Jaycar/SC kit questions ...

Posted: 1/4/2007 12:25:40 PM

Joined: 1/4/2007

Thanks for reading, I'm after a bit of help!

Just built my first kit from thereminkits.com in Australia. The instructions weren't great but readable and no support section on their website.

I had to make some changes to the kit which included:

1. The Box. Got a much cooler blue see through box from maplins. And bigger too which is a bonus!

2. The speaker. It has an internal speaker which I wont use much but instead of drilling 9 holes on the case lid for the sound to come through, I have one large hole the size of the speaker.

3. The ariel. This was a pain. With what came supplied, It was impossible for me to attach the ariel so I had to make a bracket and snapped the ariel provided but just bought another from maplins. Would this affect it? Does it use a special kind of ariel?

4. Output socket. It came with an RCA socket for audio output which I presumed is an Australian thing so I got a 1/4" Jack socket.

So, what happened ... I turned it on, and ... nothing. Not a bean. No pops, buzzes, crackles, hums. Nothing.

And thats where I am. Should I be looking for anything obvious? I'm quite impressed with my solering which I'm going to check again and havent made any adjustments to the pots yet....

Any help would be fantastic as I'm pretty new to this fabulous world!

Posted: 1/4/2007 3:08:17 PM

From: Undisclosed location without Dick Cheney

Joined: 2/21/2005

Firstly, the new antenna *could* be a problem if it's a significantly different size from the original. ("Significantly", for a theremin, is not very much.) If it's the same diameter and it extends to the same length, it *should* be okay, but no guarantees.

If you haven't adjusted the pots yet at all, that's the first thing I'd think of correcting. If a theremin is sufficiently far out of calibration, it will do nothing. Get some of the little plastic screwdrivers that are used to adjust pots (sometimes known as "fiddle sticks") and try gently adjusting them to see if you can get it into a state where it will respond in some way.

Other than that, the usual remarks on home built electronics apply: make sure that all of your solders are firmly connected in place, make sure you don't have any little runs of solder connecting any two or more points that aren't supposed to be connected ("solder bridges"), etc.
Posted: 1/4/2007 3:44:15 PM

Joined: 1/4/2007

Cheers for that Tom, I didnt know that adjusting the pots could have a big affect, I will do that next then check soldering ... I'll keep you posted!

Oh, and if anyone else wants to chip in...
Posted: 1/4/2007 4:00:42 PM

Joined: 1/4/2007

PS ... I measured both ariels and the new one is 220mm shorter than the original, about 2/3rds its length.

Is that bad?
Posted: 1/4/2007 4:46:31 PM

Joined: 1/4/2007

OK, managed to try the old ariel, still nothing. But ...

I got the output going into my sound system and when I plug the power lead in with the power switched to the 'on' position, i get a pop. So there must be power going in!

Cant find any plastic screwdrivers or similar .. any suggestions?
Posted: 1/4/2007 5:08:07 PM

Joined: 1/4/2007

oh, and I didnt use the pins to connect the wires to the pcb board, just pushed the wires through then soldered from the other side.

Posted: 1/5/2007 12:38:32 PM

Joined: 1/4/2007

Ok, Got it working ... kind of!

Changed about 4 things then tried it and I got a sound so I don't know which of the 4 things it was but I'm happy!

But, the volume plate is adjusting the pitch and the ariel only slightly affects the pitch.

I have tried adjusting V2 & T4 and the ariel now doesnt work and the volume plate is still adjusting pitch.

Should I carry on and stert adjusting other pots?

Meanwhile, I had this response from the website I bought it from:

Hi Matt,

I'm sorry your are having trouble with your theremin. We find that there are very few problems with these kits, but I'm happy to help whenever support is needed.

If the theremin is not producing any sound output the most common cause is the volume coils being incorrectly tuned. If the volume circuit is set too low there will be no output so the theremin appears dead. Of course its also possible that there are problems in construction but if all the parts are placed correctly and there are no solder bridges or other errors then the coil tuning is the most likely problem.

The instructions do show how to tune it in with a multimeter but I think its probably easier (and quicker) to tune it by ear. So here is the method.

Tuning Coils

The T1 coil is the reference coil that the others are tuned against so its best not to move it much as any adjustment to this will put the others out requiring retuning. So if you set it to be more or less centred it will be fine.

The pitch is then adjusted by very fine adjustments to T2 to get a good pitch response from the telescopic antenna. Once you have a reasonable pitch
response the final pitch fine tuning is done by raising and lowering the antenna. Just a few inches can make a surprising difference to the pitch response. Usually the antenna is set at 70-80% extension but you can experiment with this to see what you prefer.

T4 and VR2 are related to the volume circuit, some very fine movements with both T4 and VR2 are done to get good volume response from the horizontal
plate. The volume circuit is very sensitive so you will need to do some very fine adjustments back and forth in a trial and error manner to get it right.

The T3 is usually not adjusted, you should only need to change this if you find that the pitch and volume antennas interact. If this happens it is because the T1 and T3 are operating too close together so some fine adjustment to T3 would be needed. If T3 is adjusted however, the T4 and VR2 will need to be tuned again.

See how you go tuning the theremin this way and if you still need help please feel free to email again.



So I guess its just adjusting the pots then!

Posted: 1/5/2007 5:45:17 PM

Joined: 1/4/2007


So i havent started to adjust the pots yet, need those plastic screwdrivers first. The ariel is doing nothing and the volume plate is till affecting pitch, but I will have a play with it.

Meanwhile, I have pimped it a bit more with some LEDs and put a pic on my website:


Looking forward to your comments ...

Posted: 1/6/2007 3:31:42 PM

From: Undisclosed location without Dick Cheney

Joined: 2/21/2005

So, a couple of thoughts for you.

First, you really have to stop modifying the thing until you've actually got it working. When you're building electronics, the first step is to make it work as designed. After it works, you can change something, make sure it's still okay, and undo it if you broke it. You've changed a lot of stuff about your instrument before making it work. Theremins are incredibly sensitive to change: even a different phase of the moon can alter their tuning sometimes. Any one of the changes you've made could be enough to make it nonfunctional, but you've made them all. If adjusting it doesn't make it work, you've got a real problem to determine what exactly is wrong with it, with all those modifications in there.

The other thing is, you've posted your pictures to Myspace. I can't find them on your front myspace page, and it won't let me see your pictures page if I don't register, and I don't want to register. By placing your stuff on a page that can only be seen by registered users, you restrict it from being seen by search engines, which limits your web traffic. You'd serve yourself better to get an open web host.
Posted: 1/6/2007 4:09:25 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Or you could just post a link directly to the image and circumnavigate mySpace's registration requirements.

Like this. (http://a640.ac-images.myspacecdn.com/images01/34/l_dfc4df2aeaaa468370309e77ca21ca4f.jpg)

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