Cleaning a scratchy poti of the older Ernie Ball volume pedal

Posted on Leave a commentPosted in Effects, Mark Knopfler gear

The Ernie Ball volume pedals often become scratchy after a long time of usage. While you can replace the current poti model with a brand new poti, it is almost impossible to get a replacements for the older poti types. However, the older potis can be opened and cleaned which – not always but often – cures the scratching. As I did this successfully a few days ago, I took some pictures to demonstrate the procedure.

The poti was the Canadian type used in the mid 90ies but the previous Allen Bradley / Clearostat poti used before can be treated in the same way.

First, I recommend to remove the two screws that hold the black metal block which holds the poti. The string can be released from the poti easily then (you might take pictures before so that later you know how it was assembled).

With these poti types, the wires are plugged to the poti and can be removed without any soldering (again, take notes where they were, or take a picture).

 

Bend open the two mounting tabs with a screwdriver. Be careful not to bend too much as these might break. Often is is enough to open only two of the four tabs, on the side that exceeds the metal block.
Bend open the two mounting tabs with a screwdriver. Be careful not to bend too much as these might break. Often it is enough to open only two of the four tabs to remove the cover, on the side that exceeds the metal block.
Remove the cover, then put a piece of fine sanding paper between the wiper and the carbon resistor. Turn the poti several times to clean the wiper.
Remove the cover, then put a piece of fine sanding paper between the wiper and the carbon resistor. Turn the poti several times to clean the wiper.
Repeat this a few times. Note the amount of dirt removed by this procedure.
Repeat this a few times. Note the amount of dirt removed by this procedure.
Next use a pipe cleaner soaked with pure alcohol to clean the carbon resistor.
Next use a pipe cleaner soaked with pure alcohol to clean the carbon resistor.

Now the poti should be clean. Note that disassembling the wiper from the carbon resistor is not possible with these poti models so you need to clean it like this. Mount the case again, bend down the tabs to close it. An instruction how to assemble the string again can be found in this video:

Note that you can clean a modded volume pedal in the same way, just make sure to assemple all wires and the string exactly as they were before!!

Another note on this topic: I meanwhile tend to believe that the different taper on Mark Knopfler’s volume poti is not due to a different poti model but to an electronic solution possibly built into his rack. A first prototype circuit works promising, and also avoids the noise of a scratchy poti electronically. Watch out for future updates, I hope to offer something here soon.

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Ernie Ball volume pedal modification to make the taper like it was with the old Allen Bradley poti

Posted on 22 CommentsPosted in Effects, Mark Knopfler gear

Regular readers of this blog might know my first article about the different behaviour of Mark Knopfler’s Ernie Ball volume pedal compared to recent Ernie Ball models. In short: In the 80ies  a different poti was used that caused a completely different sweep curve than later ones (see diagram below).

Knopfler’s pedal changes volume drastically over the first part of the pedal sweep range. This allows him to perform the violin-like fade-in notes he is famous for with much more intensity than the new pedals.

Also, during the last part of the pedal sweep – from middle to full – Knopfler’s pedal changes the volume only moderately which means you can adjust the overall volume of the guitar much more precisely than with the new pedal. Let’s say you want to set the level to something like 80% (which Knopfler often does), the new models require a pedal position  that must be accurate to a tiny fraction of an inch, just a bit more and you are instantly at 90%, a tiny bit less and you are at 70% or even less. I found this extremely difficult to perform with your foot while playing and singing. Knopfler’s pedal can be rolled back for an inch to have the desired level, half an inch more and you might have 85%, half an inch less and you are still at let’s say 75%, so it is much easier to adjust.

Again:

Old style: great change in the first, small change in the second half of pedal sweep –> great for fade-ins, great to adjust volume
New style: small change in the first, great change in the second half of pedal sweep –> less intense fade-ins, difficult to adjust volume

Knopfler himself is aware of the problem so his roadie Ron Eve (or was it already Glenn Saggers?) just bought the remaining stock of the old potis from Ernie Ball to have replacements for all times.

My findings and measurements in detail

I have examined Ernie Ball pedals from the last decades but almost all had the new type of volume curve. I just managed to find one from 1986 which seems to behave like Knopfler’s, while my 1989 is already wrong. Surprisingly both the 1986 and the 1989 have an Allen Bradley poti, both made in Mexico. Later they came with a Canadian poti, today with one from Japan (custom-built by Tocos). I took a lot of measurements to see what really happens (diagram below), and found that all the newer potis behave almost identically.

Left to right: 1989 Allen Bradley poti - 1996 Canadian poti - the new Tocos poti

Unfortunately the original poti is no longer produced 🙁 . Allen Bradley was sold in the 80ies and soon stopped making them. The original type is – as I found out – extremely sought-after, in other words almost impossible to get. In addition, Ernie Ball changed some details of the pedal itself – e.g. to accommodate the new potis which have metrical threads instead of inch threads – so a direct replacement is often impossible anyway. Since these potis were all designed for heavy-duty usage (“extended life”), replacing it with some ordinary poti wouldn’t be a good idea – and possibly not easy anyway.

Knopfler has an Allen Bradley poti - note however that these look identical to the later Allen Bradley potis that had the wrong curve

The taper switch on some newer Ernie Ball pedals

Ernie Ball reacted to the situation and implemented a switch which enables two different volume curves, something that seems like a solution. However, my measurements showed me that it in fact changes the curve, but not really to what it was with the old poti. If you look at the diagram you will see what I mean. Besides, with the additional 220k resistor the taper switch puts in, you will lose a bit more treble, too (by the way, this is the reason you cannot simply increase the value of the resistor to make the curves more similar).

Quote from the Ernie Ball website FAQs on the problem

Q:I recently had you guys rebuild my older EB Volume Pedal and the new pot does not distribute the volume like the old pot did. Is this correct?
A: We have used at least 4 different companies to custom-build our potententiomers since the pedal’s inception in the 70’s. Since 1998, we have been using Tocos pots, which we feel are among the very best available today. However, they do have a different “sweep” than the older pots do. On top of the fact that potentiometers in general have very wide tolerances, the fact that upon rebuild we are removing one vendors pot and replacing it with another, there will be some obvious differences in the pedal’s sound. Here’s the scoop: we no longer stock the pots of old, not only because we can’t get them, but also because we do not think they are as consistently good as the Tocos pots. The Tocos pots are the most consistent, high quality pots we have tested. With regards to the sweep changing, that is due to modern day pot manufacturing techniques that are used across the industry.

In my first article I described that I swapped the cable from the guitar and to the amp on my pedal, so I got a curve closer to the old ones. This however had a technical drawback: you lose a lot of treble when the pedal is not at full position (much more than you normally do), so it was not really a solution.

Measurements

Measuring the output in relation to the pedal position
Ernie Ball volume pedal curves - After my modification (red curve) the pedal behaves just like the sought-after version from the early 80ies (yellow)

Without being a technician, you can see huge differences in the diagram. On the horizontal axis we have the pedal position, on the vertical we have volume output. The 1989 Allen Bradly (red) and the Canadian  poti used in the 90ies (blue) have almost identical curves. This is only slightly changed with the taper switch (green).

The yellow curve is the original poti style, and the orange curve is the 1989 poti after my modification (see below). Believe me, I myself am very pleased with my result 🙂 , and don’t forget that potis differ due to tolerances, so even two identical models will not measure 100% identical.

Now the great news

Coming from a family of engineers, I could not sleep (well not really 😉 ) before I found a solution for the problem. I finally managed to modify my two pedals to behave almost 100% identical to the old poti style, and this without any drawbacks, like the need to use (and first to find!) some low-quality poti with a similar curve, or to build in active electronic components that require a battery and introduce noise. The ease of use, look  and reliabilty of the pedal is not decreased in any way! The modification was  very tricky at first (you need inch allen keys that are difficult to get here in Europe,  or you constantly wish for thinner but longer fingers to operate things inside the pedal) and required a lot of experimenting (including making myself a little tool), but finally I got it done. I was really surprised about how close my modification is to the original curve (see diagram).

If you want me to modify your pedal (should work with all Ernie Ball types, at least for the common 6166 and the 6180 Junior pedals), I will happily do so. I thought it is fair to charge you the same fee as you pay for a repair at Ernie Ball – US $ 55 or 42,- € via PayPal (and what I do is more work than what they do, plus for some pedal models they even charge you US $ 75.)  Shipping: You pay shipping to me (Germany), I pay shipping back within Germany, within the EU it is  plus 5,- € . If you are from outside the EU, please ask for details before since customs seem to make handling rather difficult. Also ask for alternatives if you don’t want to use PayPal.

Use the contact form of this blog for first communication. I will reply via email then!

BTW, I will leave in your original poti which means if it is already scratchy, it probably will still be after (although one of mine was cured for some reason after the modification :). I also can open your poti when scratchy to see if I can clean it inside, please inquire for details in such a case.

Update: Check the MK-guitar.com shop for our stock of Ernie Ball pedals that are already modified.

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Some new thoughts on the Ernie Ball volume pedal

Posted on 1 CommentPosted in Effects, Mark Knopfler gear

On the recent Get Lucky tour I became aware of a little technical detail I had never paid attention to before: I was sure that the guitar cable coming from the guitar would first go into the Ernie Ball volume pedal and then back to the area on the right side behind the stage where Mark Knopfler’s effect rack and amps are placed. Instead, I observed that a long cable leads directly from the guitar to where the amps are. In other words, the input amp of the effect rack (or some other) seems to be the first part in the signal chain. Here the signal is boosted to line level, then (before or after the other effects in the rack) it seems to go back to the volume pedal in the front area on stage, and back to the effect rack again from where it runs to the amps.

I always wondered why Mark’s volume pedal behaves different than the Ernie Ball pedals  I have tried out (the response curve seems to be totally different, see here for more). Maybe Mark’s pedal really has a different poti (like some rumours say), or it just reacts differently because it works on a much higher signal level (after the first gain stage in the effect rack the signal becomes “active”, which means more level and a lower impedance). Theoretically it is also possible that Mark uses the version for line levels of the Ernie Ball pedal, which has a 25 kOhms poti instead of the 250 kOhms of the standard version.

I tried my pedal with a low impedance signal to see if it makes any difference: it did not, but I could not test with a higher level yet.

Another consequence of this signal path is that the long first guitar cable surely changes the colour of the tone. The longer a cable is, the higher its capacity which means it moves down the position of the pick-ups resonance frequency peak. It acts like a small capacitor put into the circuit. This way the cables capacity can easily shift the resonance peak of a standard Fender pickup (normally at about 6 kHz) to something like 3 or 4 kHz, which means that glassy high end at 6 kHz is reduced and the “presence” frequencies at 3-4 kHz are boosted.

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