electronics: where to get pots with "idents"?

[tony sayer]

In article , fred scribeth thus

FWIW sometimes a DC voltage caused bu a leaky isolating cap will cause volume pots to crackle. Might be a consideration...

[Arfa Daily]

It's not so much that WD40 won't do the job in this case, Fred - it probably would. However, once people get the idea that WD40 works on one part of some electronic equipment, they will try to use it to cure everything from a blown fuse to a slipping belt, and trust me when I tell you that in the 35 years that I've been mending electronic equipment every day for a living, I have seen many an otherwise servicable item, wrecked beyond reasonable recovery, by the use of WD40. The smell is so characteristic that as soon as an item thus treated arrives on your bench, the response is "Oh no, it's been WD40'd ...". Once in there, it has a tendency to 'creep' around and seek out and wreck anything that is vaguely related to rubber, and the 'waxy' deposit that it leaves behind, is nigh-on impossible to remove.

That's why I would recommend using the proper stuff. It's easily obtained, cheap, and won't do damage to other components if you get a bit liberal with it. Right stuff for the job. You wouldn't run your barbecue stove on acetylene, would you ? :-)

Arfa

[dave]

Thanks for all the helpful replies. A few things:

The pot is definitely a built-in detent/indent. I was surprised at this because the pot in Q is a miniature one. There is no sign of any external mechanics - but it is soldered to a pcb - maybe when I remove it I'll see something - but I don't think so.

I'll get some switch cleaner and give that a go first. It'll save me removing the preamp - which is quite a fiddle. I have this irrational thought that switch cleaner is just wd40 with a different label on the can :) but grp say maplin RS is ok so will try some. Finding an orifice on it will be fun. I wonder if running some around the spindle with spindle pintig upwwards would work? I don't think the seal/bearing would be liquid proof?

The prob is crackling volume when rotating the pot - esp. the 1st (most used) quarter section. Reproducible - every time, but I don't think is leaking cap as rest of pot is fine and never crackles.

Yes I could use a non-detent one but much prefer the detents.

[Arfa Daily]

Almost always, there is a small hole where a section of the pot case is pressed in to form the rotation end stop, and that is a good place to get switch cleaner in. Failing this, they are (almost) never sealed around where the tags come out, so turn the unit upside down and get some juice squibbed in through that hole. The technique is to turn the pot fully anticlock, and fire some cleaner in. Then turn the pot fully clockwise, and squirt some more in. Doesn't matter if it's dripping out by now, it won't do any harm. Now, with the amp on so that you can hear if you are doing any good, VIGOROUSLY scrub the pot from one end to the other for at least 30 seconds. You might find as you do this, that the 'area' of crackle moves up the pot. If this is the case, then you will almost certainly be on the road to a total recovery of the pot's previous quiet operation.

Whilst you are at it, I would recommend similarly treating any other pots, whether they appear at this time, to need it or not. Likewise, any switches (excluding the mains switch).

Do not try to get switch cleaner in through the pot shaft bearing. The degreasers in the cleaner will wash the grease out of the bearing onto the track, spoiling the 'stirring treacle' feel, and possibly exacerbating the original problem.

And switch cleaner is most definitely *not* WD40 in a different can ...

Arfa

[Man at B&Q]

Rubbish. They're called "detent" pots and they're just not as common as they used to be. The detent mechanism is part of the pot, not a separate assembly.

A single centre detent used to be common for balance controls. Alps still make ones with multiple detents

just give you a series of clicks as you turn them.

MBQ

[dave]

At the risk of wearing out this thread (& as I'm well out of touch with things electronic), I see pots have "taper". Last I remember was pots were either log or linear (which I do understand) . Is lin or log mean whether the track is linear or logarithmic perhaps?

Eg the Alp site has pots with things like 15A 1B 3B etc. Could you pls enlighten me as to what this means?

The amp I'm working on (and have actually got working!!!), is rather old and the pots in it are just marked "log".

[Man at B&Q]

Taper just describes the way the resitance varies. 1B is a linear taper, 15A is audio or log taper and 15C is a reverse (audio) log taper.

MBQ

[Adam Aglionby]

Servisol Aeroklene50, yellow label, is a good solvent only switch cleaner, think it might be ether based, ether solvent if you can get your hands on it is an excellent switch cleaner.

Servisol Switch Cleaner, red label, otoh is the work of the devil and appears to attract crap.

Adam

[Dave Plowman (News)]

As will any oil type product. But that Servisol red will keep a pot quieter for longer than just cleaning. It's what I use. New pots have a sort of grease on the track.

[Arfa Daily]

Likewise. I have used the Servisol product professionally, for as long as I can remember, and have never had an issue with its long term durability.

Arfa

[Adam Aglionby]

[e-mail]...

=A0 London SW

Suppose my negative view is having to get it out of pinball relays and steppers, Servisol Red is not good on relay contacts no matter what they claim,neither for that matter is a 400mL can of WD40 on everything.....

Lot of our American cousins rave about Blue Shower, not sure if there is a direct UK equivalnt:

[meow2222]

You say there are no detent pots, then you mention how they work. One of us is confused.

Thanks Man at B&Q, detent not indent!

NT

[Arfa Daily]

You say there are no detent pots, then you mention how they work. One of us is confused.

Thanks Man at B&Q, detent not indent!

NT

I think he's trying to say that it's not the pot itself which has the detents - rather that it's a mechanical feature of the case that the pot element is in. Over many years of mending this stuff, I have seen a lot of different schemes for producing these rotational 'clickstops'. Pots with the detents all the way round, as opposed to just in the middle for the centre position of a balance control, or the 'flat' setting for a tone control were, I suspect, a way that the Japanaese manufacturers could 'simulate' the pots fitted to really high end 'professional' equipment, which were actually rotary switches and individual precision resistors. It gave their kit what they perceived to be a 'technical' feel. As others have said, most use a scheme of a spring-loaded ball in an arm either inside or outside the pot casing, with the ball dropping into detents pressed into that casing. Some I've seen use a similar idea, but with a sort of 'wavy washer' instead of the pressed detents. Still others have the wavy washer move with the pot spindle, and the spring-loaded ball is the bit that stands still.

But all are nothing more than a 'standard' pot element and wiper, with fancy mechanics on the bit that turns. They can be replaced with a non-detent type, as long as you observe the value (which often isn't that easy in itself these days, with the limited range that are produced) and the log / lin / reverse log characteristics (taper) of the original.

Arfa

[George]

Thats true,however did you manage that?

Thanks Man at B&Q, detent not indent!

NT

[Dave Plowman (News)]

Relays are different as they don't have a sliding surface and decent ones will have a contact surface that doesn't corrode - gold, etc. You can't use that with a pot. But I'd use it on a rotary switch which would be similar to a stepping motor? However if this is well used perhaps the tension or contact material is simply worn out so nothing will sort it?

[Bob Eager]

Actually, it was me!

[Dave Plowman (News)]

I'm looking at a balanced H rotary fader from a BBC type A mixing desk. It's about 6" in diameter and slightly deeper. Multiple stud tracks to resistors - designed to give a constant input and output impedance regardless of attenuation. Steps are IIRC 1dB in the main part of the range with larger amounts towards the extremities. Must have cost an absolute fortune to make.

[tony sayer]

In article , Dave Plowman (News) scribeth thus

I had some of those quadrant ones many years ago made by Painton?, same principle magnificent bit of engineering absolutely smooth but I believe no good on tone as you hear the level changing as it switched in the different attenuators!...

[Adam Aglionby]

=A0 London SW

Pinball stepper relays , dinnae make em like this anymore

[Dave Plowman (News)]

It wouldn't have been a balanced H if a quadrant. But not needed anyway since they were then used with individual channel amps. The fully balanced ones shared an amp for some applications. Strange to contemplate in these days of cheap electronics - but not in valve days.

These (quadrant faders) were a later device invented for TV where they required more channels on the desk - and rotaries take up too much space, and only two can be operated at once. With quadrants you can balance three per hand if they are adjacent. Some reckon one per finger - but I'm not convinced. ;-)

Incidentally, the operators of the time at the BBC chose away for up - the reverse of current practice. It's what I got used to and still prefer it for seriously fast mixing - like on a sports or current affairs type magazine prog.

You could certainly hear them switching on tone - but the steps were set so it was meant to be inaudible on prog material. In theory at least.