Momentary Kill Switch popping like Orville Redenbacher

[mudtaco]

I just finished a very time-consuming, but very fun project. Everything works, sounds and plays beautifully. Save one issue.

The momentary kill switch makes a loud popping noise when used. It's not just killing the signal as it's supposed to, but adds a harsh noise as it cuts in and out.

I replaced it, no help. I rewired it altogether, no change. So, can yall take a look at my wiring and see if anything sticks out, in case the issue is there. I am at a loss, since all else is just fine.

Oh, and everything is brand new (except the neck pup) and good quality.


Thank you

[stevewf]

Hi, mudtaco. Maybe you meant to post your wiring so we can have a look.

Meanwhile, I've seen lots of posts around the web complaining about just that. My Telecaster's kill switch suffers the same problem, in fact.

For solutions, what I've heard most often is wiring a 2MΩ resistor across the two terminals of the momentary switch will cure that. There'll be a cost to that approach, of course - some amount of volume and perhaps tone. Whether that loss is acceptable is up to the guitar owner. And if the pop persists, then lowering the value of the resistor will be more effective (at greater levels of the aforementioned cost).

What I personally would like to see is a two-step switch; one that first shorts the signal to ground through a high-value resistor, then as the button is pressed further, shorts it completely. All within a small amount of travel (like less than 2 or 3 mm). Or if necessary, even a multi-step switch. Or even a rheostat. The fact that they don't yet exist makes me think that it might not work, though.

[Yogi B]

Jun 15, 2023 22:50:14 GMT -5 stevewf said:

For solutions, what I've heard most often is wiring a 2MΩ resistor across the two terminals of the momentary switch will cure that.

If we're talking about a simple (push-to-make) SPST switch shorting the output jack, I don't see how that's supposed to help much, as in almost all cases the switch will already have a 250k—500k resistor wired across it: the volume pot.

I'll be honest I've never put too much thought into this before. In the past I've vaguely attributed such popping to the abrupt jumps between the pickup's regular output voltage and ground, possibly compounded by contact bouncing. However I now realise there are two related things to which I previously had not given enough consideration: the fact that we're attached to a pickup, and the current flowing through it.

What happens when the tip of the jack is shorted directly to the sleeve? Usually we're thinking about the amp-side of the circuit: the output of the guitar is now as close as it is able to be (at this end of the cable) to ground, thus the amp gets virtually no input signal and is nice and quiet. But what happens on the other side of the circuit? Faraday's law of induction doesn't cease to apply, the pickup still pushes electrons around a complete circuit — a circuit which thanks to the closed kill switch now has much less resistance, thereby allowing significantly greater current. This current flows though the pickup (predominantly an inductor) and results in greater energy being stored in the magnetic field than what occurs under the usual (kill switch open) conditions.

This isn't an issue until the kill switch is re-opened. At this point the circuit is back to including significantly more resistance, limiting current through the inductor and once again causing the magnetic field to change (in this case, to suddenly collapse back to the previous levels). This change induces an EMF in the inductor which aims to minimise the collapse of the field. Thus attempting to maintain the same current that flowed whilst the kill switch was closed, even though it is now open. Since the current is the same but the resistance is (much) larger, V = I R means that the output voltage must also be (much) larger — causing a temporary voltage spike. So, that's what I'm now thinking is a major contributor to kill switch popping: inductive kickback.

---

What would eliminate the above issue, and thus hopefully solve the popping problem, is by using a (break-before-make) SPDT switch as the kill switch. The common terminal (exclusively) connected to the output jack tip, one throw connected to ground, and the other to the rest of the guitar's circuitry (e.g. output of the volume pot). A high value resistor bridging from the output over to the jack (in order that the two are never completely disconnected) may also be worthwhile.

Unfortunately, depending on limitations imposed by component availability or through combination of the kill switch function with other features, use of such a switch may not be possible. In such cases other options include: going active (inserting a buffer between the kill switch & the pickups, in order to isolate them from the change in loading / current flow); or, using (an anti-parallel pair of) diodes to limit the maximum voltage spike (n.b. this would not prevent the popping, just lower the volume of the loudest pops; additionally the diodes would need to be carefully chosen so as to not clip the regular guitar signal).

[stevewf]

Jun 16, 2023 5:35:27 GMT -5 Yogi B said:

If we're talking about a simple (push-to-make) SPST switch shorting the output jack, I don't see how that's supposed to help much, as in almost all cases the switch will already have a 250k—500k resistor wired across it: the volume pot.

Ah yes, so it has. And also the tone pot (with a cap in series). So it would seem that a high-level resistor would have no (or very little) effect. I wonder why so many ppl report having success with this method, then. Another Guit-myth?

It must by now be apparent that I myself haven't tried the so-called solution (i.e. a high-level resistor across the terminals of the SPST momentary kill switch); maybe it's time to try it, just to put this to bed (for my purposes, anyway).

[Inductive Kickback] isn't an issue until the kill switch is re-opened.

I could have sworn that I get popping on both opening and closing the switch. So I just ran over to the rig to test: yes, I get pops on both closing and opening the kill switch. (explicit confirmation: this guitar has a SPST normally-open momentary switch that I've wired to short the jack's hot with the jack's gnd when closed.)

Interestingly, the pops that occur on closing the switch tend to get more noticeable as the guitar's sustaining strings are fading. I mean, I strike a chord and sustain it; then I press and release the kill switch repeatedly while still sustaining, and the pops on closing seem to get louder as the sound fades. When the guitar is silent, there are pops on closing. I acknowledge that my perception may be imperfect, hence the emphasis on "more noticeable" and "seem".

The pops on opening happen only when there's sound from the guitar (consistent with yogi's theory).

Both pops are accentuated when the gain is up, either through pedals or right on the amp.

Ideas on what could cause pops on closing the switch, and steps to reduce/eliminate it?

[mudtaco]

That's strange you can't see the image. I can see it. So, I checked with my phone and I can't see it there. I'll try to upload it again.

I was wondering if it would help if I moved it. Now it is between the volume pot's output and the jack. What if I put it in between the selector's output and the volume pot?

[mudtaco]

[sumgai]

Uh oh, somebody's brought an extra cap to the party.


muddy, is there any difference in the pop (volume, tonality) when the cap is switched into the circuit versus when it's out of the circuit?





sumgai

[mudtaco]

I double checked and noise when the kill switch is engaged and disengaged is the same across the board. It does matter where the toggle is or if the elder mod cap is employed. The noise is slightly less with the volume rolled back some and the same with the tone cap engaged, but the difference is minimal. 
So, do you think it would make any difference if I moved the kill switch to the other side of the volume pot?

[sumgai]

Jun 18, 2023 4:05:49 GMT -5 mudtaco said:

So, do you think it would make any difference if I moved the kill switch to the other side of the volume pot?

Not normally what's done, but it certainly can't hurt to try it. Cheaper than just about anything else you can do, that's for sure.   The Volume control, being a resistance, might be enough to "calm" the popping, though you'll want to monitor your tone for any differences.

The last thing you can do is to swap out the switch itself.  Test it for the condition mentioned by Yogi, is it a break-before-make, or the other way around. Many, but probably not most, switches made for momentary use (like yours) are make-before-break.  To us, it sounds more like you have a break-before-make.  That small amount of time that the contacts are completely open is likely enough to introduce that condition mentioned by Yogi, the collapse of the magnetic field causing a rather large (by comparison) jump in current. There's a science behind all this, but for your purposes, we needn't get into it until your problem is resolved. Then we can satisfy your curiosity.


HTH




sumgai