wall wart for a minimum theremin

Posted: 11/8/2008 6:01:35 PM

Joined: 10/31/2008

is there a way to easily connect a wall wart to a minimum theremin? i don't want to chew through batteries.

i have a nine volt wall wart and the appropriate plug, but i want to make sure that it is really as easy as connecting the wall wart plug to the + and - terminals where the battery connector once was...

Posted: 11/10/2008 1:18:49 PM

From: Escondido, CA

Joined: 2/6/2008

Typically walworts don't do much filtering. In the worst case they contain a transformer and a bridge rectifier.

If you have access to an oscilloscope you can determine how good of a power supply your walwort is by connecting a load across it. If you use a 680 Ohm, 1/4W resistor, you will be drawing around 15mA ... which is probably more than your minimum theremin draws.

You want to set the 'scope for AC coupling and the lowest amplitude setting. Ideally you want to see a "straight line", at worst case you will see a fairly large sawtooth waveshape.

If you don't have a 'scope, you can just assume the walwort is not that clean and put a 100uF to 1000uF, 25Vdc electrolytic capacitor (make sure the plus sign is towards the positive side of your circuit!) across the battery terminals.

To be safe, you should insert a 1N4001 diode in series between the walwort's "hot" side and the battery + terminal. The banded end of the diode (cathode) should be connected to the + battery terminal (the electrolytic capacitor's plus side should be connected to the diode's cathode) and the other should go to the wallwort. This will keep your theremin safe if you have the terminals reversed on the wallwort! If you have this arrangement, the worst that will happen is that the theremin just won't work with the wrong polarity and will work with correct polarity.

Wrong polarity, no diode = frying the IC(s) in your minimum theremin!

Posted: 11/10/2008 3:21:34 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Or you could use rechargeable batteries.
Posted: 11/11/2008 8:57:03 AM
RS Theremin

From: 60 mi. N of San Diego CA

Joined: 2/15/2005

This AC/DC adaptor will work with built in filtering and regulation, also they throw in the power tip of your choice for the female plug you are using.

RS Walwart (http://www.radioshack.com/product/index.jsp?productId=2552558&cp=&sr=1&kw=adapter+ac+to+dc&origkw=adapter+ac+to+dc&pg=2&parentPage=search)

Be sure to observe the proper polarity when fitting the DC power tip on the line cord.


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