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.]

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Don LaCourse Sr.

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

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.]

Just my HO.

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.]

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.

I mentioned earlier that I was looking to buy a second volume pedal as a back-up for gigs. Well, I've finally gotten one. A used Goodrich 120 in immaculate condition (Thanks to forum member T.S. MacDonald). The pedal has the OEM J-pot (with the logarithmic taper).

As you know from my previous post, my other volume pedal (also a Goodrich 120) has the Clarostat pot with a linear taper and that after changing the pot from the log taper to the linear taper I hadn't noticed any difference. Well, apparently, I had subliminally made both a physical and mental adjustment to the linear taper pot and had just gotten used to it. I say this because, when I received the "new" 120 pedal from Tom I decided to A/B the two pedals with my rig to see if I truly don't notice a difference. BOY WAS I WRONG!!! There is a considerable difference.

Now, here's the surprise, even to me...I like the linear taper BETTER than the OEM log taper. The reason is, with the log taper the pedal movement/volume swell ratio is greater and therefore, more forgiving to sweeps in pedal movement. With the linear taper, pedal movement/volume sweeps are very linear and much more critical. Hence, small amounts of pedal movement result in more pronounced volume swells.

I believe I have simply, just gotten used to the "feel" of the linear taper, because when I tried the new pedal I found that my right foot seems to have to make exagerated movements on note and chord sustains and that the pedal has to be depressed more for a mean average volume. I realize that what I have noticed is the "norm" for this pedal and that I have gotten used to a highly controlled and sensitive feel for my volume pedal. I also realize that, although I personally prefer the feel of the linear taper and will probably switch the pot on the new pedal to a linear taper; it is not for everyone.

One final point: the tone of my steel with both pedals is identical. In other words, the tone of the linear taper across it's sweep is the same as the log taper.

Now, you can honestly decide for yourselves if a lower cost linear taper is really the right answer for you. Thanks for "listening" and...

Keep on pickin'!
Glenn

[This message was edited by G Suchan on 19 July 2000 at 02:12 PM.]

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 I said before, the linear pot may not be for everyone. That was the reason that I posted my A/B comparisons. I didn't want to see any fellow forum members trying a linear taper without knowing my additionl findings. At any rate it works for me.

However, you are incorrect in your interpretation of the resistance roll-offs of the linear and logarithmic tapers. It is as I previously posted: (edited)

"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 100%(r)=0%(R); 99%(r)=1%(R); 90%(r)=10%(R); 50%(r)=50%(R); 10%(r)=90%(R); 1%(r)=99%(R); 0%(r)=100%(R)."

"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...."

Donny, with this information in mind, a linear taper volume increase is directly proportional to pedal travel and full volume occurs at the end of pedal travel NOT before. This may feel overly sensitive for a volume pedal. With the log taper the volume increase is less than equal proportional at the beginning and the end of pedal travel; only at the middle travel is it equal. And once again, full volume occurs at the end of pedal travel. The reason almost all users prefer the log taper is that volume increases are not as sudden at the beginning of pedal travel as they are with a linear taper.

I hope clarifies these functions for you. This post is not intended as a "flame"

Keep on pickin!
Glenn

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.

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".

I think the competition will help stabilize the price of the pots. The big problem is the fact that that particular model pot is almost exclusively used for volume pedals and the market for them is relatively small, which causes the pot to be priced the way it is. If it was a common value pot used in many applications the price would be a lot less than what it is.