Audio transformer feedback loop

Ronken · 15th January 2012, 01:05 AM

Hello forum,
planning for a phone preamp and having not seen such a circuit so I have to ask one question:
Is it possible to connect the negative RIAA feedback in a two stage phono amp from the anode of the second tube to the cathode of the first tube when the second tube is coupled with transformer coupling interstage to the line stage?
This has been done many times with feedback from a transformer output stage to the previous stage without RIAA correction but my worries are the correctness of the RIAA amplitude if the anode transformer choke is a nonlinear device instead of a linear resistor in the anode?

Thanks for answers,
Uwe

DF96 · 15th January 2012, 02:20 PM

Stability may be a problem. RIAA response is supposed to continue on down past 20kHz, but this may cause problems if the transformer HF resonance is too low. If you are happy debugging loop stability then fine.

15th January 2012, 01:05 AM	#1
Ronken diyAudio Member Join Date: Nov 2011	Audio transformer feedback loop Hello forum, planning for a phone preamp and having not seen such a circuit so I have to ask one question: Is it possible to connect the negative RIAA feedback in a two stage phono amp from the anode of the second tube to the cathode of the first tube when the second tube is coupled with transformer coupling interstage to the line stage? This has been done many times with feedback from a transformer output stage to the previous stage without RIAA correction but my worries are the correctness of the RIAA amplitude if the anode transformer choke is a nonlinear device instead of a linear resistor in the anode? Thanks for answers, Uwe

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15th January 2012, 02:20 PM	#2
DF96 diyAudio Member Join Date: May 2007	Stability may be a problem. RIAA response is supposed to continue on down past 20kHz, but this may cause problems if the transformer HF resonance is too low. If you are happy debugging loop stability then fine.

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