Etherwave component help

Posted: 1/16/2012 9:30:34 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

There is no directly visible effect.

The buffer stage makes sure that the supply voltage for the pitch and volume tuning potentiometers is very clean so that RF artifacts (which are modulated onto the power supply rails) don't come back to the oscillators via the tuning stage, thus preventing unwanted feedback, intermodulation, ghost tones etc. In my eyes it's like taking an umbrella along, even when it doesn't rain.

A second, more obvious effect is that thanks to the combination of the 2k2 resistor and the 100uF capacitor, there is a time delay of about 200ms which can reduce most of the "pop"s and "squeek"s during the power on or off phase.

Out of that there is no influence on the sound and the playbility of the instrument.

You can easily see if you have already this circuit or not: Open your Etherwave and look near the 10pin connector which goes to the front panel. If there is a transistor Q9, an electrolytic capacitor C33, a ceramic capacitor C34 and a resistor R41, your Etherwave has this buffer stage.

If newer models perform slightly better, it's not because of this buffer stage.

It's the improved circuit board layout starting with version 211C which gives less parasitic capacitance around the linearization coils. That makes the tone spacing in the high register somewhat wider and allows a more extreme tuning up to more than 4 octaves above middle C while older circuit boards allow only to go up to somewhat more than 3 octaves and this with a smaller tone spacing. The disadvantage of the newer layout is that the pitch field is more sensitive to the environment  and you can easily "overtune" the variable pitch oscillator, making the instrument first instable and then killing the oscillators' transistors due to a too high resonance current. That's why I don't stop telling people that touching L5 is strictly forbidden if they don't have the equipment to make sure that the resonance current will remain below the critical value.

Posted: 1/17/2012 8:37:30 AM
alrj

From: Belgium

Joined: 1/14/2012

Thank you so much for sharing your knowledge with us.

Even if it's only to avoid the "pops", this buffer stage seems worth implementing. Especially seeing how simple it is :)

Posted: 1/17/2012 11:42:47 AM
Thierry

From: Colmar, France

Joined: 12/31/2007

And here is the schematic:

EW negative supply buffer

Posted: 1/18/2012 1:55:03 AM
Jason

From: Sammamish, Washington

Joined: 2/13/2005

Cool, thanks for sharing this.  I smell some solder warming up in my garage in the near future!

Posted: 9/30/2012 12:59:11 PM
Blala

Joined: 9/30/2012

Hi! I am completely new to electronics, just some very basic knowledge, but i would like to learn by trying to build the EW theremin. I have found most of the parts, but i am not sure which fixed inductors i should order. Are these going to work?


http://gr.mouser.com/Search/ProductDetail.aspx?R=RLB1314-470KLvirtualkey65210000virtualkey652-RLB1314-470KL

http://gr.mouser.com/Search/ProductDetail.aspx?R=15223Cvirtualkey58010000virtualkey580-15223C


What is the difference between power, rf inductors and choke inductors? Also, is there and practical difference between using axial or radial inductors?

Posted: 9/30/2012 10:11:32 PM
FredM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

Hi Blala,

Those components you linked above are completely unsuitable.

See:
http://www.thereminworld.com/Forums/T/28594/antennas-antenna-coils-for-em-theremin

This question has been asked before: 1. What properties of antenna coils are essential exept for the inductance itself?

Answer: Low capacitance (High SRF .. SRF = Self Resonating Frequency)

see:

http://www.thereminworld.com/Forums/T/28568/coils-in-series-question

The coils I have used which work well are the Bourns/Miller 6300 series:
http://www.digikey.co.uk/product-detail/en/6306-RC/M10163-ND/1949387

Dont try to cut costs by going to cheaper inductors - the 6300 series is the minimum specification you can get away with, IMO.. Anything cheaper and you may as well not use an equalizing inductor.

I have linked to Digikey UK, as this is where I bought mine.. But I think Mouser and Farnell supply them, and Digikey is US based I believe.

IMO, series connecting lower inductance coils gives better performance - for example, if you need 30mH, using 6*5mH inductors in series is better than 3*10mH in series (provided they are placed so that they dont couple) - but whatever, IMO you need at least 3 of these inductors in series for best results.. for 30mH, having two 10mH in series closest to the oscillator, followed by two 5mH closest to the antenna works well.

Fred.

Another 'trick' is to connect at least one inductor directly to the antenna - as in, a short section of the inductor lead directly to the antenna mounting screw / terminal, with a (thin) wire from the other end to connect to the other inductors on the board.. this way the board capacitances are reduced by the low series capacitance of the final inductor/s.

Posted: 9/30/2012 10:34:16 PM
FredM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

"The disadvantage of the newer layout is that the pitch field is more sensitive to the environment  and you can easily "overtune" the variable pitch oscillator, making the instrument first instable and then killing the oscillators' transistors due to a too high resonance current" - Thierry

Facinating! - Why the hell didnt they change the damn transistors for ones with a bit more beef? - Zetex (and others) make transistors with equivalent / better spec, and much better current / dissipation spec, at only a few pennies more.

Fred

Posted: 10/1/2012 1:48:11 PM
Blala

Joined: 9/30/2012

Fred, thanks for the answer! But i was asking about the inductors L12, L13 and L14 in the EW schematic, i should have been more specific.

 

For the antenna coils i found these inductors from another topic:

http://gr.mouser.com/Search/ProductDetail.aspx?R=1535Bvirtualkey54600000virtualkey546-1535B

 

http://gr.mouser.com/Search/ProductDetail.aspx?R=6304-RCvirtualkey54200000virtualkey542-6304-RC

 

and the one you posted.

Posted: 10/2/2012 6:51:42 AM
FredM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

" L12, L13 and L14 in the EW schematic" - Blala

Hmmm - Have no idea what the value of these inductors are.. there are only 11 sequentially numbered inductors on any EW schematic I have seen..

Fred

Posted: 10/2/2012 9:58:06 AM
Blala

Joined: 9/30/2012

the schematic is from this article:

http://www.suonoelettronico.com/downloads/HotRodEtherwav.pdf

i thought that schematic was popular from what i 've seen from this forum :p

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