Building EM Theremin / rebuilding EtherWave circuit

Hi Thierry & FredM,

I'm sorry that my thread & my questions result in differences between both of you. I appreciate all of your help and I hope this will not lead to disrespect between you (sorry for that bad english).

[i]As far as I can see, it's not possible to connect the circuit directly to a PC or something like that, because the audio signal is separated from the volume circuit. is this correct?[/i]
[b]Thierry:[/b][i]If you really MUST go into the PC (why ?)...[/i]
[b]FredM:[/b][i]I do not really understand what you want to do..[/i]
PC is currently my only audio IO device :)
I don't have any amplifiers or something else yet...

[i]The AUDIO-OUT from the VCA (via R33 and the filter / attenuator C26 and R34) is nominally at line level, and the amplitude of this signal is controlled by the volume antenna.[/i]
Ah, understanding of the circuit has grown again: The volume output (VCA_OUT on pin 2 of expansion connector) affect the amplifier bias of U3A and therefore the volume is also included on the audio signal, isn't it?

I apologize if my questions are noob-like, but usually I don't get into contact with analog circuits, it's mainly digital and microcontrollers :)

Regards,

Scotty

Scotty, you are right: The output signal at the line output is naturally volume controlled by the VCA (sorry that I didn't understand your question, for me it was self-understanding that a theremin with a volume circuit would control its own output)

[i]"Ah, understanding of the circuit has grown again: The volume output (VCA_OUT on pin 2 of expansion connector) affect the amplifier bias of U3A and therefore the volume is also included on the audio signal, isn't it?" - Scotty[/i]

Yes - You got it! ;-) ..

[i]"I apologize if my questions are noob-like, but usually I don't get into contact with analog circuits, it's mainly digital and microcontrollers :)" - Scotty [/i]

No need to appologise! The way the schematic is drawn does make it difficult to understand (If I had a technician on my team who drew a schematic like that, I would make them re-draft it.. U3B should (in my opinion) be placed somewhere which makes the the control / signal paths clearer)

Thierry - I am going to delete my last posting.. Lets try to be friends, and be less sensitive about things which are probably just misunderstandings. I respect you, and I know you respect me - So let us both try to remember this whenever we feel we are being "got at" ! :-)

Hi Thierry & FredM,

[b]Thierry:[/b][i]The output signal at the line output is naturally volume controlled by the VCA (sorry that I didn't understand your question, for me it was self-understanding that a theremin with a volume circuit would control its own output)[/i]
Yes, it [b]is[/b] clear to me that the output volume should be controlled by the volume circuit :)
But first I saw no dependance between U3A and U3B, and I read signal paths usually from left to right ;)
But by reading datasheet, etc. it's getting more clearly to me :)

[b]FredM:[/b][i]The way the schematic is drawn does make it difficult to understand (If I had a technician on my team who drew a schematic like that, I would make them re-draft it.. U3B should (in my opinion) be placed somewhere which makes the the control / signal paths clearer)[/i]
Yes, at least some notices on the schematic would be fine.
I oriented my schematic on the original EW schematic, to control if I've captured it correctly. I think I will use more than one sheet for the schematic, enabling me to set some notices, arrows, etc. to document the circuit.

Regards,

Scotty

Hi,

schematic capture is finished, and I began to place the components on the PCB layout, using the component orientation/placement as shown in the hot rodding article. But I've found some inconsistency.

Capacitors C10 & C11 are shown as non-polarized in the schematic, but appear polarized on the component layout of the hot rodding article.
So, are they polarized or not?

That's confusing, because I don't know if used the correct footprint. Can anyone post a photo of the board? This would help much!
By comparing against the schematic of the EM Theremin, I [b]assume[/b] the component layout picture is taken from a earlier version of the schematic, because there were polarized capacitors used.

And I wonder if I could use a vertical footprint for the antenna coils to save space. Or would this result in trouble?

Regards,

Scotty

I'd prefer non-polarized capacitors for C10 and C11 since they are only 0.47uF.

And keep the linearization coils horizontal in order to avoid coupling and interferences. The best would be, if you use the 3-coils solution as in newer Etherwaves, to place them perpendicular. That means that the first coil comes in the place of L1 (L7) and the third in place of L4 (L10). The second should be placed in a 90° angle across the position of L2 and L3 (L8 and L9).

This solution with three 3-pi wound coils in a
| -- | position is responsible for the improved linearity of newest Etherwaves.