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9505 Theremax
http://www.paia.com/talk/viewtopic.php?f=4&t=25
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Author:  PAiA-Scott [ Mon Mar 16, 2009 10:52 am ]
Post subject:  9505 Theremax

Subject:
Re: theremax pitch range


Hello Jared.

When Theremax is in a much smaller case it is likely there could be something too close to the antennae mounts such as the metal case bottom or some wiring (power supply or panel to circuit-board. Also, if there is not a good connection between the antenna cables and the antennae, then the range would be very limited (just the same as if the antennae weren't there. They should each have the same 7v dc that is on the attached transistor collector in the first and fourth oscillator circuits.

Inspect the point-to-point ground circuit wiring on the panel to be sure the solder has flown on all these joints. Nudge each link looking for movement in the joint. A loose connection along the way here can interrupt the ground out to the Pitch and Volume Trim controls which are parts of the first and fourth oscillator circuits.

Attached is a pdf with tips and suggestions for checks and tests you can make to be sure all the V+, Vr, and the oscillator transistor voltages (7v on each collector) are OK. Also notice the way the wiring is shown on the image--away from the oscillator circuits and the antennae mounts. Tuning using the method described here can work to provide the best range and linearity for the hand to pitch and volume antennae. There are also recommended substitutions for capacitors C39 and 44 (100pF) and an added 6800ohm to the R81-3 & R81-2 terminals for improved waveshapes on the Timbre control extremes. A change of C37 to 100pF works for better hand-to-antenna volume response.

Thank you.

Sincerely, Scott Lee



jared shapiro wrote:
> hey
>
> I built the theremax a nubmer of years ago, got it working ok, and then put it in a drawer, where it's been until a couple of days ago when my girlfriend found out i had a working theremin and begged me to play with it.
>
> here's the thing. i put it in an enclosure that is significantly smaller than the wood case you guys sell. i'm not sure if its a shielding problem inside with regards to the wires coming from the antennae's or if there is another problem but the pitch and volume ranges i get in really miniscule. not only that but the pitch is locked to a very high octave... the pitch pots dont really make much of a difference. any ideas? do i need to do anything to shield the wires inside? if you dont think that is the problem, what can i do to get more range... especially from the pitch?
>
>
> thanks!
>
> jared
>
>

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