Custom potentiometer?

[zoltan]

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.

[dom0]

Looks like an ALPS part. They do custom parts (extensively).

[zoltan]

Yes, it looks like the Alps RK14K series, but with different pinuot, and for sure different turning range.

Any hint how to find replacement?

[zoltan]

Yes, it looks like the Alps RK14K series, but with different pinuot, and for sure different turning range.

Any hint how to find replacement?

Bend pins backwards and trim them, then solder bulge wires.

That'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?

[tautech]

Yes, it looks like the Alps RK14K series, but with different pinuot, and for sure different turning range.

Any hint how to find replacement?

Bend pins backwards and trim them, then solder bulge wires.

That'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?

You'd be best to find the right 4K7 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.

[zoltan]

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 respond
Sent a mail to info (at) alps-europe (dot) com, well see they response (if any).

Thanks

[bookaboo]

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.

[Richard Crowley]

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.

[zapta]

Sure it won't match the legend but always better to make your own new legend/scale numbered 0-11 in any case.

Check the datasheet first to make sure the pot can handle the 11.

[nctnico]

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.

[zoltan]

Well, Alps responded to my email, but the answer was as expected:

thanks for your interest in our products.

 

However, we are not selling any spare parts to end customers.

Please contact the producer of your device and ask for a spare part.

 

Also for us it's very difficult to identify which part you exactly need.

Bose 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.

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.

It 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.