KBK, I apologize if I appear to come on too strongly about exceptional phenomena being discussed on this thread. Personally, between you and me, I would be happy to converse about these things, but it gets things off track, because of the hear and believe-no-difference contributers here. It is hard enough just to describe successful engineering approaches as it is. Please, keep contributing to this thread, however.
KBK said:
Hmmm. Cutting through the marketese, it appears that instead of two (metal) contacts we now will have four contacts: metal to pill, pill to metal. Does anyone have an idea how the contact between the metal part and the pill is? How consistent, how linear? Would you trade that in your audio circuit for a well established gold or silver hermitically closed set of contacts?
Furthermore, 1 ohms 'contact resistance' is much, much more than a good switch contact. And how linear is that 1 ohms?
The off resistance can go up to 10M apparently, but what is the practical off-value in a switch when build-in? How linear is THAT?
These are all potential degrading points, and the only positive one I can see is the 'controlled change' to go smoothly from open to closed. Not sure when I would need that in audio.
Jan Didden
alansawyer said:
This is just John's way of dealing with people who question what he says. He doesn't realize that other smart people can walk and chew gum at the same time; i.e., be objective, be subjective, measure, listen and be open-minded all together.
This is a shame, because John is one of those people who, actually much of the time, combines all of those traits.
Cheers,
Bob
For the record, I still believe in Bybee devices and wire differences. I will continue to do so, as long as they work in my audio system. Yet, I cannot discuss what I have found in these areas on this thread, without overt AND covert criticism. And people take exception to my mild comments on this?
Now, I would like to get back to the volume control question.
Many here probably think that this topic is 'over the top'.
After all, how could such a simple process of reducing gain in a linear fashion, be so difficult?
Historically, we used to depend on manufacturers of potentiometers, who often made units with wire-wound or baked carbon elements. Professionally, 40 years ago, Allen Bradley A 'baked carbon' was the leading industrial pot used. It was actually pretty good, and it was round cased with a metal covering.
Then, about 1970, AB changed to a square, plastic cased pot with similar specs. Ah, the march of progress! We could buy these in singles duals, quads, etc, etc. I still have a whole drawer full of exotic blends. But, on further inspection, I found that ALL of these pots had measurable distortion at certain settings on the pot and certain loadings on the wiper. What happened?
Many here probably think that this topic is 'over the top'.
After all, how could such a simple process of reducing gain in a linear fashion, be so difficult?
Historically, we used to depend on manufacturers of potentiometers, who often made units with wire-wound or baked carbon elements. Professionally, 40 years ago, Allen Bradley A 'baked carbon' was the leading industrial pot used. It was actually pretty good, and it was round cased with a metal covering.
Then, about 1970, AB changed to a square, plastic cased pot with similar specs. Ah, the march of progress! We could buy these in singles duals, quads, etc, etc. I still have a whole drawer full of exotic blends. But, on further inspection, I found that ALL of these pots had measurable distortion at certain settings on the pot and certain loadings on the wiper. What happened?
I stopped using pots for volume controls in 1985,
and started using simple stepped attenuators instead. Back then with those "nasty" metall film resistors. Today with TX2352 resistors, but I am right now trying some different resistors, too.
The pot is one of the most important components in a line amp, IMHO. No way I will make any serious compromise for that component!
Sigurd
and started using simple stepped attenuators instead. Back then with those "nasty" metall film resistors. Today with TX2352 resistors, but I am right now trying some different resistors, too.
The pot is one of the most important components in a line amp, IMHO. No way I will make any serious compromise for that component!
Sigurd
john curl said:
I essentially agree with your approach Sigurd. Of course, most of us, in hi end, use this approach in some way, today.
However, I started talking about problems with pots that were discovered 35 years ago, with the square Allen Bradley pots.
What to do? First, we found that loading or passing AC current through the wiper of the pot, aggravated the problem This meant that we could not load a linear pot with a resistor to make a audio taper pot, and we could not use the pot as a variable resistor, so a pot in the feedback loop was out too. Of course, we tried to find alternative manufacturers.
We found that Bourns made a similar pot that did not have the same problems, and then I found that Penny and Giles actually made a rotary pot, that was not sold for audio use, but for the military, and it was VERY good. I pointed Mark Levinson in that direction, and he paid plenty to get a quality rotary pot from Penny and Giles. Later, I settled for the P&G linear attenuators, which are at least as good as the rotory pots, for the JC-80.
However, I started talking about problems with pots that were discovered 35 years ago, with the square Allen Bradley pots.
What to do? First, we found that loading or passing AC current through the wiper of the pot, aggravated the problem This meant that we could not load a linear pot with a resistor to make a audio taper pot, and we could not use the pot as a variable resistor, so a pot in the feedback loop was out too. Of course, we tried to find alternative manufacturers.
We found that Bourns made a similar pot that did not have the same problems, and then I found that Penny and Giles actually made a rotary pot, that was not sold for audio use, but for the military, and it was VERY good. I pointed Mark Levinson in that direction, and he paid plenty to get a quality rotary pot from Penny and Giles. Later, I settled for the P&G linear attenuators, which are at least as good as the rotory pots, for the JC-80.
john curl said:
Hi John,
I don't think this is over the top at all. Pots are big, legitimate concern, and a potentially big expense. I do remember those great old round Allen Bradley pots, especially the mil-spec versions of them.
Virtually every one of us has experienced the obnoxious behavior of a dirty or noisy pot, so it is not a big leap of faith to believe that more subtle behaviors of a mechanical wiper could cause significant audible distortion, especially when current flows in the wiper.
Even with a very high quality pot mechanism, there is still the concern of channel-channel tracking, especially at low levels.
I know you're not a big fan of ICs, but do you think there is any hope here in regard to IC VCAs or the like for high-end applications?
I realize that an electronic solution might never be as good as a well-built stepped attenuator with really good resistors and outstanding switch contacts, but at the same time the mechanical wiper approach would seem to be vulnerable to being bested by a really good IC approach.
Have any listening tests been done where some of the best IC VCAs have been compared with pots and stepped attenuators in a reasonable apples-apples way? Has anyone here had experience with, say the VCAs by THAT? I believe that a lot of VCAs are being used in studios, although in many cases those analog approaches may now be being displaced by DSP level controls.
What do you think?
Cheers,
Bob
Most serious audio designers have tried virtually everything at one time or another.
Generally, we go back to motor driven switches. Everything else is compromised to some degree. How important it is, depends on the quality of the rest of the reproduction chain. Often a relatively cheap carbon pot does pretty darn well, subjectively. Think of it like an automobile tire. Relatively cheap tires will get you to work and back. Expensive ones are necessary, IF you have the vehicle that can use them, AND you like twisty back roads, or very high speed.
Tracking is yet another problem, and it used to be quite serious. Today, merely serious, with some quality Japanese pots. It is the first thing that I complained to Bourns about the the AES a few years ago. They may have made improvements, I hope so.
Generally, we go back to motor driven switches. Everything else is compromised to some degree. How important it is, depends on the quality of the rest of the reproduction chain. Often a relatively cheap carbon pot does pretty darn well, subjectively. Think of it like an automobile tire. Relatively cheap tires will get you to work and back. Expensive ones are necessary, IF you have the vehicle that can use them, AND you like twisty back roads, or very high speed.
Tracking is yet another problem, and it used to be quite serious. Today, merely serious, with some quality Japanese pots. It is the first thing that I complained to Bourns about the the AES a few years ago. They may have made improvements, I hope so.
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