Need some advice on a couple of decent, but reasonably priced, 5k volume pots.
They are for an old Yamaha Professional amp. The are working, but as it is 30 years old, I would replace them.
You’ll need dimensions - both body and shaft diameter and length, plus pin-out if they’re snap-in types.
You may well find the maker’s part# on the body, and that may even still exist, or at least data for it.
There is enough room for most variations.
Was hoping for a suggestion about particular brands used. Maybe an upgrade on the £2 pot, in there now.
I have found a Noble, and lots of Chinese stuff.
Alps blue or such.
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Don’t think they do a 5K pot any more, but that’d be the go-to.
Ah, fair enough.
I have found a Vishay and a Bourns, cermet.
Pots tend to fail due to track wear. You’ll know if this has happened because there’ll be noise when you rotate the control. If there’s no noise then the 30-year old originals may still be as good as new. Vishay and Bourns are very large-volume (no pun intended) producers for the regular electronics industry. The quality and durability of their stuff will be a reflection of their price point. I’d guess it would be ‘perfectly fine, but nothing special’.
Things which can matter include details like whether the pot’s casing is metal or plastic and, if the shaft is metal, what it’s connected to at the bushing and inside the pot. Plastic casings don’t provide much shielding against hum pickup (perhaps the Alps pots’ biggest weakness) and a non-grounded metal shaft can lead to buzzing every time you touch the (metal) volume knob. That said, hum and buzz may be much less of an issue in a 5k circuit than in, say, a 470k one.
Presumably you’re after a stereo control. The toughest thing with conductive track pots (carbon, cermet etc) is maintaining good balance between them when they’re right down at the bottom of their settings. Of course most people, most of the time, don’t use them down there, but it might be worth bearing in mind if your setup is an exception.
Stereo stepped attenuators don’t suffer from track-mismatch or track wear, although switch contacts can go noisy I guess. They’re bulky though and not cheap, so you’ve probably ruled them out already.
Apologies if this is egg-sucking for grannies, but I’ll say it anyway, volume controls commonly need to be ‘log’ taper. Manufacturers will make both log and lin versions and it can sometimes be hard to tell which one a seller is listing.
It’s just a cosmetic thing, I suppose, but if the replacement pot’s bushing isn’t a tight fit in the panel hole then it can be a right faff getting it centred to line up with all the other controls. And if the original knob is for a 1/4" shaft but the new pot has a 6mm one then even assuming you can tighten the knob’s grub screw (another one for you Andy @Penance 
) up you’ll find that it rotates eccentrically as the centres won’t be coaxial.
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Two mono pots needed.
The old ones are probably okay, but in a pro amp, I imagine they were heavily used.
The amp is very easy to work on, and I just thought replacing them, with something of a higher quality, might increase the lifetime of the pots, as well as possibly giving a small sonic benefit.
Two mono pots is easier in some ways and harder in others - you don’t have the track matching problem but there’s a lot less demand for mono log controls these days (except in pro gear) so maybe less supply.
Are there any wirewound options ? If they’re not passing a lot of power (and they won’t be) then they can last for ever. They can sometimes be a bit ‘steppy’ though.
Blore-Edwards are still in business and they used to make some posh pots https://www.blore-ed.com/potentiometers.
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Won’t they have just been left turned up to 11?
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What you should really do is redesign it to fit a relay driven attenuator in there, using foo resistors.
Tis the way to go.
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