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Old 10th June 2005, 06:54 PM   #1
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Default 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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Old 10th June 2005, 07:12 PM   #2
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I would think that a bad idea as the gain would go up as the frequency increased.
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Old 10th June 2005, 07:17 PM   #3
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Ahhh... OK.

So maybe this is a better idea? An inductor in series with the resistor from the feeback loop to ground?
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Old 11th June 2005, 08:59 AM   #4
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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 )

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Mauro
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Old 11th June 2005, 12:17 PM   #5
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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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Old 12th June 2005, 01:15 AM   #6
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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
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Old 12th June 2005, 07:58 PM   #7
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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.
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