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LTSPICE HELP! strange simulation results
LTSPICE HELP! strange simulation results
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Old 20th November 2019, 09:07 AM   #1
cucicu is offline cucicu  Italy
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Default LTSPICE HELP! strange simulation results

Hi at all, I have a strange problem with LTSPICE when simulating a sugden a48mk2 amplifier.
I attach the simulation file for someone who wanna have a look at.
the problem is that changing R24 (bias adjustement) or R11 (sets the mid voltage point on the positive side of the output capacitor C1), sim gets slow or gives some thick lines as sinusoidal curve.
hope someone can explain what's going on.
thank you all.
regards
Attached Files
File Type: asc SUGDEN a48mkii.asc (7.4 KB, 10 views)
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Old 21st November 2019, 11:17 AM   #2
bordodynov is offline bordodynov  Belarus
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You're not seeing stability. I.e. oscillation at megahertz frequency is observed. I have added a resistor for stability.
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File Type: asc SUGDEN a48mkii_AB.asc (7.5 KB, 8 views)
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Old 21st November 2019, 11:24 AM   #3
Mooly is offline Mooly  United Kingdom
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LTSPICE HELP! strange simulation results
The simulation seems very model specific, it runs OK using 2N5550 and 2N5401 default models and TIP41/42C as outputs.
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Old 21st November 2019, 11:36 AM   #4
cucicu is offline cucicu  Italy
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Thanks for the reply. My scope is noto so good, it measures just to 200khz so I can't see that oscillation if it is in the Mhz range.
I attach the simulation, removing your resistor and replacing C2 from 470pF to 1000pF because I have not the place in the pcb to add that resistor. It seems to block the oscillation the same way than the resistor. Could it be also a good solution?
thanks a lot
BR
Attached Files
File Type: asc SUGDEN a48mkii_ABC.asc (7.7 KB, 5 views)
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Old 21st November 2019, 12:04 PM   #5
cucicu is offline cucicu  Italy
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Quote:
Originally Posted by Mooly View Post
The simulation seems very model specific, it runs OK using 2N5550 and 2N5401 default models and TIP41/42C as outputs.

Sure it is! Tip41 has an ft of 3Mhz, 2sc from Toshiba have 70Mhz...so this could explain the reason...?
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