Sound of potentiometer materials?

[JohnRoberts]

I would like to see distortion plots for these suspect pot media. In my experience pots were not significant sources of nonlinearity.

JR

 

[Newmarket]

I would like to see distortion plots for these suspect pot media. In my experience pots were not significant sources of nonlinearity.

JR

From my time at P&G last century - I can say that distortion / non-linearities were never debated or the cause of customer comment IIRC. Mostly faders, some rotary pots. All CP. Lots of other issues addressed - "Cut Off" ; lubrication ; oil migration ; cross-talk ; screening ; wear characteristics. But not distortion.
In terms of signal path a major point was the conductive epoxy used to connect wires to the track(s). In relation to impairing "Cut Off".
Like the stuff used to repair car rear screen heaters that often doesn't work because it's too dried out.
The stuff was mixed in house on a shaker table using silver loaded epoxy IIRC and had to be used that shift.

 

[Ricardus]

Does carbon really do that ? Not aware although tbf I was only involved in working with CP pots / faders.
Any figures / results as to the magnitude of the harmonic(s).

Yes !

I keep hearing this claim on multiple forums but have yet to see a citation.

 

[JohnRoberts]

From my time at P&G last century - I can say that distortion / non-linearities were never debated or the cause of customer comment IIRC. Mostly faders, some rotary pots. All CP. Lots of other issues addressed - "Cut Off" ; lubrication ; oil migration ; cross-talk ; screening ; wear characteristics. But not distortion.
In terms of signal path a major point was the conductive epoxy used to connect wires to the track(s). In relation to impairing "Cut Off".
Like the stuff used to repair car rear screen heaters that often doesn't work because it's too dried out.
The stuff was mixed in house on a shaker table using silver loaded epoxy IIRC and had to be used that shift.

In hindsight I have encountered some misbehavior from dirty wiper contacts inside unsealed pots, over the decades.

I have more than a little experience with inexpensive potentiometer manufacturing from dealing with production problems inside the Peavey factory. We used millions of pots a year. Inexpensive resistive pot elements are a slurry of carbon media, screen printed on a substate then cured (cooked, resistance changes with curing time).

This century I had some experience with carbon ink used to replace gold plating on PCB switch patterns. The carbon ink seems suitably reliable.

JR

 

[waltzingbear]

I seem to recall most of the reports about distortion in components really has to do with quality of termination. Much like Newmarket's experience in P&G, must be done properly. I could see the same factors in a pot, the crimp of the carbon button into the wiper, the end transition into connectors, etc.

Cheers
Alan

Hi Bri

 

[Gold]

Lots of other issues addressed - "Cut Off" ; lubrication ; oil migration ; cross-talk ; screening ; wear characteristics.

The problem I had with P&G RF15's was significant and widely varying series resistance at the end of the throw. If the pot is buffered it's not a big deal but becomes a big deal if used as an output fader with no buffering.

 

[Mr. Moscode]

they can only make noise when you are moving them...

JR

I wouldn't say that's true, especially in an older open pot. There are millions of noisy receiver controls in consumer equipment. Wipers and resistance elements wear and oxidize, especially in unsealed pots creating little diode contacts which are non linear with voltage and don't need to be turned to cause havoc.
I'm not an expert on what's the best material so anyone who needs to know has to do their own research, but suggestions would be welcome, I'm sure.

 

[JohnRoberts]

I wouldn't say that's true,

your option

especially in an older open pot. There are millions of noisy receiver controls in consumer equipment.

? noisy with no signal when not being moved...?

Wipers and resistance elements wear and oxidize, especially in unsealed pots creating little diode contacts which are non linear with voltage and don't need to be turned to cause havoc.

I have never seen that with the exception of crud on wiper fingers, as I already shared..

I'm not an expert on what's the best material so anyone who needs to know has to do their own research, but suggestions would be welcome, I'm sure.

In my decades in the trenches my experience is that pot resistive elements are far from the weakest link and not a significant source of audible distortion. Of course opinions vary (apparently).

JR

 

[Tubetec]

I have seen a handfull of pots where a tough layer of oxide formed on the wiper , more or less cut signal off entirely , needed to be scraped away

 

[JohnRoberts]

I have seen a handfull of pots where a tough layer of oxide formed on the wiper , more or less cut signal off entirely , needed to be scraped away

are you sure it was oxide? I have seen some gear pulled out of smoky clubs that had a layer of crud on everything inside.

Wipers often pick up dust causing scratchy, intermittant contact.

JR

 

[Mr. Moscode]

your option
Indeed.

? noisy with no signal when not being moved...?
Only when turned off.

I have never seen that with the exception of crud on wiper fingers, as I already shared..
Give it time. It's early.

In my decades in the trenches my experience is that pot resistive elements are far from the weakest link and not a significant source of audible distortion. Of course opinions vary (apparently).

I guess it depends on how your perceive distortion.

JR

In my trench I used to fix receivers and TVs for a living as a "yout'". Yes, signal distorted or open missing signal in some positions. If there was DC on the pot - grid, gate or base current through the wiper can cause noise. Resistors get noisy, why not pots? And the metal ring the other end of the wiper rides on can get crunchy, too. Oxidation, salty sea air, city pollution.

Anywhere there's a contact there's a problem waiting to happen, IMHE. Including solder joints.

That said, your mileage varied from mine and thanks for posting your experience.

Mr. Moscode

 

[JohnRoberts]

I remember fixing TVs as a kid... but back then it was grab the tubes and ride your bike down town to the drug store, because they had the only tube tester in town... find the weak tube(s) and replace. As often as not that was all it took. We used to use a "cheater" cord to bypass the safety lock out that prevented us from powering up the TV without the back on it. Got my first few zips poking around inside old TV sets (sometimes even after it was unplugged).

I guess it depends on how your perceive distortion.

I can measure distortion that I can not hear... I never heard distortion that I could not measure but back in the 70s I rolled my own two-tone IMD analyzer to better parse out HF non linearity that wasn't well revealed by typical THD+N measures (any active circuit with a LPF would roll off the higher distortion products too).

In my trench I used to fix receivers and TVs for a living as a "yout'".

I fixed stuff for free...(as a kid), when older I designed stuff for a living.

Yes, signal distorted or open missing signal in some positions.

yes I've seen my share of faulty pots, but not many new ones, bad because of "what" they are made from (while I have seen some new ones fabricated incorrectly).

If there was DC on the pot - grid, gate or base current through the wiper can cause noise.

and don't forget leaky or backwards electrolytic caps..

Resistors get noisy, why not pots?

I don't know about resistors "getting" noisy, while even new resistors start out with several kinds of noise (Johnson noise, excess noise, etc.)

And the metal ring the other end of the wiper rides on can get crunchy, too. Oxidation, salty sea air, city pollution.

glad I never had to deal with marine repairs. Salt water sux... just ask those Tesla owners who got flooded in FL The salt water turns their car batteries into time bombs.

Anywhere there's a contact there's a problem waiting to happen, IMHE. Including solder joints.

that makes for thousands of potential problems in a console. I experienced lots of problems with insert jack switch contacts, They could get oxidized and intermittent if not plated properly by the manufacturer (cough... Switchcraft).

That said, your mileage varied from mine and thanks for posting your experience.

we all rock a different path... but the same laws of physics apply to all of us. We all can learn from each other.

JR

Mr. Moscode

 

[Gert]

John Roberts and I are on the same page re. null testing. Can anyone find a long length pair of rusty barbed wire, wrap it in duct tape, and null test it with a similar length of Mogami/whatever cable??

Bri

Good idea

 

[Newmarket]

I wouldn't say that's true, especially in an older open pot. There are millions of noisy receiver controls in consumer equipment. Wipers and resistance elements wear and oxidize, especially in unsealed pots creating little diode contacts which are non linear with voltage and don't need to be turned to cause havoc.
I'm not an expert on what's the best material so anyone who needs to know has to do their own research, but suggestions would be welcome, I'm sure.

Being a mechanical device a "pot" is clearly subject to faults and wear'n'tear and environmental pollution.
What you are describing are pots that are faulty or need cleaning. All valid points and we all love a good veer, but just a reminder that the OP question was specifically on the track material:
"Any opinions on the sonic aspects of conductive plastic as compared to Cermet? "

 

[Matt Syson]

I have a few hundred metres of barbed and plain galvanised wire that I could use as a 'test'. It can't be immediately because it is keeping some cows in my field and the 30kV 'pulser' is still in use. It must be working well at the moment because I can hear the 'crack' of an arc-over 300 metres away.
Other than that due to my earlier life I know more about pots than I really want to, in terms of 'failure' modes so in terms of 'carbon versus Cermet' for 'pots that are intended for regular use I would tend to propose 'carbon' although I think 'polished carbon' is viable too. The contaminants they are likely to be subjected to will also have significant influence. The 'self cleaning' properties sometimes mentioned rely of at least occasional use be it a full rotation once a week or whatever.
I think it was 'Morganite' and/or Plessey who made pots where the track was cast into an insulating 'block' and had a carbon tipped wiper and were relatively well sealed.

 

[abbey road d enfer]

I wouldn't say that's true, especially in an older open pot. There are millions of noisy receiver controls in consumer equipment. Wipers and resistance elements wear and oxidize, especially in unsealed pots creating little diode contacts which are non linear with voltage and don't need to be turned to cause havoc.
I'm not an expert on what's the best material so anyone who needs to know has to do their own research, but suggestions would be welcome, I'm sure.

It's important to distinguish between noise, that happens mainly because of a malfunction (dirt, worn track or wiper), and distortion, which is the original question.
We all know that a part that has been damaged is susceptible of various detrimental effects, whether a potentiometer, a switch, a resistor or capacitor.
The question here is how much the material in a reasonably new pot damages performance.
I don't really have the answer (but enough years of tinkering allowed me to forge an opinion).

 

[nielsk]

I can find samples of all the crappy wire ever use from the beginning of audio gear!
I just don't have time to play with it... I could probably send an assortment to someone if they do.
I can tell you that hit records were made on all the gear that had this stuff inside, (and on ADATS and Pro Tools MIX systems, too! Who knew) and I can also tell you that trying to make a record with scratchy pots and iffy switches is a real drag, and that probably more pots & switches go bad from lack of use then over use ...
As to how different pot track materials sound, that's deeper than my knowledge. I am pretty happy if they work cleanly and consistently over time. A long time!

 

[Newmarket]

I can also tell you that trying to make a record with scratchy pots and iffy switches is a real drag, and that probably more pots & switches go bad from lack of use then over use

Good to bear that in mind. I recall a 'studio tech' discussing how they would periodically move channels on a big desk because the highest number channels didn't get used as much as the lower and middle numbers. You know...like the top notes on a piano that only get played by cats

...
As to how different pot track materials sound, that's deeper than my knowledge. I am pretty happy if they work cleanly and consistently over time. A long time!

Shhh...don't tell anyone but they all 'sound' the same

 

[JohnRoberts]

I can find samples of all the crappy wire ever use from the beginning of audio gear!
I just don't have time to play with it... I could probably send an assortment to someone if they do.
I can tell you that hit records were made on all the gear that had this stuff inside, (and on ADATS and Pro Tools MIX systems, too! Who knew) and I can also tell you that trying to make a record with scratchy pots and iffy switches is a real drag, and that probably more pots & switches go bad from lack of use then over use ...
As to how different pot track materials sound, that's deeper than my knowledge. I am pretty happy if they work cleanly and consistently over time. A long time!

Audio electronics is actually pretty mature technology. Wire has been pretty well investigated with hyperbolic claims debunked. Back in the 1980s I used to write a column in Recording engineer/Producer magazine called "Audio Mythology". Funny speaker wire was one of my column topics and IIRC I cited AES papers (Griener?) and more.

JR

 

[Newmarket]

Audio electronics is actually pretty mature technology. Wire has been pretty well investigated with hyperbolic claims debunked. Back in the 1980s I used to write a column in Recording engineer/Producer magazine called "Audio Mythology". Funny speaker wire was one of my column topics and IIRC I cited AES papers (Griener?) and more.

JR

It seems to me that for analogue audio signal 'wire is pretty much wire' once you get beyond mechanical strength - so not especially thin or in case of solid core not so big that it has too large a bend radius. I know there's the OFC Copper thing but I'll bypass that for now.
The real questions arise around "Cables" where there is more than one wire - construction / capacitance / screening type and material / twisted / starquad etc.
And then the connector debate...
"Funny Speaker" cables get you into a whole other area.
Actually the term has a certain ring about it - "Funny Speaker Cable Company" ?