Question on push-pull OT LEads

howe0168 · 2nd March 2012, 03:51 PM

OK, so this might be a dumb question but why does reversing the primary leads on a push pull output transformer drive an amp into parasitic oscillation? Looking at the basic transformer wiring schematic it appears be symmetrical? Is there a standard to know which lead has to go to the input side and which lead has to go to the side with negative feedback applied? thanks.

Osvaldo de Banfield · 2nd March 2012, 04:46 PM

Does the amplifier have negative feedforward from any secondary of the transformer? IF any, reverting input get it to positive FB, converting the amp in an oscillator.

DF96 · 2nd March 2012, 07:12 PM

This is not parasitic oscillation, but loop oscillation. Parasitic oscillation occurs within a single stage, typically the output although it could be an earlier stage. It is caused by parasitic components e.g. stray capacitance, lead inductance.

AJT · 3rd March 2012, 05:40 AM

secondary phasing is important, if you get it wrong, there will be oscillation, you get it right and you get the nfb working correctly.....it is a 50-50 chance you will get it right the first time....

2nd March 2012, 03:51 PM	#1
howe0168 diyAudio Member Join Date: Feb 2012	Question on push-pull OT LEads OK, so this might be a dumb question but why does reversing the primary leads on a push pull output transformer drive an amp into parasitic oscillation? Looking at the basic transformer wiring schematic it appears be symmetrical? Is there a standard to know which lead has to go to the input side and which lead has to go to the side with negative feedback applied? thanks.

2nd March 2012, 04:46 PM	#2
Osvaldo de Banfield diyAudio Member Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina	Does the amplifier have negative feedforward from any secondary of the transformer? IF any, reverting input get it to positive FB, converting the amp in an oscillator. __________________ LW1DSE

3rd March 2012, 05:40 AM	#4
AJT diyAudio Moderator Join Date: May 2003 Location: Palatiw, Pasig City	secondary phasing is important, if you get it wrong, there will be oscillation, you get it right and you get the nfb working correctly.....it is a 50-50 chance you will get it right the first time.... __________________ http://www.elab.ph/forum/index.php?topic=32688.0

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2nd March 2012, 07:12 PM	#3
DF96 diyAudio Member Join Date: May 2007	This is not parasitic oscillation, but loop oscillation. Parasitic oscillation occurs within a single stage, typically the output although it could be an earlier stage. It is caused by parasitic components e.g. stray capacitance, lead inductance.

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