One more time on guitar Pots!

[Deleted]

OK, this subject of a tolerance built into a pot still has me confused! I just looked at a few videos, and now I am more confused than ever.

 It is said that most pots have a 20% tolerance + or -. So I can take any pot, let's say, and add 9 or 10% tolerance to it and come up with a 550k pot.

 IN the last video he shows 4 500k pots that read out at 550k give or take. But what he was saying, the tolerance was measured between the pots to get them a close to each other as possible. Now, that is the way I was taught a long time ago. You measure a tolerance between the pots. So If you have a pot, they read 548 and one that measures out at 550. Then that is your deference or tolerance.

 Not taking a pot and saying it is a 550k pot and when you measure it out it reads no where close to what it's supposed to be and call it good after you add 9% 10% or 20%. To me, you could take any 500k pot and say it's a 550k pot If a pot reads less than 500k or 550k, like the 4 pots I bought some time ago. Those 4 pots were all over the place. NO two were the same. One was less than a 500k reading. Only one measured out to 550k. But on the back of the pots they are stamped 500.

 In the last video I watched, he did say that some sellers will say a pot is 550k (when they know that they are not 550k) in order to get more money for the pots. In the video, he says they get away with it because they say it has a built-in tolerance.

 I had one pot that measured out at 498. It is supposed to be 550k. The seller says they have a built-in tolerance of 9%. So if I add the 9% to that, that equals out at 440.82. That is no where close to the 550k pot I was sold.

 So I was sold 500k pots that somehow with the tolerance become 550k pots. I wish people would be honest in what they sell.

I did remeasure the pots to make sure. One is at 550k, one is at 515k and the other one is at 498 and one is at 519. NO way are these 550k pots. Someone is selling snake oil. Like I said they are 500k pots, nothing more, nothing less.

 What a way to sell stuff!  

[dnic]

+ or - 20%. 500k + 20% is 100k giving a total of 600k so - would be 400k. So a pot stamped 500k needs to be within those numbers. If the pot is stamped 500k no one can say is something else. If the pot is not marked than it could called either 600k or 400k. Then the tolerance would start from that called out number.

In your instance I'm not sure if the pot was marked. But assuming it was... 550k + 9% = 49.5K = 554.5. Or - = 500.5k So out of the 4 pot you were sold the 498k does not fall into tolerance. So marked the 498k is wrong and even if not marked but called so by the seller the 498k is wrong.

Now when checking tolerance to match pots in the guitar. I would put the closest to call out in the volume spot. Of course two volume pot guitars would like the the two V pots to be close but I suppose there are different schools of thought about that. For instance the hotter pot might go to bridge to kill some of the highs.

That's my take on it anyway. I'm sure someone else will chime in and help out.

[Deleted]

Sept 23, 2023 9:59:47 GMT -6 dnic said:

+ or - 20%. 500k + 20% is 100k giving a total of 600k so - would be 400k. So a pot stamped 500k needs to be within those numbers. If the pot is stamped 500k no one can say is something else. If the pot is not marked than it could called either 600k or 400k. Then the tolerance would start from that called out number.

In your instance I'm not sure if the pot was marked. But assuming it was... 550k + 9% = 49.5K = 554.5. Or - = 500.5k So out of the 4 pot you were sold the 498k does not fall into tolerance. So marked the 498k is wrong and even if not marked but called so by the seller the 498k is wrong.

Now when checking tolerance to match pots in the guitar. I would put the closest to call out in the volume spot. Of course two volume pot guitars would like the the two V pots to be close but I suppose there are different schools of thought about that. For instance the hotter pot might go to bridge to kill some of the highs.

That's my take on it anyway. I'm sure someone else will chime in and help out.

Those pots I got are marked 500 on the back. The seller tried to me that 500 was a part number. The pots do not have the letter k on them.

 Only one put measured out at 550k. None of the others did. I do have a set that are stamped on the back at 525k. And they are all spot on to that 525k. Both set are from CTS. I do think the so called 550k pots are not real CTS pots. They are counterfeit. I have been using CTS pots for a lot of years. I have never had them be off by the readings I got off these 4. The reading are all over the place. The other thing is when you turn the pots up or down, it's not smooth at all. One is loose, the other is tight. I just cannot believe that these are the real deal.

 I have not even had cheap pots with so much range between them. Thanks for your help, Dane. I am trying to decide if I am going to use the pots or not. I think I'm going to trash them. They now have this huge MOJO on them. Don't know if I want them in one of my guitars.

 From now on if I buy anymore I'll get them from someone that have done business with. That is what I should have done from the start. Never again will I buy parts off of eBay. I don't like buying them off Amazon, but at least they will give me my money back if need be.

 But Stew Mac and Bitterroot, is where I buy from. Don't know why I tried to go somewhere else. Been getting parts from Stew Mac since the late 70s. Been buying from Bitterroot since the started. Both are good places to get parts from.

 

[antares]

Pry back the tabs on those junkers and pull them apart. Look at the carbon tracks inside. It should then be obvious why they are sold with "acceptable variations" which we know as "tolerances". Flip- some of them are such abject rubbish that the tracks aren't even tapered- they're stepped!

It's the same across engineering generally- I never worked to a drawing that didn't quote the general tolerances in the legend. If a potentiometer of (in this case) 550 kOhms boils down to a carbon track on a substrate with a wiper, there has to be a trade off between what a consumer is prepared to pay and accuracy. ("The marginal propensity to consume")There is no way you'll ever buy a 500 kOhm pot for a few bucks that someone has sat on a stool next to a bin full of thousands, measuring each one to isolate the odd happenstance accurate ones, and selling off the rest as cheap tat. No one would ever pay for those top tier pots when all they want to do is roll off a bit of volume.

Then there is the accuracy of the measuring device. The multimeter will have its own quoted tolerance(s) too, and that will only ever be valid during its quoted calibration period. I have some good meters here, one of them is even "True RMS" (if you know what that implies.) None of my meters are within calibration, but in terms of expectations regarding accuracy, they're good enough for me. How certain can you be that the accuracy of any meter meets with the manufacturer's claimed accuracy?

Moreover (and especially for analogue meters) you'd need to know whether or indeed how many times it has been abused / needle end-stopped by hapless operators "choosing" the incorrect range. Also, a "digital display" is only numbers and does not indicate accuracy. The numbers of digits on a display has zero bearing on accuracy- it's just another way for humans to interpret what the meter's internal circuits reveal *within its own tolerances*. Even more- you have to allow for the meter loading the circuit under test, and digital meters are good there because they're ultra high impedance, but low impedance analogue meters need to be a minimum of 20 kOhms / volt full scale. That said, it's not a consideration for measuring a pot, but if it's in a circuit (like wired into a guitar) then it really is something to take into account.

So where does that leave us? I've never heard of 9% tolerances other than in this thread. 0.5%, 1%, 5%, 10%, 20%, sure, but I've never encountered 9%. If you had a 550 kOhm pot measuring 498 kOhm subject to 9% tolerance using a meter that is probably let's say 3% tolerance on the 1 Mohm range (plus a quoted number of digits on a digital meter if you know what that implies) within its calibration period, and you paid 5-6 bucks for the pot, well, I'd be satisfied with that and move on.

Bottom line; if the pots are mechanically sub-standard as you say, I'd trash them and buy some more from a reputable outlet like Mouser, Digikey or Newark (There are other suppliers but I'm not familiar with the USA market place.) If you want (and are prepared to pay for) quality pots, look for "Bourns" pots, but they'll still be subject to manufacturer's quoted tolerances. There is no escape from tolerances- they just might be closer at the increased cost because they've invested in tighter manufacturing processes and improved quality assurance, all at cost. Remember, all you actually want to do is roll off some volume.

Regarding engineering generally, I like genuine Alpha Industry's "M65" coats and pants. (that's trousers to us in the UK!) Although they are just fabric clothing stitched together and robust servicemen's clothing at that, they must be made to pretty close tolerances. I hold 'em up with a Soviet era instant release belt which is a tight fit through some of the belt loops. I get about 12-15 years of pretty much constant wear out of a pair of M65 pants and I've had three pairs in total. Every one has been exceptionally tight on exactly the same belt loops and a little bit easier on the others. Now I continuously read on advertisements and forums (fora?) about things being better because they're made "right here in the good ol' USA" and these pants are a great example of that. Except of course that over the years, Alpha has offshored production to Vietnam et al. Impressive reproducable accuracy on those pants though! Good remote QA by Alpha (and Winfield too as it happens.)

And now the rest of the day beckons!


でつ e&oe ...

[Deleted]

I do understand tolerance to a point. Don't forget, I used to build Hot Rod cars. I dealt with close tolerances in the building of engines all the time. I also used to rebuild diesel engines as well.

Those are tolerances I can understand. But when it comes to electronic pots...? Seems to be a cop out to sell something and not get sued. By some, one could sell a 500k pot and say it's a 550k and get away with it because of the tolerance. I can take any 500k pot and say it something that it's not.

 But like I said, I have never had any manufacture of the pots I used in the past measure out like these did. Not even the super cheap one I bought in a big bag once. Maybe I just got a bad batch? But nevertheless, the seller was and is not willing to stand behind what he sells. I showed him my test results. But got nothing but bad things said to me from him.

 He did say for me to send them back (at my expense) and after he inspected them he would then decide if he would give me my money back. So, I never sent them back. Why? Because you know, as well as I do, he would never have given the money back. He would have a reason not to, and then I would still be without the money and the parts.

 But I still wound up with nothing. I'll never use the pots. I may take them apart to see what's under the hood. Something is going on with them.

 If you look close at them, you can see where someone had them apart at some point. I think the cans had been taken off to mess with the stamping.

But you can see on the tabs that hold the can to the pot that they were bent over by hand. You can see like plier markings on them. Not like on the other pots I have on hand.

 But thanks for the help on tolerances. I just needed to understand it more. I hate paying for something and not getting what I paid for. But like we said, or I said, I'll never again buy from someone that is not 100% legit business and will back up what they sell. So what, it cost a little more. I would rather spend a little more and not have to deal with someone that is up to no good. All the grief I have gone through over some $30.00 parts. Is not worth it!

[dnic]

Steve, you make me want to quote Solomon. " All is vanity"

I do like Bourns pots and that is typically all I order any more. From past experience I know the Alpha pots turn a bit stiffly so I ordered one of those for my lap steel customer that keep accidentally turning his tone knob while playing.

[dnic]

Eddie, I'm you and Steve on this. Open them up and have a look and then toss the whole mess into the trash. Call good and move on.

[Deleted]

Sept 24, 2023 7:41:37 GMT -6 dnic said:

Eddie, I'm you and Steve on this. Open them up and have a look and then toss the whole mess into the trash. Call good and move on.

I know, it's time to move on from it. It sometime takes me a while. Mostly because, I can't get my head wrapped around the tolerance thing. It really seems to be an excuse to sell items under a claim of something being something that it is not. LOL!

 Wish, when I was in printing, I could have used a tolerance as an excuse for not getting print on paper right dead on a sheet of paper.

Would have made my life a whole lot better! Been nice to tell a customer you have to add or subtract a 10% tolerance. HA!

 If and when I feel like it, I might open them up. Really depends on my mood that day when I have nothing to do. I had thought of smashing them up, put them in a box and send them back to the seller. LOL! Bet that would stir up a hornet's nest.

[antares]

Well when you type set, you arrange for strings of words to align both left and right justified, so what has to give? The inter word and/or inter letter gaps? I'm guessing that there will be optimum "gaps" associated with a given font, so a tolerance towards a variation in those gaps is accepted by default without even giving a second thought. Whoa armchair Hippie- not at all good to tread on skilled printers' tradecraft who will certainly know better by virtue of experience? That means I'm on theoretical thin ice here and I'm entirely ready to be pulled up short!

でつ e&oe ...

[Deleted]

Sept 24, 2023 12:36:06 GMT -6 antares said:

Well when you type set, you arrange for strings of words to align both left and right justified, so what has to give? The inter word and/or inter letter gaps? I'm guessing that there will be optimum "gaps" associated with a given font, so a tolerance towards a variation in those gaps is accepted by default without even giving a second thought. Whoa armchair Hippie- not at all good to tread on skilled printers' tradecraft who will certainly know better by virtue of experience? That means I'm on theoretical thin ice here and I'm entirely ready to be pulled up short!

でつ e&oe ...

I started out setting type. Hot type, that is. Then they came out with a line of type. Much easier to use. It was still hot type. Setting things up takes a lot of skill and knowledge of the type, The sizes of leading, you had to know how to read a pica rule. Know how to lock up the type.  And so on-and-so on.

 I did not matter what one would set up for, it had to more than pleasing to the eye.

When I set type, it was spot on. All my spacing and letters were the most accurate of many setters of my day. And I was fast at it. For a time I was in high demand because I was so skilled at it.

 Later on with computers' things changed a lot. In the early days of setting type on a computer, one had to know how to program the computer to set type. You had to know all the command lines to enter into a computer and input all that line of code before one could even begin to start typing. If you got one thing wrong, you had to start all over. This was a lot slower than setting type the old way. But it was the first time we could set it up and read it before it went to press, without putting some ink on a proofing machine.

 Over time, the computer took over, and it has now become easy to type out words and see them before it is printed. But as far as a tolerance goes, What I was saying is that, If by some reason I did not hit the mark on a page I wish I could have said, "you have to add a 10% + or - Then it will be spot on." LOL! That would never work in printing. Or in a lot of other things.

 I started in printing in 1970. I have set type, did the darkroom for negs and strip them up to make the plates for printing press. Ran presses from small to huge 4 and 6 color presses. There in nothing I don't know about the printed page. I was one of the best in my field. There is not a machine out there I could not run. But if you want to talk about tolerances. The printing press is a huge hoge poge of tolerance. The hardest thing to do with a press it to get it to register spot on sheet after sheet of paper. (0n a sheet fed press) The bigger the sheet, the harder it is to do. But I had my "tricks of the trade" I never met a press I could not get it register. That my fiend is where you don't want any tolerance. Not when you are doing multi colors on at a time or 2 at a time. You have to be spot on sheet after sheet.

 But now in days most places have gone digital. Now the printing press is almost gone. But they still need to be accurate. If the work is bouncing around, it is real hard to cut the job down if the image is all over the place from sheet to sheet. If a sheet moves a 1/4" from one sheet to another, you cannot cut a job to size and have it come out right. You cannot stand and cut 5,000 sheets one at a time. You have to cut them in stacks. Otherwise, you will be there for days cutting paper.

 I had many of arguments with print shop owners over the early day of digital printing. They were the worst at keeping things accurate. But somehow that was all my fault. But then the techs would come in and try and tell me that machine had a tolerance in it. So in other words the tech could not make the machine accurate and that was their excuse. "Tolerance" If I tried to tell my bosses an excuse and use the word "tolerance" I would have been fired on the spot.

 So again in a lot of cases, like in the Pots I bought, the word "tolerance" is nothing but a huge excuse for sloppy work. I can go on when it comes to printing. I have a long lifetime of experience in it. I even know how to work on printing presses. I can tear them down, to the frame, and rebuild them.

 The word tolerance is like the word tone to me. It's all too subjective. But used correctly, it can make a huge difference in the thing we do.