ALPS Potentiometer Odd "Feel"

[TriodeLuvr]

I recently purchased a 250K ALPS pot that has an odd feel to it. Whenever it's left in the same position for a while, it slightly "sticks" there. Once it's moved away from that spot, starts and stops are smooth. It doesn't stick again unless it's left in one position for about an hour or so. What's even odder is that I can feel the position where it was stuck as though there's a slight detent there. That goes away if the post is rotated around that point five or six times. The next time it's left in one position for a while, the same thing happens. Doesn't matter exactly where it was left, that's where it sticks and that's where the feel of a slight detent will be. I've never experienced anything ike this with any pots I've used. Any thoughts or similar experiences?

Jack

 

[Lavane]

I had bought a 10K ALPS Blue Velvet that did this at first. I'm pretty sure it was a cheap Chinese knock off as many are unfortunately. After awhile it started feeling rougher when turned. I wound up replacing it.

 

[TriodeLuvr]

This potentiometer was purchased from Angela Instruments a few months ago: ALPS Blue Velvet 250K Dual
I noticed this characteristic as soon as I opened the box, but was hoping it was due to sitting on the shelf a long time. By all appearances, it's a real ALPS pot, but who knows? It tracks well and the taper is what I wanted for my current line stage project. In fact, I was going to buy a few more and install one in my main preamp. That currently has a TT potentiometer that feels like it's turning in oil, but the log taper is too aggressive. Now I'm not sure what to do. Retrofitting the ALPS is a lot of work. I have to strip everything off the front panel and re-machine the back side. This is all very disappointing.

Jack

 

[gadget73]

Maybe excessive wiper pressure and/or excessively soft conductive track? Can't say I've ever had that sort of thing before, usually they just get crunchy or gummy from some sort of lube failure or extreme wear on the conductive surface but it doesn't form any sort of temporary detent that goes away with a few cycles of the pot.

 

[TriodeLuvr]

I just realized the Angela ALPS does have a somewhat different label. Here are a few I found for comparison. The printing at "250KA x 2" is different on the pot from Angela, but I don't know if that means anything:

ANGELA:


PARTS EXPRESS:


ALPS on eBay:


Another ALPS on eBay:


Jack

 

[Lavane]

Besides the printing, notice the casing and fit. The one from Angela seems to have a better fitment between the two halves of the casing. The others also look to have some warping on the case halves as well compared to the picture of the one from Angela. Maybe it has just been sitting too long on a shelf and the lube isn't uniform anymore?
I'm with you though, I would be hesitant to use it since some machine work needs done to the face plate.
I had to do the same with a 3/8" thick face plate. I had to relieve the front to be able to get a nut on the selector, and relieve the back for the ALPS.

 

[llwhtt]

I have a real Alps Black Beauty in front of me and the labeling is the same as the one from Angela, no spaces between the numbers and letters.

Craig

 

[TriodeLuvr]

I have a real Alps Black Beauty in front of me and the labeling is the same as the one from Angela, no spaces between the numbers and letters.

Craig

Thanks, I found a few pics of 100K blue pots that also look like the Angela. This discrepancy probably isn't meaningful.

Jack

 

[painttoad]

Thanks, I found a few pics of 100K blue pots that also look like the Angela. This discrepancy probably isn't meaningful.

Jack

i think that there is something to it but exactly what, i can not say.

a couple of those looks like the entire label was printer at the same time(the 2 in the middle) a couple of the others looks like the main label was printed then the specs were printed separately, later. the latter is how i would expect it to be.

i'm far from an expert on alps.

 

[TriodeLuvr]

I'm with you though, I would be hesitant to use it since some machine work needs done to the face plate.
I had to do the same with a 3/8" thick face plate. I had to relieve the front to be able to get a nut on the selector, and relieve the back for the ALPS.

Indeed, it's a lot of work. My faceplate is 1/2" thick aluminum. The back side has been counterbored for all the various components, including the anti-rotation posts on pots and switches.

I'm thinking about ordering one of these from Parts Express, just to see if it feels the same. That raises another issue though, so I just sent them a technical inquiry. ALPS makes at least two log tapers, 10A and 15A, and the part numbers on the label apparently don't specify which it is. I'm hoping PE will have this information.

Jack

 

[painttoad]

10A and 15A, and the part numbers on the label apparently don't specify which it is. I'm hoping PE will have this information.

isn't the "a" for audio taper(logarithmic). an "L" would be linear taper.

i don't know

 

[TriodeLuvr]

isn't the "a" for audio taper(logarithmic). an "L" would be linear taper.

i don't know

Yes, "A" is log taper. Linear taper is "B" (like an ALPS 100KB x2). The problem (as described in this AK thread) is that there are dozens of log tapers.

Jack

 

[painttoad]

is that there are dozens of log tapers.

i did not know that.

 

[TriodeLuvr]

Maybe excessive wiper pressure and/or excessively soft conductive track? Can't say I've ever had that sort of thing before, usually they just get crunchy or gummy from some sort of lube failure or extreme wear on the conductive surface but it doesn't form any sort of temporary detent that goes away with a few cycles of the pot.

I'm very suspicious of the origin of this ALPS pot. Even ignoring the issues described in the first post, rotation just feels wrong. ALPS pots I've used in the past had a very different feel, more like they were turning in heavy grease. I've ordered a couple 250K from another vendor for comparison. If they behave as expected, I'll open up the one I'm using now and take a look at the construction.

Jack

 

[Lavane]

Good idea. Im curious as well what went wrong with it. I didn't open up the one I had that wasn't right. I should have I guess. I just tossed it after replacing it.

 

[TriodeLuvr]

I made the necessary mods to the front panel today. I had forgotten that the rear of the panel is counterbored to a thickness of 1/8" everywhere around the controls and switches. The counterbored area is large enough to accept the ALPS body. Also, the existing TT Electronics volume pot is fitted using a smaller 1/8" plate that sets into this recess, so I only had to modify that plate a little for the ALPS. While the mill was running, I cut a few adapter rings to center the smaller ALPS bushing (.315") in the 3/8" panel hole. It turned out that the anti-rotation posts on the two pots are identical - same diameter, spacing and orientation. Good luck for once! I'll need shorten the ALPS shaft slightly, but that's simple enough. Now I just need the new pots...

Jack

 

[TriodeLuvr]

The new ALPS pots came in from Parts Connexion, and they have the correct feel. I performed several important tweaks on the preamp while it was on the bench. The new pot is installed, the other work is complete, and it tests well on the bench now. I'm hoping to put it back in my system tomorrow, then open up the line stage that I built for backup and disassemble the ALPS pot that started this thread. It's still functioning fine electrically, but the detent is becoming worse and I think it's starting to turn a little roughly. I have suspicions about the cause, but I'll wait to open it up.

Jack

 

[Hajidub]

The new ALPS pots came in from Parts Connexion, and they have the correct feel. I performed several important tweaks on the preamp while it was on the bench. The new pot is installed, the other work is complete, and it tests well on the bench now. I'm hoping to put it back in my system tomorrow, then open up the line stage that I built for backup and disassemble the ALPS pot that started this thread. It's still functioning fine electrically, but the detent is becoming worse and I think it's starting to turn a little roughly. I have suspicions about the cause, but I'll wait to open it up.

Jack

Newbie question, but does the supposed bad pot measure as advertised. I wonder if the hitch in the turn, after sitting, effects the stated resistance (just curious). Glad you got the issue corrected.

 

[TriodeLuvr]

I disassembled the pot this evening and noticed two things right away. First, as soon as the two screws were loosened, the detents disappeared. Second, the rear of the back rotor has a vinyl pad installed under the clamp, and it's very off-center. This isn't the cause of the problem, because the pad moves with the shaft and rotor. Nevertheless, I'm hard pressed to think ALPS would make it like this. I would expect the hole in the pad to be sized for the shaft such that it couldn't be installed so cockeyed, even by a careless worker.

After seeing this, I reinstalled the rear case and screws. The detent came back after it sat for a couple hours, although it wasn't as noticeable as before. Detents created previously in different positions were gone. Thinking this might be due to some type of damping material or foam elsewhere in the pot, I removed the rear rotor, pulled the front half of the case off and inspected the front section. There is absolutely no sign of anything that could cause this. Nothing touching anything it shouldn't, and nothing touching the moving parts other than wipers running either on the carbon tracks or (in the case of the shaft) running on flat bearings between the wipers and the metal case.

Because this pot feels so completely different than all other ALPS pots I've used, the only remaining culprit seems to be incorrect materials. The detents are probably due to a soft bearing surface, perhaps a thin plastic under the front shaft bearing that is deforming because it's too soft. I would like to have sent this to ALPS for inspection rather than opening it up, but you have to pick your battles. Anything I receive in the future like this will just go back to the supplier right away.

Here are a few pics of the rear rotor. I have nothing to compare it to, but maybe someone else will see something out of place.



Jack

 

[TriodeLuvr]

Newbie question, but does the supposed bad pot measure as advertised. I wonder if the hitch in the turn, after sitting, effects the stated resistance (just curious). Glad you got the issue corrected.

It measured well. I believe this to be only a mechanical defect, although more might have been revealed if I had kept using it.

Jack