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Re: How to make a Voltage Controlled Oscillator



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Been there, done that. That NE schematic sucks unless you use a
thyratron designed to work that way; or add a thyristor so the NE lamp
latches it into the open state.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com








Re: How to make a Voltage Controlled Oscillator
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Thyratron has variable breakdown (when grid is biased to the "linear"
region), but it's just as noisy as the neon.  They make bad sweeps, but
they're easy to synchronize thanks to the gain.

They do tend to discharge the capacitor more completely, for a wider range
of capacitances.  Neons tend to turn off in the 20-60V range, lower for
bigger C (~1uF makes bright blue-orange flashes :) ).

How do you "latch it into the open state"?

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms



Re: How to make a Voltage Controlled Oscillator



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Connect the lamp to the gate of the thyristor, discharge the cap through
the thyristor. That solves the turn off problem, especially as the
thyristor hold current is much higher then that of a lamp.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Re: How to make a Voltage Controlled Oscillator

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Two components plus a high voltage power supply and shielding :)

Re: How to make a Voltage Controlled Oscillator
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Fun,  I'll have to bread board it.

George H.

Re: How to make a Voltage Controlled Oscillator

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Square wave or sawtooth is fine. This is for a chiptune synthesizer.

Re: How to make a Voltage Controlled Oscillator

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Tuning range?  (fmin...fmax)
        
                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: How to make a Voltage Controlled Oscillator

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About hearing range. 30hz - 16khz would do.

Re: How to make a Voltage Controlled Oscillator
Cem Uzunoglu:

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You can't hear notes that high. 66 Hz - 5 kHz will do.

Re: How to make a Voltage Controlled Oscillator

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Well, believe it or not I do. My phone's ringtone is a 10khz pulsed sine
wave.
In fact I just checked with a frequency generator patch on my PC, I was
still hearing about 16khz, then it fell down quite fast after that. It
can be that my hearing curve comes to and abrupt end there, or the nyquist
effect from  my 44.1khz sampling rate sound card kills it.

But I admit many people don't hear >8khz and it is musically m00t. So
let's say 8khz.

Re: How to make a Voltage Controlled Oscillator
Cem Uzunoglu:

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I believe what you say, I just don't believe that what you're hearing is 10
kHz, unless, by "hearing", you mean "feeling a weird, rather unpleasant
noise".

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In my first job I drew the PCB for a graphic terminal, but my most
appreciated ability was to spot immediately if the newly programmed synch
generator was working within the CRT's specs.

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Let's say 4186 Hz.

--
Saluti

Re: How to make a Voltage Controlled Oscillator

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4186 Hz it is then. I can't say no to you after all that :)

Re: How to make a Voltage Controlled Oscillator
Cem Uzunoglu:

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:)

Re: How to make a Voltage Controlled Oscillator
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Most healthy adults can hear upto at least 12kHz pure sinewave. Some
younger children can hear nearly 20kHz. As a youngster I recall hearing
an annoying whistle from the line flyback transformer on some TVs
(presumably the ones with something loose). That is around 15k6Hz. I can
still just about hear pipestrelle bats calls - though presumably only
sidebands off their chirp since the fundamental is ~45kHz.

I had the opportunity to to test a moderate sized audience with a pure
sine wave pulsed and the kiddies hands started going up at 18kHz last
year. I could hear it at 14kHz and most adults were around 10-12kHz. A
few elderly folk still couldn't hear 5kHz but by then it was getting
annoyingly loud for the rest.
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C8 is just the pianos highest note. Nothing special about that and most
people can easily hear it. It won't sound much like a piano note though
unless you include at least the third harmonic. There is something
seriously wrong with your hearing if you cannot hear 4kHz.

I set my Theremin up to do 50Hz-10kHz which covers the range most useful
for its ethereal style weird music. Linearising hand movement for
logarithmic frequency control was a nightmare. The Dr Who theme is
harder to play than it sounds as is Good Vibrations.

People may not hear higher frequencies distinctly, but that doesn't
prevent other parts of the ear detecting the sharper rise time. You can
squeeze intelligible speach over a very limited bandwidth, but it
actually takes skill to get broadcast quality high fidelity audio right.
UK DAB radio has failed in this respect at least for classical music.

Regards,
Martin Brown

Re: How to make a Voltage Controlled Oscillator
Martin Brown:

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Exactly. What is the frequency of the third armonic of C8?
16744 Hz, that, according to you, lies outside the range of most adults and
is anyway rather near the Nyquist frequency of a CD.

--
Saluti

Re: How to make a Voltage Controlled Oscillator
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Could be a linguistic thing here but in English the second harmonic is
2f and the third is 3f or around 12k5Hz which is borderline for many
adults and probably why the piano keyboard stops where it does.

According to you the alias from 16744Hz sampled at 44k01 for CD at
5376Hz is still above the range of human hearing. This is obvious
nonsense unless you were a roadie for loud heavy metal rock bands or
work in a boiler making shop.

Regards,
Martin Brown

Re: How to make a Voltage Controlled Oscillator
Martin Brown:

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Right, I said "harmonic" and calculated the octave.

The point is that Cem would like to build a Moog-style synthesizer, and
there is little reason to complicate the VCO in order to produce notes that
are outside a piano keyboard. All the further shaping of the fundamental
note he's going to produce is very likely to be useless, at such high
frequiencies.
 
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I'm not sure I understood what you mean.

Re: How to make a Voltage Controlled Oscillator
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It depends on age. When I was young I could hear the 15.625kHz whine
from TV sets (line frequency). It stopped irriatating me sometime in
my twenties.

http://en.wikipedia.org/wiki/Presbycusis

--
Bill Sloman, Nijmegen

Re: How to make a Voltage Controlled Oscillator
Ken S. Tucker:

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I hope so. :D

--
Saluti

Re: How to make a Voltage Controlled Oscillator
On Wed, 27 Oct 2010 02:24:03 +0200, "F. Bertolazzi"

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I have a _severe_ drop-off above 2kHz... mostly affecting movie and TV
watching right now.  Ordinary conversation I don't seem to have much
trouble.
        
                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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