The original ALPS pots are no longer available.

All the ALPS pots have a rotor with a rim around the edge.  This is either to help keep out dust or for some other purpose, such as taking the strain of excessive downwards force on the shaft, which would otherwise be taken by the centre of the phenolic paper-board which holds the resistive and conductive tracks.

The outer rim extends leftward in a slightly curved shape here, which is also a spring, as evidenced by the gap between this section of the rim and the rest of the rotor.  This is from a resonance pot - a dual 50k log, so there are two sets of wipers.

Here is a general view of the same rotor, with the two sets of wipers.

Here is the phenolic paper-board part of an ALPS resonance pot, with some wear from this outer rim.  This only happens when the shaft is both turned and pressed downwards.

Not all the ALPS pots have this white epoxy where the metal tags are riveted to the metal tracks.  Those without it may be less reliable, with open circuits developing between the tag and the track.

Starting from the outside we have:

Here are some extreme cases of pot wear.  I don't know exactly how this occurred, but there must have been a lot of turning and pushing to cut through the tracks like this.  This must have continued well after the pot failed electrically.  Perhaps someone was hoping to make them come good!

"Scratchy" pots in a device which has not been used for years can be caused by a thin film of grease on the conductive and/or resistive tracks.  I find this can often be made to go away by turning the pot a few dozen or maybe a hundred times.   However, at least with these ALPS pots, please don't push on the shaft when you do this!

By the way, there is very little trouble with the ALPS volume and tempo pots.  Replacements are available from Chipforbrains, as noted below.

Before affixing the knobs, I insert a 1/4" disc of leather inside the knob.  This means the knob sits about 1.2mm higher than normal.  This makes the knob easier to grasp and reduces the likelihood of unwanted downward pressure and wear of the case around the knob.

I also use a little Blu-Tack (poster putty) in the knob to stop them falling off.

Do not glue knobs onto the shafts!

Don't spray anything in or on pots and switches unless you really know what you are doing.  My life has been complete without having to do this (apart from a little alcohol in one or two isolated cases).  It seems to be common to spray oily things into pots and switches.  I think this is a bad idea.

Without these pots, we would be in trouble.  Despite the difficulties noted here, I am very grateful that these pots have been manufactured and made available.  They are available only in sets of six.  Likewise, pots for the TR-606 are also available, though I haven't used any of them yet.

This information may not be relevant to the pots currently on sale.  Below I refer to pots I purchased in 2006.  There were some earlier versions of the pots which I don't refer to here.

To purchase the pots, check in "Items for sale" at Chipforbrains eBay page: myworld.ebay.com/chipforbrains/ .  There are none for sale at the time of writing (2008-01-27).

Apart from the Resonance pot, these do not have a rim around the edge of the rotor.  So, apart from the Resonance pot, they should not suffer from the problem of cut tracks due to downwards pressure.

In my experience the pots have been good, except for the problems described below for the Resonance pots.  One thing to watch is soldering the two metal mounting tags of each pot.  They can be hard to solder, so you might want to file away the plating on both sides and the edges - and use a high-powered soldering iron.  These tags are more than mechanical. In the TB-303 they carry Ground to various parts of the circuit.  The machine will not work unless all the pots are soldered in to complete these ground circuits.  

It can be difficult to solder the pots in exactly the right orientation so that the knobs do not brush against the case.  It may be necessary to melt the joints and press against the pot shafts to slightly change their orientation once you have found a scraping knob problem.  The latter is only apparent after the back has been screwed on and the knobs put on.

Shaft splines too large

The first problem is that the shafts of these pots are too large to fit comfortably into TB-303 knobs.  There is no prospect of filing the shaft down - the splines are numerous and the material is hard nylon, or something similar.  Filing would just make a mess.

There seem to be two flavours of knob - some with a larger hole.  These can be found in the one machine, as if some parts from the mold are to one pattern and the rest to another.  

Sometimes one of these larger hole knobs can be pressed onto the Resonance pot shaft, but it can be very hard to get off.

That is not such a problem with a TB-303, since the knob can be forced off with pliers, levers etc. from below, pressing against the metal body of the pot, once the case has been removed.

For a Devil Fish, this is not possible.  The knob has to be removed before the case can be removed.  It can be tricky to hold the knob with enough force, for instance when using adhesive tape to grip the knob.  So forcing a knob onto a larger shaft would lead to serious trouble the next time the machine needs to be dismantled.

My usual solution to this problem is to drill the knob almost down to the bottom of the spline with a nice sharp hand-held (in a chuck) 15/64" drill bit.  Then the knob will fit OK, with enough spline left to lock it against the shaft and stop rotation.  The splines in the knobs seem to be narrower at the bottom of the knob than the top, inside the knob.

Not linear

The second problem is that the pots are not linear.  They have a "logarithmic" taper at both ends of the rotation.  This can be seen by the thicker layers of resistive material printed at both ends of the resistive track:

It looks like layer 1 is printed first, to about 10 and 2 o'clock.  Then the main resistive track is printed, followed by a third low resistance track to about 9 and 3 o'clock.

The result is that most of the range is beween 10 and 2 o'clock - rather than 8 to 4 o'clock in the ALPS pots.  This doesn't change the sound of the Devil Fish or TB-303.  It only affects what position the knob must be in to achieve a particular sound.

One or two pots have failed due to "scratchiness"

The only other problem I am aware of is of "scratchiness".  This has occured in one machine I sent to a customer in the USA.  I had installed a set of pots he purchased some time earlier, I guess in 2007 or 2006.  This set of pots looked identical to the ones I bought in 2006.  He had the faulty pot replaced by a local technician - and then he sent the faulty pot back to me.  Below is what I found.  Another customer in Sweden reports the same trouble, and he will be sending his machine back for me to fix it.  It is reasonable to assume these two pots have the same problem.

This is one or two pots out of probably 15 I have installed.  The problem may only affect one batch of pots, or a few individual pots, so it doesn't necessarily mean that other Resonance pots are bad.

The problem is with the outer section of the pot and I think it is due to problems with the outer conductive track.  I built a test circuit: wire up both sections of the pot across 5 volts and then have a 100k to ground from each wiper.  Then I look at the wiper voltage with a CRO, and listen to it audibly via a 0.1uf capacitor and another 100k.   I mix these two, for the outer and inner sections, together so I can hear any scratchiness due to lack of wiper contact on either section of the pot.

Note how the outer and inner conductive tracks are plain metallic tracks.  In the original ALPS pots (the first photo above) they are metallic tracks for low resistance, topped with a carbon track, except for one sector of the central track.  I assume ALPS know that this is a better surface for the wipers.  ALPS know a lot about pots.  The little RK09K113 pots used on the Devil Fish boards have never (to my knowledge) failed, despite the hard work they have done, in some machines since 1993.

I wonder whether these metallic tracks will wear away faster than the carbon.  

I wonder whether they will corode over time.  If they do, we are in trouble . . .

I am assuming the problem described below is due to some kind of residue remaining on the surface of the conductive tracks after manufacture.  Therefore, if it is fixed, the pot should be fine for a long time.  If it is a corrosion problem, then the trouble might re-appear.

Why didn't I pick up this scratchiness when testing the machines after replacing the pots?  I am not sure.  I did not test this returned pot in a TB-303 - only on my test jig.  Maybe the noise is not so apparent and I didn't do a lot of knob turning during test.  Hopefully it is the case that the problem exists in the pots to start with, and does not get worse over time.

I was able to get rid of the grey-brown blotchy contamination on the outer conductive track by wiping with ethyl alcohol (methylated spirits).  It came off quickly, leaving a clean metallic track.  Then the pot worked perfectly.

There is a bluish-purplish tinge on the lower right - that is oxidation from some oven step in the manufacturing process.  That was not affected by the alcohol and does not seem to be a cause of the trouble.

Although the wipers had visibly cut through the contamination and had made a metal-to-metal track where they rubbed, it is apparent that there were moments where both wipers were disconnected as the pot was turned.  These momentary breaks in both wiper's connections result in the "scratchiness" and only occured while the shaft was being rotated.

I looked at another five pots I had in stock and found contamination in most of them, but less of it than in the photo above of the pot which was in fact scratchy.  They all worked fine, but I washed away the contamination to reduce the chance of things going wrong in the future.