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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 3rd Mar 2023, 2:36 pm   #1
kostas_sv3ora
Triode
 
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Location: Athens, Greece
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Default Level selective amplifier circuit needed

Dear all,

I wonder if a level selective HF amplifier circuit exists out there.
An amplifier that amplifies more the high level signals above a settable threshold and less (if not at all) the low level ones.

This is not the same as a squelch circuit, but rather exponential level amplification.

Any help towards this direction, would be much appreciated.

Thank you
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Old 3rd Mar 2023, 6:57 pm   #2
G6ONEDave
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Default Re: Level selective amplifier circuit needed

I thought thats what graphic equalisers were designed to do having several frequency set ranges, perhaps I misunderstood the question.

Dave
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Old 3rd Mar 2023, 8:48 pm   #3
Radio Wrangler
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Default Re: Level selective amplifier circuit needed

No, it's not a graphic equaliser, it's actually an expander, AGC achieving the opposite effect - increasing the variation in input signal level.

I can't think of a use for one.

David
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Old 3rd Mar 2023, 9:15 pm   #4
Cruisin Marine
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Default Re: Level selective amplifier circuit needed

You would need a level detector driving a comparator and some switching, or maybe something more elegant.
Are you asking for an expander/noise gate?
What is your intended use?
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Last edited by Cruisin Marine; 3rd Mar 2023 at 9:24 pm.
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Old 4th Mar 2023, 9:14 am   #5
RogerEvans
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Default Re: Level selective amplifier circuit needed

An OpAmp with a PN junction in the feedback path has a transfer function which is either logarithmic or exponential depending on where you place the diode. This was used a lot in the days of analogue computing, it has the disadvantage of poor temperature stability in its simplest form. Is that anywhere near what you need?

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