When is a pot Shot?

Greg Derksen · From: Alberta, Canada

I have an old Sho-bud Volumn Pedal that
scratches like crazy even after spraying
contact cleaner in it. Is the pot shot or is
there a repairable solution? Thanx. Greg

Glenn Suchan · From: Austin, Texas

Greg,

When the potentiometer in your volume pedal starts to make scratching noises, it's on it's way to the "Big Parts Warehouse in the Sky". There's nothing you can do to correct the problem or prolong the life of the pot. By spraying cleaner in the pot, you probably have accelerated the dying process of the pot. Most potentiometers used in volume pedals have a graphite contact surface which wears out causing the "scratching" sound. When you spray cleaner on that surface, you're cleaning off what little graphite is remaining.

My advice: Stock extra potentiometers. (Hint: They are a little cheaper if bought from an electronics parts distributor such as Newark Electronics or Allied Electronics. $12 to $15 as opposed to $25 from some music equipment dealers.) A better choice and one I'm trying to do is to buy an extra volume pedal and have it ready in any playing situation you encounter.

Keep on pickin'!
Glenn

[This message was edited by Glenn Suchan on 03 May 2000 at 10:45 AM.]

Greg Derksen · From: Alberta, Canada

Glen Thanx for your reply, I guess I will
get a new pot. As long as its the same 500K
Type J Pot I should be okay, right? Thanx
Greg

Jack Stoner · From: Kansas City, MO

Yhe ONLY pot that will work satisfactorily is the exact replacement Clarostat (formerly Allen Bradley) pot. There are other 500K audio that are supposed to be equivalent but they do not have the same resistance taper.

It's unfortunate because we're stuck with it and have to pay the outrageous price for them.

Glenn Suchan · From: Austin, Texas

Greg and Jack,

The 500,000 ohm potentiometer aka J-pot info is as follows:

Military specification: #RV4NAYSD504A
Commercial equivalent: 53C3 Series
Manufacturer: Clarostat
Newark Electronics stock #01F2649

I bought 4 of them a couple of months ago and paid $8.75 a piece from Newark. (a far cry from $25.00 which is like a 300% mark-up)

Road Runner, what model of Goodrich Pedal do you have? I'm interested in a Model 120. If it's a 120 and is brand-new then e-mail me with purchase details. Thanks!

Keep on pickin'!
Glenn

[This message was edited by Glenn Suchan on 03 May 2000 at 02:12 PM.]

Lee Baucum · From: McAllen, Texas (Extreme South) The Final Frontier

I agree that 300% is a bit steep in the mark-up department; HOWEVER, I don't mind paying a bit of a premium to a dealer who caters to pedal steel guitar players. If it weren't for them, we would have a tough time getting all those toys we are in love with. If we don't support them, they aren't going to support us.

Just my HO.

Lee, from South Texas

Jack Stoner · From: Kansas City, MO

Glen, are you sure they are the EXACT replacement?? I'd like to try one. I've tried ordering pots from electronics parts houses and they also quoted me "this Clarostat is the exact replacement" but they are not and the inital resistance curve is not the same. Back before Clarostat bought out Allen Bradley they made an equivalent pot (as listed in their spec's) to the Allen Bradley but it was not. I know one guitar builder that used them in his volume pedals and wound up having to replace them with the Allen Bradley as everyone was complaining.

Jack Stoner · From: Kansas City, MO

I just checked a new one that I have and it is marked "JA1N056S04AA" Clarostat 500Kohm, Type J. From this type number I would say the Newark ones are not identical. The "AA" is the resistance taper, the Newark unit is an "A" taper and also not a Mil Spec model and probably where the difference is.

Greg Derksen · From: Alberta, Canada

Thanx for the Info Guys! Greg

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Jack, you are correct! The Newark pots are "NOT" the same 500K pots. They have the wrong taper. It "MUST" be a "LOG" taper to work the best. Yes, other tapers will work, but not as good as a "LOG" taper. To get a pot that works, you must special order it. That means buying quite a few to get a good price.

------------------

Jack Stoner · From: Kansas City, MO

Keith, the difference is not that the other pot isn't an audio or "log" taper pot. It's the particular taper of the "real" one - it's first 25% of the resistance taper is different than other audio pots (I don't remember which way - faster or slower - so I won't say). That and the "real" one is made to mil standards, which means ruggedized and a thicker resistance element and better contacts on the wiper (which makes it last longer than a "commercial grade" pot.

Glenn Suchan · From: Austin, Texas

Jack, Keith, and Lee,

A little additional information regarding the replacement pot I suggested. This information is not intended as any sort of "flame", just as helpful information. So please, don't read any more into it than that.

Earlier, today I had a telecom with Sergio Vargas, Applications Engineer for Advanced Sensor Systems aka Clarostat. What follows is based on that conversation.

Jack, with regard to the Mil. Spec. number: In most cases where a product has a Mil. Spec. (Military Specification) number, that product is the standard production configuration which will meet a specific Mil. Spec. criteria. In such cases, the manufacturer may apply for a Mil. Spec. rating for the product and if accepted, will be required to provide an additional quality control inspection by a government authorized, in-house, inspector along with normal QC inspection. In such cases, a given product may have not only, a Mil Spec. Number but also the normal rating. In this specific case we are talking about the "Commercial Equivalent" series number. This was verified by Mr. Vargas. Hence, Mil. Spec. #RV4N and the Commercial series #53C3 are manufactured to IDENTICAL specifications. Furthermore, Mr. Vargas supports the fact that RV4N and 53C3 potentiometers are completely interchangeable with JA1N potentiometers.

Jack, I think you might have forgotten a characture in the JA1N part number. It should read: JA1N056S504AA. You are right about the "AA" representing a "Log Taper".

That said, I will clarify the differences between the "RV4N" and "JA1N" pots:

Both share the following specs. Hot-molded, carbon composition resistance element; Single, clock-wise rotation of the shaft; 2-watt rating; 500,000 ohm resistance; All dimensions including locating lug.

Difference:
RV4N: Linear taper
JA1N (with "AA" suffix): Logarithmic "Log" taper

The definition of a linear taper is: the change in resistance value is directly proportional to the degree of shaft rotation. In this case, where "r" equals the resistance value in %, and "R" equals the total shaft rotation in %, then, 1%(r)=1%(R); 10%(r)=10%(R); 50%(r)=50%(R); etc.

I am waiting for details to be faxed to me by Mr. Vargas with regard to the Log Taper of the JA1N pot. In the meantime, Mr. Vargas states that the log taper allows for "more control" through the first 50% of shaft rotation. When I queried about actual resistance variation, I asked if, in graph form, the taper appears as a paraboloid or as an equal radius curve. He indicated that it is more of an equal radius curve.

Lee, about the cost of the potentiometers: It seems, that if the music dealers I mentioned in my previous post, are selling the JA1N056S504AA pots, their selling price is probably justified. This particular pot is a custom "production run" for Clarostat and as such, sells for a higher price. Newark carries the 10K, 50K, and 100K versions which sell for approximately $18 each. Keith, you are right, the 500K version would have to be special ordered in 100 piece quantities. So, my appologies to the music dealers at large. They all are "The Salt of the Earth".

Finally, and this just my personal observation; I have been using an RV4NAYSD504A potentiometer for quite some time now. I recently installed a second one in my volume pedal. Any differences in the way the pedal reacts are minimal to the point of unnoticeable by me. This may not be true for everyone, but at $8.75 each, it might be worth looking in to.

I'll post the "log taper" specs of the JA1N pot as soon as I get them.

b0b, sorry I hogged the bandwidth with this post. I'll hop off the soap box now....

Keep on pickin'!
Glenn

[This message was edited by Glenn Suchan on 04 May 2000 at 11:57 AM.]

b0b · From: Cloverdale, CA, USA

We no longer have a bandwidth problem. Hog all you want!

Lee Baucum · From: McAllen, Texas (Extreme South) The Final Frontier

Glenn - No offense taken, or intended. I just wanted to express my opinion. We need to help out these guys that are in business to support steel players. If we don't, they won't be around very long.

Lee, from South Texas

Randy Reimer · From: Ardrossan, AB

Or you could by one of the new Hilton pedals

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

I just received a special order Clarosat dual 500k pot from local vendor, ( dual because I wanted to incorporate the Myrick Mod in this pedal again) and I paid about the same as most of us paid for the single pot.

Jack is right !!!! not all of these pots are the same. the OEM part is "AB" (Allen-Bradley) who sold this part of the business to someone else. ( I think Clarostat) The one I use is an industrial grade unit, made in Canada. The regular (consumer grade) pots are a bit more ecomonical but they don't last near as long as the industrial units.

Just my 2 cents

Donny Hinson · From: Glen Burnie, Md. U.S.A.

I have tried the linear taper pots, and they "come on" much too fast for me! Audio, or log taper, pots are designed to make volume changes "evenly proportional" throughout the entire range.

What you can "get used to", and what's "comfortable" are two vastly different things!

Jack Stoner · From: Kansas City, MO

The Audio or Logrithmic taper pots are designed to increase (or decrease) level in proportion to how the ear senses sound levels.

There would be an obvious difference between the Linear and Log pot pedals. Most would not "condition" themselves to the linear taper pedal and are more comfortable with the conventional log pot pedal.

As far as tone difference, you are correct there is no tone difference, since both pots are are the same resistance value (500K).

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Right you are Jack! With a log taper pot, half-pedal equals half-volume. With a linear taper, half-volume "comes in" at about 1/4 pedal and the last 1/3 of travel does almost nothing!

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

I see you fellows have brought back a old topic. Let me ask some questions. Jack, the Clarostat pots are rated at a million back and forth movements. It is obvious that many of these pots won't last the million movements. What usually happens is they get scratchy sounding when turned. This scratchy sound is made from tiny pieces of hot molded carbon. That is the material used inside, hot molded carbon. Did you fellows ever wonder why this carbon material comes apart causing a scratchy sound? Jack Stoner can tell you how electronics manufacturers "must" protect against static electricity. A person can easily generate 4000 volts just walking across a carpet. Musicians have several pieces of equipment hooked together, and each one has it's own power supply. As these devices, that are hooked together, are turned on or off, huge surges of currrent and voltage can come down a guitar cord. Guess what----the POT in your foot pedal has no protection of any kind from static DC electricity. The pot in your foot pedal has no protection of any kind against current and voltage surges that happen when equipment is powered up and powered down. I say that these huge surges of DC can blow tiny pieces of the hot carbon in POTS loose. Therefore, if your POT is not very old ,and is starting to sound scratchy, it has probably got a surge of current and voltage. Jack---Hartley Peavey and I protect our electronic devices from these current and voltage problems. POTS have ZERO protection. Jack, I have a wonderful solution to this whole problem----Jack, I am smiling!

------------------

Jack Stoner · From: Kansas City, MO

Keith, you are describing a "worse case" situation, not a normal every day application. Also, think of this - if there is a preamp device with protection before the volume pedal (e.g. your digital sustain unit) and the amp after the volume pedal. Both, by design are protected from surges caused by static electricity and in doing so the volume pedal's input and output are both protected.

Keith, you are hung up on static electricity and although a factor, in reality it's not as big a factor as it is percieved. While I was working, I got deeply involved in a static report that SSA did because of the potential for computer equipment failure and of eary CMOS devices. However, as it turned out, the worst fears of the people that initiated the study never turned out. Equipment (computers/terminals/PC's) that SSA purchased after the mid to late 80's were not as susceptable to static electricity related failures. There were some failures that were or could have been attributed to static but the percentage was so small that it was not a factor in the overall failure rates.

Although as a designer with the aim of making a device "bullet proof", would reqire dire protection methods in practicality you also have to look at the probability that it will happen. Using your logic, we should abandon the current simple pot design for a device with input and output current and voltage limiting protection and make the device's cost several times higher.

You have done that with your volume pedal, which gives everyone an alternative (except the few that feel a linear volume control is better) if they feel the less costly mechanical volume pot pedal is inadequate. To many musician's cost is not a factor and for them your pedal is a viable application. For those without deep pockets or that do not feel the simple pot pedal is passe it is still the choice.

If this was an electronics engineering forum static electricity and the various parameters would be a hot design topic.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Jack you are correct, I am totally hung up on failure protection. You never know what is going to be plugged into the input, or output of a device. If a device fails, I want to know why. I want to do everything in my power to prevent failure. Jack, how long do you think it would take to ZAP the transistor junctions of a pre-amp hung on the leg of a steel guitar if there were no protection? Over 50% will experience failure within the first year. Some will last forever. Some people have wondered why their POT has failed before the rated million turns. Since these POTS are sealed according to military standards, it doesn't seem possible that it is dirt. There is always a reason for failure. By the way, someone told me you had deep pockets! Just kidding!

------------------

Jim Smith · From: Midlothian, TX, USA

FWIW, I bought a Goodrich L-120 in the early 1980's. Since then I've played six nights/week for a couple of years, and played on average every other weekend since. I've NEVER had a pot problem and NEVER replaced the pot. I have changed pots on Sho-Bud, Dekley, and Emmons pedals so either I got a good one or the Goodrich pedals are more air and dust resistant than the others.

Jack Stoner · From: Kansas City, MO

Keith, as a designer/manufacturer you must be concerned with equipment reliability. Part of that reliability is input protection of whatever type (signal overload, shorts, static, etc). However failsafe or reliable a piece of equipment is, there is still going to be failures. If things never failed warranties would not be needed and service technicians would not be needed. But, failures do occur, whether due to poor design, poor material QC/burn in, poor or no manufacture QC, premature component failure to do a manufacturing defect that did not show up in component QC acceptance, failure due to user abuse, and failure to to the age of the equipment. There's many reasons a component or unit can fail, but my experience as both a user and a technician says static electricity is not a major cause of component failures. I find most failures are either manufacture/assembly/QC or user induced.

I did an experiment back in the late 80's with some CMOS chips, in a digital device I had built, by intentionally touching them without grounding myself to eliminate any static. The chips were internally static protected and I was never able to cause the logic device to have an error or device failure, even with repeated "zaps".

As far as volume pedals that use pots, the MTBF is dependent on the user. Those of us that are not constantly up and down on the volume pedal will find the pot lasts much longer than those that are constantly using the volume pedal. I'm not passing judgement on proper user of the volume pedal, just commenting on the MTBF. Since the pot used is made to military standards and is "sealed" (for all practical purposes) the type of volume pedal design - open on the bottom like an Emmons pedal or closed like a Goodrich should have no influence on dirt getting into the pot.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Jack, you have been around a few days like me. We both used to use Allen Bradley POTS, before Clarostat bought Allen Bradley out. Clarostat POTS are no longer made by American workers, they are made in MEXICO.
Jack, what is your HONEST opinion;Are the Clarostat POTS as good as the old Allen Bradley POTS? It just seems to me that the quality is not like it used to be with the Allen Bradley POTS made in America. We had a recent discussion about the fact that Clarostat no longer has a monoply on the world of steel guitar. This is because Paul Franklin Senior is selling a different company's POT. I am thrilled to death that people have a 2nd choice besides Clarostat. Way to go Paul Franklin!!!!!!

------------------

Forum Index > Electronics	Goto page 1, 2 Next	Next oldest topic :: Next newest topic