Anyone replace pots with presets ?

I would have said that the description " preset " tells you all that you need to know on that score. These components are designed to be set and left, pretty much for the lifetime of the equipment, so I can't see them standing up to the rigours of regular use for long. Add to this that as they are not designed to be rotated repeatedly as a user control, the wiper / track interface has not been designed to be specifically quiet. I also think that the control will feel bad to a user, as it will not have that " stirring treacle " feel that a proper user control has, courtesy of the drag grease that the manufacturers put in the spindle bush. Why not replace controls with manufacturer's originals ? Most group amp builders supply spare parts. Failing that, there are plenty of reasonable quality pots available - even the range that Maplin keep are pretty fair quality - and if you really want to fit top quality pots, these are also available from audiophile outlets.

Arfa

shroud

pot

standard

wiper

they

think

drag

if

I had not considered the feel, which agreed is very 'scratchy'. Squirting silicone oil in one and turning back and forth a hundred times is very much improved, and resistive track still ok. What is the point of the feather-light touch of the flimsy pots if the downside is they just don't last. I don't see the point of replacing with an exact match when the original is say one of 8 and has only lasted for use once a week for 2 years before internally failing , ie not abuse. In fact they seem to be the pots that are not used much if at all, that's why I suspect clumping or something in the lubricant. I'll try a 1000 times and re-measure to see if the track fails.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I'm actually really surprised that you seem to come across so many bad pots in group amps. I have been repairing these for many many years, and do lots of all makes and models, for a local shop, and I really don't have to replace many pots that aren't physically broken through taking knocks. I have found in general, that most manufacturers appreciate that this gear is going to last its owners for a lot of years, and tailor their design criteria, and component spec-ing to suit. I would agree that the pots fitted these days tend to be Japanese ( probably Chinese actually ) small-bodied types, which are not as good quality as say the large body Wellyns or the typical RS components pots that you used to find in them a few years back, but still, I don't seem to have that much trouble with them. If you really think that the problem is insufficient spring tension on the wiper fingers, just pile a bit more on. It's easily done with a pair of long-nosed pointy surgical tweezers.

Arfa

rethink.

pots

scaled

just

pot

you

them

and

the

pots

lots

is

fitted

fingers,

The present problematic is a Carvin Pro Bass 100, PB100 which will come bouncing back next weekend. The new fault , could well be due to another pot failed, symptoms over the phone so far, the previous one I replaced is fine. I still have the previous original one lying around . No makers name , a logo like cross-section of a flying saucer, a thin elipse laid over a circle, just the outermost lineforms. The wiper is only 0.15 mm thick , 0.6mm wide and using a force gauge, it starts deflecting at only 12 grams pressure.

Followup on my endurance test on a preset, I survived 1000 turns back and forth , whole track, as did the pot. No wavering on mid-track resistance readings. The rough feel has returned but I doubt that is due to the wiper action. Cracking it open, one obvious shiny, but not broken through to paxolin, track from one nib and vague partial thin trace from the other nib. I would estimate it could have done more than 10,000 rotations before both tracks were worn through.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

In that case, go for it. I would be interested to know how you get on with such transpants, and which presets you ultimately find most suitable. Also, how quiet they are in actual practical usage.

Arfa

I'm interested to know how the OP plans to reliably connect a standard shaft to a preset, I`m presuming his idea of a preset and mine concur.

One other point, presents don`t normally come in log tapers, do they?

Ron(UK)

Hi Ron. That is a very good point, and one that I hadn't even considered when thinking about his original plan to use these. If you look in the post that started the thread, he says that he is intending using the presets that you can get a 6mm shaft for that turns them into a ( semi ?? ) user control - I'm sure you've seen the idea on stuff where there is an adjustment that would be a good idea to have available to the user, but not in a way that encourages him to *use* it. The shafts that I've seen usually have a lightly splined finish so that they can be gripped, and a screwdriver slot in the end. I think he intends to pass one of these through a panel mount shaft bush, and then persuade the knob to fit.

Arfa

with

Also,

I should have said the failed original in the 0.6mm was 2 wipers , the metal is split into 2 wipers and nibs, absolutely no trace of wear on the track.

I have a few hundred Piher presets that have an enlarged slot to take rod extenders with pair of pauls to engage the back of the slot, quite strong enough to be used as unabused pots. The very light action of the originals I would have thought were a disadvantage, on stage, as you could easily dislodge a neighbouring pot. Some of these Piher presets are log tracks, agreed unusual but useful

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Ah ok, Piher do a range of shafts for their min presets. I`ve used them on radio mike receivers etc. to replace the output level and squelch controls, invariably because the user has been heavy handed with them. The combined cost of preset and shaft is quite high compared with a normal pot.

Personally I like the Omeg ECO plastic pots for replacements on gear that takes standard quarter inch bore knobs, Rapid Electronics stock the pots with the monkey metal slotted and splined short shaft that fits a lot of the Chinese product

Ron(UK)

Never IME.

Graham

post

that

not

usually

screwdriver

If you mean the Vishay 12/13mm footprint pots then they are the right size but the manufacturer's pdfs don't give the wiper dimensions , if of thickness of a coarse human hair , 150 microns, then little point in using, as will be back to square 1 in a few years.

I didn't, I meant Omeg, but the Vishay pots will certainly be better than anything fitted as an original part by the vast majority of manufacturers.

Ron(UK)

It's really a moot point though. One can still buy very high quality pots from a reputable manufacture. That's the route to take rather than trying to hack in something different. A good pot will last the life of most equipment. I use Bournes pots in arcade game controllers, they seem to hold up well to the abuse.

Hi James. That was my original feeling also, but as I said further up, I repair lots of group equipment, and really don't seem to suffer that much from bad as opposed to broken pots, anyway.

Arfa

What do you mean by "Group equipment"?

BTW,

Musical Instrument amplifiers and the like.

Graham

post

that

not

usually

screwdriver

The thread concerns 12/13 mm footprint pots (sub miniature), no problem with

One thing that concerns me about using a preset as a user control is the 'end stop' arrangement. Is the mechanism that prevents a user from turning the control past it`s fully on or fully off position rugged enough on a preset to to the job considering what heavy handed users there sometimes are in the music business.

Also, if the end stop IS strong enough, is the mounting arrangement of a preset strong enough to withstand the turning force of a typical death metal guitarist after several pints of Krugermeister?

Ron(UK)

Er, equipment used by groups ? Like bands ? Beatles, Rolling Stones ? Do you not call them "groups" your side of the pond ? Never heard the term "groupies" for the girls that follow them around ? In terms of this thread, we have been talking specifically amplifiers for musical instruments, but in general, at least over here, "group equipment" covers anything that a group or band may be using on stage ( or off-stage ) to make their sound or image, so amps, mixer desks, effects units / pedals, wireless mics, lighting effects and so on. I know from our past

- errr ... 'conversations' shall we say - that you have been involved in the repair of this equipment, so I'm sure that you probably have a valid opinion on the substituting of panel-type pots with presets made into panel mounting types ?? Back to you, friend ...

Arfa