Theremax volume not working

Posted: 3/18/2006 8:52:49 AM
Alex W.

Joined: 3/18/2006

Hi,

I'm totaly new to the theremin thing, but I had a week off of school and thought it would be a fun project. I've wanted a theremin ever since I was at one of these electronics shows/educational things put on by IBM. Anyway they had a theremin and all the kids there (probably like 7-10 years old) were going up and waving there hands around it and a friend of mine said "Alex, close your eyes and imagine they're torturing R2-D2." That pretty much made my day, and got me hooked on the idea of a theremin.

So, on to my problem. I ordered a PAIA Theremax and have assembled it; I have the pitch circuit working, but there is an unbearable amout of hum in it and the output seems really low (I have to crank the amp to hear it much, but then the hum is wicked loud). The volume circuit is not working at all.

I have been though all the help documents PAIA has and after finding that the volume was shorted (sheild touching signal wire) and correcting that problem I can only find one thing that is off: the voltage to pins 1 and 2 of IC 1. Pin one has 0v and pin two has 8v. Neither of which is in the speced 1-7v range. Also this has me confused because pin 1 should be pitch which is sort of working, but there is no voltage here. And volume doesn't work, but there is over-speced voltage here.

I keep thinking there is a loose connection that is causing the hum, but I can't find anything. Maybe the hum is just what there is and it's just there because I have to crank the amp so much to get any signal output.

Any ideas for a quick and easy solution?

Any ideas for a long and hard solution?

Thanks for any help!


Alex W.
Posted: 3/18/2006 10:18:49 AM
Dayfan

Joined: 10/8/2005

Check the wiring carefully. Have somebody with a fresh set of eyes check it. But first: Sounds like a power supply problem. Check the polarity of any electrolytic capacitors. Be sure that the minus sign on the capacitor is grounded or pointed in the specified direction.
Posted: 3/20/2006 8:15:48 PM
Alex W.

Joined: 3/18/2006

Thanks,

though I've been over it yet again and can find nothing wrong. I'm thinking there's something screwy with the IC1. What are the chances of overheating it or accidentaly giving it a static shock that would break just one of the four channels?

Thanks

Posted: 4/8/2006 6:11:03 PM
Jason

From: Sammamish, Washington

Joined: 2/13/2005

Have you had any luck troubleshooting it yet? If not, you might try calling Paia - they might be able to offer some tips over the phone.
Posted: 4/9/2006 9:31:33 AM
Alex W.

Joined: 3/18/2006

Yes, I finally got it working last week. After a couple conversations with Scott at Paia, who was very helpful, I got it to work. We were able to verify the opperation of IC1, which was not opperating properly because a metal desk lamp was loading the volume antenna. Also I found that L4 needed to be nearly 2 turns in for propper tuning on L3.

Thanks for your concern,

Alex W.
Posted: 4/24/2006 4:40:48 PM
NinetyNein

From: Vancouver, BC

Joined: 1/23/2006

I'm having a similar problem with my theremax. It sounds like I'm getting another pitch tone from my volume circuits, and the volume doesn't adjust properly.

Can you clarify what exactly was grounding out?

Thanks,
Posted: 4/24/2006 7:35:42 PM
Alex W.

Joined: 3/18/2006

Hi,

The sheilded cable from the volume antenna had shorted. When I soldered it I did a poor job and caused the sheild to melt through the plastic between the sheild and the main conductor wire. I would take an ohm meter and see if there is any conductance between the sheild and the conductor of the two sheilded cables.

Alex W.
Posted: 4/25/2006 11:26:49 PM
teslatheremin

From: Toledo, Ohio United States of America

Joined: 2/22/2006

Hello,
Welcome!
The T-Max is quite a bargain.
By the way, I call the guy at PAIA 'Excellent Scott'.
He knows the T-Max and all the mods. Always look at
'Excellent Scott's' page first before following any of the advice on Theremin World. 'Excellent Scott' knows best where the T-Max is concerned. The T-Max PC Board design and layout has changed at least three times in production. Mods are very PCB dependent--- get the exact info.
Best wishes with the crazy sounds you'll make!
TeslaTheremin
Posted: 4/26/2006 11:26:05 AM
NinetyNein

From: Vancouver, BC

Joined: 1/23/2006

Many thanks to both of you. Currently I'm running the t-max through my PC running Revalver (guitar amp software), so there are way too many things in the equation. I'm going to snag an amp from my brother, and try again. I suspect I'll end up with Scott on the phone at some point...

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