Author Topic: (Audio) Amplifiers: attenuation + fixed gain OR no attenuation + variable gain  (Read 1580 times)

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Offline trevortjesTopic starter

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Hey everyone,

I was wondering which of the two following ways to achieve audio amplification is best:

1) Signal -> Attenuator (voltage divider) -> amplifier (fixed (high) gain)
2) Signal -> amplifier (variable gain)

What are the pros and cons? As far as I know many audio amplifiers use (1) to achieve audio amplification but other's say that (2) might be better for SNR.

EDIT:

For example the LM386. It is possible to add an attenuator in front of the input, but it's also possible to utilize the gain pins.
« Last Edit: February 17, 2020, 04:11:09 pm by trevortjes »
 

Online Benta

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The main issue with option #2 is stability and frequency/phase response.
 
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Offline TimFox

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The main problem with no. 1 is noise.  Attenuating the signal before the gain stage will always increase the effect of the amplifier noise.  If the amplifier noise referred to its input is very small (compared with the signal level) then this may not be important.
 
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Offline fcb

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If audio quality is the prime concern then attenuate+fixed gain.

If audio quality doesn't matter then attenuate+fixed gain. :-DD

The increased noise from the attenuate+fixed gain setup matters if it's perhaps a mic amp (they tend to have attentuators and variable gain stages) - but if it's just plain old audio (you reference an LM386) the noise won't matter and stability is more important.  Also, difficult to make an amplifier have a gain of 0 (when you want zero volume) and be adjustable for a gain of say x30 (max volume).
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Offline David Hess

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Attenuation is usually used with a fixed gain amplifier because altering the gain of the amplifier changes its frequency response which has implications for stability.  However at audio frequencies, active volume and tone controls where amplifier gain is variable are very feasible and commonly used.  Their chief advantage is that a wide non-linear control range can be achieved with linear potentiometers.

Look up Baxandall volume controls and Baxandall tone controls.
 

Offline Kleinstein

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The usual audio amplifiers have a rather limited range the gain can be adjusted. This is because of stability issues at to low a gain. The more common non inverting configuration can not go below gain 1 anyway.

So a variable gain for the output stage can not be used for the full range. It may be an option for something like 2 overlapping ranges in addition to a divider in front of the amplifier for fine adjust.
 


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