Seymour Duncan JB confusion

[CRU JONES]

Wire up a switch with two different value caps, like a .02µF and a .047µF. Wire it up to the pot in the normal way, one end of the two caps to ground, and the other end to the switch and then the tone pot. Keep the pot on 10 and without looking at which cap you are switching to, switch it back and forth and listen. Tell me if you hear a difference. What you are hearing is the resistance of the pot.

Really? I thought everybody could hear this.

I have a guitar like this that I have used for more than a decade. I know which position I like best. I like "UP"! not sure what the cap values are... But "UP" is where it's at! Tone Baby!

Tell you what. This sounds like a challenge. Is this a challenge? IF it is a challenge, I'll rig up a guitar with whatever tone caps you think would work good, record samples and post them here. The ONE condition is: I get to choose the value of the Tone pot. If a majority can hear the difference, you have to put. "The JB is the brightest pickup known to man" as your signature. What do you think? Deal?

<- smiley face means. "good deal, not a trick!"

Ethan

[Mike Sulzer]

Obviously if you make the tone pot small enough you will hear a difference. But for values such as 500K or 250K, the difference on 10 has to be extraordinarily small. This is because the impedance of either value of cap is small at higher frequencies, compared to 500 or 250 K, and the impedance of the pickup is small at low frequencies so the tone control has little effect there in any case.

The relevant test is: can you hear the difference between , for example, .022 and shorting out the cap, that is, a cap with infinite value? The dominant effect of the tone control is resistive loading of the pickup until the pot is turned most of the way down. I have done the test and do not hear a significant difference between cap and short. By that, I mean that there are so many other things that matter, this is not something to spend too much time on.

On that guitar you have, are you sure that"up" and "down" change nothing but the cap value?

Really? I thought everybody could hear this.

I have a guitar like this that I have used for more than a decade. I know which position I like best. I like "UP"! not sure what the cap values are... But "UP" is where it's at! Tone Baby!

Tell you what. This sounds like a challenge. Is this a challenge? IF it is a challenge, I'll rig up a guitar with whatever tone caps you think would work good, record samples and post them here. The ONE condition is: I get to choose the value of the Tone pot. If a majority can hear the difference, you have to put. "The JB is the brightest pickup known to man" as your signature. What do you think? Deal?

<- smiley face means. "good deal, not a trick!"

Ethan

[CRU JONES]

Yup! David Got me on that one! Just going to have to suck that one up

You are both correct. The 22n and 47n make very little... OK... NO Audible Difference! My guitar has the smaller than traditional cap value of 4n7 in the "up" position. The sound is smoother in that setting versus the "down" setting of 22n. You definitely can hear/ feel it. A 4n7 has more low end than a 22n. Its warmer. I can imagine it is different for different pickups. I wish I could tell you the impedance of the pickup, but I wound it before I started to figure that stuff out.

Ethan

[David Schwab]

I like small value caps; when the tone control is turned down you get a nice resonant tone like a wah pushed part way down.

[fieldwrangler]

I like small value caps; when the tone control is turned down you get a nice resonant tone like a wah pushed part way down.

Me too. For me, .015 has been a good starting point with conventional pickups for a long time.

Bob Palmieri

[Steve A.]

Are you holding the wires against the probes with your fingers? That can give a false reading.

I have read that so much that it is almost like an urban legend that has gone viral.

I was an HVAC service tech for 20 years and I had plenty of opportunities to measure the resistance between the fingers on my opposite hands when I was bored, and unless I was sweaty or wet it usually ran somewhere between 4 Meg and 7 Meg. When adding together resistances in parallel you add the reciprocals and then take the reciprocal of the sum. Very easy to do with the Calculator that comes with your computer. So if we added 5 Meg in parallel with the 15k pickup leads the sum in k ohms would be 1/(1/4000) + (1/15) or 14.94 which 0.4% less than the 15k DC resistance of the pot. Granted that different people will have a different DC resistance between their hands so that figure could vary a bit. If the finger resistance was 1M then that would bring the 15k value down to 14.78K which is 1.5% lower than 15k. As for measuring the 15k pickup connected to a typical 500k volume control, that works out to something like 14.56 which is 3% of 15k. (If we had a 10k pickup connected to a 500k pot would be something like 9.8k which is a 2% variance.)

My point is that the difference on pickup resistance created by your fingers or a volume pot isn't usually that much. Of course for an accurate reading you would want to disconnect at least one of the pickup leads and use test clips (which are much better than using your fingers when measuring voltages of 300 to 450vdc. ) Your fingers or the wiring harness will introduce some variations from the actual value but they don't usually add to much. Now if you were measuring a 2M2 resistor holding it with your fingers there would be a very considerable variation. I do believe in having good work habits so I usually have several different size clips on hand for more accurate measurements. And in my experience test probe tips often don't make a very good contact when measuring resistance (when you measure a good sized voltage or current it will jump across a resistance on the probe tips that would screw up a resistance measurement).

Just letting my OCD run loose tonight- no offense intended. You guys make damned good pickups, I just do the math.

Steve Ahola

I usually measure around 1 M when grabbing the leads. It can be 400 K at times.

Great- I think that everyone should know their hand-to-hand DC resistance so that they can compensate for it accordingly. FWIW I have never noticed much of a difference when the surface area of contact with the probe is increased or decreased. Is that the case with you, too?

BTW have you ever measured how much voltage you can generate just squeezing hard on the test probes? Some days I could crank out a few millivolts (microvolts?) but on other days nada, zilch, nothing.

[Mike Sulzer]

I usually measure around 1 M when grabbing the leads. It can be 400 K at times.

[David Schwab]

I usually measure around 1 M when grabbing the leads. It can be 400 K at times.

Same here. I have dry hands so I usually get a high reading.

Just for fun once I held one side and had my wife hold the other so we could see what the resistance was during a kiss. lol I was showing her how it can read across your body.

[David Schwab]

I have read that so much that it is almost like an urban legend that has gone viral.

I stopped holding the wires because I was getting inconsistent readings. Your body's resistance might be large, but it's enough of a parallel resistance to change your measurement at times.

Now I use test clips, which is more handy (no pun intended) anyway.

[Ward]

I just measured a pickup I have on the bench here, holding it with my fingers reads, 12.68k, without fingers 12.73k. Another storm in a teacup.

[Steve A.]

Just for fun once I held one side and had my wife hold the other so we could see what the resistance was during a kiss. lol I was showing her how it can read across your body.

That reminds me of the time when my next door neighbor and I were screwing around with a loose electric motor while kneeling on the concrete floor of my parents garage, we connected the motor leads to an AC pigtail without wire nuts or tape. In addition to learning how a body (and concrete) can be a conductor I also learned about one of Newton's law that day: every action has an equal and opposite counter reaction: when we plugged the pigtail into a live extension cord the starting torque caused the motor itself to roll very powerfully right into us (we were back a little ways just to be safe, or so we thought. ) The hot AC lead touched my friend who jumped back, bumping into me and we got a hell of a shock! Many lessons learned that day the hard way. Kinda like how I learned that filter capacitors can hold a charge- "not fair- it wasn't even plugged in!" That was when I tried to convert a discarded stereo into a guitar amplifier knowing absolutely nothing about electronics but with an uncontrollable urge to take everything apart to figure out how it worked and perhaps fix some minor problem. In many cases that was "worked" in the past tense because when I'd put it back together it was dead as a doornail.

For a pickup maker like you accurate DC resistance readings are important- if you label a pickup as 7.8k when it is actually 8.0k that is an error of 2.5% which may not be acceptable to a customer. But if a guitarist is trying to figure out why his guitar stopped working (no output), it usually doesn't matter if the reading is off a bit; if the DC resistance of the pickup is within a normal range (perhaps 6k-20k?) it would indicate that the problem is probably not with the pickup but with the wiring, pots, caps or output jack. Or more often, just the guitar cable. D'oh! (BTW I do hold the test leads when checking a guitar cable since I am looking for a very low ohm reading and the resistance between your hands would not make a difference, even if it was as low as 100k.)

I agree with you completely that using test clips is a very important work habit. However if you don't have your test clips handy you might want to use your fingers if the reading isn't very critical and there is no voltage involved. "That's close enough for rock and roll (or government work.)" I think it is also important to have at least two meters to make sure that one of them isn't giving you bad readings; if a reading is not what I'd typically expect I would confirm that with another meter before digging in and taking things apart.

So what were your readings in the experiment with your wife? You might want to try it again to see how many millivolts or microvolts that the both of you can generate.

Steve

[David Schwab]

I just measured a pickup I have on the bench here, holding it with my fingers reads, 12.68k, without fingers 12.73k. Another storm in a teacup.

Wet your fingers and try it again. Either way, it's an inaccurate reading.

[Steve Conner]

Just for fun once I held one side and had my wife hold the other so we could see what the resistance was during a kiss. lol I was showing her how it can read across your body.

You should tell Randall Munroe, if you're lucky he may do an XKCD comic strip on it.
"See, this meter shows that I'm irresistible."