Howlings, whistlings: the Microphonics' Monster

Introduction

You plug your preferred guitar on your preferred amp and, when going up on your gain level, you start to hear microphonics issues. Whistles, howlings, an uncontrollable feedback that ruins your tone and pains your ears. WTF?. Everything sounded fine yesterday!. What's happening?.

Microphonics is one of the big Monsters that eat our tone and ruin our performance and, they can happen everywhere in our gear but, WHY our gear goes microphonics?.

I want to share with you a recent experience, among other well known issues that I had in the past. I hope, it could help you to defeat your own monster.


Why do we have microphonics?

To make a large history short, we have microphonics because some device in our signal path has metallic parts that can freely vibrate. The sound pressure coming from our speaker makes that parts to vibrate. Such a vibration is being catch by our pickups, amplified by our amp and sent back by the speaker. The metallic part vibrates even more, being catch by our pickups, amplified again and sent back again at higher volume, what increases the vibration and... well... you get the picture. This is an eternal feedback that goes every time louder and that creates some howling or whistlings in the resonance frequency of that vibration.


Where do we have microphonics?

Mmmh... free vibrating metallic parts, do you mean?. I have not such a thing on my chain!.
Well, dude, you are damn wrong!.
Let me show you some examples and be prepared for some surprises.


Cords and Patch Cables

Cords and patch cables with solid core conductor have no microphonics issues but, since they are in fact a continuous bar of copper, they aren't flexible enough and, they are not normally used for guitar cables or patch cables. Cables with multiple thin copper strands are being used, instead.

High end cables (not necessarily, super expensive cables) are well built and, even that they are slightly prone to microphonics issues, they stand in a good position.
But, cheap cables, with cooper strands and a cooper mall for the cable' shield have a lot of little metallic parts that can freely vibrate!.

While your guitar is plugged on your amp, and your high gain stuff cooking the amp, create a loop in a short portion of the cable and, firmly grave the two extremes of the loop in your hand. With the other hand, beat the cable with a solid piece of whatever you have around (the bridge's tremolo, by example) on any part of the loop. If you clearly hear the beat sounding thru your speakers. You have a microphonics cable.
You can test on that way even your patch cables.

The only cable with multiple cooper strands on its core that I know is trying to reduce that micro-collisions between strands is The Forte, by Evidence Audio, who is treating every strand individually with a protective coat that avoid the direct contact metal against metal.


Jacks

Loose jacks are often a source of microphonics (among other) issues. Review your jacks and be sure their nuts and washes are strongly screwed and the jack seems tightened.
Jacks are everywhere on your gear: pedals, amps, guitars...

A warning also about cheap jacks. If their internal plates move freely, they can become microphonics. Use quality jacks, as the swiftcraft's ones, by example.

Take also into account cheap jack plugs. If the internal parts of the plug can freely move, they can be microphonics. Once again, try to use quality jacks, as Neutrik's ones, by example.


Pedals

Well, at least that the pedal was wired with solid core wires (what I seriously doubt, even on the expensive ones), they are using multi-stranded core wires and... we already discussed that, right?.
If your pedal goes microphonics because of its wiring... there is really few you can do, apart of try to reduce such a feedback by using a Noise Gate on your chain.

Pedals have also jacks and, we already talked about this.

Pedals have also mechanical switches, with movable parts. If the switch isn't of quality, it can be another source of microphonic issues.

If the pedal goes microphonics, check first if there is inside something that needs to be tightened: as the screws of the circuit, the jacks, whatever and, if everything is tight then... consider to remove such a pedal from your chain or use a Noise Gate (if it works).

Switching systems, with lots of loops, have lot of wire and lots of jacks to review!.


Guitars

Guitars are usually the main source of microphonics issues.
We have wires inside (that can be microphonics).
We have the guitar's jack.
We have a lot of movable metallic parts, even than some are more critical than others.
And, we have pickups. Pickups are the main source of microphonics issues on a guitar.

A pickup has one or more magnetic coils, wrapped with long lengths of cooper wires, thin as a human hair.
To avoid the free movement of those long turns of a single wire, pickups are nowadays Wax Potted the most of times. But, we aware that most of the Antiquity, Vintage-right, or whatever name they have to make an exact reproduction of a vintage model, are usually un-potted and then, very prone to microphonics, once gain reaches some level.
Even, if they are potted, sometimes some pickup isn't correctly potted and, becomes microphonics.

Then we have some pickups with a metallic base plate. This metallic base plate is being used for two things: to bound back the magnetic field generated by the pickup, what increases the middles and the punch and, to serve as the bridge ground (since pickup' screws are in contact with the plate and the metallic bridge (in Telecasters).

We have pickups that are being mounted with metallic springs, those can vibrate, as well. Some pickups' makers, as Seymour Duncan, are including surgery tubes instead of metallic springs for pickups' screws, what mitigates vibrations of the screws themselves, which can be transmitted to the plate and catch by the pickup and... well... well... you know the history.

And we have bridge plates, as in the Telecasters, that can be prone to little vibrations and become microphonics.

I was working on a Telecaster of a friend of mine, wiring it. When I went to test the Telecaster, as soon as I switched on bridge pickup, the amp started howling and screaming as a crazy. I've change every electronics parts with new brand ones: pots, switches, jack, caps, wires... everything new brand!. And the howling didn't disappeared.
I was stuck for a long while, running out of ideas. Checking the wiring with a multimeter, with the logic saying that the design and implementation were absolutely right and, trying everything it came to mind without success.

Desperate, I've searched on Internet and found that this is a common issue with Telecaster bridge's pickups. Telecasters with steel bridges form part of the magnetic field of the pickup itself. The plate under the pickup increases the strength of such a field, also so, at the end, you have some kind of big pickup very sensitive to anything that moves around a big magnetic field.

Well, in those cases, there are a lot of things to test, increasing the difficulty:

1. To firmly glue the plate to the pickup's base. I've used Loctite for that.
2. To substitute springs with surgery tube or any proper plastic, vinile or rubber tube.
3. To use screws with higher gauge to fix the bridge's metallic plate to guitar's body. Any loose screw there and your plate will vibrate and create feedback.
4. To wax pot your pickup
5. To drill to additional screws in the front of your bridge's plate to force it to remain over the body without additional vibration.

In my case, I've totally fixed the issue gluing the base plate to the pickup, substituting the springs with a plastic tube on every pickup's adjustment screw and, substituting the 4 screws that secure the plate against the body with 4 new screws with an slight bigger gauge.
That fixed the issue instantaneously and, now, my friend can enjoy his loved Tele.


Amps

We have wires also. The most of well built amps will use solid core wires to wire the different components but, they can use multi-strand wires so...
We have jacks, also.

But, honestly, the most of microphonics issues that occur in an amp are related to tubes and, specially to the very first preamp tube (usually named V1).

The tube has a lot of metallic parts in its structure, inside the bottle. The constant vibration that are getting from the speaker itself and, some degradation due to the use, can make some little parts loose and then, microphonics issues attack us again.

Microphonics in amps are usually solved just swapping the first tube with a low-microphonics high quality tube. Power tubes can go bad also, after some time so, if your work on preamp solves nothing, maybe it's time to swap your power tubes.

As ever, review jacks also and, any other potentially movable metallic part inside.


Conclusion

Once you have a microphonics issue, you need to isolate the source first. Use your guitar directly plugged to your amp and, try to determine if it's the amp, the guitar or the cable what is microphonics (check with other guitar and other amp, check a loop in the cable as explained above...).
If it's the amp, try to swap first V1.
If it's the guitar, your pickups are probably the source of the issue.
If it's the cable, try another cable.
If your amp hasn't a gain channel, try then with your gainer pedal between your guitar and amp.

Usually, tubes, pickups or cables are the common source but, be prepared for any other source, as we have explained above. Sometimes, a microphonics issue can take a long time to be chased but, at least, you now where to search now.