The EM Theremin - Pitch and Volume Antenna: not working.

"Your Bass Mod is working perfect, thank you very much,"  - betabox

You are most welcome - nice to hear that it's working out for a couple of folks here!

Hi,

I'm pretty much in the same boat here. Built my first one based on the schematic. I’m not unfamiliar with building things from schematic as I own a music shop and do a lot of repairs and mod work. Decided to build one as I always wanted one to play around with but I’m a bit stuck now.

I guess my issue is with my coils. Theres no output from the device. I know the amp and psu work fine. Working from papers I have read and checking all the voltages I am stuck as although I am seeing about 12vac on L1 I am seeing nothing 0vac on L5 and L6 and at last time I checked nothing on R24 (detector). But no idea where next to go.

Having a business in music as such I passed this on to my electrician who has worked for us for about 30 years and is a magician in these things and he cannot see why it doesn’t work as its perfect to the schematic. He did add he doesn’t really see why you would get 10vac on the board at that point of a DC circuit but Im guessing its the oscillation that is the ac?

I dont have the codes handy but I used 47uH coils from radio spares in the UK.

Following the guides on bridging connections we get a hiss noise and bridging other connections that all disappears as the guide implies it would it just doesn’t seem like there’s any oscillation.

Anyone have any thoughts on this?

Thanks

Hello Lev,

When you say " I am seeing about 12vac on L1 I am seeing nothing 0vac on L5 and L6 and at last time I checked nothing on R24 (detector)" I wonder what you mean by "see" - as in, what are you using to look? - These HF circuits can be impossible to put a probe on - as soon as you do, everything changes.

I will leave it to others to comment - but I am in the UK and could give some hands-on help if you need.. See my avatar for contact details. I am moving away from on-line help.. The repository here on TW now covers probably the majority of common faults, and using the search feature one should be able to find almost every answer to almost every problem - IF you have the required understanding... If you dont have this understanding, a few hours of reading posts here and cross-referencing stuff you dont understand with other on-line resources should enable you to obtain it.

Which then just leaves the really unusual problems - And sorting these on-line or for those without the right test equipment is just too much effort for me - could solve the problem in 10 minutes "in the flesh" but spend several hours getting nowhere on the forum.

Fred.

When you say " I am seeing about 12vac on L1 I am seeing nothing 0vac on L5 and L6 and at last time I checked nothing on R24 (detector)" I wonder what you mean by "see" - as in, what are you using to look? - These HF circuits can be impossible to put a probe on - as soon as you do, everything changes.

Hi,

thanks for the reply.

I'm afraid it was a mild exaggeration as until today i have been doing a stage show in the midlands. When I got back to my shop my electrician put it back on my desk and said he took it home to his workshop for the last 10 days and it was his words that were "I went over all the tests on your sheets and although there is 10vac on l1 there isnt on l5 or 6 and I don’t see how there would ever be"

So that wasn’t me that could "see" it so I’m not sure how it tested it, although in fairness why would it be a test criteria if you couldn’t measure it?

At the moment its a side project between the guitar and amp work I do. If your happy for me to maybe drop you and email as in your avatar sometime that would be great. I certainly know and appreciate what you mean by the difficultly with online help.

Thanks

In this thread http://thereminworld.com/Forums/T/29565/oscillators-tunning?last=True I did an exhaustive description of the whole volume section of the EW/EWS Theremins on page 2 postings n°18 and 19. This should help debugging everything on the volume side.

"why would it be a test criteria if you couldn’t measure it?"

Back in the days when that article was written - (the days when most electronics hobbyists had a better understanding of electronics than many of our present "engineers" whose focus is so narrowly on one specific aspect of this huge field, that some couldn't even comprehend what goes on in a simple analogue circuit...) articles were written for these hobbyists.

In those days, people knew that you couldn't put (say) a 10pF scope probe onto a circuit point where a change of a few pF would shift the frequency hugely - Ok, that's an extreme case.. But people did understand, and authors didn't need to spell out every minutia of detail... Oh, they would tell you if you needed a VTVM rather than a bog standard meter... But assumed you knew that you needed to take the loading of your instruments into account.. Hobbyists had a wide range of different test kit with different specifications, often home-built.. It would have been impossible to say "if you've have a 20k ohm/V meter, you will see 12VaC, but if you've only got a 1k/V you could damage the transistor..." There were just too many variables

They ran series continually, explaining the basics.. But projects like the EM theremin weren't for beginners - they weren't for those who could just build a circuit to a schematic.. They were for those who first read the article, who understood, and who knew they were capable of building and debugging, and that they had the kit needed to do so.

But electronics has become a sort of glorified Lego Technic these days - People think that if they see an inductor symbol in a schematic, and stick an inductor somewhere on the circuit board, if correctly wired it should work..

They don't notice little details - like the fact that the inductor is part of a transformer.... They could never have understood even the remotest basics of how the circuit should work - But they build it and expect it to!

IMO, anyone who has no idea at all about how the circuit they plan to build actually works, shouldnt even think about building it!

Fred.

Sorry if the above sounds gruff - its not specifically targeting anyone... But so often one jumps in to help a person who seems interested - spend a lot of time and takes a lot of care in the reply (as Thierry did in the post linked above) - and the person on whom all this effort was expended doesnt even have the manners to say thanks - they just vanish..

So I now want to let people know that real effort goes into technical replies - and help from me will only come if I see some effort from the enquirer.

Thanks Thierry I will have a good read through that hopefully tomorrow.

FredM: Yeah I do understand that help on these levels is a two way process and you have to put in the work yourself to get the results. I was mearly questioning to understand. As I say my electrician has had mine for the last 10 or so days and as he is an 80 year old guy who has worked all his life on analogue circuits, valve tv systems etc I would trust him to be the type of person who would know about loading and measuring circuits. I shall have a ready though the provided link above next and see if I cant come up with a few more answers or thoughts next.

I apreciate the replies from all of course.

Thanks

"As I say my electrician has had mine for the last 10 or so days and as he is an 80 year old guy who has worked all his life on analogue circuits, valve tv systems etc "

Sorry Lev -

I wasn't specifically targeting you..

Also, the term "electrician" to me refers to people who wire up low frequency power outlets and the like - not those who work with electronic circuits that include anything more than loads or ballasts or things like that.

I go OTT sometimes, sorry!

ps .. my email is down - should be back within 48 hours, but anyone emailing me may get a delivery failure message.. Haven't determined exactly where the problem is, but think its my ISP (has happened before)

Fred.

Hi,

No problem at all, I get similar things all the time through my own work.

I guess as I never deal with low freq power in my work I always just referred to my tech guys as electricians without thinking its confusing as to what they work in. Rest assured they are all only the kind who work with this kind of thing and most are analogue only.

I did consult the guy who looked over it regarding how he measured the ac on l1,l5 and l6 he said his meter and scopes are high resistance so shouldn’t effect the circuit in such a way and doesn’t seem to on L1 where he measured 12vac

He has dropped off some hand written schematics he had from the 70's for other versions some using am radios and others not that I might look into. Just not until I have finished this one.

Thanks

Hope your email sorts itself out soon anyways, if I have no look with the other pages on here I may pick your brains over that if you don’t mind.

Just thought I best post I had a bit of a eureka moment.

Found that I was getting 2.6v on Q5 not -2.6v and a quick rewire put that right and suddenly I was getting about 17vac on L5 and L6. So I popped it into an amp and low and behold it works! So sorry for wasting peoples time a little I felt sure it wasn’t something obvious I missed as both myself and my electrician spent so much time on it but I guess we fell into a woods for the trees moment and couldn’t see a fault that was clear in front of us.

The range is still awful as it happens all the in the last inch but that’s all down to tuning and my bad choices for antenna I guess. Volume still doesn’t work but that’s something to look at now there’s a sound.

I do appreciate all your time and help even though it was my own fault in the first place.

Many thanks