Question about inductors.

Russ White · 10th June 2005, 06:54 PM

I was wondering in cases where you are building a preamp with an opamp and a buffer, if there is any benefit to adding an inductor in series the output of the buffer prior to the feedback loop. I wonder if this could help make tricky opamps easier to tame by filtering out very high frequencies.

Is this a bad theory?

Any pointers appreciated.

Bill Fitzpatrick · 10th June 2005, 07:12 PM

I would think that a bad idea as the gain would go up as the frequency increased.

Russ White · 10th June 2005, 07:17 PM

Ahhh... OK.

So maybe this is a better idea? An inductor in series with the resistor from the feeback loop to ground?

mauropenasa · 11th June 2005, 08:59 AM

You suggestion to use reactive components ( cap. & Ind.) in the NFB nets only if have not other choice. The insertion of this elements in a function of transfer produces a series of dynamicses ( poles and/or zeros ) that have to be controlled with precision. The inductors in particular, they hear again a lot of of the external interferences (EMI), and risks to build a AM radio. If then have a magnetic nucleus, lose totally the follow-up of the situation(various THD form).

lead always a RF shutters RC net in input to your circuits, because in the "realities" audio signals is practically always a external RF components. Besides you put always a resistance in series to the output, on behalf of avoiding instability ( even this much diffused on account of the elevated capacity of the audio cables )

Ciao

Mauro

Russ White · 11th June 2005, 12:17 PM

Thanks Mauro,

It looks like it is not common practice to add an inductor in the feedback loop at any point. I was only wondering, because I saw a commercial pre-amp schematic with on inductor after a buffer, and just wondered why.

Sincerely,
Russ

XELB · 12th June 2005, 01:15 AM

Quote:

Originally posted by Russ White
Thanks Mauro,

It looks like it is not common practice to add an inductor in the feedback loop at any point. I was only wondering, because I saw a commercial pre-amp schematic with on inductor after a buffer, and just wondered why.

Sincerely,
Russ

Maybe it's because the bass

I prefer punchy bass to long(slow) bass.
Try to add an inductor to your amp, you will see how the bass will sounds

peranders · 12th June 2005, 07:58 PM

Quote:

Originally posted by Russ White
Thanks Mauro,

It looks like it is not common practice to add an inductor in the feedback loop at any point. I was only wondering, because I saw a commercial pre-amp schematic with on inductor after a buffer, and just wondered why.

What you saw was probably some RFI/EMC stuff. Inductors in the feedback is very rare, towards non-exsistant.

10th June 2005, 06:54 PM	#1
Russ White diyAudio Member Join Date: Jan 2005 Location: Nashville, TN, USA	Question about inductors. I was wondering in cases where you are building a preamp with an opamp and a buffer, if there is any benefit to adding an inductor in series the output of the buffer prior to the feedback loop. I wonder if this could help make tricky opamps easier to tame by filtering out very high frequencies. Is this a bad theory? Any pointers appreciated.

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10th June 2005, 07:12 PM	#2
Bill Fitzpatrick diyAudio Member Join Date: Jun 2001 Location: Eugene, OR	I would think that a bad idea as the gain would go up as the frequency increased.

10th June 2005, 07:17 PM	#3
Russ White diyAudio Member Join Date: Jan 2005 Location: Nashville, TN, USA	Ahhh... OK. So maybe this is a better idea? An inductor in series with the resistor from the feeback loop to ground?

11th June 2005, 08:59 AM	#4
mauropenasa diyAudio Member Join Date: May 2005 Location: TN	You suggestion to use reactive components ( cap. & Ind.) in the NFB nets only if have not other choice. The insertion of this elements in a function of transfer produces a series of dynamicses ( poles and/or zeros ) that have to be controlled with precision. The inductors in particular, they hear again a lot of of the external interferences (EMI), and risks to build a AM radio. If then have a magnetic nucleus, lose totally the follow-up of the situation(various THD form). lead always a RF shutters RC net in input to your circuits, because in the "realities" audio signals is practically always a external RF components. Besides you put always a resistance in series to the output, on behalf of avoiding instability ( even this much diffused on account of the elevated capacity of the audio cables ) Ciao Mauro

11th June 2005, 12:17 PM	#5
Russ White diyAudio Member Join Date: Jan 2005 Location: Nashville, TN, USA	Thanks Mauro, It looks like it is not common practice to add an inductor in the feedback loop at any point. I was only wondering, because I saw a commercial pre-amp schematic with on inductor after a buffer, and just wondered why. Sincerely, Russ

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