Author Topic: Amp signal to swing between set values  (Read 1228 times)

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Offline laejfTopic starter

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Amp signal to swing between set values
« on: January 30, 2019, 09:35:28 pm »
Hi. I'm wondering if there is any way of automatically amplifying an audio signal to vary between +-3.3V. I'm working on a signal sampling circuit and would like to increase the signal to noise ratio as much as i can. The problem is that i'm only able to use the circuit with an oscilloscope since the signal vary with the volume set on my computer and i need to adjust the resistance connected to an OP amp to keep it in the wanted interval. I'm guessing some sort of feedback could be involved by i cant come up with any and i dont know what to google for.

The set interval of +-3.3V is the lowest voltage my sampling signal can go, it's a sawtooth-wave that a comparator compares against my audiosignal.

How does a consumer level sampling circuit work? Does it sample the low level audio signal that can be as low as 10mV in my case? That has to introduce a lot of noise.

Would be very glad for ideas! Thanks
 

Online Ian.M

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Re: Amp signal to swing between set values
« Reply #1 on: January 30, 2019, 10:13:06 pm »
A keyword you may want to look up is: compander
https://en.wikipedia.org/wiki/Companding

 

Offline EmmanuelFaure

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Online David Hess

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Re: Amp signal to swing between set values
« Reply #3 on: January 31, 2019, 12:21:10 am »
An AGC (automatic gain control) loop comprising a detector, comparator, and gain control element can do that.  This is a pretty common function.

In your case the detector should measure the peak-to-peak value which is easy enough.  The gain control element could be an operational transconductance amplifier or Gilbert cell multiplier.
 

Offline SilverSolder

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Re: Amp signal to swing between set values
« Reply #4 on: January 31, 2019, 02:06:36 am »
The circuit you are looking for might be called either an "Audio Compressor" or "Automatic Gain Control" (AGC) - you can google that and find tons of circuits on the Internet.
 

Offline laejfTopic starter

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Re: Amp signal to swing between set values
« Reply #5 on: January 31, 2019, 09:23:12 am »
Thank you! Now I can start somewhere. I will check up on this stuff and hopefully get it to work
 

Online Zero999

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Re: Amp signal to swing between set values
« Reply #6 on: January 31, 2019, 10:13:50 am »
Yes an AGC is fairly easy to make. I investigated using an AGC on a project a year ago which was scrapped.
https://www.eevblog.com/forum/projects/mic-pre-amp-circuit-discrete-or-ic/msg1410745/#msg1410745

If it's digital and all you're doing is trying to get the best out of the ADC, then how about using a programmable gain stage to dynamically set the gain to the correct level?
 

Offline laejfTopic starter

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Re: Amp signal to swing between set values
« Reply #7 on: January 31, 2019, 03:41:58 pm »
For now it is not digital. But I will consider it!
 

Offline laejfTopic starter

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Re: Amp signal to swing between set values
« Reply #8 on: January 31, 2019, 03:49:24 pm »
It seems that automatic gain control is exactly what I was looking for. Thank you
 


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