This information was posted by Blue Circle's Gilbert Yeung in the Blue Circle forum.
"This is a topic I have been thinking about posting for a long time and never had a chance to do it. But nows the time.........
In order to understand what I am going to tell you and learn something from it, you must have an open mind. Forget everything you have ever learned about the three terms Volume Control, Attenuator and Gain or you are just going to be confused more and more and use the wrong terms every time.
First, let me tell you my interpretation of the above three terms related to audio use.
VOLUME CONTROL: A device which will allow the operator to adjust the sound level of the system. The sound level can be increased or decreased depending on the direction the operator turns or slides the control.
ATTENUATOR: A device which will decrease or increase the level of signal. The term attenuator usually suggest the decrease of signal. However, negative attenuation means increasing the signal.
GAIN (in this case, we are talking voltage GAIN only): The amount of amplification of a given device. Gain in audio is usually understood as an increase of signal. However, gain can also be used in a negative way. If negative gain is applied, the level is decreased. The unit of gain is usually expressed in dB (decibels).
Why do we need a volume control in a preamp?
Because a preamp has a gain stage and usually it has a fixed amount of gain. Therefore, the signal must be attenuated (decreased in this case) before being fed to the input stage. The volume control in this case can be also called an attenuator. Volume control in the digital domain may not work the same and cannot be called an attenuator, however, we will stick to an analog volume control and preamp at this time.
These days preamps usually have a range of gain from 0dB (passive preamp) to 35dB. Some of you know people that are using a passive preamp with a power amp and have plenty of gain. And then there are others using an active preamp thats supposed to have 25dB of gain but they have to turn the Volume Control up to 2 or 3 Oclock before they can obtain any reasonable volume. WHY?
The answer lies with the setting of the volume control, and NOT the gain of the preamp. When using a passive preamp, volume controls are usually set at max. attenuation 75dB to 80dB with audio taper. Audio taper volume controls have been used since way back in the 50's. You will find these audio taper controls usually give you lots of volume between 6 OClock and 8 OClock. Remember back in the late 70's, there was a receiver war and one of the major factors was the power of the receiver. Manufacturers used these audio taper volume controls so they could make the receiver sound very loud when the volume control only pointed at 8 OClock position. Did anyone use it up to 2 OClcok? Does any one know what happens when you turn these audio taper volume control up to 2 O Clock?
These audio taper controls are set at a non-linear increment. For example, 80dB max. attenuation at 6 OClock. By 7 OClock, it has 70dB attenuation and 65dB attenuation at 7:30. Between 6 OClock and 7:30, there is a 15dB decrease on attenuation or 15dB increase of sound level output. When the control pass 10 OClock, the increment starts to decrease rapidly. 3dB, 2dB and finally 1dB and 0.5 dB when it hits the 3 OClock position.
Ask yourself, when did you ever turn your receiver up to 3 OClock when you were older than 25 years old. Dont answer this question to anyone becasue your answer may not be true to yourself. Keep this one for your own.
Times have changed, people have changed. Many people like to listen to their music at lower volume in their small apartment at night without disturbing their family members. Or they simply enjoy low level music in the background. Also audiophiles realize the lower part of the volume control is not as good as the upper part.* Thats why many manufacturers have started to provide volume controls which can be turned higher up without getting too loud. There are many fine settings of these type of volume controls. The most common is the linear taper. Even with linear taper, the first part (6 OClock to 7 OClock) would still be about 5 to 15 dB different. This is because when the level is down to about 80dB attenuation, to human ears, there is almost no difference between 80dB and a 78dB attenuation.
Linear taper means every step of the volume control attenuates an equal amount of dB, this usually happens when the volume control hits 8 OClock position. There are exceptions, like some of the digital volume controls, but again we are sticking with analog at this moment. Linear taper volume control give you a lot more fine adjustment between the 6 OClock and 12 OClock positions. To obtain the same level of volume at a 10 OClock position on an audio taper control, you will have to turn it up to about 2 OClock on a linear control. Many people have concerns about the volume control being turned too high. I say thats great, you are actually using almost all of the volume control, you are getting your moneys worth. There is absolutely nothing wrong by turning the volume control up to 2 or 3 OClock. That only means you have a lot of fine adjustment on the lower setting.
However, if anyone wishes to have very loud volume at 9 to 10 OClock, ask for the audio taper volume control. It will give you what you need at 10 OClock, however, you will probably not able to use anything higher than 1 OClock.
All of the above is based on typical cases. Power amps having gain of 18dB to 26dB, speaker are somewhere in between 86dB to 92dB and CD player/DAC has a standard 2V output. If you throw a single-ended triode amp with only 13dB and / or a horn speaker with 104dB or even a tube amp with 40dB of gain. Then the equation has to be re-calculated. Therefore, a typical volume control may not have a range wide enough to compensate. There are solutions to this problem.
When most people have an actual gain issue to solve its with too high or too low gain of a power amp, or even a extra high output DAC or CD player. They blame the gain of the preamp being too high or low. Most of the time, they are wrong. The preamp is the last one to blame. The preamp is the one piece of equipment that ALWAYS has a volume control. Without a volume control, that piece of equipment cannot be called a preamp. So, what if someone has a volume control or gain control on their power amp, then what? Then adjust the volume or gain control on your power amp to suit the most comfortable level on your preamp. You are essentially adjusting the level or the gain of your power amp to suit.
If they dont have anything else to adjust other than the preamp volume control, then what? In most cases, you are screwed. Go find something that is designed normally. Or if youve got a Blue Circle preamp with a Shallco attenuator, then it time to talk to me. Tell me what your problem is, then I can adjust the attenuation increments of the Shallco volume control(s) to your solve. In 99% of cases, the actual gain of the preamp does NOT need adjustment, just the volume control(s) increments.
If anyone asks whether the Shallco will change the sound of their system. My answer is no.
Why anyone would use a power amp with a 40dB of gain is another totally different issue than the volume control. But it is semi related since the whole chain in the audio path is involved in it. If anyone of you wishes to have low noise floor in your system never buy a power amp that has more than 28dB of gain. The higher the power amp gain, the more it amplifies the residual noise of the system.
* This theory does not apply to our Shallco attenuator. Since the Shallco attenuator has individual resistors at each position, there is no sonic difference between any position of the control. The only difference is the level of volume or level of attenuation."
Gilbert Yeung, President, Blue Circle Audio.