Theremin Circuits Scratchpad

Fred I actually already found all of those (been seriously looking at LCR meters, reviews, prices) but thanks very much for all of your effort!

The LC200A for ~$36 USD shipped is perhaps what I'll end up buying.  I really need smallish L & C measurement, the R not so much as my Fluke 76 has a decent low ohms mode.  Funny how the experimental group seems to be ahead of the traditional test equipment manufacturers on the low end.

[EDIT] Just ordered the LC200A.  Will let you know how well it performs.

"Fred I actually already found all of those (been seriously looking at LCR meters, reviews, prices) but thanks very much for all of your effort!" - Dewster

No effort at all, actually! - I have been looking at some really high-end units (budget up to about £10k per unit) for a client - I designed a capacitive high resolution encoder/decoder for their EV in-wheel motors, the prototype worked ( just did the design based on simulations - havent even seen the prototype!), so now they need a load of test kit for the production line... I would love to have been able to take the job of designing an ATE for them - but they want it yesterday.

Not seen the LC200A before..

All I can say is that if it performs to even 1/4 the specification given, it is an astounding bargain!

Measurement accuracy:1%

 0.01 pF - 10uF   ...1uF-100mF
The minimum resolution: 0.01 pF

0.001 uH  - 100mH    ...  0.001 mH - 100H
The minimum resolution:0.01UF

Test frequency: L/C about 500KHZ Big inductance about 500HZ(can display current test frequency value)

........

At that price, with the spec above, well - shall we just say that I find it extremely hard to believe...

But at that price, WTF!  You got to buy it! (If you didnt, I would! ;-).. I await your report with great interest - ;-)

Fred

Not holding my breath based on this single review of the likely base product (but the guy doing it might not be totally up to snuff):

http://rustybolt.info/wordpress/?p=382

But, as you say, if it performs to even 1/4 the specification given it will probably be OK by me.  Famous last words, if something seems too good to be true, we can only hope, yadda yadda. :-)

Some that should work are:

2N5484, 2N5485, 2N5486, J111, J112, J113, BF256B.

All of these are in stock at Mouser, and are cheaper than dirt.-W0TTM

Just checked and as of today, nearly all TO-92 JFets are "Discontinued"! -WHA!

Did this just happen?- not just mouser either, no one has them, well NTE still, but otherwise all manufactures seemed to have axed them.

sad day

19.899 pieces of 5484 available for immediate delivery at mouser. Well, the MMBF5484..

SMD+magnifiers+tweezers=how promising.

Farnell and Rapid still seem to be selling them, and do not have them marked as "end of line"

http://uk.farnell.com/fairchild-semiconductor/2n5484-d74z/rf-jfet-n-channel-15v-to-92/dp/1268655

http://www.rapidonline.com/Electronic-Components/Junction-Field-Effect-Transistors-66262

RS Components has one type:

http://uk.rs-online.com/web/p/jfet-transistors/1577214/

Digikey has a fair range:

to92 JFets

I bought 500 2N5457's for about 2p each 6 months ago, and still have a few ;-)

I dont think its time to panic just yet!

- But the trend towards SMD is relentless - To me, the real problem is more about maintanance of theremins in the future.. When I started, I limited myself to selecting components which were common and "wouldnt" dissapear - but this is now becoming impossible - every month some "standard" part seems to become available only as SMD, or discontinued..

And new components which are set to become tomorrows "standards" (low noise high speed opamps and comparators, 4Q multipliers and the like) are only produced in SMD form.

It is really starting to look like, if one wants ones design to be maintainable, one needs to fit SMD parts (or lay the board out to accept a SMD part if the TH part is discontinued)

This is the route I am taking.. I cannot work with SMD - So lay the board out for parts I can see, but have the pads for equivalent SMD in place. This way I can build my boards, or get SMD versions built if TH parts become unavailable when / if I go to production - and hopefully in 30 years if a component fails, some replacement can be obtained.

Fred.

I´d love to see the SMD equivalent for the variable inductors.

"I´d love to see the SMD equivalent for the variable inductors."

Please! Dont tempt fate!! ;-)

>>> Quick search of suppliers and manufacturers to determine the situation, leads me to believe the following:

1.) Some parts are listed as "end of life" and some (the 2n5457 for example) are difficult to get now.

2.) Central Semiconductor Corp. seems to be providing some of these "discontinued" parts in To92, including the 2n3819 and 2n5486.. I am glad to see the 3819 is still available.

Mouser (uk) has a big stock of quite a few jfets - as these are shipped from the USA I am surprised if they are not shown in the US catalog:

http://uk.mouser.com/Semiconductors/Discrete-Semiconductors/_/N-6hpe7Zscv7?Keyword=jfet&FS=True

.. Actually, they are!

http://www2.mouser.com/Semiconductors/Discrete-Semiconductors/JFET/_/N-96ngc?Keyword=jfet&No=25&FS=True

There are enough to92 jfets available now to build a few hundred thousand theremins, LOL ;-).. I have enough to build about 100 theremins - but will wait until I can get some more at 2p each like I did with the last lot!

I personally wouldn't care too much about component availability and continuity...

As I actually see while reworking a Henk theremin from 1994, one can always find someone on eBay who sells a few NOS items which one is looking for. It needs sometimes a little patience but up to now I found all what I needed.

I also would not think about keeping thousands of FETs at 2p/pc in stock because IMHO there will never be a mass market for theremins but rather individual or semi-customized manufacturing. And my experience with Ondes Martenot shows that the fact that every instrument is a little different (although there has been a kind of mass production in the seventies and eighties) makes it more interesting because it allows to see how Martenot dealt with the availability of components, how there was a smooth evolution from one instrument to another and how he updated older instruments during the regular maintenance and servicing.

"I also would not think about keeping thousands of FETs at 2p/pc in stock because IMHO there will never be a mass market for theremins but rather individual or semi-customized manufacturing." - Thierry

Yeah, I agree Thierry.. certainly not worth going out buying thousands at their present 20p ish price, just in case they vanish..

But at 2p each, I bought the whole stock (550) - A little over £10.. If I had bought them "as needed" at the 20p each they were selling + P+P etc, well - I have about 500 left, so have used  about 50.. The 500 I now have are effectively paid for by those I have already used, had I bought them as I needed them.. And I could always sell packs of 10 on ebay at £1 and certainly make no loss.

If one is only playing with theremins, I agree that large stocks of anything are probably not worth the storage.. But I do have a small business in capacitive sensors which brings a little trickle of work in.. and has become quite busy in the last 6 months.

This is one of the big problems with electronic parts - the economies of scale are HUGE .. In some cases one can buy ten items for twice the price that one item costs, once one factors in postage etc.

Fred.