Theremax question

Posted: 10/11/2005 1:53:09 AM

From: Kansas City, Mo.

Joined: 8/23/2005

Thought you'd like to know that the source of the roughness of tone that I was electical interference from one of my scsi drives.

I can't believe how clear the tone of the Tmax is, now -- not having to use any Hum Eliminators or anything else -- just patch it in and play!
Posted: 1/3/2006 9:33:03 AM

Joined: 12/28/2005

I have exactly the same problem.
I always thought there was something wrong with my build, but since you have the same problem, maybe it's a design problem...

I will try your work around.
Posted: 1/4/2006 12:32:56 AM

From: Kansas City, Mo.

Joined: 8/23/2005

For the record... the last time I recorded with the Theremax I patched it thru the Ebtech Hum Eliminator and grounded the Theremax to myself via a wriststrap.

This method provides me a consistantly clean signal.

While I can get a clean signal without the Hum Eliminator and wrist strap, the result has not been predictable.

btw -- you can hear this recording on the "Spellbound Holiday Special" on my rendition of "Oh Christmas Tree". I was able to manage this with the stock antenna however it took an inordinate amount of effort to get a useable take. I keep talking about putting a better antenna on it... there is another thread regarding upgrades to Tmax's antenna that I am following with great interest.
Posted: 1/4/2006 3:35:02 AM

Joined: 12/28/2005

Sorry, I meant the sluggish response of the pitch voltage controller (for controlling a synthesizer).

Just like you, I have no problems with the volume antenna voltage controller, although it's the same circuit.
Posted: 1/4/2006 11:56:06 AM

From: Kansas City, Mo.

Joined: 8/23/2005


I removed a capacitor and fixed the sluggish pitch CV problem... I will review it when I get home and post the mod here this evening. (I am away from home and can't remember which capacitor it was).
Posted: 1/4/2006 12:03:37 PM

Joined: 12/28/2005

Anyway, I think you mean C24 capacitor (did you bypass it or remove it?).
What seems so funny to me is that we have exactly the same problem.
The volume antenna has the same circuit and it worls well for you and for me. So why not in the pitch antenna? So weird...
Posted: 1/4/2006 11:25:37 PM

From: Kansas City, Mo.

Joined: 8/23/2005

Ok, just checked my notes.

I removed C24. Also, I changed C21 from a 10uf electrolytic to a 5uf electrolytic capacitor.

This eliminated the lag in the Pitch CV output.

Posted: 3/5/2006 9:28:07 PM

From: Kansas City, Mo.

Joined: 8/23/2005

Yesterday I decided to replace the stock Theremax antenna with a better antenna.

I simply used an 18" chrome water supply pipe. At the bottom, it is connected to a 90 degree angle copper piece -- the pipe fits into the connector via a compression fitting.

The toughest part was soldering a lead to the copper pipe -- I had to use a torch to heat the copper up enough to melt the solder.

Again, the only thing I did was to replace the stock antenna. I had to tweak the adjustment on coil L1 -- other than that, no other adjustments were needed.

The new antenna makes a HUGE difference. The main difference is that the new antenna is NOT overly sensitive to up/down motions as is the stock antenna. With the new antenna, I am able to do precision playing thru about a 3 octave range. The notes any closer than about 8" from the antenna are tough to play. In order to play in the higher range, I just tune the pitch higher (such that zero beat is behind me). This throws higher pitches into the "sweet spot" of the antenna's field.

My next mod will be to add a pitch preview.

Stay tuned!
Posted: 3/7/2006 9:48:23 PM

From: Kansas City, Mo.

Joined: 8/23/2005

Not sure why I had put off installing a pitch preview on my Theremax. For some reason, I thought the mod required active circuitry. In reality, the mod requires only a capacitor and a resistor (the mod is detailed on

The mod was easily installed in less than an hour.

So, with a working pitch preview, and the antenna (described in the post above), I set out to play some of the music that I have been playing on the Epro.

The new antenna is pretty linear beyond 10" from the antenna rendering about a 2 1/2 octave range of linearity. I found though, that my playing had to be more "careful" when going after jumps to high notes.

The good news is that, within the linear range of the Theremax, I found it's playability similar to the Etherwave Pro. The difference with the Epro is that one can play accurately to within an inch or two of the pitch antenna -- the Epro's range of linearity spans better than 4 octaves (this is a conservative figure).

The Theremax is more sensitive to vibrato than is the Epro -- one must excercise care or else the vibrato quickly becomes too wide (wobbly) on the Theremax.

To play with precision on the Theremax is possible however requires careful, conservative playing.

I enjoy playing the Theremax -- I built it from a kit and it has been a labor of love, really.
Posted: 4/26/2006 12:22:29 AM

From: Toledo, Ohio United States of America

Joined: 2/22/2006

Are you sure that your post about the oscillator coupling post had the correct information?
My skepticism could be wrong, but is the following copied post correct?
"~~ summary of mods ~~

. connect a 10K resistor between R6 and R11 (see Paia website) to acheive oscillator coupling and non-symmetry in the heterodyne signal."

This could be correct on another T-Max PC Board series earlier than June of 2005. I am sorry if I am mistaken, but the PAIA site wants a different resistor pair to be jumped to obtain oscillator coupling. That would be R4 and R9 with a 10K resistor.
If I am incorrect, I apologise.

You must be logged in to post a reply. Please log in or register for a new account.