If a pot isn't audible, it's broken. They're supposed to bring volume up and down.
Yes.
It's the time domain behaviour of pots that's the killer - if you clean the wiper by adjusting the control immediately before taking a misbehaviour measurement of any type I'm sure it will be brilliant, or at least pretty good. But leave it alone for half an hour, or even a day - and check the reading again - I would be quite surprised if it was identical to the earlier one ...
This sort of behaviour used to drive me batty in my early days of tweaking - the only decent long term solution for me was to rip every pot out of the system ... ahhh, problem solved ... 😀 .
Last edited:
Cyril Bateman has done some analysis on variable resistors and pots in his CapSound6 part of his series :
Capacitor Sounds, Speaker Cables and Crossover Inductors.
A mystery to me is how people can still use pots having a value higher than 10 kOhm
to control the signal in solid state analog designs.
Capacitor Sounds, Speaker Cables and Crossover Inductors.
A mystery to me is how people can still use pots having a value higher than 10 kOhm
to control the signal in solid state analog designs.
Define "incorrect" & please don't bother using words like "bright", "muddy", "lazy","precise" or "coherent" et. al. .....NO WORDS please, show me the numbers & your DBT of Audibility from unit to unit.
__________________________________________________Rick......
Some collective knowledge has been gathered also here:
http://www.diyaudio.com/forums/chip-amps/40676-so-i-did-try-all-those-different-potentiometers.html
http://www.diyaudio.com/forums/chip-amps/40676-so-i-did-try-all-those-different-potentiometers.html
As I said, for best behaviour a pot wiper needs to drive a high resistance load. Then it doesn't matter how poor is the wiper-track contact. Pots are like other components: people use them carelessly then proclaim to the world that "pots should be avoided". Poor design should be avoided.fas42 said:
Thank you, DF96, for putting forth an important point in the discussion.
Loading of the wiper seems to be the primary way that pots become troublesome, but when and how can we be sure that we do not excessively load the wiper of the pot?
For example, I have a 100K pot, here. How to I measure it with almost no wiper loading with an HP339, ST1700, etc, that have a 50k input impedance?
So I guess we should not use 100K pots? Then how do I control the gain of my Marantz 10 tube tuner properly? Generally, 10K is about as low as you really want to go, but 100K is a bit noisy, and prone to distortion due to finite loading. What to do?
Loading of the wiper seems to be the primary way that pots become troublesome, but when and how can we be sure that we do not excessively load the wiper of the pot?
For example, I have a 100K pot, here. How to I measure it with almost no wiper loading with an HP339, ST1700, etc, that have a 50k input impedance?
So I guess we should not use 100K pots? Then how do I control the gain of my Marantz 10 tube tuner properly? Generally, 10K is about as low as you really want to go, but 100K is a bit noisy, and prone to distortion due to finite loading. What to do?
An other factor is how long it will last. Some pots are guaranteed for 1 million turns, and will last a lifetime. Others for just 1 hundred turns, these are a bit cheaper.
I'd like to hear anyone's opinions on what happens to the SQ when the signal has to pass through dissimilar materials of the wiper (metallic) on conductive track (non metallic) and that it is a very light "touch" contact as well.
Cheers George
Cheers George
If a potentiometer is a problem, then the best thing is to get rid
of the problem. Pure, unaltered, fully amplified signal.
of the problem. Pure, unaltered, fully amplified signal.
IME the alternatives which are frowned upon by 'serious' audiophiles are exactly what do bypass any issues - digital volume, IC control, ...
Last edited:
Some dissimilar materials create a nonlinear junction. That was how the old cat's whisker radio receivers worked, by poking a wire into a crystal of some mineral or other you got a crappy diode. However, nobody makes pots out of those materials.
I have seen one old dirty pot that seemed to have a high resistance wiper with lots of excess noise that depended on the current flowing in it.
The best digital attenuator ICs still have more distortion than a pot. The semiconductors inside them are less linear than the pot wiper contact. However, the distortion is nothing to worry about, and they track perfectly, don't wear out, and can control a whole lot of channels at once.
I have seen one old dirty pot that seemed to have a high resistance wiper with lots of excess noise that depended on the current flowing in it.
The best digital attenuator ICs still have more distortion than a pot. The semiconductors inside them are less linear than the pot wiper contact. However, the distortion is nothing to worry about, and they track perfectly, don't wear out, and can control a whole lot of channels at once.
Last edited:
The ICs may have more distortion in a technical sense, but they don't have the time domain problems - at one stage the audible degradation of wiper contacts was driving me crazy, so did an experiment with a reputable IC unit - ahh, resolution ... achieved stability of the subjective quality, which is far more important than having nominally better numbers from a spec sheet, etc.
Since we've gone from a serious forum to the lounge... 
A Russian overkill solution to the potentiometer "problem" ? Almost 1000cm³ of robust engineering: PP36 21 Russian Military Rotary Switch 35 Steps 2 Plates 8pcs | eBay
Just for fun, I bought a pair, cleaned one and turned it into a 10k serie attenuator. The action is smooth but firm and 35 steps allow for precise settings. Still... it has no particular magic compared to a good old ALPS blue.
A Russian overkill solution to the potentiometer "problem" ? Almost 1000cm³ of robust engineering: PP36 21 Russian Military Rotary Switch 35 Steps 2 Plates 8pcs | eBay
Just for fun, I bought a pair, cleaned one and turned it into a 10k serie attenuator. The action is smooth but firm and 35 steps allow for precise settings. Still... it has no particular magic compared to a good old ALPS blue.
Why do parts have to have "magic"?? The recording, correctly reproduced, is the magic - every time ... parts often get in the way of that, by introducing audible, disturbing artifacts ... the aim of the game is to identify the parts that are doing the damage, and sort them out, fix the problem. That may be achieved by replacing a part, a superior one for an inferior - but the magic occurs because of the fixing, nothing else ...
Last edited:
Engineering is one possible approach. 😀
Start by recognizing the difference between measuring and using. Then move on to actual engineering the application- for example, understanding what the grid impedance of a non-pathological small-signal tube is.
I assume that what you're saying here is just for effect and that you know all this.
Mooly just showed how to do it 'wrong'. Sorry Mooly, but when you load a linear pot you can have real problems with distorton. The original Levinson JC-2 preamp used that technique, and we HAD to change it to log-hi Z loading. Some pots may be OK, but cost will not tell you which.
Attachments
Last edited:
- Status
- Not open for further replies.