Pickup resistance question - mystery

Frank Montmarquet · From: The North Coast, New York, USA

I have an Emmons student push/pull from the 1970s. I have read some things here than mention pup resistance (don't think it's impedance) so I decided to measure mine. I put an ohm meter on the guitars output jack (didn't want to unwire anything) and measured 450K.

Since the volume control is probably a 500K pot and the pup is in parallel with the pot I think 450K would be very unusual. A 20K pup across a 500K pot should result in about 19K. The 450K could be the actual value of the pot, within 10%, however it would mean that the pup resistance is very high, much higher than 500K, or there is a cap in there somewhere that I don't see. (tone control had a cap but I removed it.)

Any ideas on what is going on? Anybody made a similar measurement? Is this a normal result or might there be something wrong with the pup.

Thanks

Bill Moore · From: Manchester, Michigan

For what it's worth, I have an Emmons student model, the pickup resistance measures 14.5k. Are you setting the scale of the meter to the correct range? Does it sound OK? I once had a Sho-Bud that measured very, very low; the pickup was bad. It was very thin sounding and had low volume. After re-winding by Jerry Wallace, it was much, much better. And the resistance reading was in the normal range. If you are sure you are measuring correctly, there might be a problem with the pickup.

Frank Montmarquet · From: The North Coast, New York, USA

I set the meter to "auto" and get 443K, if I set the range manually I get .443M, same thing. As I turn the volume control on the guitar down, the resistance drops to near 0, which is what it should do. I will double check and maybe take a measuement at the pot to see if there is a difference.

It sounds OK, but I have never heard one like this before so I don't really know what it should sound like. I am using a Roland cube 80, seems plenty loud without turning all the way up.

I hooked up an oscilloscope and measured about 0.1 V peak-to-peak. Don't know what it should be.

Paul Arntson · From: Washington, USA

Hi Frank.
I would bet there is a wire broken in the pickup down deep inside. There are enough windings close to each other to pass the higher frequency part of the signal (capacitor coupling), but if you put it next to a 100% functional pickup it would sound a bit tinny. Also 0.1V is a bit low for a pickup output in most cases, but not bad.

Running the numbers backwards from a 500K volume control and a measured parallel value of 443K gives a pickup resistance of around 3.9 Meg. This is in the right ballpark for a broken pickup.

The formula I used is (500K x 443K)/(500K-443K). You can check the value by using the regular formula for two resistors in parallel which would be:
(3886K x 500K)/(3886K + 500K)=443K

If you like the tone, maybe don't worry about it.
Just keep an eye on it in case it gets worse.
If it bothers you, you might check the solder joints by remelting them, but be real careful, that #42 wire is only like a couple thousandths thick.

Happy New Year!

Frank Montmarquet · From: The North Coast, New York, USA

Greg Cutshaw · From: Corry, PA, USA

Your pickup could be totally open resistance wise and still produce quite a bit of output. I had a Sho-Bud pickup that sounded a little off and it turned out to be "open". There's still planty of coupling in the pickup to pass a strong signal despite the open windings but of course the tone is way off but recoverable through the amp controls.

Greg

Paul Arntson · From: Washington, USA

"If there is a bad joint, the resistance would be high, but would there be enough capacitance to pass a signal?"

Good point. Probably not, Frank.

Greg, thanks for chiming in. You got all the info across in 3 clear sentences.

Frank Montmarquet · From: The North Coast, New York, USA

Thinking more about this, if there is a bad high resistance solder joint a usable signal would still get through because the amp input impedance is high. But the capacitance in the cable would make a low pass filter and kill more highs than normal.

What now, should I fix this? Who rewinds pickups? Get a new one, some don't seem too expensive. Will a new one fit? If it does I could use it on a more modern guitar when I get one.

This guitar stays in tune and works fine otherwise. It seems like a good one to learn on.

Paul Arntson · From: Washington, USA

You might try
http://www.jerrywallacemusic.com/

There are also several other forum members in this business, I believe.

I had mine done by Jason Lollar, who is local here in Pac NW but I see he has quit rewinding according to his website.

Minimizing down time is another thing to consider.
If it were me, I'd consider sending a mounting plate photocopy scaled 1:1 to Jerry and see if a stock pickup would fit. Then you could have the existing pickup rewound at your leisure.

I would also consider just living with it if it works ok. Then wait until it starts causing problems.

What pedals and knee levers does your guitar have?

Greg Cutshaw · From: Corry, PA, USA

I wish I would have saved my old "OPEN" winding Sho-Bud pickup as a conversation piece. Would make an interesting demo at a steel guitar convention. Plus you wouldn't believe how many people don't believe my story. I used that pickup for a long time that way but eventually replaced it with a great sounding pickup off of an old LDG steel and I was off to tone heaven! The combination of high series inductance and capacitance yields a reactance that does not favor low frequencies.

Greg

Frank Montmarquet · From: The North Coast, New York, USA

Paul Arntson · From: Washington, USA

Hi Frank,
I am not too experienced on different pickup dimensions. Perhaps someone with more experience on your particular guitar could chime in here.
I know my early Excel has an uncommon mounting pattern, and so I made my own pickups from scratch when experimenting.
This would be a good subject for a brand new thread. This question could use some good reference material.
Best of luck to you.
-Paul

Lane Gray · From: Topeka, KS

Most steels conform to the "wide" standard, and should drop right in.
I'd just ask the maker of the pickup. Given that there're hundreds, if not thousands, of student model Emmonses around, they'll already know. And if it needs a different footprint, they might even have them in that spec.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects

Frank Montmarquet · From: The North Coast, New York, USA

There is no cavity to drop in, the pup sits on the top surface of the body. So, if a new one is not the same height (9/16") as the old one I might have to make a cavity to keep the distance to the strings right.

I'm thinking that some of the Emmons pup are probably the same height.

Lane Gray · From: Topeka, KS

I don't have my guitar here in the semi to measure.
I'd still suggest talking to Jerry Wallace and maybe some of the others.
While that sounds shorter than any of my Truetones, I bet he's familiar with the guitar and could make you one to fit.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects

Frank Montmarquet · From: The North Coast, New York, USA

Pulled the pup off, it measured about 800K, a little on the high side Sad

Sent it to Jerry Wallace for a rewind. Was thinking about a new one but his TrueTones are 3/4" high, as are most others. Alumitones are .88"

George McCann · From: Maui, USA

As an old guitar builder L know we had to disconnect the Volume pots to get a true measurement as the the resistance mesured through the pots would only equal the the pot's resistance. But it sounds like you tried that.

Frank Montmarquet · From: The North Coast, New York, USA

Got the PUP back from Jerry Wallace today, it now measures a little less than 15K. Hooked it up without the vol. control. Don't have the time to play around with amp and EQ settings but just straight there is a BIG improvement in tone. Very Happy

Justin Griffith · From: Taylor, Texas, USA

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