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This question already has an answer here:

https://www.fairchildsemi.com/application-notes/AN/AN-6603.pdf Page 3 top left of this also shown in this screenshot: http://i.imgur.com/rp3lYsl.png

How would you modify Figure 11 to make a voltage controlled attenuator instead of a voltage controlled amplifier?

A previous stack exchange post talks about DC inputs and using a switch instead- I'm not asking about those in this post Voltage Controlled Attenuator My input for example could be audio and the purpose could be to decrease loud sounds

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marked as duplicate by Spehro Pefhany, PeterJ, Daniel Grillo, Bimpelrekkie, Scott Seidman May 2 '16 at 22:03

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  • \$\begingroup\$ You could modify it by driving the gain control in reverse - from max to min. \$\endgroup\$ – rdtsc Apr 28 '16 at 17:33
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Put an attenuation stage after the VCA. Then your gain will range from the attenuation factor (when the VCA is at unity) to the attenuation factor times the VCA max gain (when the VCA is at max gain).

A simple voltage divider and op-amp buffer will probably suffice for most applications.

However, this solution has a bound on maximum attenuation (i.e. you cannot have an infinite amount of attenuation (gain = 0), which may or may not be appropriate for your application.


Or you could find a different circuit entirely, because I don't understand why you have to modify that circuit instead of using a completely different circuit.

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  • \$\begingroup\$ Let's say the VCA has gain from 1 to 10. Then if we put a resistor divider attenuation after the VCA we might have gain from 0.1 to 1 but the problem is we still basically have a voltage controlled amplifier where higher signal means higher gain- whereas I'd like as the signal increases in volume, then there to be more attenuation \$\endgroup\$ – LongApple Apr 24 '16 at 4:16
  • \$\begingroup\$ Then you can invert your control signal first (and probably add an offset), and then feed it into the same circuit. \$\endgroup\$ – uint128_t Apr 24 '16 at 5:28

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