Jaycar Mk11 Build questions

Hello Theremin World and thank you for your hard work love and support.

My young nephew exhibited and interest in electronics and I always wanted a theremin so I bought him a soldering iron and a Jaycar theremin DIY kit not really knowing what I was getting either of us into. 

Two months into the project he has done a pretty good job albeit dumping an assembled though not working theremin in my lap. I have read many of your posts and realize that with out the tools and know how that we are flying blind though look forward to any light that the collective community can shed on our project. 

I found the following,

- All polarised parts are fitted correctly.

- A short on one of the chips, (I cant remember which one or what terminals but could this blow the chip)

- He has been adjusting the transistors with a magnetic metal screw driver and they seem striped.

- There is only a couple of millivolts not 2.5 volts between TP GND and TP2.

- The power pack that we purchased from Jaycar is 1 amp and unregulated Part No. MP3026. please follow link for more info

https://www.jaycar.com.au/12vac-1a-plugpack/p/MP3026 

Thanks for your time.

Shane and Ben

Difficult to tell at distance if the solder short has blown the IC... Also difficult to tell at distance if the use of a magnetic screwdriver has damaged the variable inductors, basically, there are special ceramic or plastic tools for that.

You should perhaps follow my exhaustive and detailed diagnose/tuning instructions in the first post of this thread to locate potential problems. BTW, to prevent the typical beginner's fault, don't try to tune a theremin on your workbench, there is too much conductive material on and in it, thus the antennas and the circuit can't react in a normal way. Best is to set up the theremin on a microphone stand on the floor with a clear space of a radius of 1.5m (5ft) around, and at a height about the floor of at least 70cm (2 1/3ft). Then use portable versions of the digital multimeter, frequency counter, and oscilloscope. That's how I diagnose and fix successfully theremins.

Hi Thierry,

Thank you for your timely turnaround. Yes I came across your thread.

I do not have access to a scope though I do have a good multi meter with Hz function. Initially I was hoping that someone could get back to me on the Power pack (1 amp and unregulated) and proprietary test issues (between TP GND and TP2) questions as perhaps a member has had a similar problem. 

I've called a few electronics repairers in my area (Sydney Aust) and they dont want to know me.

Thanks again.

Shane and Ben

Hi,

I have just wasted quite a few days trying to get a silicon chip theremin working with no succes whatever. I built a Mk 2 two some years ago from the article in 2008 (repeated in EPE) never got it working properly but donated it to local museum for kids to play with (it did at least make some sort of variable noise.) It evidently ceased working and I tried to rescusitate it without success. I then noticed the the magazine had brought out an "improved" theremin in an article in 2009. This article stated that it was an improvement on their 2000 design (no mention of the previous year's Mk 2) I have now built this and despite checks and rechecks of the pcb  and all the components all I can get to work is the pitch circuit at very low volume. The volume circuit appears hopeless. I have since spotted Max's article on modifications which seems to refer back to the 2000 circuit. I am now totally dispirited and confused and suggest the anyone contemplating building one should think again. There appear to be numerour circuits and it is almost impossible to relate articles on mods or trouble shooting to any particluar one ! Whilst new to theremins I have successfully completed many electronics projects in the past but this one I am giving up on. As a last throw of the dice I have now ordered the shield for an open theremin as that seems to be pretty well organised and I am familiar with the arduino ! Just posting this as a warning to potential new builders. The kit from Jaycar may well be OK but don't for heavens sake try to build one from the magazine articles !!!

"I have just wasted quite a few days trying to get a silicon chip theremin working with no succes whatever."  DavidFMarks

Do you use an oscilloscope in your efforts to figure out what was going wrong?

I have an ancient Philips PM3217 scope which I have been trying to use without success. To be honest I think the scope is working but my brain which is a lot older than the scope isn't. I shall shut myself away and study it  . watch this space 11

Still getting nowhere fast ! Pitch control is working  but very low volume  (with an amp on line out). Movement near the volume antenna just alters pitch. Scope seems to be OK and shows output of Fixed osc (measured at pin1 on the 1496) as about 450kc/s at 50 mV peak to peak and the pitch osc measured at pin 10 to be also about 450Kc/s at 60mV peak to peak. The ouput of the volume oscillator measured at the base of the bc548 is also about 450 kc/s at 2.0 volt peak to peak. The output of the 1496 measured at pin 12 is about 10Mv peak to peak with what appears to be a very high frequency component superimposed (i.e. a fuzzy sine wave) which is probably too high for my scope to see. If anyone can make any sense of this I would be most grateful before I just bin the lot.