cool way to read resistance in installed pups

[Curly]

*** please note:
the following is a quick troubleshooting method for determining the nominal (as opposed to exact) resistance of a pickup.
It is not meant to be a method of taking an exact resistance; that is best done by measuring a pickup that's not in a circuit ***
---------------------------------

some of you will say, "duh, I already knew that", but some of you will find this handy

basically, you can take a resistance reading on an installed pickup by plugging in a guitar cord, and putting the hot lead of your meter to the tip and the ground lead to the shaft

I saw this tip in the latest version of Vintage Guitar in Erlewine's column.

I had a strat that has a problem - it's always sounded weak on the neck pup. I've opened it up to check the solder joints, but forgot to take a reading on the pups while I had it open.
So this morning I plugged in a cord and took a reading with my meter, and sure enough, it worked. It verified that the pup was indeed weak - under 5K

anyway, you can take readings on all the switch positions ... just have to turn up the volume to get your readings

 

[Marcel]

Re: cool way to read resistance in installed pups

remember you always read a bit less:
for example: you got a 16k (=:R1) PU and a 500K (=:R2) Vol Pot
you'll read
R=1/(1/R1 + 1/R2) = 15.5k (http://www.google.de/search?q=1/(1/500+1/16))
which makes 3% tolerance

you can easily correct this with
R = 1/(1/R_mes - 1/R_vol)
where
R_mes - is the value you measured (f.e. 15.5kOhm)
R_vol - the value of the pot (f.e. 500kOhm)
R - the corrected dc resistance of the PU
again google do the calculation for you: http://www.google.de/search?q=1/(1/15.5+-+1/500)
and you got the right value

remember Vol have to be on 10 while measuring

 

[STRATDELUXER97]

Re: cool way to read resistance in installed pups

It's not as accurate though Curly....If you can access the leads(like in a guitar with an open cavity)I just read from ground and the hot lead to the pickup at the pot....

In a strat or a Tele,you really need to use a cable or a jack to get a ballpark reading,otherwise you have to pull the guard...

I've known about this method for several years now actually...

 

[Marcel]

Re: cool way to read resistance in installed pups

It's not as accurate though Curly....If you can access the leads(like in a guitar with an open cavity)I just read from ground and the hot lead to the pickup at the pot....

If the PU is still connected it doesn't make a difference if you read at the Pot or at the plug!

 

[Curly]

Re: cool way to read resistance in installed pups

well, I thought someone would say it's not accurate, but for my example, I wanted to diagnose a problem without opening the pickguard if I didn't have to, so I think it's still a good tip

thanks for the Googling, Marcel

 

[Marcel]

Re: cool way to read resistance in installed pups

well, I thought someone would say it's not accurate, but for my example, I wanted to diagnose a problem without opening the pickguard if I didn't have to, so I think it's still a good tip

thanks for the Googling, Marcel

Yeah it's accurate enough in most cases coz 3% isn't much tolerance! I didn't google I just use it as a calculator

 

[martinsixstringcustoms]

Re: cool way to read resistance in installed pups

Never heard of that one, Curly. Thanks for sharing

 

[Sludgenutz]

Re: cool way to read resistance in installed pups

That method is a good to know for giggles. However, this method should not be used as a crutch to paid technicians who are too lazy to perfom a professional diagnosis. It would just be some customer's luck that some paid "genius" would swear upon this method for years before encountering a true exception. "Uhh...Soory dude, It worked on 300 other guitars I've worked on"! :smack:

Marcel does a great job displaying the mathematial formula! However, one must assume that the pot (or any other link in the circuit) is working correctly. One should not assume that because is says 500k on the pot, that this figure is accurate at all. Nothing is more accuate than taking readings from each component, especially if there is a nagging problem. Mathematical calulations are accurate only if all the variables are truly known.

Cool, Yes!
Accurate, for the most part. Too much is assumed with is method.
Professional? No.

 

[theodie]

Re: cool way to read resistance in installed pups

some of you will say, "duh, I already knew that", but some of you will find this handy

basically, you can take a resistance reading on an installed pickup by plugging in a guitar cord, and putting the hot lead to the tip and the ground lead to the shaft

I saw this tip in the latest version of Vintage Guitar in Erlewine's column.

I had a strat that has a problem - it's always sounded weak on the neck pup. I've opened it up to check the solder joints, but forgot to take a reading on the pups while I had it open.
So this morning I plugged in a cord and took a reading with my meter, and sure enough, it worked. It verified that the pup was indeed weak - under 5K

anyway, you can take readings on all the switch positions ... just have to turn up the volume to get your readings

Thanks Curly but, I am few years ahead of you! It is a good trick to get a ball park figure!

 

[STRATDELUXER97]

Re: cool way to read resistance in installed pups

If the PU is still connected it doesn't make a difference if you read at the Pot or at the plug!

If you put your meter right at the leads "before" the pot,you get the accurate reading...The best way to get the reading though,is by measuring the pickup out of the circuit and at the leads...

Curly knows that the normal readings of the pickups he uses is say between 5K and we'll say 13k.....When his pickup is rated for 6k and he sees a reading of between 5.5k and something like 6.5k,then he knows the pickup isn't open...I always double check my pickup installs by measuring the way Gary did it,but I normally will permanent mark the actual value on the plate of the pickup for reference..

 

[Curly]

Re: cool way to read resistance in installed pups

hey, I appreciate the input

even though I have "The Repair Guide", I hadn't run across this method before

I didn't mean to suggest it as a method to get an accurate resistance, but again, in my example it helped troubleshoot a problem, and verify what I was hearing, without opening the guitar up.

I'm sure there are many here who record the actual resistance when installing a pickup, and record it. (I know Dr. Barlo seems to know the exact K reading for all his.)

still, others have run across pups they haven't installed, or didn't get a prior reading on, so I think this will come in handy

for instance, it seems like it's fairly often that someone will say, "my guitar is weak in the ____ position, what's going on?" In cases like that, this might be a quick check method to verify or narrow down a problem.

 

[STRATDELUXER97]

Re: cool way to read resistance in installed pups

hey, I appreciate the input

even though I have "The Repair Guide", I hadn't run across this method before

I didn't mean to suggest it as a method to get an accurate resistance, but again, in my example it helped troubleshoot a problem, and verify what I was hearing, without opening the guitar up.

I'm sure there are many here who record the actual resistance when installing a pickup, and record it. (I know Dr. Barlo seems to know the exact K reading for all his.)

still, others have run across pups they haven't installed, or didn't get a prior reading on, so I think this will come in handy

for instance, it seems like it's fairly often that someone will say, "my guitar is weak in the ____ position, what's going on?" In cases like that, this might be a quick check method to verify or narrow down a problem.

It's fine buddy and it works accurately enough overall for trouble shooting....I measure each and every pickup before I install it and then I'll either mark it or I'll write the reading on a piece of masking tape stuck to the base plate...I'm kinda anal like that...:laugh2:

 

[pinto79]

Re: cool way to read resistance in installed pups

I measure each and every pickup before I install it and then I'll either mark it or I'll write the reading on a piece of masking tape stuck to the base plate...I'm kinda anal like that...:laugh2:

I commit them to memory... :laugh2: :banana:

 

[STRATDELUXER97]

Re: cool way to read resistance in installed pups

I commit them to memory... :laugh2: :banana:

My memory is shot! :laugh2: Best to write things down.....:laugh2:

 

[Rev Donzo]

Re: cool way to read resistance in installed pups

its good to hear that somebody actuly put a number on it ((( 3% )))
Thanks so much..

I have a modifide meter I'm woring on, thats just for reading up top 20k ohms its in a tiny pocket size with a guitar plug /prong--- my SPI Tool!

 

[Marcel]

Re: cool way to read resistance in installed pups

its good to hear that somebody actuly put a number on it ((( 3% )))
Thanks so much..

np that's my job I am going to be a physician . Just a rough estimation.
As shown in the second calculation you can easily calculate backwards if you know the value of the vol pot. But most cheap multimeters have a bigger tolerance than this I think.

 

[STRATDELUXER97]

Re: cool way to read resistance in installed pups

:beerchug:

its good to hear that somebody actuly put a number on it ((( 3% )))
Thanks so much..

I have a modifide meter I'm woring on, thats just for reading up top 20k ohms its in a tiny pocket size with a guitar plug /prong--- my SPI Tool!

Here's to hoping you're a better electronics scientist,than you are a speller! :laugh2: :beerchug:

 

[Sludgenutz]

Re: cool way to read resistance in installed pups

np that's my job I am going to be a physician . Just a rough estimation.
As shown in the second calculation you can easily calculate backwards if you know the value of the vol pot. But most cheap multimeters have a bigger tolerance than this I think.

hummmm...I really hate to sound like a c**ks*cker, but you are still assuming you know the value of the pot/pots!

To ACTUALLY KNOW the value of the pots in question, you would need to unsolder the pickup! Well, if you had to go through all that, why not take a direct measurement off the pickup!

I do not wish to belabor the point that was made with the original post. But, this site is rather instructional to the entire Globe. Would-be techs are better off taking direct readings from only the pickup...regardless of the convenience factor afforded through a quick'n'dirty method.

If there is something I am missing, please school me. Thanks in advance!

 

[Marcel]

Re: cool way to read resistance in installed pups

hummmm...I really hate to sound like a c**ks*cker, but you are still assuming you know the value of the pot/pots!

To ACTUALLY KNOW the value of the pots in question, you would need to unsolder the pickup! Well, if you had to go through all that, why not take a direct measurement off the pickup!

I do not wish to belabor the point that was made with the original post. But, this site is rather instructional to the entire Globe. Would-be techs are better off taking direct readings from only the pickup...regardless of the convenience factor afforded through a quick'n'dirty method.

If there is something I am missing, please school me. Thanks in advance!

Calculate or measure it and you see the error will be small... approxm 0.1k at a 5k pub!

But you're right! It is a quick and dirty method! If you want it exact you have to unsolder the pub! Maybe it's wired weird or anything strange on the circuit.