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 Forum index » DIY Hardware and Software » Developers' Corner
converting single dc to dual voltage(?)
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overshadow



Joined: Nov 07, 2009
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Location: portland, oregon, usa

PostPosted: Thu May 24, 2012 11:32 am    Post subject: converting single dc to dual voltage(?) Reply with quote  Mark this post and the followings unread

Hello All!!! I may be posting this in the wrong section, and if so, I appologize.

I generally work with single voltage circuits running on 12v or less but I'm building myself a synth/workstation that currently runs on a single +12v dc and I'm now looking to introduce an adsr running on +-12v.
I'm really not trying to redo the entire power system for the entire piece for this one circuit.
I'm searching for a simple solution...so...
My question is; Is it possible to run the main +12v power into two independant 12v voltage regulators (thereby resulting in two independant 12v), sending one to the +12v and one to the -12v of the adsr circuit?
Or is -v actually inherently different (flipped)?
If that's the case, does anyone know of a simple solution to this problem?
many thanks
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Mongo1



Joined: Aug 11, 2011
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Location: Raleigh NC

PostPosted: Thu May 24, 2012 1:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

You can't use two regulators as you suggest. That is strongly related to perpetual motion.

There are some chips out there that can do the conversion for you. Depending on your needs though, I'd really suggest converting over to a dual supply system. Doing that would really open up the number of circuits you could use.

Gary
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overshadow



Joined: Nov 07, 2009
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Location: portland, oregon, usa

PostPosted: Thu May 24, 2012 5:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Mongo,
thanks for the reply.
looks like I'll need to upgrade to a dual supply.
Out of curiosity though, would it be possible to run a +-12v circuit off two independant power supplies (one for the -12v and one for the +12v)?
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Mongo1



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PostPosted: Thu May 24, 2012 6:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
would it be possible to run a +-12v circuit off two independant power supplies (one for the -12v and one for the +12v)?


Yes - that's pretty easy. You would connect the positive side of one supply to the negative side of the other. That would be your system ground.

Gary
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elmegil



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PostPosted: Thu May 24, 2012 7:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Be wary that you'll want the two to switch on/off at the same time. I recall something about it being a bad idea to have two wall warts hooked up such that one was on and the other off, for example.
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richardc64



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PostPosted: Fri May 25, 2012 6:32 am    Post subject: Re: converting single dc to dual voltage(?) Reply with quote  Mark this post and the followings unread

overshadow wrote:
If that's the case, does anyone know of a simple solution to this problem?

I love how that one word always seems to fall by the wayside in these threads. It's like it causes a blind spot.

Although a dual supply would allow more types of circuits to be used, if you really don't want to "... redo the entire power system for.. this one circuit" it might be possible to adapt that particular ADSR to single supply, since envelope generators in general take in a unipolar signal (the gate and/or trigger,) and put out a single-ended voltage -- the envelope.

Let's see it.

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Uncle Krunkus
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PostPosted: Fri May 25, 2012 7:45 am    Post subject: Reply with quote  Mark this post and the followings unread

You can buy (although they are quite expensive) DC to DC converters. These days they come on one big black chip, say,.. matchbox sized. You put one DC voltage in, and get another out. Up, Down, and I'm sure Scott Stites told me about one which took in say 12DC unipolar, and converted it to +/-15V with a centre ground.
Keep in mind that they can't supply anymore wattage than what you put in, in effect, even less with efficiency. So If you had 12VDC unipolar in @1A, you wouldn't get +/-15V at anymore than 300-400mA.
Apart from that, I'd say, just bite the bullet and invest in a good quality linear PSU +/-15VDC @1A
It will pay for itself in frustration very quickly if you plan to do much more Synth DIY.

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analog_backlash



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PostPosted: Thu Nov 01, 2012 5:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

I've not tried it myself, but I've seen circuits in the past where a very simple DC-DC converter is made from an oscillator (often CMOS) and a couple of capacitors and diodes. This generates a negative voltage which can be used to supply the the -V pins of op-amps. There is an example shown here:

http://www.extremecircuits.net/2010/06/negative-auxiliary-voltage.html

The current supplied is small, but if it's just to power a few low-current op-amps, it might just work. It's worth a go as nothing much is likely to go wrong.

However, it's still a better option in the long run to build a dual-rail supply. The one I'm using now was built by my cousin for me when I first started getting into electronics. It must be 30 years+ old now!

Just a thought,

Gary
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