Volume control vs. attenuation control

Can someone please explain the difference between a volume control on an amp and an attenuation control on a pre amp.

You start with a very small voltage signal from a source like phono cartridge and follow that with a series of amplifiers that make the voltage bigger. Typically some voltage gain stages in the phono section, more in the preamp, and more in the power amp. The gain of these amps is fixed. To control the volume you insert at least one voltage divider in the path to control how much gets through.

Attenuator sounds more impressive than volume control but they are exactly the same thing. They are voltage dividers that reduce (attenuate) the voltage to the level you want. It could be at the output of the source, input or output of the pre, or input of the amp, basically anywhere in the signal path, or you can have one in all of those places. Whoever made your stuff decided to call the one in the preamp an attenuator.

Technically an 'attenuator' cuts the signal before any amplification stages.

No, attenuate means to reduce, it doesn't matter where you do it. If it reduces the amplitude of the signal it is an attenuator no matter whether it is before or after the gain stage.

Anything that attenuates the signal also reduces the volume so therefore they are the same thing.

A volume control actually changes the active amplification of the signal, from well below less than what it comes in as, to increasing it.

That would be extremely unusual. As stated above, the gain of almost all active stages is fixed. The volume control is merely dividing the voltage so you get the level you want. It isn't possible for a typical volume control to increase the amplification of the signal.

Let's say you had a preamp stage with a gain of 10 which means if you put 1 volt in and turn it all the way up you would get 10 volts out. If you wanted only 2 volts out you would have to turn the volume control so it was a 5:1 voltage divider.

1 times 10 divided by 5 = 2

.

Everything I said is correct. The problem comes when trying to explain technical terms to non-technical people.. I'll drop it after this because it is clear that most who have contributed are using terms the way non-technical people use them. There is no way to educate them to a sufficient level in this forum that they will fully grasp all of the terminology. By taking technical terms and applying very narrow audiophile meanings to them we get confusion.

You are taking a technical term "attenuator" and saying you can only use it the way some manufactures use it, which by the way, is also often incorrect. How can they call a knob an attenuator when at some positions it results in the preamp having an increased output?

it is incorrect to say that an attenuator and a volume control are the same thing, because they aren't. depending upon the volume control setting you do often get gain as a result of the volume control

but you, of course, never get gain from an attenuator.

Perfect examples, you use gain in the non-technical sense which assumes an increase. In many cases the output of the preamp is less than the input which means it has a gain of less than 1. As long as the discussion mixes the meaning of terms we will just be going in circles.

The only way your statement correct is if you consider the entire preamp to be the "volume control." The knob you turn which is often called a volume control is indeed a voltage divider that can only reduce (attenuate) the level. Any gain (in the incorrect non-technical sense of increasing amplitude) comes from active stages either before or after this divider and that gain is indeed fixed. If you want to change conventional terminology and say a voltage divider plus an active gain stage equals a volume control then you would be correct.

On the majority of preamps the knob you turn labeled "volume" is a voltage divider at the input. It is an attenuator. It has no positive gain. A few put it at the output but it is also a voltage divider which reduces the voltage which again makes it an attenuator.

The other problem is you misquoted me.

it is also incorrect to say that the gain of a preamplifier is fixed:

I never said that. You are confusing the "active stages" I was talking about inside the preamp with the entire preamp. Once again, a confusion between what is technically correct and how non-technical people sometimes incorrectly use the terms. Although many preamps contain active stages they are not equivalent terms.

You insist an attenuator differs from a volume control even though they both attenuate, they both control volume, and depending on where they are set in a particular preamp they both might result in an increase in amplitude.

I'll stick by my explanation. It is technically correct.

.

Not exactly. Gain is simply the ratio of output to input. the 0db setting isn't arbitrary, it is the point where out = in.

If the gain is less than 1 (output less than input) we say the preamp is attenuating the signal. With 2 volts in and one volt out the gain would be .5

If the gain is greater than 1 (output more than input) then it is amplifying the signal. With 2 volts in and 4 volts out the gain would be 2

If the output equal the input the gain is 1.

This is commonly expressed in dB which for voltage is 20 times the log of the gain. If gain is less than 1 that comes out as -dB, a gain of .5 is -6dB. A gain greater than one comes out +dB. a gain of 2 is +6dB. Unity gain when out = in comes out to 0dB so that isn't an arbitrary position.

Your preamp is attenuating the signal when you have it set to -dB, amplifying when it is set to +dB, and not changing the level when set to 0dB.

It accomplishes this with a combination of an active stage that amplifies and a voltage divider volume control which attenuates. The volume control can have a gain from between 0 and 1 and the active stage some positive amount. Multiply the 2 together to get the overall gain.

.