Just Bought An ALPS RK27 With Notchy Feel...
Sep 13, 2008 at 12:10 PM Thread Starter Post #1 of 11

mwofsi

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Hi, I've just bought this 10k ALPS RK27 from a Taiwanese ebayer. It was cheap, £5.80 including postage, in auction.

It seems well enough built, but I was expecting a nice smooth action like my previous unit. Instead it has a mildly clicky/notchy feel. Also the edges of the front and rear boards are different in colour/finish.

This is as far as I want to take it apart at the moment. So the question is "is it the real deal"?



 
Sep 13, 2008 at 12:28 PM Post #2 of 11

tomb

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Quote:

Originally Posted by mwofsi /img/forum/go_quote.gif
Hi, I've just bought this 10k ALPS RK27 from a Taiwanese ebayer. It was cheap, £5.80 including postage, in auction.

It seems well enough built, but I was expecting a nice smooth action like my previous unit. Instead it has a mildly clicky/notchy feel. Also the edges of the front and rear boards are different in colour/finish.

This is as far as I want to take it apart at the moment. So the question is "is it the real deal"?



I would say no. There is an RK27 option for a center detent, but none for a "notched" feel. At the same time, RK27 fakes are rampant.

Tangent, Amb, and beezar.com order RK27's directly from US ALPS representatives. The 50K version is not a stock item from ALPS. It is a special manufacture and must be ordered in lots of hundreds.

If the deal was too good to be true, then it probably wasn't.
 
Sep 13, 2008 at 12:39 PM Post #3 of 11

mwofsi

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Thanks tomb.

Here in the UK I also have Rapid as a source, but can't resist a bargain.

I'm a bit nervous about naming'n'shaming the supplier though. The guy has a 99.7% rating, one negative rating in twelve months, and that seems to relate to a shipping problem!

Of course the other possibility is that it's faulty.
 
Sep 13, 2008 at 1:29 PM Post #4 of 11

mwofsi

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Well I sent a query to the seller, and got back a reply.. which was a copy of my original question!

Resistance varies between channels from less than 1% to about 6% at full value. There are 40 notches per rotation.
 
Sep 13, 2008 at 1:40 PM Post #5 of 11

MrMajestic2

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Actually when reading the datasheet it looks like there is no detent, center detent and also pots with 21, 31 and 41 detents.
 
Sep 13, 2008 at 2:01 PM Post #6 of 11

mwofsi

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Quote:

Originally Posted by MrMajestic2 /img/forum/go_quote.gif
Actually when reading the datasheet it looks like there is no detent, center detent and also pots with 21, 31 and 41 detents.


Well I certainly could be miscounting/not-including one notch!

Thanks for pointing that out, I find the ALPS sheets more confusing than most datasheets

I can't make head nor tail of the numbers ALPS put on the back label., except the 10k, which makes sense for a 10k pot!
 
Sep 13, 2008 at 2:13 PM Post #7 of 11

tomb

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Quote:

Originally Posted by MrMajestic2 /img/forum/go_quote.gif
Actually when reading the datasheet it looks like there is no detent, center detent and also pots with 21, 31 and 41 detents.


Hmm ... yes, MrMajestic2, it appears that you are correct.
I was looking at the "Recommended Products List" table on the first page, which essentially shows a choice between center-detent and without. It's a bit further confusing, because they appear to use the code "31" for a Center-Detent. Then later on, the third page lists "Detent Variety" of "Center," "21," "31," and "41." Unlike the table on the first page, that seems to make it clear that there are choices for multiple detents.

I've posted the data sheet here: http://www.diyforums.org/data/RK271.pdf

The actual part number for the one we use in DIY headphone amplifiers:
RK27112A-S25-C0-A503


EDIT: The numbers on the back label appear to be internal mfg run identifiers. I have three separate batches, with different numbers on the label. True to form, however, the boxes themselves are a quality work of art. Add a bit of padding and you could easily transport eggs with these things:
AlpsBlueRK27-640x480.jpg
 
Sep 13, 2008 at 2:35 PM Post #8 of 11

mwofsi

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Ok, i'm going to accept that it's probably genuine.
I don't want to name the seller, but I've left neutral feedback at his ebay store pointing out that I received a 41 detent version.

Edit: I've now received a reply assuring me that the item is genuine direct from Japan and offering that I return it for a refund.

I think that this form of pot is probably quite useable, but I prefer the 'normal' smooth version.
 
Sep 13, 2008 at 4:08 PM Post #9 of 11

mwofsi

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They've now offered to send me a gold plated knob as compensation. I've asked that they revise their descriptions instead

Edit: They've agreed to revise their descriptions and send me the gift as well.
 
Nov 2, 2008 at 6:01 PM Post #11 of 11

tangent

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The white thing that looks like a gear and the matching bump pattern on the back cover of the pot is present in the smooth-action pots as well. You can see it in my video How a Potentiometer Works. They shouldn't touch each other normally. I always assumed that there was something ALPS inserted between them, like a small ball bearing, to cause the detented feel, but I don't see any such thing in the pictures above.

mwofsi, if you can find the part I'm speculating exists, just removing it should return the action to smooth.
 

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