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Old 1st September 2011, 12:58 PM   #221
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OK, I have disabled soft clipping, and overdriven to saturation and latchup.
You can see the active tail can and will rescue from the latched condition,
but only seems able to achieve this over half the input cycle. Better than
having to pull the plug and start over, I suppose....

While this was going on, the output looked a fully clipped squarewave, just
as you would expect from normal clipping. Output phase not reversed or
anything weird that would alert the listener to the temporary latch...
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Last edited by kenpeter; 1st September 2011 at 01:05 PM.
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Old 1st September 2011, 02:06 PM   #222
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Here's what I got so far.
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Old 1st September 2011, 02:14 PM   #223
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Quote:
Originally Posted by kenpeter View Post
Here's what I got so far.
If you include the .ic, the circuit remains stuck.

This means that in practice it will, that's why clipping schottky's are indispensable.
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Old 1st September 2011, 06:30 PM   #224
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Exactly what is this .ic thing are you including?
I thought you just meant measure collector current?

Last edited by kenpeter; 1st September 2011 at 06:32 PM.
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Old 1st September 2011, 08:34 PM   #225
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Quote:
Originally Posted by kenpeter View Post
Exactly what is this .ic thing are you including?
I thought you just meant measure collector current?
It is an initial condition.
By default, the simulator makes no assumptions about the initial voltages of any node (except for ground and where there are voltages sources with Rs=0).

By specifying an ic, you can force force an initial current into an inductor, or a voltage at one or more node, either to make the sim converge more quickly, or to test the effect of some condition or event.

Here the base of Q2 is n(008) (generally a good idea to rename it to avoid name changes each time the circuit is modified).

I forced it to 2V to see how the circuit would recover after a transient event (typically power-on, or some sort of spike).
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Old 1st September 2011, 10:42 PM   #226
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And you are saying input diodes will rescue from 2A .ic?

I think between my soft clip, and active tail, I'm at least
as well protected against 2A suddenly and mysteriously
appearing in a circuit that normally conducts 3.25mA.

Negative resistance is only a dynamic slope. Even in the
worst latch, its not going to conduct more than 50 volts
into 1224.7ohms. 40ma worst cased, not 2A...

----

Wait, now its 2V, not 2A? I am completely confused...

You never answered my silly question about DIACs or
Tunnel Diodes, or basakwerdz oldskool 2n2222 negistors
as base stoppers in a negative resistance amplifier.
If regular resistors get inverted and make it less stable,
what happens with stoppers that are negative to begin?

Last edited by kenpeter; 1st September 2011 at 10:51 PM.
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Old 2nd September 2011, 12:46 AM   #227
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OK. I understand the 2V .ic now.

Active tail and soft clip discourage latch,
your limiting diodes definitely help too, but
nothing recovers a hard latch forced by .ic

Last edited by kenpeter; 2nd September 2011 at 12:58 AM.
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Old 2nd September 2011, 01:44 AM   #228
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An absurd experiment proved absurd... What was I thinking???

So I was wondering if I series x with another x, would -R's cancel?
And if both x' saturate in unison, reverse of reverse is no problem...

Doesn't latch anymore, but oscillates like mad...
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Old 2nd September 2011, 07:55 AM   #229
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Quote:
Originally Posted by kenpeter View Post
You never answered my silly question about DIACs or
Tunnel Diodes, or basakwerdz oldskool 2n2222 negistors
as base stoppers in a negative resistance amplifier.
If regular resistors get inverted and make it less stable,
what happens with stoppers that are negative to begin?
In theory it would be possible. In practice, it would be like jumping in the swimming pool to avoid the rain.
Diacs are not practicable anyway, they require ~30V to function, and they do not have a continuous characteristic with a defined negative slope, they mostly break down.
Tunnel diodes should be more suitable, but given their price, rarity, and the necessity to bias them very accurately, they are not practical either.


Quote:
Doesn't latch anymore, but oscillates like mad...
It is not caused by the diodes themselves, , it is just that the amplifier is marginally stable, and the .ic is sufficient to trigger oscillations when the amplifier recovers.
It is just a symptom of the marginal instability of the global loop.

This is confirmed by the apparition of oscillations when the amplifier is overdriven:
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Old 2nd September 2011, 12:27 PM   #230
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I observe no such oscillations in clipping until I add your Schottky diodes.
(0 1 1 K) (0 1.25 1K) (0 1.5 1K) (0 2 1K) (0 2.5 1K) all simulate fine.
2.5 moves us beyond soft clipping into genuine hard clipping
recovers a little weirdly from this, but still isn't oscillating.

Add your pair of BAT54, now anything over 1.25 oscillates in clipping.

-------

Diodes, what diodes? I was talking about an x stacked upon an x.
Yes, it oscillates... Too bad, since I was hoping it might avoid the
reversal in saturation issue by dubious "virtue?" of reversing twice.
I don't have any models for a real negative resistance diode.

Last edited by kenpeter; 2nd September 2011 at 12:52 PM.
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