Hi,
I posted about a year ago with problems building my first theremin although i work in musical electronics repair I was having one of those moments. Due to work and what not I never finished it and only jsut got it back out yesterday. In true sods law fasion I fixed in 1 hour what was cuasing weeks of head scratching last year and its now all up and running.
My only issue now is something weird with the volume.
At the moment i have a 3inch wire comming off the board which when i power it up works just like it should as I move my hand the volume goes up and down just as expected. As I turn L11 the reaction of the antenna changes so that seems right.
The main issue is once I connect this wire up to an antenna it stops working, its almost like its responding as if I hand my hand on the antenna (volume off). If I pull the connection from the antenna it works on the 3inch wire perfectly but the second its put back on voluem drops to nothing. Now I thought this was something like the antenna i made was adding too much capacitance or something so it was treating it like i was holding it but i tried just a loose bit of wire too about 9 inches long and you get the same thing no volume.
On top of this following the classic instructions to tune the volume using the voltage on U3-12 getting it to zero. It doesnt matter where I turn L11 it always remains at a steady -11.49v. Now I had a little troubleshoot over the circuit and everything seems fine the right values etc in the right places. The curious thing is if the circuit wasnt working or connected fine surely the 3 inch wire wouldnt work like it does? and turning L11 wouldnt change the responce as it does?
These things seem to imply that although turning L11 doesnt change the voltage on U3-12 at all that the circuit seems to be working. I would still guess the fact a short wire works the volume and a long one doesnt is down to the tuninge but Im not sure.
Can anyone offer any advise on this? Its just one of those pain in the ass problems where everything appears to work so finding the issue is ten times harder.
Thanks
Matt