Interstage coupling feedback

Ronken · 16th January 2012, 09:37 PM

Hi folks,
in an interstage coupled two stage tube amp, which kind of negative feedback can be applied? I read that a feedback loop from anode of the second tube to the cathode of the first tube has to be avoided as it is a loop wraped around a transformer coupled stage. So which feedback is to be prefered as the above mentioned often sounds good with cap coupling and is practical.
Thanks, Uwe

pieter t · 16th January 2012, 10:11 PM

When the interstage transformer is a good one, with good low and high frequency bandwidth (which is not that difficult to achieve with a 1:1 type), I see no problems applying a feedback loop as phase shifts will be minimal.
You can sooner expect problems with a feedback loop from amplifier output (after the output transformer) back into the amplifier circuit as phase shifts will be larger.

Ronken · 17th January 2012, 07:36 PM

Thanks, Pieter.

16th January 2012, 09:37 PM	#1
Ronken diyAudio Member Join Date: Nov 2011	Interstage coupling feedback Hi folks, in an interstage coupled two stage tube amp, which kind of negative feedback can be applied? I read that a feedback loop from anode of the second tube to the cathode of the first tube has to be avoided as it is a loop wraped around a transformer coupled stage. So which feedback is to be prefered as the above mentioned often sounds good with cap coupling and is practical. Thanks, Uwe

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16th January 2012, 10:11 PM	#2
pieter t Account disabled at member's request Join Date: Apr 2009	When the interstage transformer is a good one, with good low and high frequency bandwidth (which is not that difficult to achieve with a 1:1 type), I see no problems applying a feedback loop as phase shifts will be minimal. You can sooner expect problems with a feedback loop from amplifier output (after the output transformer) back into the amplifier circuit as phase shifts will be larger.

17th January 2012, 07:36 PM	#3
Ronken diyAudio Member Join Date: Nov 2011	Thanks, Pieter.