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Old 22nd Dec 2006, 10:43 pm   #1
adibrook
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Default The NoiseMachine prototype 1

Hi people. I havnt really been here for a while. Been busy.

My friend who likes synths and electronic music has been asking me for a while to make some kind of wierd analogue valve based sound producing/modefying equipment. His taste in music is even stranger than mine, with such genres as Power Noise. I dont claim to understand it myself....(yes...even I consider some music strange).

Basically, he asked me to make a device which will make ambiant noise. Not like a synth or anything, but just...umm...noise. So he can stand with it on stage, tweak all the dials and buttons, scream into a mic and, it turns out people actually listen to that . Dont ask me how it works but i'm pretty open to music genres. This particular genre only hurts my ears. But it seems people like it.

So anyway, i'v been trying out different oscillators and modulator arrangements, and i'v built a workign prototype of one stage of this machine.

http://img.photobucket.com/albums/v4...emachine-1.gif

There are two oscillators. A neon oscillator producing a low frequancy sweep wave, and a triode oscillator producing a higher frequancy sine.

The neon oscillator is pretty conventional i think. One of the pots controls its supply voltage and the other one controls anode current i think. With both pots used the device can produce some pretty whacky noises on its own. The pots mainley control the frequancy of it. This setup is very general, and most of the range of the pots is unused, and very prescise tweaking is needed. But its only a prototype.

The 2nd oscillator is a triode sine oscillator. I cant remember what this class of oscillator is called. I built it out of random parts. I'm not sure if this design is correct, but it does work in that it produces a sine wave. The tuning cap controls the frequancy. The 100k pot is there because i wasnt sure what resistor to put there. No resistor at all and it will consume too much current and probably overheat...and too much resistance and it doesnt oscillate. So i put in a pot, and i set it to the highest resistance possible to still sustain oscillation. The triode runs pretty cool. i havnt measure its anode current but nothign smokes and it runs cool so for now ill leave it.

Next stage is the mixer/modulator thing. I'v actually been thinking baout this for a while. What would happen if i used a frequancy changer for audio. So, instead of posting about it here i decided to just try it. It seems to work. When the neon oscillator is set to a pretty lowe frequancy and the triode produces a higher frequancy i think ot produces AM.

The only thign that concerns me is for some reason one of the grids of the ECH81 glows orange. You can see that as well as the heater, both grid support wires either side of the heater also glow. I'm not sure which grid it is...the valve seems to run under pretty much datasheet conditions, exept audio insted of RF. Only one grid glows, and the rest seem to be ok.

So...any opinoions?

In the actual full noise machine i want to really improve the neon osc, so for example the voltage pot is set up when its at minimum its just on starting voltage and when its on maximum its just before the voltage gets high enough for oscillations to stop. At the moment all this is covered by maybe 70 degrees of the pots swing. If the whole swing of the pot covers that area than finer control could be achieved. Also, the triode oscillator could be improved. I'm pretty sure the ECH81's on board triode can be used for that.

The final machine will have more oscillators and mixers.

My friend has herd the prototype so far as seems pretty pleased. I'm pretty sure he wont be able tog et sounds like that from digital equipment!

Last edited by adibrook; 22nd Dec 2006 at 10:50 pm. Reason: mistake in schematic
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Old 23rd Dec 2006, 3:35 am   #2
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Default Re: The NoiseMachine prototype 1

You genius!. I'd love to hear it. Digital sound effects are fine but they haven't got the same impact, it's weird.

Baz

Last edited by Paul Stenning; 23rd Dec 2006 at 3:10 pm. Reason: Language...
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Old 29th Dec 2006, 1:49 pm   #3
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Default Re: The NoiseMachine prototype 1

Adi, it's possible that the screen grid resistor (20K) is allowing too much current to flow. Try a 68K or thereabouts. If that doesn't work I'm not sure what is causing the grid to glow, but it's a bad sign. Why not use an ECC83 configured as a long tailed pair as your mixer, instead of an ECH81?

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Old 29th Dec 2006, 11:19 pm   #4
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Default Re: The NoiseMachine prototype 1

I thought it may be the screen grid, but then i thought that the ECH81 has two screen grids. If one is glowing than the other would show some kind of distress too...right?

I decided to try the ECH81 because for a while i'v wandered what would happen if you use one at audio.

I will try a higher screen resistor anyway. Maybe that is the problem.

thanks..
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Old 30th Dec 2006, 9:35 pm   #5
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Default Re: The NoiseMachine prototype 1

Are you sure it is the screen grid glowing? I once thought I had this problem and during my investigations, disconnected the screen grid supply resistor and the grid kept on glowing. It turned out that it was a reflection of the cathode on some of the grid wires!

Best thing to do is measure the current through the screen and check it is within the valve rating. I don't have that to hand but it can't be more than a few milliamps for one of these.


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Old 1st Jan 2007, 9:56 pm   #6
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Default Re: The NoiseMachine prototype 1

Ok...i replaced it with a 47K reistor and the grid is still glowing. Maybe youre right...it could just be the reflection of the cathode's glow.

Another good reason to develop the heptode idea is that battery radio heptodes work at low voltages and low currents.

I could try to come up with the modulator only by building a small inverter to knock 9v up to 90, and then an LM317 regulator for the filiement. Then the entire device could be powered from a 9V power supply, and will therefore be compatible with other effects easily because it can be connected to a normal 9v distribution line.
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Old 4th Jan 2007, 12:09 pm   #7
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Default Re: The NoiseMachine prototype 1

The ECH81 does make a great audio mixer. I've seen a classic design where it mixes treble and bass channels and the triode provides phase inversion. Great design Adi- you'll have to make some sound clips soon!
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Old 4th Jan 2007, 4:36 pm   #8
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Default Re: The NoiseMachine prototype 1

Working on that. The sine oscillator is being abit wierd. I htink the 100K pot needs to be changed to a fixed resistor, and the on-board triode of the ECH81 can be used for this oscillator.

The neon osc has allredy been refined abit too. now it goes from about 0.5Hz on one end of the pot to maybe 5KHz on the other. The 2nd pot has been replaced by a fixed 470K resistor.

As soon as i'v sorted out these problems, i'll get some sound clips of it.
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Old 5th Jan 2007, 11:26 am   #9
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Default Re: The NoiseMachine prototype 1

How does a neon oscillator work anyway- how did you come up with the design? I'm guessing that initaially the supply voltage is enough to start the neon, but the instant it starts conducting the voltage drop across the pot extinguishes it again- sound right? Must give a pretty high amplitude wave- but I'm guessing it's not a sine wave though?

So this ought to work with a gas regulator valve or even a zener diode too surely?

(I hope so 'cause I found a box of 90C1s and it'd be cool to have a gas tube tremolo on my next amp!)
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Old 5th Jan 2007, 5:16 pm   #10
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Default Re: The NoiseMachine prototype 1

Merlin
Not quite.
It charges the capacitor exponentially until voltage is such that the neon strikes - the current through the neon discharges the cap quickly so the neon extinguishes when the voltage is below the striking voltage.
This latter is the crux, and the reason it is able to oscillate.

The resulting waveform is a sawtooth.

You could not do it with a zener, but a thyratron, UJT or SCS or diac would work in a similar way.
Thermionic voltage regulators are neons, so would work.

It is quite an old idea. Bird organs used them as locked frequency dividers, and thyratrons were used for frame (sorry, field!) oscillators in TV. This was carried on using SCS or UJT in later TV timebases, notable the Philips G8. They also used the diac on the same principle in its power supply.

HTH
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Old 5th Jan 2007, 5:19 pm   #11
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Default Re: The NoiseMachine prototype 1

Quote:
Originally Posted by Mike Phelan View Post
It charges the capacitor exponentially until voltage is such that the neon strikes - the current through the neon discharges the cap quickly so the neon extinguishes when the voltage is below the striking voltage.
This latter is the crux, and the reason it is able to oscillate.
Mike, that's very close but you missed the vital point. The voltage needed to sustain a discharge is much lower than the striking voltage. If this was not true, the design wouldn't work very well. The neon extinguishes when the voltage is below the maintaining voltage.

I remember playing with neon oscillators when Iwas about 11. I used a B126 battery to make nice neon flashing lights. I also learnt the meaning of hysteresis.
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Old 5th Jan 2007, 5:29 pm   #12
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Default Re: The NoiseMachine prototype 1

Drifting off a bit here I think. However I used one when in an experimental oscilloscope as the timbase generator. I think the circuit was called a 'Neon Relaxation Oscillator'. I was about 15 at the time. Worked OK but I dont think it was much good for anything other than audio frequencies.

Like Jeffrey, I also made an array of flashing neons using a B126. Learnt a lot by doing things like that!



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Old 5th Jan 2007, 9:58 pm   #13
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Default Re: The NoiseMachine prototype 1

The posts relating to Ian Loveday's Soundbox have been moved to this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=13678
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Old 6th Jan 2007, 9:45 am   #14
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Default Re: The NoiseMachine prototype 1

Quote:
Originally Posted by ppppenguin View Post
Mike, that's very close but you missed the vital point. The voltage needed to sustain a discharge is much lower than the striking voltage. If this was not true, the design wouldn't work very well. The neon extinguishes when the voltage is below the maintaining voltage.

I remember playing with neon oscillators when Iwas about 11. I used a B126 battery to make nice neon flashing lights. I also learnt the meaning of hysteresis.
Thanks, Jeffrey - quite correct. When I read it now, I spotted I had used the word "striking" instead of "maintaining" when I was concentrating on the essential hysteresis/negative resistance effect which a zener does not have.

Blame it on having to replace hundreds of neons in Bird frequency dividers.
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Old 6th Jan 2007, 3:06 pm   #15
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Default Re: The NoiseMachine prototype 1

The neon i use in this design is a 0A3. I used a normal indicator bulb at first, but then switched to the 0A3 because it sounded slightly better in my opinion and is physically bigger more robust.
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Old 7th Jan 2007, 1:35 pm   #16
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Default Re: The NoiseMachine prototype 1

I managed to find a brief discussion of neon oscillators in an e-book. Finally a use for all these gas regulators!

I've been thinking, if you put in a resistor to slow down the discharge of the cap throught the neon, you should be able to get something that approximates a triangle wave yes?
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