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Further to the thread below about the DC path to ground and the influence of its resistance on the AC behavior of the amp (especially the Coupling Cap and Grid Choke combination before the driver), I now added the bias supply in the simulation (above).
When doing an AC analysis on this, the AC behavior is completely different (compared to the version without the bias supply posted earlier).
It seems response is highly dependent on the Series Resistance of V7. In the simulation it's now set to 1meg, giving the result above.
These 'odd' results I always get are the reason I always maintain separate versions for AC and for Transient simulations. For some reasons my model of the power transfomers always seem to screw up AC analysis.
(by 'odd' I mean the 'dip' in the response around the very 'suspicious' frequency value of 100Hz).
Please help.
NC
Follow Ups:
Is the voltage source for the bias supply also sweeping?
look at the waveform of the CT of the bias transformer seconday
dave
The response on the CT is this...
I almost never combine power supplies and amplifier circuitry in one model. I sim the supplies separately to verify their operation, then I substitute simple voltage sources with their "AC amplitude" blank or zero in order to power the active circuitry. If the goal is to determine how the amplifier interacts with the bias supply, simplify it first. Drive the two last filter components in the bias supply with a negative voltage source. Avoid installing more than one AC source unless absolutely necessary.
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Edits: 11/14/14
But its tedious and should actually not be needed,
NC
FWIW... the ac voltages in spice are all peak so the 230V on tour bias supply primary is actually 161Vrms.
dave
Yes, correct... I keep forgetting that.
Thanks.
NC
The series resistance of the mains power source is very low and typically omitted from the simulation.
Edits: 11/15/14
Try modeling the bias supply as a simple Full Wave Bridge with the positive side grounded and the negative side supplying the negative bias and the center tap floating. Use 500uf - 5K - 500uf - 5K - 500uf as the filter, (bin the 20H choke for now). See if that takes care of the weirdness.
"It seems response is highly dependent on the Series Resistance of V7. In the simulation it's now set to 1meg, giving the result above."Is this a typo? Why would you have a 1M series resistance for the mains voltage source?
Edits: 11/14/14
With that value the response is more or less resembling would I would expect.
Choosing another value make the response only look more odd.
Do you have a suggestion for the value?
I would think an impedance of zero would be closer to reality but then I don't understand how spice works.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
This result :-/
NC
Are we still looking at the same simulation? Why is the gain so much higher than the one you posted eariler? I did a quick sim and could not duplicate your results, i.e., the AC response looked pretty normal to me...
Edits: 11/16/14
Someone smarter than me will have to explain that one.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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