Post your Silicon Chip/Jaycar kit questions here!

Posted: 10/18/2006 2:03:36 AM

Joined: 10/11/2006

in reply to gavsteed. i thought (and i may definitley be wrong) that the normal and midi kits were almost the same and that main difference between the midi version and the standard version is that instead of running the output of the hetrodyning oscillators through an amplifyer circuit and turning it in to an audio signal it runs the output through the appropriate circuitry to turn it into a midi signal. if this is true then why dont you build the midi kit and add an amplifier ciruit like that in the normal kit then put in a switch which allows you to choose whether the signal goes to the midi circuit or the amplifyer circuit. before you do this you would obviously want to check with one of the more experianced builders here to see if this is right before you take my word for it.
Posted: 10/18/2006 1:34:13 PM

Joined: 10/6/2006

Hi again guys,
thanks for the feedback, i too am hoping that the it would be as simple as adding an amplifier circuit instead of the midi generation circuit to the midi theremin, TomFarrel , you appear to be quite learned on the subject and i'm sure more experienced than i so i really appreciate the feed back.

i understand what you are saying about the interference but yes you are correct, i would only have one circuit powered at a time...both of you have given me some ideas on how to continue with this so thanks again and of course any progress i make i'll document it and theremin world is welcome to a how-to or whatever when i get through this!
Posted: 10/19/2006 12:46:15 AM

From: Undisclosed location without Dick Cheney

Joined: 2/21/2005

One of my buddies is a professional electronics technician, and he's agreed to help me with the Jaycar kits.

We're going to try to get together sometime within a month or so to take an initial look together at the kits, the instructions, the mods I want to make, sketches of the cabinets I want to build, etc. While we're at it, I'll ask him to look at the MIDI instrument circuit to see if he thinks it's possible to cut in an amp somewhere.

So, if you're not in any rush for an answer, I'll try to post his response here in a few weeks.
Posted: 10/19/2006 3:52:19 AM

Joined: 10/6/2006

thats really nice of you Tom i appreciate it, i had a quick look at the schematics last night, there is alot of similarity with the analog part of the MIDI theremin and the regular one so i think it would be possible. I'm actually a computer engineering student in ireland so i have access to all of the necessary components/equipment/breadboards etc. and i'm gonna throw something together in the next week or so and i'll let you know how i get on!
Posted: 11/7/2006 12:44:50 PM
Space Ritual

Joined: 11/7/2006

Hello, I'm new to the forum, and to the theremin. I recently completed my Silicon Chip theremin, and it lasted 2 days! The instruction manual unhelpfully asks you to tune the antenae for pitch the wrong way round, so I retuned it again, and a lead came off the PCB which was leading to the pot for volume. I presume the static burnt out a component....

As for the gold pins that came with the kit, I resoldered the wires which lead to the output, electrical input etc onto these pins, which I soldered into the correct holes.

Is there anything else that could have burnt out anything on the board?

Also, who at Silicon chip chose to use an RCA output instead of Quater inch, and why use a 3.5mm electrical input?!?!

Finally, I adjusted T1 and T3, which apparently didn't need adjusting (according to the manual) so could I have done damage there?
Posted: 8/22/2007 5:27:10 PM

Joined: 8/22/2007

just bought and constructed an SC theremin a couple of days ago.

as far as i am aware there are no problems with solder briges etc.

i have a problem with the tuning. I have a multimeter to help with this, but I am fairly new with using one. the instructions tell you to find voltage readings for specific points eg "Adjust VR2 so that pin 1 of IC2 goes to about +4.3v and wind VR1 slightly clockwise from its fully anitclockwise position."

You need 2 points to connect on the circuit board so apart from pin 1 of IC2 whats the other point you contact to get the voltage reading.
Posted: 8/22/2007 9:06:53 PM

From: Australia

Joined: 1/21/2006

Hi markforces

The other point you want is Ground. So just put the black prong of the multimeter on one of the many gruond points of the circuit. (i.e the black lead from the battery of power source) and then the red one on the pin of the IC.

Good luck

Posted: 11/6/2007 4:55:52 PM

From: London

Joined: 11/6/2007

Are there any good fault finding guides for this Jaycar kit? I'm getting no output...

I've gone through the quick calibration setup. Everything on the gates looks good on the scope. The anode of D1 is approximately 1.7V RMS. I adjusted VR2 to get 4.3V on pin 1 of IC1 (VR2 is _very_ sensitive). Inputs to the MC1496 look good to me (though I'm not certain what they should be). I'm not seeing anything on pin 12 of note though (looks completely flat to me). I tried removing the chip and connecting the output from a music player to the pin 12 connection (amp input and the music player ground to speaker ground). This played through the speaker and VR1 adjusts the volume. So I have an amp at least

To me it looks like the amp works and the input side works. So must be MC1496. However I'm thinking its very unlikely that I've got a bad IC! Any good sites on fault finding for these? I did know electronics (have a degree) but its been 7 years since I did any in practice...

I think what would be useful is knowing what to expect on MC1496 inputs and outputs in normal operation. e.g. approx frequencies, amplitudes and relative voltages.


Posted: 11/7/2007 9:02:25 AM

From: London, UK

Joined: 6/5/2007

As far as I know, there are no sites on actually fault finding these, just use the techniques you were taught at College.
If you're still pulling your hair out, get in touch as I've built 2 of these and "faultfixed" some others.
Am also based in London.


Posted: 11/10/2007 6:24:19 AM

From: London

Joined: 11/6/2007

Thanks MarkT. After removing the MC1496 and trying again I'm still thinking thats the cause... I see on the pins (relative to T1 ground):
1: 2V + 1V sine wave 455KHz
2/3: 0V (NC) - 1K between them
4: 2V flat
5: 4.3V (I adjusted VR2 to keep volume high for now)
6: 6Vish
8: 4V flat
10: 4V + 1V sine wave 456KHz
12: 6Vish
14: 0V

Rest seem to be NC. If anyone has a scope handy -> Does this match your working setup?

If I apply an audio signal between pins 6 and 12 (e.g. headphone output from mp3 player) the amplifier works.

I guess I need to test the MC1496 separately... I'll have a look at the data sheet.



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