Replica RCA Theremin

How can you tell if it is a malfunctioning theremin or lack of playing skill?

bisem said: "How can you tell if it is a malfunctioning theremin or lack of playing skill?"

These are probably one in the same. (-'

Who is building the wood enclosure for the fine Keppinger Design. With my old logic selling these cabinets by themselves, only the wood parts, could be more in demand and less responsibility if the price is practical for both buyer and seller.

For the engineers and this professor (-' the enclosure is the most difficult aspect of theremin design.

Anyone have any connections to the woodworker?

Christopher

Not sure where the malfunction is on that Kep -

But one thing I am sure of - it sounds nothing at all like an RCA! ;-)

Just reading about tubes, and there seems to be huge sonic differences between the same tubes made by different manufacturers, and huge changes occurring as a result of aging etc -

It seems that theres even more variation and ambiguity about "tube sound" as there is about "theremin sound", and one would need to spend many hundred $ to get a load of different tubes in order to find the combination which suites ones taste.

Im sort of wondering if any of this is delusional nonsense! ;-) .. It seems that its always the rarest, most expensive brand / vintage of tube which sounds best - even if these are rare because they were designed for cold-war rockets, so theres no huge NOS stock remaining ;-) ... I find it kind of strange that a tube engineered for a specifically non-musical destructive application should sound better than a similar plentiful tube specifically engineered for audio application...

Fred.

Another tube issue I find is that the AC mains float up and down less than 1 volts in my test room. This affect can be heard at the lower audio frequencies as the pitch floating around on the same low note. Higher frequencies this is not noticeable. My battery backup for my computer will power my Altermen for two hours, need to see if the pitch still floats plug into that, unplugged from the wall. This happens even when I disconnect my optical pitch tuning which with a trick setup might be able to compensate for this. The affect has about a 1 sec cycle faint wobble. Most likely the RCA would do this also.

Christopher

"the enclosure is the most difficult aspect of theremin design." - Christopher

Hey, im not going to argue this one! ;-)

But whilst the large wooden lecturn may be (is) beautifull, its entirely impractical for "normal" folks who dont live in large homes, or who want to transport their theremin on a bus.. Hell, its hard enough carting an EW and amp and mic-stand to some venue, let alone some big fragile piece of furniture!

I do agree there probably is a market for theremin enclosures - in fact, theres a real hole in the market when it comes to enclosures for electronic equipment that have the size / format suitable for portable theremins - I think the wooden "lecturn" type enclosure would have much smaller demand.. But a wood crafter who could provide self-assembly kits for both markets could probably do quite well.. Particularly if they also provided antennas..

Fred.

I hadn't fixed the intermittent oscillator issue when this vid was made. I had decreased the grid/ground shunts (Rg) to around 80K from the design 100K and that solved the intermittency. But it also had unwanted side effects.

I had initially "jury rigged" the intermittent oscillator issue via change of Rg instead or Cg. The ratio of Cg to Rg is a time constant issue; eg. the tank wasn't getting kicked often enough by Cg to keep it going round and round and round. Changing Rg to correct an intermittent oscillator runs the bias point way too far into the linear region of the tubes and removes a lot of character.  Reference Termen's Radio Engineer's Handbook for solving oscillator starting issues. So, we went back to the Rg = 100K and halved Cg by series installing another C of like value.

You should hear Gabriella now. It's nice (ask Kevin Kissinger---he's played it).

One thing, however, is that you NEED to use full size antennas. The aerials are exact repros of RCAs except I opted for natural brass finish instead of nickel plated. Full size aerials make the instrument very responsive. Anyone running a theremin with coat hanger wire or other small gauge stuff is wasting their time.

Couple large cross-sectional area antennas with BHCs (Big Honking Coils) and you get an instrument where the playing field is EXTREMELY linear.

The Kepp design, IMHO, is perhaps the second nicest sounding tube theremin around, if constructed and adjusted properly, with a primo RCA taking the number one spot. And adjusting these boogers is more art than science.

A non-RCA cabinet design is available that works well with Kepps. Drawings available on the Yahoo Group. 

Cheers!

Feeleep

This theremin with fine craftsmanship has been relisted on eBay.

Take a Peek

Seller you did not learn from your first posting. In theremins "seeing is not believing" people need to hear it.

The selling price is fair if she sounds as good as she looks. I am tired of all these cheap theremin versions trying to strip out the Class from the Classic Theremin which must not be forgotten.  Maybe I have overlooked the sound sample 0-'

Christopher

Relisted with the same misleading representation - Its not a "RCA Replica" (except visually if you dont look at its guts).

" I am tired of all these cheap theremin versions trying to strip out the Class from the Classic Theremin" - Christopher.

What is the "Class" thats being "Stripped out" ?

Is this "Class" perhaps more a visual thing than a sonic one? Does having the theremin built into a large piece of furniture give it "class" that  a theremin in a portable plastic enclosure could never "have" regardless of how it sounds ?

A badly configured tube theremin can sound horrible and have far less sonic "class" than a well configured solid state theremin.. Is a bad sounding tube theremin more "Classy" than a good sounding transistor theremin ?

IMO, theremins dont need to look like they are 1930's antiques to have "class" - And all that one can say about this advert (given that there are no sound samples of any kind) is that this theremin looks like an acceptable (but not exceptional) tube construction built into a lovely piece of furniture.. Is this enough to give it "class" ?

Add to the above the complete lack of "class" in the wording of the advert, and the deliberate attempt to present this instrument as something it is not, and it fails to have any appeal to me whatsoever. As I said before, at $3k you shouldnt be making derigatory comments about a $400 "competitor" - you should be in a "class" so far ahead of such a "competitor" that they arent even worth thinking about or mentioning! "Rymes with Rogue" just says it all for me - Anyone making such a comment deserves as much attention as a common spammer IMO - as in, ignore them or vilify them or both!

Real "class" to me would be a "classic" sounding instrument with good playability and  good engineering / reliability (low drift, good linearity, good sounds, protection from ESD destruction etc), ideally in a visually appealing (probably wooden) enclosure of the "right" size (and shape) to be functional and portable.

IMO, "class" is the last thing thats conveyed to me by the advert, However, Rip-off springs to mind readily!

Fred.