odd tone anomaly?

[thedoc735]

Hi again!

I couldn't resist the temptation of trying this: www.premierguitar.com/articles/27869-mod-garage-swap-that-tone-knob-for-a-warmth-control 

...it was crap in my case, gave no tone control what so ever!

...but, I also wanted to try the Emerson .022uF tone cap. So, I kept the extended leads with alligator clips connected to the tone pot and compared all my previous tone caps with the Emerson 'cap'; I really liked the subtle change in tone! So, I got rid of the test leads and fixed the Emerson in position (attached to the tone pot/soldered), I changed nothing else at all...

...but now there is no change in the tone what so ever?   ...bright full treble frequencies all the time, the tone pot now does absolutely nothing when it is adjusted? i.e. full bright tone permanently! 

I tested the Emerson on a capacity meter before I fitted it, and it was 'spot on' and worked fine during the alligator clip test!

So, how can there be no tone control now whilst everything else still works fine?

All I did was swap one cap for another and this is the result!

Very strange! ...can anyone shed a light on what has happened here?

Why was one leg of the Emerson cap coated in red dye?

Many thanks!

[newey]

Better test the tone pot itself, you might have fried it. Either that or one of the connections is bad.

I have no idea what the "Emerson 0.022µf tone cap" is, but if it's within spec, that's not the problem.

The author of the PG article, Dirk Wacker, gets roasted quite a bit around here for being inaccurate. With cap values that small, he claims a "subtle effect", I'd agree with your assessment, no effect whatsoever. There's a reason that 0.022µf has become the standard for single coils. The famous "woman tone" was about 0.015, and some folks like 0.10, but to go much lower than that probably won't suit most players.

If you want to see why this is, a 5 spice simulation would tell the tale. (You can save yourself a lot of soldering by doing a sim first.)

[thedoc735]

newey

surely you mean .022uF for humbuckers not single coil, which has .047uF?

what is 5 spice?

Surely if the tone pot or the cap is 'fried', then no sound will be output via the jack?

[newey]

Aug 27, 2020 5:56:50 GMT -5 thedoc735 said:

Surely if the tone pot or the cap is 'fried', then no sound will be output via the jack?

Not necessarily. The signal "hot" (as typically wired) goes from the volume pot to the output. An operable tone pot simply shunts some signal to ground, with the cap setting a range of frequencies so affected. Break the internal resistance within the tone pot, and now nothing gets shunted to ground, the entire signal goes to the output. Same thing if the cap is kaput.

surely you mean .022uF for humbuckers not single coil, which has .047uF?

No, usually it's the other way around. In my builds, I typically use .033 for both HBs and SCs.

what is 5 spice?

It's a (free) software package that allows one to simulate circuits. JohnH has posted (in references) his "guitarfreq" software, which is based on spice software but is more attuned towards guitar use. If you have Excel available, or other software that can run Excel files, you can use that to run guitarfreq to give you a frequency response plot with different tone caps.

[thedoc735]

newey

this is emerson .022uF cap. emersoncustom.com/products/emerson-paper-in-oil-tone-capacitors?variant=42819295306

...well, got the meter out and first tested all the grounds to sleeve of socket and were all OK. (continuity) 

Then tested the cap's, capacitance and measured .021uF. OK

Then, tested the resistance of the pot around the 'track' (1 lug to the other) and measured 560k.

Then measured the resistance between the 'wiper' and the 'track' and it measured 000 - 560k (as wiper is turned)

(it's vintage inspired 550k VIPOT).

I also tested continuity of the cable from the volume pot to the tone pot and it is OK too! Volume pot works normal, as does the pickups and the pickup selector switch. The cables from the volume pot to the blade selector switch, and the one to the tip of the socket are all fine too.

There doesn't seem to be any short circuits by looking at the wires?

The cavities are all grounded including the bridge tremolo, also bridge is grounded and obviously the pickups.

Just in case, switched everything off and back on again (and disconnected all exterior cables) left a few minutes gap but that made no  difference!

Now what?

cheers!

..the wiring:

[newey]

No need for the diagram or for testing all that stuff if the problem is the tone pot. And the cap checks out.

Then measured the resistance between the 'wiper' and the 'track' and it measured 000 - 560k (as wiper is turned

)

Hmmm. Is this a "no-load" pot?

[thedoc735]

newey

no, it's not a no load pot.

[thedoc735]

anyway, more info:-
 
 I took the circuit out again and tested everything individually by un-soldering the components and the cap and the pot tested 'good'. So I re-soldered the extension leads with alligator clips and tested all my .022uF caps; and they worked 'fine'! So, back to the emerson cap, installed it into the alligator clips and IT WORKED FINE! (outside the guitar cavity). I didn't change anything else at all as there were no short circuits etc.

So, I guess my only option is to reinstall the emerson cap in the control cavity tomorrow? (and see if the problem re-occurs)?

Summary: the emerson cap works on extension leads with alligator clips, but doesn't when attached directly to the 'pot' itself?

weird or what?

...maybe it is the grounding of the tone pot when fully tightened down to the grounded active control cavity? (that causes the anomaly)? Maybe put some insulator tape between them?

Cheers! 

[newey]

Aug 27, 2020 21:23:33 GMT -5 thedoc735 said:

Maybe put some insulator tape between them?

Yep, if it works outside the guitar but not inside, something is touching something it shouldn't be in the cavity.

[thedoc735]

newey

...could this be happening if I over tighten the nut on the outside or a stray bit of solder got trapped?

[newey]

Aug 28, 2020 21:40:16 GMT -5 thedoc735 said:

...could this be happening if I over tighten the nut on the outside or a stray bit of solder got trapped?

If only the metal base or bottom of the pot is touching the shielding, that shouldn't matter. Pot backs are typically grounded anyway. One of the pot's lugs, or the wire(s) going to one of the lugs, would need to be contacting something. As far as a "stray bit of solder", it depends on where it is and what its contacting.

Did you try the tape?

[thedoc735]

newey

please look again at the last image, I only mentioned the three rivets (that actually secure the lugs), touching the active grounded cavity! Anyway, I didn't need to use the tape because there is adequate spacing/gap between the rivets and the grounded cavity i.e. no short circuits 'there', or anywhere else for that matter! I did put some heat shrink on the Emerson cap. to cover the ends and left it on a shortened version of the test leads but without the crocodile clips (obviously), put heat shrink on the lug that is connected to the Emerson cap.

Put it back together, tightened it all down, and it worked fine!

So nothing has changed except I put the emerson cap. 'on legs' rather than attaching it directly to the pot.

Totally mysterious, no explanation or reason why it didn't work before (i.e. no tone control), but now it's fine?

many thanks!

[newey]

Had to be a dodgy connection to the cap as originally wired.

[ashcatlt]

Aug 30, 2020 21:51:38 GMT -5 newey said:

Had to be a dodgy connection to the cap as originally wired.

Yeah. I’m sorry, I could have told you nothing was shorted to begin with, but by the time I got here, y’all were already almost done.

Anything actually shorted to ground on the tone control is going to have some effect on the signal. If you short across the cap, it will still work as a tone control except that it’ll also act like a volume control when it’s turned way down and will go to silence when all the way down. Shorting the “hot” lug is just going to short the entire guitar so you get silence no matter how the pot is adjusted. Shorting the pot lugs together would be like turning it all the way down, but if that was caused by the shielding inside the guitar, it would also be shorting hot to ground, so you’d still just get silence. The only way for it to not work but still make sound that’s not obviously muffled is if the path to ground is open. That is, the cap must have been disconnected at one end or another, or else the body of the pot was not properly grounded. But you checked continuity of the body of the pot to ground, so it was definitely something about the cap’s connection.

How might one test for this? You can’t check continuity through the cap because it’ll block the DC current that your meter uses to check such things. I think the easiest would be to turn the pot all the way down and then measure the capacitance across the output jack. That’s ultimately what you really want to know anyway.

But resoldering fixed the problem (because the original soldering was the problem) and it’s over now. There are a number of reasons I refuse to (try to) solder to the back of a pot...

[thedoc735]

Aug 31, 2020 11:57:22 GMT -5 ashcatlt said:

Aug 30, 2020 21:51:38 GMT -5 newey said:

Had to be a dodgy connection to the cap as originally wired.

No! ~ I tested the connection from the lug to the pot casing and it was fine. From those test points with probes the capacitance was fine (.021uF), no dodgy connection or soldering.

[ashcatlt]

I mean, it can’t have been shorted, so it must have been open, and simply reinstalling the cap fixed the problem, so... gremlins?

[newey]

Aug 31, 2020 14:02:22 GMT -5 ashcatlt said:

so... gremlins?

When something electrical works, then doesn't, then works again, my motorcycling buddies would invoke the "Fat Electron Theory". This theory holds that, contrary to all known principles of Quantum Mechanics, that all electrons are not the same, some are fatter than others, and can become temporarily lodged or stuck in a wire somewhere, until they get joggled loose and begin to flow again.

I'd put that explanation right up there with gremlins . . .

[thedoc735]

the red arrows show where I measured the capacitance of the capacitor @ .021uF.




...so the soldering must have been OK?

[thedoc735]

ashcatlt

I measured the resistance @ the jack socket, as it is now.

Both pickups, 'HB', in phase.

VOL.        TONE:
up            up            5.08
down        down        0.00
down        up            0.00
up            down        5.08

...as per your guidance.

[sumgai]

Welp, time to dust off the ol' wand-of-weird-things, and wave it around for a bit.


'doc, newey's "Fat Electron" has more than a grain of truth in it. Here's the skinny: Let's assume a perfect solder joint, absolutely no resistance at all to any kind of current. Now ask yourself, "why did sumgai just call out, specifically, any kind of current?". It's because no solder joint ever made by man or machine is perfect.

And therein lays the rub: know that solder, like almost anything else in electronics, has a wetting current. This is the minimum value for a signal to cross the joint from one conductor to another. If that current is less than the minimum, nothing gets through.   (Which is why we say, don't depend on solder to carry a current - it's supposed to be a mechanical back-stop that ensure a connection won't break physically. Soldering to the back of a pot is considered a kludge at best, and is absolutely forbidden by high-stakes manufacturers. (Think medical, aircraft, satellites, etc.))

Now to apply that new-found knowledge.  Your pickups generate somewhere between 1/2 and 1 vAC, and at not much more than a few milliamps (mA). That's a pretty low level of power (amps x volts = watts (power)). Contrast that to a meter, any meter ever made, I don't care what brand it is or how much it cost - they all use a 1.5 vDC cell (you call it a AA battery when you go shopping for one). And that cell can output not only 1.5 vDC, but do so at as much as 300-500 mA. (Perhaps an exclamation point would be appropriate here.)

Back to the "any kind of current" motif. If (and I did say it) volts x amps = power, then it should become obvious that if a pickup can't generate enough volts and amps, i.e. generate enough power to exceed the solder joint's minimum value, then nothing is going to get through. Whereas if a meter's battery has enough juice to operate the display, then for sure it will have enough ooomph to force a non-zero reading onto said display.

(EDIT: I did mean to say "force a significant value onto the display, be it zero or otherwise.  A reading of "OL" or something like that would indicate a "no continuity" condition, and that's what I meant by "non-zero".  Sorry for any confusion.)

ash and newey are correct - you had a bad solder joint, no matter what you may have believed from your testing. But don't feel bad, most Electrical Engineering students don't get the kind of detailed info I just gave you, that only comes after some time in the field, whereupon an old-and-experienced tech or Engineer passes along this kind of stuff whilst on the job.

</today's lesson>

Questions?





sumgai

[reTrEaD]

Aug 31, 2020 23:28:34 GMT -5 sumgai said:

And therein lays the rub: know that solder, like almost anything else in electronics, has a wetting current.

Wetting current is a factor in switches, plugs and jacks, and other connections where there are two hard metal surfaces in contact with one another. Particularly when one or both of the surfaces tend to oxidize.

If you're experiencing wetting current issues in a solder joint, you have made a horrible joint. The flux in solder will perform a chemical reduction of oxides if the surfaces are reasonably clean to start with. The tin will make intimate contact on a molecular level with the metals being joined.

Aug 31, 2020 23:28:34 GMT -5 sumgai said:

Which is why we say, don't depend on solder to carry a current

Extremely high currents can actually heat the solder, which can cause problems. But other than that, there really isn't an electrical issue with solder joints which aren't 'wrapped'. If there was, surface-mount devices would be verboten.

[thedoc735]

sumgai

cheers! I didn't know that! Not even from Hi-Fi forums!

[thedoc735]

reTrEaD

nice to know!

[blademaster2]

Aug 31, 2020 23:28:34 GMT -5 sumgai said:

Welp, time to dust off the ol' wand-of-weird-things, and wave it around for a bit.


'doc, newey's "Fat Electron" has more than a grain of truth in it. Here's the skinny: Let's assume a perfect solder joint, absolutely no resistance at all to any kind of current. Now ask yourself, "why did sumgai just call out, specifically, any kind of current?". It's because no solder joint ever made by man or machine is perfect.

And therein lays the rub: know that solder, like almost anything else in electronics, has a wetting current. This is the minimum value for a signal to cross the joint from one conductor to another. If that current is less than the minimum, nothing gets through.   (Which is why we say, don't depend on solder to carry a current - it's supposed to be a mechanical back-stop that ensure a connection won't break physically. Soldering to the back of a pot is considered a kludge at best, and is absolutely forbidden by high-stakes manufacturers. (Think medical, aircraft, satellites, etc.))

Now to apply that new-found knowledge.  Your pickups generate somewhere between 1/2 and 1 vAC, and at not much more than a few milliamps (mA). That's a pretty low level of power (amps x volts = watts (power)). Contrast that to a meter, any meter ever made, I don't care what brand it is or how much it cost - they all use a 1.5 vDC cell (you call it a AA battery when you go shopping for one). And that cell can output not only 1.5 vDC, but do so at as much as 300-500 mA. (Perhaps an exclamation point would be appropriate here.)

Back to the "any kind of current" motif. If (and I did say it) volts x amps = power, then it should become obvious that if a pickup can't generate enough volts and amps, i.e. generate enough power to exceed the solder joint's minimum value, then nothing is going to get through. Whereas if a meter's battery has enough juice to operate the display, then for sure it will have enough ooomph to force a non-zero reading onto said display.

(EDIT: I did mean to say "force a significant value onto the display, be it zero or otherwise.  A reading of "OL" or something like that would indicate a "no continuity" condition, and that's what I meant by "non-zero".  Sorry for any confusion.)

ash and newey are correct - you had a bad solder joint, no matter what you may have believed from your testing. But don't feel bad, most Electrical Engineering students don't get the kind of detailed info I just gave you, that only comes after some time in the field, whereupon an old-and-experienced tech or Engineer passes along this kind of stuff whilst on the job.

</today's lesson>

Questions?





sumgai

Wow - wetting current.


I was aware of that for contacts where oxidation forms, usually in switches, but I never considered it for guitar circuits. Isn't the use of gold plating on contacts (as opposed to other metals that oxidize less, but still do to a small extent) supposed to eliminate oxidation and prevent this? Certainly in a solder joint, where flux was used, there should be a gas-tight connection whether or not there is direct metal-to-metal contact besides the solder itself and oxidation would be prevented or seriously impeded. That is also different from "contact potential" of dissimilar metals, right? That would then be a dc voltage offset, which I think would be inaudible (until they form oxides, which brings us to the first point).

[ashcatlt]

These kinds of things are frustrating and it’s usually not worth trying to figure out what went wrong. Everything seemed right, but it didn’t work. Did exactly the same thing and now it does. Shrug.

[sumgai]

'doc,



ash is correct (after two wrongs ) - sometimes things go bump in the night, and no one can explain it. Best to not lose sleep over it and just get on with life.

And I'll stand by my assertions above, 61 years of experience (in near-adult- or adulthood) haven't gone completely to waste, TYVM.   Remember, solder is composed of two components, tin and lead, and one of those is considered an ideal insulator.  Get the application the slightest bit wrong, and.....  (I'm leaving flux out the equation for the moment, but yes, it also plays an important part.)




sumgai

[reTrEaD]

Sept 3, 2020 10:25:59 GMT -5 sumgai said:

Remember, solder is composed of two components, tin and lead, and one of those is considered an ideal insulator.

SPOILER: Click to show

[Yogi B]

Sept 2, 2020 12:08:41 GMT -5 ashcatlt said:

Thankfully USB-C adoption might now actually be getting somewhere...

Not that you can't have reversible USB-A or USB-B micro connectors:
(Reversible USB A to Reversible Micro-B Cable - 2m - SparkFun Electronics)

Sept 3, 2020 12:01:46 GMT -5 reTrEaD said:

Sept 3, 2020 10:25:59 GMT -5 sumgai said:

Remember, solder is composed of two components, tin and lead, and one of those is considered an ideal insulator.

SPOILER: Click to show

Uh-oh!

SPOILER: Click to show

[thedoc735]

sumgai

thanks!

...yes lead of course! (if it is lead?)

[thedoc735]

reTrEaD