THE lowly volume control, one of the simplest parts of an amplifier or receiver, is also one of the most misunderstood. Dozens of misconceptions have arisen and been applied to this little-or big-knob without their having any basis in fact. For example:
The volume control on my amplifier (or receiver) is turned three quarters of the way up. Therefore the amplifier is delivering three quarters of its maximum power output.
My amplifier plays as loud at a 12-o'clock volume setting as Fred's does at a 2-o'clock setting. Therefore my amplifier is more powerful (no matter what the specs say).
With receiver A, I have to crank the volume way up to get the music loud enough. With receiver B, I just touch the control and I'm deafened. Receiver B is obviously much more powerful (again, no matter what the specs say).
My old speakers blew out when I played them at half volume. My new speakers are rated to have twice the power-handling capability. Therefore I should be able to play them at full volume with no problem.
I paid $75 for this state-of-the-art phono cartridge and I have to turn the volume control up much higher than I did with my old cartridge. Obviously I got stung.
ANY of the above conclusions could be true. However, all of the reasoning that led to these conclusions is completely false, be cause the setting of the volume control simply has nothing to do with any of these matters.
Let's consider an amplifier as a signal-strength multiplier, which is what it really is. For the sake of argument we'll take a hypothetical amplifier that has a multiplication factor (or gain) of 100. Any signal (from a tape machine, let's say) that we apply to its input gets multiplied by 100, and the result is delivered at the output. All of this works very straightforwardly and reliably up to a point.
That point is the amplifier's maximum power-output capability, which we'll arbitrarily set at 1,000 (not 1,000 watts, just 1,000). There fore, any input signal up to a value of 10 (10 x 100 = 1,000) is okay, but if the input signal exceeds 10 at any time the amplifier can't do its multiply-by-100 trick without going into over load or clipping-which is what normally hap pens to an amplifier that is being asked to put out more than it is capable of.
The volume control is merely a rather simple device that adjusts the amount of input signal that gets through the amplifier. When it is turned fully up, all of the input signal gets through. When it is fully down, none (usually) of the input is allowed to pass. For intermediate settings the control admits or inhibits signals to a degree that is determined by the control "taper" chosen by the amplifier's designer. If he wants almost all of the signal passed at the barest upward twitch of the knob, he can select a volume control that does that. If he wants the level to go up smoothly and gradually as the knob is turned, he'll choose another type of control taper. But these choices are only design preferences; they affect the intrinsic operation of the amplifier not one whit.
To refer back to our earlier example, if the input signal level has a value of 10, the amplifier will be delivering its full power at a full volume-control setting. If the input signal is 15, the amplifier will deliver its full power well before the volume control is at maximum. If the input is 5, the amplifier will not deliver its full power no matter where the volume control is set (but presumably you'll still be able to get the music loud enough to suit you; if you cannot, you probably need a stronger input-signal source, not a more powerful amplifier.
Looking back at the misconceptions we began with, we can see that none of the assumptions made about amplifier power on the basis of volume-control setting is valid. The only measure of an amplifier's power-output capability is how loud it will play (no matter where the volume control is) before the distortion associated with amplifier overload is heard.
And if you want to compare amplifiers, the comparisons should be made with the same speakers and (ideally) in the same room, since speakers and rooms differ in their power requirements for a given loudness level.
As for the speakers that should be able to withstand "full volume," the assumption is incorrect-and hazardous to the health of your loudspeakers. Doubling the volume-control setting almost never has the effect of doubling the amplifier's power output. In fact, it's impossible to predict exactly what it will do unless you've studied the individual amplifier and the speakers it's being used with. Also, there is no way to determine how much power is actually going to a speaker unless you sit down and measure that power with the appropriate test instruments.
And finally, the phono cartridge in the example above simply provides a weaker input signal to the amplifier and therefore requires a higher volume-control setting to achieve the same loudness. This is a common occurrence.
In designing top-quality phono cartridges engineers frequently sacrifice some output level to achieve other characteristics they want more. If you can get the loudness level you want from your cartridge without any marked increase in the electronic hiss you can hear from your speakers, then everything is fine, and you can forget about how high the volume control is set.
CONFUSION about volume controls doesn't end here, however. Note, for example, that many audio systems have two or more volume controls: one main one and perhaps one or more subsidiary ones on tuners, tape decks, or even on power amplifiers if the system employs a separate preamp. What's to be done with these? Usually the manufacturer of the component offers ample advice in his instruction manual. If he doesn't, here are the general rules:
Volume or output-level controls on program sources such as tuners and tape decks are there primarily for convenience. With them you can match the typical level you get from one program source to that of another (the record player, for example), to permit switching between sources without having to make large adjustments in the main volume setting. Volume (or "gain") controls on power amplifiers are usually set full up. However, if this results in very high sound levels for very small main-volume settings, it may be convenient-and also beneficial for the signal to-noise ratio-to adjust the power-amp controls for your normal listening levels when the main volume control is about at mid point.
To sum up, if you want to impress some friends with your amplifier, don't show them how loud it can play with a 10-o'clock volume-control setting; that doesn't prove a thing. Show them how loud it can play period. And then, please, be kind and turn it down a little.
Also see: AUDIO QUESTIONS and ANSWERS: Advice on readers' technical problems
Source: Stereo Review (USA magazine)