Loudness - Why has the industry stopped producing amplifiers with this feature any longer?

Yes, dusty, worn POTS and oxidized contacts on switches can be a problem. But that is why we have DeOxit ;-)

DeOxit has a dicey reputation in this regard. Its not exactly the best medicine if you are dealing with a part that has the resistive element on a phenelic substrate. In a nutshell its bad chemistry.

So people that are really concerned about longevity of such parts (usually collectors) use specialized vacuum cleaners to clean out the pots and see how they behave after that is done before resorting to control cleaners like DeOxit.  

Us designer types that like to make high performance circuits have different concerns. For example, I like tubes for preamp circuits and tubes tend to have some fairly high impedances that cause stray capacitances to roll off the top end. If you really want your circuit to have 3D depth and width, you have to eliminate phase shift; to do that you need bandwidth (2KHz-100KHz at a minimum; 200KHz is better). When you have a switch to bypass a tone stack you're asking for trouble in this regard. Usually the presence of a tone stack suggests two things- first that the speaker is bandwidth compromised and second that getting the sound stage right is secondary to the goals of the listener.


In high end audio, getting the system to sound like the musicians are playing in the room is a pretty serious endeavor. It is rendered impossible if a tone stack is involved. You might be able to get it sound like a good stereo, but sound like its real?- nope, won't do that.

Once I sorted this out and got competent equipment, I found that I never felt like I needed any tone controls. The key is 'competent equipment' but its also important to get the speaker placement right and have a good match between all the bits in the system.

They proclaim Tone Controls = BAD!! Ummm... but there’s this thing they invented call a SWITCH..... and you and just switch them out of the audio path.... and don’t get me started on "oh but that switch is in the signal path and it degrades the sound too..." No! It does’t.

The more transparent your equipment is, the more you hear things like switches. That in itself is a pain because if you have that transparency, then you have to pay a lot more for the switches you get so that they don't cause audible degradation.


Putting myself through engineering school I worked as a service technician repairing consumer electronics. Even when the stuff was new, the tone control defeat switch was one of those parts that was a source of failure- mostly out of disuse, just like the tape monitor switch. I had to assume that as the product ages, such switches will become more problematic.


Funny thing though, once my own system got to a certain level of competency, I didn't miss the tone controls. Even at low volumes the bass was perfectly audible.

The problem with a loudness function is that there is no way to set it up right. The idea is based on the Fletcher-Munson curve, which is variable depending on sound pressure. So the loudness has to be variable, the problem is knowing how to set it. With **all** loudness controls that are essentially a tap on a volume control with an emphasis network, there is a correct setting of the control with a particular speaker, and with a particular source. So if you have two sources that are at different output levels you'll need to have a different volume control setting to obtain the desired volume, but now the loudness emphasis is different. Obviously they can't both be right, and if you don't happen to be sitting the correct distance from the loudspeaker with which the amp was designed, it will never be right.

Now some amps had in addition to a volume control, a loudness control too, so you could variably set the emphasis; the problem here is knowing where to set the control. About all you know there is that if you have the volume set lower, you might want the loudness set higher?? But the reality is that you can't have any idea, not without doing a lot of measurements...

Obviously the result has been since their inception that loudness settings are a gimmick and nothing more. So high end stuff omits it since its entirely useless and only causes colorations.