B3 dosen't seem to work

Posted: 7/3/2015 7:07:30 PM

From: Cleveland, Ohio

Joined: 12/21/2014

Hahaha, that's a good one, anyway I just opened it up and changed the power supply with one with an output of 12 V and 300mA and now it kind of works but for some strange reason it does the opposite of what it supposed to do, so it would sound just when I touch the volume loop and make the low notes as I get closer to the antenna, any Idea of what's going on?

I'm not the electronics expert around here, but I can tell you that my B3 likes 12v much better than 9.  Re:  notes going lower as you get closer to the antenna may be that you need to adjust the pitch field (the right-hand knob on the back)?  If you are not familiar w/the concept of "zero beat," maybe read the posts here and/or watch some of the videos that explain this.

Posted: 7/3/2015 7:45:33 PM

From: Colmar, France

Joined: 12/31/2007

As one can see when opening a B3, there is a 78L09 fixed voltage regulator. As people who dare opening theremins should know, the 78Lxx series voltage regulators need an overhead of at least 2.5V to work correctly, thus feeding voltages below 11.5V will never give stable results. Some have even a diode in series as a polarity protection which eats up another 0.55V, thus 12V is really the strict minimum for these devices. Fortunately, most power supplies have a slightly higher free run voltage (about 13 instead of 12V) and the B3 needs only about 30mA, so using a standard 12V supply is safe.

Posted: 7/4/2015 6:36:44 PM

From: Cleveland, Ohio

Joined: 12/21/2014

That being the case, I wonder why Dan Burns ships them w/ 9v supplies?


Posted: 7/7/2015 12:36:35 AM

From: USA

Joined: 10/18/2006

A slight adjustment of both trimmers should suffice. Careful not to bend or break the connections. Dead bug is really not how it should be done. 30ma seems high since this circuit style can be driven with only 5 ma at 9 volts.

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