Sine-Wave is rough on my T-Max

Hello,
I have built a Theremax and am unhappy with the sine-wave sound of this unit. It has a very rough edge. The unit is pitch stable, and tuned correctly,(This unit is very playable). Also, with no volume antenna culling, a 60 cycle ground hum is slighty heard. What could cause a ground hum in a wall wart powered device?
Also, I have noticed that the sine-wave is alot more quiet than the square wave,(obviously), but IS TOO LOUD. Sorry to have shouted, :). There seems to be no happy medium between the sine and square waves to be able to achieve a feminine voice timbre or even a string timbre. Is there a fix for this?
The biggest timbre problem, as I have already stated, is the rough edges of the full sine-wave timbre. Rough edges do not mean 'sine-wave'.
Also, while I am at the bitching trough, I wonder if the volume antenna volume decay hand distance can be increased?
I know I have asked alot, but can anyone help?
Thanks,
Teslatheremin

You normally shouldn't have audible hum from your Theremax. When the unit is inadequately grounded (more on that later) you will hear a lot of roughness in the tone, particularly in the tenor range. I suspect you are picking up hum because your output signal is weak and you are having to boost the gain to compensate -- thus making any hum audible.

From your description, it sounds like you have tuned your pitch coils ok. You are getting a good signal from the detector circuit because it is firing the comparator in IC1 (that is, you are getting the square wave tone). So, your pitch oscillators are ok.

The output signal is apparently degraded past the R39-R40 junction.

Now, before going further, check your volume control voltage -- you should be getting around 5 volts at the loudest and zero at the softest.

Also, do you get a nice loud signal when you connect the clip from D1 to lug one of R83?

Theremax problems tend to be caused by weak/cold solder joints, improperly oriented parts, switched parts, and solder bridges.

Since the Theremax uses a wall-wart, it isn't grounded. Any electrical interference in the area, including hum, will interfere with the Tmax's tone because the Tmax doesn't have a ground.

Thus, the Tmax is designed to be grounded through the sheilded cable connection. If you are using a portable, battery-powered amp, it STILL isn't grounded! And then, in a large equipment setup, one must be vigilant about ground loops.

So, what is one to do?

I found when plugging the Tmax into my rack, that I had occasional interference problems same as you -- resulting in rough tone.

My solution is to plug the Theremax into a EbTech hum-eliminator AND to ground the Tmax to myself via a wriststrap and wire to the Tmax.

I have one recording wherein I used my Theremax that you might enjoy hearing and I just uploaded it to my website: a rendition of "Oh Christmas Tree". Just go to http://kevinkissinger.com and follow the links :)

I did the recording before I improved the antenna and added a pitch preview and I'm looking forward to utilizing the Tmax in some future recordings.

Anyway, hang in there. Don't forget that you can contact Paia via email or phone. I too had some problems when first building my Tmax and Paia was extremely responsive.

Before long, your efforts will be rewarded with a very nice-sounding Theremin.

-- Kevin

Thanks Kevin for your reply!
My Tmax is well grounded thru a tube amp to a tested, grounded wall socket. I have yet to try the other fixes you have suggested.
Thanks again, and I will post as to me progress.
Dave

KK.,
After measuring the Volume Control Voltage on my TMax, I found that it fluctuated as much as .75 V over a period of 3 or so seconds. I immediately suspected the wall-wart. I was right! The 12V wall-wart that I was using had degradated and was faulty, only showing 7 or so volts over a few seconds.
Twelve volts is what the TMax wants, so a new wall-wart was tested and applied: 'Viola', no more ground hum! My TMax is also even more linear in play.
Thanks Much!
Dave

Great sleuthing!

I am amazed that with the degraded voltage that the pitch signal was able to drive the comparator.

For the first month or so, you may have to tweak the coil settings until the unit "settles in".

Sounds like you are on your way to a lot of enjoyment.

Best wishes and keep us posted on your progress.

-- Kevin

My Thanks Again!
Dave