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Old 21st September 2012, 11:10 PM   #1021
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Dadod, you did not exclude the 100k resistor from your input impedance measurement, so the graph did not tell us anything.

This arrangement is extremely unstable. It as oscillating into saturation, hich is hy it did not ork. I got it stable by shaping the source impedance. It ill need some compensation netorks to eliminate the resonance and positive feedback. I haven't tried base stoppers.

Graph shos input impedance.
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Old 22nd September 2012, 12:16 AM   #1022
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The ALT key thing doesn't ork.
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Old 22nd September 2012, 12:30 AM   #1023
Krisfr is offline Krisfr  United States
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Quote:
Originally Posted by keantoken View Post
The ALT key thing doesn't ork.
Try turning on your num lock key
Hold the ALT down the whole time you are striking the num on the keyboard let the ALT key go AFTER you hit the 9
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Old 22nd September 2012, 02:26 AM   #1024
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Still doesn't ork. I'm on Linux, maybe that has something to do ith it.

Dadod, you didn't exclude the 100k input resistor in your input impedance graph, so it didn't tell us anything.

This circuit is extremely unstable. Because of this it ould oscillate into saturation and ould appear to not orking. I stopped the oscillation by shaping the source impedance, but the circuit ill need some compensation netorks to eliminate the resonance and positive feedback. One concern ith this circuit is that the drivers have very lo Vce - I don't kno hether it ill ork okay in real life since the models don't have quasi-saturation.

The graph shos input impedance.
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Old 22nd September 2012, 05:31 AM   #1025
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Originally Posted by keantoken View Post
Dadod, you did not exclude the 100k resistor from your input impedance measurement, so the graph did not tell us anything.
Oh, I am sorry, I totall forgot that it is there.
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Old 22nd September 2012, 06:06 AM   #1026
dadod is offline dadod  Croatia
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With the predrivers base stoppers of 10 ohm it gets much better, 33 ohm or higher provoke terrible distortion.
Sorry Edmond for this intrusion.
dado
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Old 22nd September 2012, 07:37 AM   #1027
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Old 22nd September 2012, 07:22 PM   #1028
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Still doesn't ork Andre.

I ould not go above 2.2R base stoppers for the outputs, that is simply my preference, but I did find this helped oscillation somehat.

There is still something strange ith your input impedance chart. Check that the Ie (not emitter resistors!) of your outputs is 100mA.
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Old 22nd September 2012, 07:45 PM   #1029
dadod is offline dadod  Croatia
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Originally Posted by keantoken View Post
Still doesn't ork Andre.

I ould not go above 2.2R base stoppers for the outputs, that is simply my preference, but I did find this helped oscillation somehat.

There is still something strange ith your input impedance chart. Check that the Ie (not emitter resistors!) of your outputs is 100mA.
I used 10 ohm base stoppers for predrivers not for the output.
It is 100mA for the output transistors not emitter resistors. I have put this OPS together with my input stage in an amp (simulation) and it does not oscillate but behaves very strange. I switched back to my previous OPS and it is OK with it, no oscillation and it works quite OK.
dado
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Old 22nd September 2012, 10:11 PM   #1030
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Your output frequency response still indicates that your circuit is oscillating (upturned phase). In a real amp it may ork because the output stage has a high source impedance, but it ill still have the resonance and positive feedback problems hich ill limit it's stability.

This is another example of one of those circuits people tend to dismiss as impossible because they don't kno of any ay to stabilize them... An RC snubber in just the right place can do amazing things. Try this Dadod.

Also notice I rearranged the circuit a bit. It provides the same benefits, but this time the RF current loops are smaller and less convoluted. I like this arrangement better.
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