Frying Pan Guitar - Need R value for Pot

Radio shack has meters for less than $10.

If the pot is just noisy, then you should be able to measure it's resistance just fine.

You'll probably want to go to a guitar shop to get a pot and a knob; they may be able to tell you the value, although you want the meter anyway.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

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Thanks Tim, but I already knew all that.

I have several Fluke meters, all of which were back at the shop (in another city), so obviously NOT available to me at the time. And I'm not going to buy any Radio Shack $10 meters. Frankly, I have enough aggrevation in my life than to deal with that....!!

It's a very famous guitar. Somebody will have the answer.

-mpm

What? No ohmmeter? You would still get a proper reading since the scratchyness is related to wiper contact, so the full span reading should still be viable. If it were not, the circuit would not work at all.

To determine if it is linear or audio taper, you should be able to take readings at a few point throughout the rotation, and plot them to see the taper, if any.

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Yeah... like a decent guitar shop or music chat forum.

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Nah set the pot to central, see if the left side = the other side

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Actually, only two leads are connected (wiper and one end), so knowing the full-open isn't all that helpful, and even if the other end were open it would still work.

I am amused by all the comments & suggestions that on the surface, would seem to suggest I don't know how to use a meter, or how to measure an unknown pot value, or even that 65 year old (+/-) mechanical parts exhibit noise. For the record, I was up for my father's funeral and did not bother to pack a voltmeter. (I know, the true sign of a nerd if ever there was one. Well, that and pocket protectors. But I digress...)

While there, my brother asked me to look as his lapsteel guitar. We took the back off, it looked like a standard pot, unmarked, and that was the end of it. Mistakenly, I thought that since this was supposed to be a very famous guitar model, it would be a snap to locate the replacement value online. So far, I have heard recommendations for everything from 10K to 250K, both linear and audio tapers. (In short, nobody seems to know.)

Add to this, the US Patent Office does not seem to have the schematic scanned. (#2089171). Bummer. I can always do in the hard way... (measure voltages off the pickup, and select value from there - though it would be nice to have the parts handy next time I'm home and not have to wait on their subsequent arrival.) But thanks for the help.

-mpm

Actually, only two leads are connected (wiper and one end), so knowing the full-open isn't all that helpful, and even if the other end were open it would still work.

I am amused by all the comments & suggestions that on the surface, would seem to suggest I don't know how to use a meter, or how to measure an unknown pot value, or even that 65 year old (+/-) mechanical parts exhibit noise. For the record, I was up for my father's funeral and did not bother to pack a voltmeter. (I know, the true sign of a nerd if ever there was one. Well, that and pocket protectors. But I digress...)

While there, my brother asked me to look as his lapsteel guitar. We took the back off, it looked like a standard pot, unmarked, and that was the end of it. Mistakenly, I thought that since this was supposed to be a very famous guitar model, it would be a snap to locate the replacement value online. So far, I have heard recommendations for everything from 10K to 250K, both linear and audio tapers. (In short, nobody seems to know.)

Add to this, the US Patent Office does not seem to have the schematic scanned. (#2089171). Bummer. I can always do in the hard way... (measure voltages off the pickup, and select value from there - though it would be nice to have the parts handy next time I'm home and not have to wait on their subsequent arrival.) But thanks for the help.

-mpm

You're absolutely correct in that measuring the pickup voltage to arrive at the resistance value of the pot is doing it the hard way. Previous posters have tried to explain to you that a direct resistance measurement of the pot is the easiest, quickest, and most reliable way to find a replacement. What isn't obvious about that method?

Maybe you can explain why it isn't possible to measure the pot's resistance with an ohmmeter? And what is your procedure for measuring the voltage from the pickup and arriving at the pot's value?

I don't recall anybody inferring that you don't know how to use the meter, but it's becoming increasingly more obvious that you don't.

--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the 
address)

Experience: What you get when you don\'t get what you want

If it is being used in rheostat mode (it is), then you can use virtually ANY value high enough to attenuate the output to the desired "zero" level. Then, working toward zero ohms on the "stat" takes you toward max output.

Rheostat choice here is no brainer. A nice one or two turn wire wound. I'd start with a 50K and reduce value of pot till your amp starts to pick up the output jack signal, then read the pot for the value ballpark.

Likely less than 10k.

Yes, he does. If you had read a bit, you would have noted that he has several very expensive meters. Perhaps he can even read one better then you.

What he may be doing is assuming that a noisy pot would give an improper reading across its end to end terminals.This is generally not the case, but I can see where a completely scratched up, OLD OLD style and technology pot could gain resistance value if some of the pot resistance medium was scratched off.

What one would gain is a ballpark figure for the pot.

Since he stated that it is hooked up in rheostat mode, it will be easy to arrive at a sufficient value to solve his needs.

At least he knows how to make a proper post in Usenet. That shit news reading client you are using cannot quote properly, OR you were so stupid that you went into the settings and made the quote character a blank field.

Electric guitars with passive magnetic pickups generally use 100k to 500k log taper pots. The value isn't critical. so use whatever you can find. I doubt that active pickups were around at that time. bg

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Naa, he's an engineer, so he's too cheap to buy a meter at Rat Shack for a one-time job.

He just hasn't thought that he could leave it in his glove box for those 'just in case' moments (or packed in his overnight bag, ditto). Then he'd be a _real_ engineer.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Oh, I suppose I can read a meter quite well... I've only been doing it for nearly 50 years.

My news reader replied in the same format as the post that I was replying to... and that was posted by the OP. His reader posted in rich text format... my reader just replied in the same format.

Apologies to the OP... I should have been more polite.

--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the 
address)

Experience: What you get when you don\'t get what you want

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Dave, Get a life. The damn thing is nearly 70 years old, and in really bad shape. I wouldn't trust any reading it gave me anyway, even if that reading were correct.

I wish I had a photo of it, then you'd understand. QUIT thinking this is some pristine part out of a Digikey order. It is not.

Yes, I could have measured it - but I did not have a meter with me. What is so god-damned difficult about understanding that very basic fact?

And f*ck you anyway. Seriously. It is becoming increasing obvious (to me) that you can't understand what I previously posted. This was never about how to measure a pot. That is basic electronics

101. All I wanted was the value, and if you don't know it, then just shut the f*ck up.

As for your comment that a direct measurement is the "easiest, quickest and most reliable method...." Possibly, if you count the $140 in gas, and the 10 hours on the road it would take me to actually get back to the guitar with meter in hand. And of course, even that would assume that the device in question had never been replaced by previous owners over the past seven decades. I think you make way too many assumptions here!

Respectfully, (to the extent I can be after a post like yours..)

-mpm

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Thanks. That sounds about "right". This is a very, very early pickup design. Cutting edge at the time, involving a pair of horseshoe magnets.

I am probably just going to order a small assortment of pots (luckily, it appears to be a 1/4" shaft variety...) One of them will be "close enough". It's not about the dollars, it's about being able to fix it next week when I'm up there again. Regardless, any pot is going to better that what's in there now, but it'd be nice to get it right.

-mpm

=2E..For that matter, there's really no guarantee that there is end-to- end conductivity. It is totally possible, though I agree unlikely, that the far end of the pot has no conductivity to the far terminal. But the question as to whether or not this is even the original pot is still there, which is one of the (unspoken) reasons I was asking in the first place.

Absent a definitive answer, my current "plan" is to acquire a 10K, 50K and 250K and see what shakes. (hopefully, not literally.) Ha!!

-mpm

Sorry Tim, No more room in the glovebox. (Too much Viagra in there already!!). Let's see that get through Jim's filters.....

Actually, it reminds me of a joke:

A lady goes into the Pharmacy and starts to ask about Viagra. Woman: Does this stuff actually work? Druggist: Oh sure. It's works really well! Woman: That sounds great. Can I get it over the counter? Druggist: Well yeah, if I take two......

-mpm

Actually, I have no idea what is in my glovebox. But I do know I have a couple of spare, new, 8-pin RS-485 transceiver chips I ordered in there somewhere that go to our church's Strand lighting controller.... Does that count??

Might make for a curious "inventory experiment" next time I'm in the mood.

Apology accepted. So please ignore my last post.

I use Google Groups to post, (which I understand is the worst ever). Character substitutions do not bother me. Character assinations do. Plus, I'm in a major funk anyway I guess. I usually just let the comments roll off....

Mental note to self. Do not post late at night.

-mpm

Yes... given the way you said that it is hooked up, there is no guarantee. Good observation.

Yeah... someone even mentioned 500k. Dial down till you start hearing it and take a reading.

My best guess is 50k or 100k log taper. And it is exactly that, a guess; but typical for then normal "Hi-z" audio equipment.