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Topic: How do you check the ohms of pickup? |
Larry Gerdeman
From:
Missouri, USA (deceased)
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Posted 24 May 2012 7:10 pm |
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| Is there a way to check the ohms of a pickup without taking the pickup off of the guitar? |
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Paul Sutherland
From:
Placerville, California
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Posted 24 May 2012 7:23 pm
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| It's simple to do. You buy a digital multimeter for under $10 at a Radio Shack type store, and then connect the probes to the end of a guitar cord, which is plugged into the steel. No need to remove the pickup to do the test. |
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Ned McIntosh
From:
New South Wales, Australia
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Posted 24 May 2012 11:18 pm
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When you do this, make sure only the pickup you are testing is switched to the output socket! If both are switched to it you are measuring both in parallel and will get a very misleading (and low) reading.
You will measure DC resistance using this method (i.e. the number of Ohms resistance to a DC current). For most purposes this is all we need to know.
In reality, since the pickup is dealing with a series of alternating currents at various frequencies and voltages (generated by the vibrating strings when the steel is played), a more complex term called "Impedance" is more technically correct. Impedance contains a component of pure resistance plus a component of "phase-angle", which describes the amount by which the voltage in the pickup is ahead of ("leads") or is behind ("lags") the current, using a single complete cycle of the frequency being examined as the reference. (for the mathematically-inclined, Impedance uses Complex Numbers for calculation.)
Impedance arises due to the pure resistance of the coils, the inductance of the pickup-coils as well as the distributed capacitance of the coils. Impedance is something pointy-headed radio geeks and electronic dudes handle with relative ease. For us simple steel-guitarists we need not worry about it because we can do very little about it. It's just there.
Because it is not all that easy to measure impedance (unless a single amplitude and frequency are considered), we tend to use the simple DC resistance test to describe how many Ohms resistance a steel-guitar pickup has.
Due to the relatively high number of turns on the windings, steel-pickups tend to be significantly higher than electric-guitar p/ups. For example, a single-coil Telecaster pickup might have a DC resistance of 4000 Ohms (4Kilo-Ohms, or 4K Ohms) whereas many steel-guitar pickups are 16 to 18K, resulting in a hotter output signal, and a difference in tone.
_________________
The steel guitar is a hard mistress. She will obsess you, bemuse and bewitch you. She will dash your hopes on what seems to be whim, only to tease you into renewing the relationship once more so she can do it to you all over again...and yet, if you somehow manage to touch her in that certain magic way, she will yield up a sound which has so much soul, raw emotion and heartfelt depth to it that she will pierce you to the very core of your being. |
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Ray McCarthy
From:
New Hampshire, USA
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Posted 25 May 2012 2:25 am
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| Oh. |
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Jack Stoner
From:
Kansas City, MO
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Posted 25 May 2012 5:10 am
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Ned is correct. Measuring the DC resistance is only measuring the DC resistance of the coil wire and nothing else. If you compare two idential pickups (same pickup manufacturer, same magnets, etc) then it may tell you something. But, for example if you measure the DC resistance of an Emmmons pickup and the DC resistance of some other brand pickup even though they are the same DC ohms resistance that does not say they will both sound the same.
The AC and Inductance parameters are what is needed. Two Bill Lawrence 710 pickups, for example, can have different DC resistance but sound identical, since Bill does not use DC resistance as one of his pickup parameters. |
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Lane Gray
From:
Topeka, KS
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Posted 25 May 2012 5:43 am
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True, but with impedance a function of capacitive reactance (varying inversely with frequency), inductive reactance (varying with frequency, unless I have the two reversed, but I don't think so, but I studied that in 83, but never used the knowledge) and resistance (which the Borg told me was futile), do they pick a frequency at which to peg the value? Ever since I studied that around age 20, I've wondered about that.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects |
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Jack Stoner
From:
Kansas City, MO
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Posted 25 May 2012 6:12 am
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Lane, Talk to Bill Lawrence (if you have a couple of hours to spare) and he will detail what all the technical parameters are that go into pickup design.
I don't know what base frequency is used for testing/design.
I'm not a design engineer, even though I had to study that when I took the FCC commercial radiotelephone license tests (I had a 2nd Class FCC Radiotelephone license). I was a tech school instructor in the Air Force and taught electronics at Keesler AFB. |
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J Fletcher
From:
London,Ont,Canada
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Posted 25 May 2012 8:11 am
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Never tried this but, couldn't you measure the Z of a pickup by:
having it output a constant magnitude tone of 1Khz for example, maybe an Ebow would come in handy here, and then loading it down with a variable resistance, until the signal voltage across the pickup and the load resistance are equal. At this point the pickup Z equals the load R.
Kind of complicated, I know.
Or am I missing something? Jerry |
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Chris Reesor
From:
British Columbia, Canada
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Posted 25 May 2012 2:07 pm Impedance
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Lane, you remembered right. Capacitive reactance (Xc)varies inversely with frequency, inductive reactance (Xl) directly with frequency.
Impedance is the complex combination of Xc, Xl, and R (or resistance). It is frequency dependent.
Jerry, impedance can be measured with a bridge circuit,using a variable resistor for one leg, and, a sine wave signal generator.
If you were to take a series of measurements across the applicable frequency range, say, 50 Hz to 10 kHz, you could graph the impedance curve of a pickup and would then see the amplitude of the impedance peak at the pickup's resonant frequency.
Resonance occurs at the frequency where Xc and Xl are equal, and the amplitude of the peak is controlled by the DC resistance in the circuit, R.
The lower the R value relative to the reactances in the circuit, the higher will be the "Q" of the circuit, and the sharpness of the resonant peak.
Yes, it is a complex, but fascinating, subject.
Chris
_________________
Excel Superb U12, MIJ Squier tele, modified Deluxe Reverb RI, Cube 80XL, self built acoustics & mandolins |
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Niels Andrews
From:
Salinas, California, USA
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Posted 25 May 2012 2:10 pm
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And for clarification why does one want to know this? I have limited RAM to remember all this, but curious as to why one would want to know? What am I missing?
_________________
Die with Memories. Not Dreams.
Good Stuff like Zum S-12, Wolfe Resoport
MSA SS-12, Telonics Combo. |
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b0b
From:
Cloverdale, CA, USA
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Posted 25 May 2012 2:13 pm
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Because ohms is an indicator of the number of windings. All other variables being equal, fewer windings (lower ohms) means brighter tone.
_________________
-𝕓𝕆𝕓- (admin) - Robert P. Lee - Recordings - Breathe - D6th - Video |
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Lane Gray
From:
Topeka, KS
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Posted 25 May 2012 2:37 pm
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B0b, isn't it not just brighter, but a bit thinner with more "Twang" and bark?
I'm currently considering sending a TrueTone down to Jerry for rewinding with a tap.
Couldn't one enroll a pair of DPDT switches (or, I suppose, a rotary switch) to not only let one choose between the 12K and 18K, but also the 6K outer half?
Just goofy stuff I think about in the truck.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects |
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b0b
From:
Cloverdale, CA, USA
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Lane Gray
From:
Topeka, KS
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Posted 25 May 2012 2:46 pm
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I've heard some pickups that were both bright and full, B0b. But taps aren't as full.
By bark, I guess I mean a sharper attack, something that single coils have in spades, compared to the humbucker. And one of the reasons why folks still like the singles.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects |
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Niels Andrews
From:
Salinas, California, USA
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Posted 25 May 2012 4:41 pm
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Can't you just plug it in an amp and play it to see how it sounds?
_________________
Die with Memories. Not Dreams.
Good Stuff like Zum S-12, Wolfe Resoport
MSA SS-12, Telonics Combo. |
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Lane Gray
From:
Topeka, KS
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Posted 25 May 2012 4:45 pm
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Yes, but if you go to sell pickups, or in some cases the guitar, somebody is gonna ask "how hot's the pickup?" or a similar question.
Or perhaps the OP is just curious.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects |
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Tony Williamson
From:
North Carolina, USA
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Posted 26 May 2012 4:54 pm
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| what kind of people are all you steel players anyway...im having problems with impedance myself. one shot of testosterone and a little blue pill takes care of it...yippee yay ki yay |
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Jim Sliff
From:
Lawndale California, USA
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Posted 29 May 2012 10:20 pm
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| Quote: |
| a single-coil Telecaster pickup might have a DC resistance of 4000 Ohms (4Kilo-Ohms, or 4K Ohms) whereas many steel-guitar pickups are 16 to 18K, resulting in a hotter output signal, and a difference in tone. |
Not quite.
First, typical Tele pickups are in the 6.5-10k range.
Second, as noted partially above, DC resistance is not a valid indicator of how "hot" a pickup is. A vintage Rickenbacher lap steel pickup might measure about 2.8k but blow the doors off most pedal steel pickups volume-wise. And there are not a large number of turns either. They are a different design and use a far larger gage of wire for the windings.
number of coils can also have an affect - in many cases dual-coil humbucking pickups of a given DC resistance do not have the same output as an equal-resistance single-coil...yet in other cases the reverse is true.
Now pickups like the Alumitone have come along and changed all the rules. And Lace is not the only pickup manufacturer producing pickups based on non-1950's technology (which is exactly what the DC-resistance measuring method of comparing pickups is based on).
If I'm comparing apples-to-apples...say a couple of 1960's humbucking pickups of similar design...DC resistance is something I note because it *usually* (in that particular context) provides some baseline comparison factors.
But there are too many differences in modern pickup design for DC resistance to still be considered a useful tone or volume estimate tool.
As far as the OP's question goes - if the guitar has no controls, simply measure the resistance at the output jack. However, if a volume, tone control or both are in the circuit you need to unsolder the hot lead of the pickup and measure the resistance between that lead and ground.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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