Anybody do higher voltage negistors?

[earthtonesaudio]

Has anyone tried higher voltage (up to, maybe, 18VDC) in negistor circuits?  From what I've read about them, higher voltages will cause the transistor to start avalanching easier.  I'm thinking of building the Negistrem but using 2 batteries for a +18V supply.

I also have a list of "known to work" (from internet research) transistors... for those of us who don't have the "right" transistor to try.  Here ya go:

Negistor-worthy candidates:
bc546
bc549
bc337
2n2222
2n2222a
2n697
2n5088
2n2218
mps5172

Peace,
Alex

[John Lyons]

I tried hard to get this thing to work (well) and failed.
A friend who has more knowledge about this stuff tried it as well with poor results.
I got a very choppy trem but no clean (uneffected) signal so it's not very useful.
I think the fact that it's so simple and few parts makes it a Bitch to get it tuned in.
Granted I did not use the FETs listed in the schem!

The sound clips were nice so I really wanted to get this working better

I ran it at 9v and tried these BJTs.
2n2222
2N5088
2N3904
BC549

J201
2n5457
MPF102

I found ONE 2N5088 that would oscillate out of maybe 10 or more, all others listed would not osc.
I think the FET needs to be tested to get the correct amount of on/off action and possibly more dry signal.

I'm very interested to see what you find out. Where did you see the info about the voltage making the oscillation operate easier?

John

[~arph]

Mmm.. interesting.
All info I find so far apart from the negistrem schem seems to point to the 2N222A which is the metal can package.

Also it seems you can make it do sinewaves if you stick an inductor to ground on the output. I might try this with a simulated opamp inductor so I can play around with the values.
Could be hard because the inductor value probably needs to change with the oscillator freq. (dual pot?), I'm not that far into theory to predict all this without actually taking some time to think it over.

Some links:

Negistor sine:
http://jlnlabs.online.fr/cnr/negosc.htm

Simulated inductor
http://sound.westhost.com/dwopa.htm#inductor

[John Lyons]

Just to clarify, I was talking about Nordine's Negistrem (Tremolo).

Aren't all 2N2222 transistors metal can? Mine do not specify the "A" though...

John

[earthtonesaudio]

I'm very interested to see what you find out. Where did you see the info about the voltage making the oscillation operate easier?

The negistor, from what I can tell, operates by the fact that the reverse voltage causes the transistor to avalanche, which charges up the capacitor (at the RC time constant determined by the values of the current limiting resistor/rate control and the value of the charging cap). 

...You could do all this so far with a zener diode, but it would just charge the cap and then stay there, and there'd be no oscillation.  The reason the negistor oscillates is because of the shape of the conductance curve shown on the Keeleynet page (negative resistance a.k.a. conductance).  From zero volts there is no conduction, then at some voltage level you start to have conduction, and current flows.  Then as you increase the voltage in, the transistor actually starts to drop voltage, while the current keeps going up.  This is because the doping regions of the p-n junctions in the transistor start working as charge carriers... Uh, I think.  Hence, you have room-temperature super-conductivity, and a stupidly simple oscillator.

I too thought the Negistrem was awesome in its simplicity and decent sound.
If you go to the Keeley Net page, there's a nice scanned article at the bottom: http://www.keelynet.com/zpe/negistor.htm

The negistor oscillator works just like the old-tech neon bulb oscillator as noted here under fig. A: http://jlnlabs.online.fr/cnr/rb_ndr.html  ...well it doesn't actually work like it, but the result is similar (but at much lower voltages). 

The reason higher voltages should make it work more reliably is that a higher supply potential will give you more "oomph" to start the avalanching of the transistor.


...This is pretty crazy quantum physics stuff, from my point of view, and I like it.  Maybe higher voltages would take care of the finicky transistor selection problem.

So next part of this is the problem with the JFET being picky about device selection.  I'm a little unclear on what the JFET is doing, but I know that I'd like the negistor oscillator frequency to control gain of the output signal.  Is there a reason the JFET is biased that way in the Negistrem?  Couldn't you use an optocoupler or a voltage controlled resistance to vary the output volume? 

[John Lyons]

This is uncharted territory for me...I'll take a look at the articles linked.

I did get the oscilator to fire but the FET seemed to be the hard part.
The FET basically open and closes like a variable resistor.
WHen the FET is "on" the signal passes, then the oscillator turn off the FET making the tremolo sound. (Just thinking out loud here...)
The variable are the on signal the off region and with any luck the in between which would be the mix between the wet and dry.
I got a fully wet signal but nothing in between. I don't know what I'm doing here so I tried a few things with different caps etc but I got frustrated with it.

[~arph]

Just to clarify, I was talking about Nordine's Negistrem (Tremolo).

That was clear 

Aren't all 2N2222 transistors metal can? Mine do not specify the "A" though...

No, I have some non metal can transistors and I just ordered the metal can version to experiment with this, but I do see that the A does not specify the package since there are 2N2222A non metal can ones too.

See:  http://www.newtone-online.nl/catalog/index.php?cPath=31_32
It's in dutch but at the top of the page you see the non metal can version and the metal can one is below it.

[earthtonesaudio]

I'm going to breadboard the negistor oscillator tonight.  (For the first time... yes I know I talk a big game  )

I'm going to try a couple different things to make a "better" Negistrem. 

First, I'll see if the negistor will make an LED pulser.  If it does, I'll see if it does well as a optocoupler type circuit.  I'm kinda hoping this will work well, as it would apply to other types of circuits as well... huge potential.

Second: I'll try a more standard "JFET as voltage-controlled resistor" circuit like this one:

(source is from this page: http://www.nrgrecording.de/html/how_it_works.html)  I'm not sure if this will work though, since the C.V. is referenced to ground.

I'm also going to try some germanium transistors.  I know the literature says they won't work, but darn it, they should work better!  Their lower breakdown voltages ought to make them perfect candidates... Anyway I intend to find out.  Basically I'm trying make the negistor more repeatable.  To me, if something works with only 1 out of 20 transistors, there's a design problem somewhere.

[earthtonesaudio]

Woo, neato:
Opamp-based negistor (they call it a negatron), plus a proximity sensor type thing:
http://www.edn.com/article/CA231573.html?industryid=2281?text=negatron#ref

[earthtonesaudio]

Update:

I tried Hemmo's simple negistor oscillator (from the moosapotamus site) and... wait for it...
EVERY SINGLE ONE 
of my 2n2222a's worked.  And so did some BC337's

Well, when I say they "worked," I mean they produced an oscillator... but the output is very... um, spikey.  At low frequencies (tremolo freq's) it's more like PULSE... silence... PULSE... silence, etc.  I haven't tried the full Negistrem circuit, but I have a feeling there needs to be something in there to smooth it out.

I'll try the sinewave version and some more transistors tomorrow.

[earthtonesaudio]

Update:
The size of the first cap (from E to C/Ground) has a big effect on the time constant (duh) but so does the transistor selection.  Some of the 2n2222a's didn't go as slow as one of them. 

Also, the larger the resistance between the +V and the emitter, the slower the rate. 

D'oh moment: the Negistrem has a "tone" control built in (the pot with the wiper connected to a pot to ground) already.  Why didn't I see that before?  Great way of changing the output waveform, rolling off harmonics.  But if you make that cap large (up to 1/2 of the C1 value) it starts to affect frequency.

[earthtonesaudio]

Update:
For the FET in the Negistrem/Negistron, a J113 will also work.  I have a feeling any JFET that is designed for "low level analog switching, sample and hold circuits and chopper stabilized amplifiers" will work (from the Fairchild datasheet).  All the F113's I tried (4 or 5) worked reasonably well.

Next I'm going to try this with a transformer coupled JFET, for sinewave action.

...And I gotta say it's thrilling to have any sort of tremolo from so few parts.  Thanks Nordine!

[~arph]

Good to hear on your progress. I tried this over the weekend with various BJT's  (pn2222a, non metal can, 2N5088 and some 2N3904's) a total of about twenty transistors.

I got no oscillation action going at all. So I'm a bit disappointed, but I have some metal can 2n2222a's on the way. Btw, I figuered out that my non metalcan 2n2222a's are actually: PN2222A transistors.

I'm interested in the inductor results.

[earthtonesaudio]

Glad you're working on this as well, arph.  I'll try to document my results with higher voltages, transistor selection, and inductors as soon as I get my adjustable power supply up and running.

Maybe I just have a good batch of transistors, but I was surprised how many of them worked.  Keep on truckin, we'll get there.

[dano12]

For what its worth, every one of my 2n2222 metal cans worked in the negistor arrangement. Also worked great with the tri-negistor schematic.

[earthtonesaudio]

Update:

Tried the circuit with some of the inductors I have lying around.  Not too spectacular... sounds the same with the inductor shorted, but I don't know much about what values to use here... one page says 5µHenries, but that's for a 60Hz oscillator.  Not sure what value would be good for LFO speeds, if any.

Several other transistors will kinda work for Q2 in the Negistrem.  It's just a voltage controlled attenuator, so no big deal.

It's heat-sensitive.  Speed varies with heat on Q1. 

[~arph]

Update:

Tried the circuit with some of the inductors I have lying around.  Not too spectacular... sounds the same with the inductor shorted, but I don't know much about what values to use here... one page says 5µHenries, but that's for a 60Hz oscillator.  Not sure what value would be good for LFO speeds, if any.

Mmm..I think it requires careful tuning, too bad I don't own a oscilloscope. Maybe you can try it with the simulated inductor I posted.This way you can experiment with an endless supply of L values. I will do the same thing when I get the oscillator to fire up. (expecting components today)

It's heat-sensitive.  Speed varies with heat on Q1. 

Yeah I thought that would be the case, probably another reason why we don't see this application more. In another forum someone pointed out the Vox Repeat Percussion

[earthtonesaudio]

Tonight I'm going to do a little research on what inductor values would be needed for LFO speeds.  I'm guessing quite large, so while I'm at it, I'm going to try using the transformer from an AC to AC adapter I have lying around.

After that I will bite the bullet and try your inductor simulator.  I actually do have a scope, I just haven't made a breadboard-to-coax connector yet.  I'll have to get on it.

[earthtonesaudio]

Update:
Neither the primary or secondary side of a 117 to 15 volt AC transformer made any (audible) difference with the Negistrem.

I will try the gyrator circuit.  Jack already did a bit of work for me here: http://www.muzique.com/lab/gyrator.htm

One side note: if you hook up a real transformer, you can get LEDs to light up by connecting one end to the negistor and the other end to anode and cathode.  I think they pulse out of phase with each other, but they were dim so who knows.  Could be useful for someone doing something more complicated, maybe like a LED/LDR panning tremolo, or similar.