end -9.1 V. You know you are in trouble whenever you do that. Wink

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Wild Zebra



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PostPosted: Tue Dec 27, 2005 1:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here is a topic at a stompbox forum http://www.diystompboxes.com/smfforum/forums.html?topic=40268.from1135713069;topicseen#msg289300
Quote:
BTW, for those Soundlabbites out there, Electronic Goldmine has a +/-12V wallwart that would power the Soundlab nicely. It's a low current wart, but the Soundlab is very miserly on its current requirements (Ray's told me it would work as well). Myself, I'd regulate it down to +/-9V internally just to give it some stability. Soundlab itself would have no problem running at +/-12V.

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