Completely newbie planning to build EM theremin

'My opinion on PAiA is well known.. IMO its a pile o crap - in fact, everything PAiA ever "designed" is.' - Fred

Fred, I do like your turn of phrase!

Thanks for the tip off on the PAiA.

Regarding the TW theremin-I'd be delighted to build such an instrument.
That way it would be possible to gauge the ease of construction by someone with an 'intermediate' skill level.

Roy

Thank you all for your comments. I will do as you say!

I think i understand what means NPO, but still i have a couple of NPO-related doubts:

1) I'm going to buy some parts from planetaelectronico.com (my friend is going to buy there too so we'll share delivery costs) but there none of the capacitors are marked as NPO. Maybe they are NPO but it's not stated in the description, maybe NPO is not that important. And yet i won't get any of them because i don't want to improvise. Am i exaggerating?

2) There are a couple of capacitors in the EM schematics that are noted as 22pF NPO. But after updating the part list from EM to EW i found that they changed to 15pF so i wonder if they are still supposed to be NPO.

~Hazel

NPO relates to the temperature dependent behaviour of the capacitor - NPO / COG capacitors have lower change in capacitance as a result of change in temperature - as little as 0.01% over typical room temperatures with change of 25 degrees C, and 0.1% over the entire operating temperature which is well beyond survivable for the thereminist!

X7R capacitors vary about 5% over 25 degrees C, Y5(x) can vary by 20% over 25 degrees C.

This is the VARIATION in capacitance due to temperature, not the tolerance - Tolerance spacifies the possible variation one can get at a fixed temperature, between parts - this can easily be +/- 10%, but is not important (from a drift perspective) - its only important if one has untunable elements and need to have close tolerance.

You do need to buy NPO / COG capacitors for any tuning circuit - Or you certainly need to know what the dielectric is.. Buying a "random" ceramic capacitor is never a good idea.

You can use other capacitors if you know what you are doing - one can deliberately use a capacitor with a temperature coefficient which counters some other coefficient (like that of your inductor) so that one gets really stable operation..

But IMO, you are best sticking with NPO / COG.. Every good supplier will be able to provide these - any supplier who doesnt know what you are talking about aint worth using..

Digikey NPO COG Selected capacitors:    Digikey US - NPO / COG - Select values.

Farnell / Element 14, Newark, and probably every other big supplier has a huge range of parts - just enter COG and/or NPO in the search, select Ceramic capacitors, select Through-hole.. Then pick the voltage you need (50 Volts for oscillator circuits, 200V for antenna circuits).

Fred.

"I'm going to buy some parts from planetaelectronico.com" - Hazel

Looking at that site, although limited by language, I would say its a "maplin" equivalent - only even less into serious electronic component supply than maplin.

Forget it!

Theremins are not the sort of thing you can build by going to that sort of shop!

"I have gone a bit quiet on the RCA clone stuff because I am doing the physical building / testing / modifying at present - I suspect others are doing likewise" Fred.

Darn skippy!

My Kustom is currently occupying several square feet while I probe the Melodia type volume circuit. Amey's fuzzbox is taking shape on my bench, and I have a corner of Dad's machine shop commandeered for coil experiments and cabinet work.

Progress is slow because my employer has asked for volunteers to work extra hours in preparation for the upcoming holiday season, and being a greedy capitalist, I've been doing just that.  

One eyed cat in a fish market. Life is good.

After reading and comparing a lot, i'm finishing my shop list, but i'm not sure about some of them:

U1 LM78L12 12V positive regulator, here.
U2 LM79L12 12V negative regulator, here.
Both of them have a trailing "ACZ" in the name. They are equivalent, aren't they?
U3 LM13600. Here Thierry says that LM13700 can be used. What about a LM13700N?

PS: Good work Chobbs!!

~Hazel

thanks.

All those components should  work.

Ah, i forgot!

Q1-Q8 2N3904 NPN. But i'm going to use a 2N2222A instead (thanks Fred!).

L14 22 µH. I'm going to use a fixed inductor with Q 50. Is that ok?

maybe get a few different types of inductors to experiment with.