Then the next test if I have time is to increase the current in the test contact. If the barrier allows microscopic contact then there should be an increase in distortion with increased current.
John Curl.....
Not sure if this is the right place for this post but I am a potential buyer of your vendetta scp1; Other than having only one power supply and a different chassis, are the guts basically the same? I can find a lot of info on the scp2 but very little on the scp1. Looking for a new phono stage to mate with my Rega P7.
By the way, I have 4 of the parasound john curl designed amps - love them. Run cool and sound great!
THANKS!
Not sure if this is the right place for this post but I am a potential buyer of your vendetta scp1; Other than having only one power supply and a different chassis, are the guts basically the same? I can find a lot of info on the scp2 but very little on the scp1. Looking for a new phono stage to mate with my Rega P7.
By the way, I have 4 of the parasound john curl designed amps - love them. Run cool and sound great!
THANKS!
Don't ignore electro-migration or other tendencies for high current density to improve the contact.
Lithium coin cells that are designed for a long service life self passivate, you need to draw some current from them first to wake them up as it were, so that would have confused your assessment of what worked, if you want to repeat the experiment leave the cell for 6 months in its packet again...
Wrinkle
Ed,
This is coming late, I know, but this morning with my first cup of coffee I remembered one of your first curves showing a 'flat' portion around the zero crossing.
That looks to me as exactly 1 LSB of your equipment. Is that correct, and if so, what would that mean for the measurement?
jan didden
It was two samples long sometimes three, and it occurred where the dv/dt should have been at maximum. I do not see that result with other samples so I assume it is not the scope.
So one issue may be if this is due to contamination in a mechanical contact what are the properties of the contamination? I suspect I will try sulphur on silver wire. Once a film has formed I can cross two pieces and measure the properties of the surface barrier.
The issue is; do mechanical contacts have an electrical dead zone? I and many others have the experience of a dead audio circuit temporarily returned to life by a voltage surge, such as tapping on a dead microphone. This is occurring at a level of tens of millivolts.
The switch industry considers any voltage below 12 volts to be a dry contact that will not clear itself by a small arc. The use of self wiping gold plated switches has proven successful for handling lower level signals.
The example of a microphone tap restoring function would seem to be the same arc mechanism except it happens at a much lower voltage.
In my play I showed at the limit of my scopes resolution what may have been such a dead zone inside an electrolytic capacitor. (With your knowledge of chemistry I suspect you understand why I would pick that example.)
The idea then seemed to be to look at the distortion spectra of the signal passing through a contact. If there was no disruption the spectra would be relatively clean. I measured a soldered jumper for this baseline. I tried other mechanical contacts and I found a silver contact switch that exhibits excess noise when passing a low level signal around 1 nv at 1,000 cy. I assume the contaminant is silver sulfide. This is known as a semi-conductor (IEEE Xplore - Sign In).
Now if the resulting spectra had nice even order distortions I would have suspected rectification or at least non-symmetric current flow. The result had much more than that and so much that it appears as a rise in noise level.
The issue has been raised that at a low level of contamination that there would still be metal to metal contacts that would prevent such a dead zone. Also that the surrounding air would not conduct at such low voltage levels.
So although electrochemical methods would produce a uniform and repeatable surface, I think the issue is would natural contamination from the air born coal fired power plants form a uniform film? Or more interestingly can such a film form that would revert to conductive silver at a very low level of excitation.
It may be that the restoration of conduction is not caused by an arc type clearing but rather an electrochemical response!
I think the chemistry of silver sulfite and electrical contact problems is not in dispute.
Contact Resistance
All, fine discussion. Bringing the contact resistance/nonlinearity issue back to the audio domain: I'm sure we have all had to repeatedly operate a relay or switch or reseat a connector to eliminate a discontinuity due to an oxide-film threshold voltage phenonmenon. Anatech, I worked for years as the service manager at high-end stores and I feel your pain, it is such a common problem. In these cases, turning the volume up will sometimes cause the signal to suddenly pop back in as the film on the failed contact is bridged with an arc.
Reducing the discussion to this one simple case says to me the following: Yes; contact oxides and contamination can cause partly or non-conducting films to develop. And in my experience, repeatedly operating the failed connection will restore the audio quality (albeit temporarily in some cases). Once the contact film is shunted by the base metal contacting, or by a micro-weld, the audio quality does not improve further. This can occur with audio of widely varying magnitudes: microphone connections or high-power speaker relays. Relay manufacturers understand that this happens and design the return spring to break any weld which is made while operating the relay within it's ratings.
I interpret this to mean that there is a certain contact pressure per square area above which a gas-tight metal-to-metal connection is made with reliable, linear characteristics. It is often bridged by micro-welds which develop when the base metal begins to interact with the environment. Sufficient actuation pressure ensures puncturing of this film if the device is not left in one state for too long. Anyone who has had the pleasure of using the reliable Shallco switches knows the success of high-contact pressure integrated with wiping. This pic shows my preference for switch choice in a current project:
(The switch on the left is a ceramic high-power RF switch)
The fact that power and small-signal relays are made with the different technologies they are (evacuated with gold contacts in small signal, conductive soft oxide silver in power) shows this to be a well-understood phenomenon.
My experience is: if audio is heard, there is no film in the contact point, or it is so thin that the signal caused an arc to bridge it. If slight movements of the contact cause noise, then the film is a problem and cleaning is called for. It is another case where your ears are a fantastic diagnostic tool!
Ed, this probably doesn't address your concern about a potential film which is conductive enough to pass audio but which is nonlinear and causes distortion. Looking at ancient selenium plate rectifier technology, a case could be constructed to display this characteristic. However, due to the fact that the most commonly used contact schemes are ALSO used in our $$ test equipment we use to find these problems, I believe that part of the design criteria of switches, relays, etc. is to eliminate these non-linear effects.
I once had an audio distribution system with over 200 BNC elbows...😱
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
Edit: Ed, it appears we cross-posted, sorry for any redundancy...
All, fine discussion. Bringing the contact resistance/nonlinearity issue back to the audio domain: I'm sure we have all had to repeatedly operate a relay or switch or reseat a connector to eliminate a discontinuity due to an oxide-film threshold voltage phenonmenon. Anatech, I worked for years as the service manager at high-end stores and I feel your pain, it is such a common problem. In these cases, turning the volume up will sometimes cause the signal to suddenly pop back in as the film on the failed contact is bridged with an arc.
Reducing the discussion to this one simple case says to me the following: Yes; contact oxides and contamination can cause partly or non-conducting films to develop. And in my experience, repeatedly operating the failed connection will restore the audio quality (albeit temporarily in some cases). Once the contact film is shunted by the base metal contacting, or by a micro-weld, the audio quality does not improve further. This can occur with audio of widely varying magnitudes: microphone connections or high-power speaker relays. Relay manufacturers understand that this happens and design the return spring to break any weld which is made while operating the relay within it's ratings.
I interpret this to mean that there is a certain contact pressure per square area above which a gas-tight metal-to-metal connection is made with reliable, linear characteristics. It is often bridged by micro-welds which develop when the base metal begins to interact with the environment. Sufficient actuation pressure ensures puncturing of this film if the device is not left in one state for too long. Anyone who has had the pleasure of using the reliable Shallco switches knows the success of high-contact pressure integrated with wiping. This pic shows my preference for switch choice in a current project:
(The switch on the left is a ceramic high-power RF switch)
The fact that power and small-signal relays are made with the different technologies they are (evacuated with gold contacts in small signal, conductive soft oxide silver in power) shows this to be a well-understood phenomenon.
My experience is: if audio is heard, there is no film in the contact point, or it is so thin that the signal caused an arc to bridge it. If slight movements of the contact cause noise, then the film is a problem and cleaning is called for. It is another case where your ears are a fantastic diagnostic tool!
Ed, this probably doesn't address your concern about a potential film which is conductive enough to pass audio but which is nonlinear and causes distortion. Looking at ancient selenium plate rectifier technology, a case could be constructed to display this characteristic. However, due to the fact that the most commonly used contact schemes are ALSO used in our $$ test equipment we use to find these problems, I believe that part of the design criteria of switches, relays, etc. is to eliminate these non-linear effects.
I once had an audio distribution system with over 200 BNC elbows...😱
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
Edit: Ed, it appears we cross-posted, sorry for any redundancy...
Last edited:
You never eliminated the simple explanation of mechanical vibration restoring metal to metal contact. Last week milli-volts today nano-volts, a moving target.
Look up the fermi levels and some of the semiconductor theory nothing goes on at nano-volt levels.
Darn, you are making sense, Hhoyt. Those Shallco switches that you like are very similar to the Shallco switches we used in the CTC Blowtorch. Now, you know why.
Shallco Switches
We have been using the large open-frame Shallco switches for fifteen years. They use coin silver contacts and coin silver wipers. "Coin" silver is about 92% silver and has other alloying elements to provide stiffness and spring pressure. Pure silver is dead soft and would not work at all.
When selecting switches we do a fairly elaborate test to compare against a straight-wire bypass, carefully controlling all of the variables. (This is explained in a large ad in the latest Stereophile, August I think, with the heading "It's a real clunker". The Shallco switch is the only thing we've found that is essentially indistinguishable from the bypass.
But even though they are coated with grease to prevent oxidation (and sulfidization), they need to be cleaned by using them every few weeks. We have one switch for the input selector and one for the volume control. At the system in the factory there is normally only one source. So even though the volume control is constantly being used, the input is almost never used. If it hasn't been operated for a week or two, we flip it back and forth a half dozen times. The sound of the system improves noticeably as the contaminants are wiped off of the contacts.
We have been using the large open-frame Shallco switches for fifteen years. They use coin silver contacts and coin silver wipers. "Coin" silver is about 92% silver and has other alloying elements to provide stiffness and spring pressure. Pure silver is dead soft and would not work at all.
When selecting switches we do a fairly elaborate test to compare against a straight-wire bypass, carefully controlling all of the variables. (This is explained in a large ad in the latest Stereophile, August I think, with the heading "It's a real clunker". The Shallco switch is the only thing we've found that is essentially indistinguishable from the bypass.
But even though they are coated with grease to prevent oxidation (and sulfidization), they need to be cleaned by using them every few weeks. We have one switch for the input selector and one for the volume control. At the system in the factory there is normally only one source. So even though the volume control is constantly being used, the input is almost never used. If it hasn't been operated for a week or two, we flip it back and forth a half dozen times. The sound of the system improves noticeably as the contaminants are wiped off of the contacts.
Switches
Charles, I think other switches initially work well, but the Shallco open-frames are the easiest to maintain when the inevitable happens...and I agree about the wiping action. I have Shallcos in stepped attenuators in my mastering suites, and if they haven't been turned for a while, repeatedly rotating them cures the intermittents. The small enclosed switches in mass-market gear are a pain to clean: you have to find a hole to squirt Deoxit into or pry up a corner of the phenolic terminal plate...PITA
OT (but audio related) - Car manufacturers are designing external speakers to make noise outside the new EVs for safety reasons:
2012 Ford Focus Electric Vehicle Test Sound A - YouTube
You can't save a dumbass from themselves.
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
Charles, I think other switches initially work well, but the Shallco open-frames are the easiest to maintain when the inevitable happens...and I agree about the wiping action. I have Shallcos in stepped attenuators in my mastering suites, and if they haven't been turned for a while, repeatedly rotating them cures the intermittents. The small enclosed switches in mass-market gear are a pain to clean: you have to find a hole to squirt Deoxit into or pry up a corner of the phenolic terminal plate...PITA
OT (but audio related) - Car manufacturers are designing external speakers to make noise outside the new EVs for safety reasons:
2012 Ford Focus Electric Vehicle Test Sound A - YouTube
You can't save a dumbass from themselves.
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
Mechanical vibration! Must be one heck of a tap, as it will fix connectors at the other end of the cable!
Last week pico-voltmeters, this week nothing goes on at nanovolt levels!
One of the every so often accidents is when a train hits someone walking down the tracks. Everyone knows trains are noisy, what they don't know is it all radiates out the sides! From behind you it really is not heard often until it is too late!
let me guess - you live in suburbs, don't walk miles a day in city centers
not at all - hearing is probably more fundamental warning sense than vision - omnidirectional, can't be naturally "turned off"
silent cars can surprise pedestrians - bicycles are already a threat - with some pedestrian fatalities
many pedestrian collisions occur in marked crosswalks
not at all - hearing is probably more fundamental warning sense than vision - omnidirectional, can't be naturally "turned off"
silent cars can surprise pedestrians - bicycles are already a threat - with some pedestrian fatalities
many pedestrian collisions occur in marked crosswalks
Hello Howard,
I've never seen one go intermittent. Instead, the sound quality diminishes slightly but noticeably. The first time we figured this out we probably hadn't turned the switch for the better part of a year. One of seven coal-fired power plants in Colorado is about 1/4 mile away from our factory, but it is downwind 90% of the time. They also have some relatively modern scrubbers to remove nasties, but I would still imagine that sulfides are around. The degradation in the sound was so gradual that we hadn't noticed it, but turning the switch brought about a definite sonic improvement. They used to use a grease from Ford called "Ignition Switch Grease" or something. I'm not sure if they still use it. Running a rotary switch dry is a huge mistake!
Interesting, how do you determine the bad end without disassembly? Also your comment about condensor mics never having the problem, the other end knows?
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