Custom potentiometer?  - Page 1
Forum section: electronics / repair

author: zoltan
author_rank: Contributor
timestamp: December 14, 2015, 08:34:19 pm
content: Hi!I am repairing a volume control component of Bose Companion 3 system of a friend. And inside is a scratchy pot I'd like to replace.It's a weird thing, as it is designed to turn only a 1/4 of turn, that's how the mechanical guards are set inside the pod - and the tracks inside the pot are 1/4 to.Well, see for yourself in the photos. If anyone know where to find it, or have idea of replacing with something standard, please post.Edit: Inside photo is after cleaning.

author: dom0
author_rank: Super Contributor
timestamp: December 14, 2015, 10:07:08 pm
content: Looks like an ALPS part. They do custom parts (extensively).

author: zoltan
author_rank: Contributor
timestamp: December 15, 2015, 06:35:39 am
content: Yes, it looks like the Alps RK14K series, but with different pinuot, and for sure different turning range.Any hint how to find replacement?

author: zoltan
author_rank: Contributor
timestamp: December 15, 2015, 07:27:19 am
content: Quote from: blueskull on December 15, 2015, 07:06:51 amThat's not a problem. I can rewire the entire thing with flying wires, but how to accommodate the range?Check the first post pics, the pot full range is only 1/4 turn, and mechanically it is not possible to extend the range. Would the bigger pot (eg. 100k, 1M) have the same characteristic on 1/4 turn?

author: tautech
author_rank: Super Contributor
timestamp: December 15, 2015, 07:42:59 am
content: Quote from: zoltan on December 15, 2015, 07:27:19 amYou'd be best to find theright4K7 90 degrees rotation pot, I had a good look today thing it was a Bourns not thinking it might be an Alps.Anything else just won't work right.Send Alps an email with a request for help and a link to this thread.

author: zoltan
author_rank: Contributor
timestamp: December 17, 2015, 11:21:11 am
content: Most of requests I've sent to other companies ended like forwarding to local distributor, who again don't care of anything under 10 000 pcs, but if one won't ask nobody will respondSent a mail to info (at) alps-europe (dot) com, well see they response (if any).Thanks

author: bookaboo
author_rank: Frequent Contributor
timestamp: December 17, 2015, 12:06:21 pm
content: You need to watch out whether it's linear or log as well. Other than that I don't see why a 3/4 turn (of same value) wont do the job if you bodge it in mechanically with flying leads. Sure it won't match the legend but always better to make your own new legend/scale numbered 0-11 in any case.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 17, 2015, 01:18:05 pm
content: If you can't get a replacement part from Bose, then your chances of buying an equivalent part is essentially zero.The best you can do on your own (IMHO) is to get a 10K pot and use conductive paint to "short" the "top-half" of the rotation.You will note that the photo of the internals show an otherwise conventional 270-degree pot, but they have extended the conductive portion of the thick-film screen-printing to cover half the resistive element.Are we to assume it is still "scratchy" AFTER cleaning? There are pot lubricants available from vendors like Caig which may mitigate the symptoms.

author: zapta
author_rank: Super Contributor
timestamp: December 17, 2015, 03:40:04 pm
content: Quote from: bookaboo on December 17, 2015, 12:06:21 pmCheck the datasheet first to make sure the pot can handle the 11.

author: nctnico
author_rank: Super Contributor
timestamp: December 18, 2015, 02:24:22 pm
content: A better option would be to modify the circuit to use a voltage controlled amplifier. That eliminates potmeter problems forever. Why doesn't Bose do that? Running an audio signal through a potmeter is a big NO in high end audio gear.

author: zoltan
author_rank: Contributor
timestamp: December 18, 2015, 02:37:30 pm
content: Well, Alps responded to my email, but the answer was as expected:QuoteBose is selling spare parts, but only on "component" level. This thing is around 70-ish USD + shipping. Didn't found refurbishing kits of any kind for this particular model.nctnico, I didn't checked the topology, so I can't say if the audio is routed trough pot or not. I can only say it is not hi end product, it's just elegant and expensive.I'll leave it now as is, until my friend start complaining about scratchy pot again.Quote from: bookaboo on December 17, 2015, 12:06:21 pmIt is log pot (see drawing). 3/4 turn pot will work only if the first 1/4 turn has the same curve as the existing one, because the wise designer @Bose made the volume wheel mechanically stop after 1/4 turn. There is no scale on it, it's left to the users ear.