microphonic pedal

[1001gear]

I just got a mini booster and it does killer things like transparentate muddy tones into things of beauty. So far so good. BUT it's also microphonic. I've never had this happen although I've never had occasion to put a pedal in front of a high gain channel. I'm pretty sure the booster requires disassembly just to get at the electro parts. What causes stuff like this? Bad joints?

[Mr.Grumpy]

Are you sure it's really the pedal and not your guitar that's going microphonic due to the extra gain from the boost?

 

You can get squealy feedback with the guitar volume turned all the way down? With the guitar unplugged completely?

[1001gear]

Are you sure it's really the pedal and not your guitar that's going microphonic due to the extra gain from the boost?

 

You can get squealy feedback with the guitar volume turned all the way down? With the guitar unplugged completely?

 

Yeah pretty sure. I noticed it when while tweaking it, my pick tapped the case. Made a distinct clink like it had a tube going soft. lol Also got radio frequency hum from it as I leaned over although thinking back, this could be the power supply since that was sitting right next to the pedal. I'm thinking it might be a design flaw ($20 pedal) and asking here before I waste time at customer service.

[1001gear]

Checked it again. It is making radio. Only hits the pickups inside of a foot.

[t_e_l_e]

there is nothng what you can do, or it works as designed.

at least how a analog radioreceiver works

an antenna to pick up the signal = you pickup + guitar cable

an amplifier to strenghen the received signal = your pedal + amp

a loudspeaker

 

some pedals (like certain fuzz's) are more prone than others, also it can be location dependend

to me it happened only with sinle coil pick ups

 

so things to avoid this

turn the gain down in your signal chain

use different cables in your signal chain (different length, it will change your antenna too)

don't use single coils....

 

 

[1001gear]

there is nothng what you can do, or it works as designed.

at least how a analog radioreceiver works

an antenna to pick up the signal = you pickup + guitar cable

an amplifier to strenghen the received signal = your pedal + amp

a loudspeaker

 

some pedals (like certain fuzz's) are more prone than others, also it can be location dependend

to me it happened only with sinle coil pick ups

 

so things to avoid this

turn the gain down in your signal chain

use different cables in your signal chain (different length, it will change your antenna too)

don't use single coils....

 

 

Thanks. At least now I won't agonize over it. It's a Kokko booster and sounds gorgeous; like a Matchless clean. At 20 bucks, I'mma get one more instead of switching out this one.

[WRGKMC]

A booster pedal Cannot be microphonic on its own. Its just a preamp and has no transducer which can act like a micr and generate a signal.

 

If you're getting feedback its undoubtedly coming from your pickups or possibly your guitar cable which can produce a capacitive microphone effect if its a low quality cable or has been used as a speaker cable at some point. The High current from a speaker jack cooks a cable from the inside out, separates the core from the shield which can then vibrate independently once oxygen gets in.

 

The simple way of proving it is to find the volume levels where the feedback begins. Then unplug the guitar and its cable from the pedal then simply plug in a lone 1/4" jack so the pedal powers up. The most you should get is some hum or hiss from the extreme amplification levels.

 

The fix is of course using a quality cable and potting your pickups if they aren't already.

You can still get microphonic feedback from potted pickups, but it typically takes some dangerously high gain levels before it happens. I don't know many people who would want to abuse their circuits like that but I suppose there's one born every day.

[1001gear]

A booster pedal Cannot be microphonic on its own. Its just a preamp and has no transducer which can act like a micr and generate a signal.

 

If you're getting feedback its undoubtedly coming from your pickups or possibly your guitar cable which can produce a capacitive microphone effect if its a low quality cable or has been used as a speaker cable at some point. The High current from a speaker jack cooks a cable from the inside out, separates the core from the shield which can then vibrate independently once oxygen gets in.

 

The simple way of proving it is to find the volume levels where the feedback begins. Then unplug the guitar and its cable from the pedal then simply plug in a lone 1/4" jack so the pedal powers up. The most you should get is some hum or hiss from the extreme amplification levels.

 

The fix is of course using a quality cable and potting your pickups if they aren't already.

You can still get microphonic feedback from potted pickups, but it typically takes some dangerously high gain levels before it happens. I don't know many people who would want to abuse their circuits like that but I suppose there's one born every day.

 

Ah. I was waiting for you to get in on this. It is the pedal. While there's no feedback, tapping on the case with the pedal gain way up yields the same sound as tapping on a bad tube. The 60 cycle radiation must be from a chip in there. I've read bits here and there that claim cheap caps might go microphonic. What do you make of this?

[t_e_l_e]

picking up radio signals with guitar, pedal and amp can be a fun thing too. i had once french AM radio, and depending where you play and when it always can be something completely different what you pick up

 

unfortunately it cannot be reliably reproduced, so its not easy to make it part of your music in live situations, if the signal does not come at the venue the effect is lost...

[1001gear]

Thankfully, it's just making 60hz noise. Must be why you get that Class C Computing device warning with more "legitimate" gear.

[1001gear]

One more thing. Will the microphonic part wear out/fail or just keep on working?

[WRGKMC]

 

Ah. I was waiting for you to get in on this. It is the pedal. While there's no feedback, tapping on the case with the pedal gain way up yields the same sound as tapping on a bad tube. The 60 cycle radiation must be from a chip in there. I've read bits here and there that claim cheap caps might go microphonic. What do you make of this?

 

Chips in a device like this don't generate a 60 cycle hum, they can only amplify what comes in on the inputs and power line. The pedal should be fed clean DC. Boss and Dan Electro make zero hum wall warts which do and excellent job removing all AC ripple from getting in on the DC line. If you're using some cheap knockoff, then the hum can be coming from poor filtering in the DC supply.

 

AC hum can also come from the input cable or leak through the box itself. You have to be sure your instrument and cable are well shielded, otherwise a booster pedals is going to do exactly what its designed to doo, boost the signal and all noise, including any AC hum coming in on the cable.

 

You need to realize its not simply the signal that gets boosted. What was below your hearing perception before boosting, becomes clearly heard after boosting.

 

As far as what's causing the bell tones, Hopefully you did a check as I mentioned using a short dummy plug with no instrument plugged in so you can rule out the cable and instrument. If you still get bell tones with only 1/4" jack plugged in then the issue has to be believe it or not with the pedal enclosure itself.

 

I'd have to actually put my hands on the unit to pinpoint the problem but what you have going on is the enclosure is acting like a mic diaphragm in relation to the circuitry. In short, electronic components emit their own magnetic fields. Its called a "field effect"

 

Normally these field effects cause little trouble depending on the circuitry. Back as a green tech I was asked by the boss to repair a circuit board. In the process all the components on the board looked like crap being bent over so I went through and straightened up the components to make everything look nice and symmetrical. When the boss came back I got a major ass chewing for doing that. he said, don't they teach you anything in school about field effects?

 

Those components were individually "tuned" to prevent magnetic bleed from one component to another. The component is angled so magnetic field is out of phase with another key component so the signal doesn't leap from one part of the circuit to another. How its done is by injecting a test signal then tracing it through the circuits while watching an oscilloscope. You bend the components till the wave winds up being pure throughout and if something is deforming the wave you find the culprit and bend it to minimize the problem.

 

These are very common techniques used by radio technicians by the way. People who work in audio only rarely deal with the issues except in cases like yours or when they are receiving radio stations or noise at levels that shouldn't be there.

 

To be specific with your problem you have a SS amplifying device which is close to the enclosure and likely at the very beginning of the circuitry. When the case is vibrated, the field is disrupted by the case vibrating at a different speed then the component and it generates sound. Which component and how exactly it might be acting like a transducer would require finding it first. It can be something as simple as a wire laying next to the case acting like a guitar pickup does or a SS device close enough to the case to act like a piezo element.

 

Fixing the issue shouldn't be all that difficult. You can run the unit with the thing open then use a pencil eraser as a probe to dampen one component at a time while tapping the case to find out which one's causing the problem. (wrap the metal band around the pencil with tape so it doesn't short anything.

 

Once you find the component there are two elements involved in eliminating it. You need to decrease the field effects and/or dampen the physical vibration. If for example its a transistor right up against the case, you could bend it away from the case to reduce the field effect then put some hot glue over it to absorb the vibration.

 

You may need to add additional padding to the inside of the case or shim the board farther away using additional washers.

Some board mount right to the Bypass switch, By adding an additional nylon washer, positioning the nuts on the switch so the board sits deeper or shallower, or adding some hot glue (which is non conductive) in some certain strategic places you can often make a microphonic enclosure dead quiet.

 

Some use 100% Silicone sealant for this but it can take a good 6 hours to fully cure and risk powering up. The hot glue is electrically safe to power up as soon as its cool and hardened within a minute or two. Works excellent for guitar plugs by the way and the good part is its removable with heat so its not as permanent as silicone glue or epoxy.

 

That's about it. The units functioning so its not like its malfunctioning. Its just an oddball field effect happening which can happen every so often due to poor quality control. The people building boxes don't know jack from Jimi when it comes to these kinds of issues. At the most that stuff the parts in a PC board, and see if it works passing a signal, that's about it. You have the choice of returning it for another or dampening the effect yourself.

I'd take care of that thing in no time.

 

Flaws are pretty common in cheap pedals. I bought a pedal a month ago that had one of its knobs that wasn't working out of the box. I removed the knobs and nuts that held the pots in place and it allowed the board to be raised. I reheated the solder pads where the Pot was soldered in place and it instantly fixed the issue which was nothing more then a cold solder joint.

 

Yours is working. I'd use a pencil and tap inside on each component and isolate where its coming from then use the tricks I posted here to minimize the issue. Just use some common sense in the process too.

[1001gear]

Thanks for all that info. I had no Idea board design was so involved.

 

Should clarify that the hum happens when the coils on the guitar are in close proximity to the box. I haven't really sussed this one out as another Cino box that was in use at the time also produces the effect. So whatever the cause, the effect is 60cycle hum; about the same as putting the guitar up to a fluorescent light but not as pronounced.

 

The pinging is another thing. With the "drive"/volume past 75%, just placing a toe on the foot switch is clearly audible. While I want to do the trouble shoot you describe, this is a mini pedal with zero access except by disassembly. There aren't even screws for the back plate ! The case is held shut by the pots and jacks. The good thing is once I have it open I'll be looking at the operational side of the board with no further disassembly required. HOPEfully.

 

Gotta wait another two weeks for a spare before I try this.

[WRGKMC]

Yea, the AC comes from an AC source. The pedal runs on DC so it cant radiate AC into the guitar. All it can do is amplify what's coming in.

 

AC hum is tricky stuff to nail down and eliminate however because it can get to the hot lead of the signal cable through the air and get amplified. or it can ride in on a, AC cable, ground or DC power wire which isn't filtered enough. (or the wall wart doesn't have the right current value)

 

The way you can tell them apart is, the AC that leaks past the Power supply, or is created by a ground loop doesn't change in intensity. It remains the same no matter what angle the instrument is at.

 

AC coming in on the guitar lead is typically airborne before it gets to the guitar and its amplitude can change depending on what angle the guitar wiring and pickups are to the source. Because the wiring and pickups act as a radio antennal the signal can be increased or nulled just like a portable AM radio when you move the unit or its antenna so it aligns with the radio station.

 

Single coils are the worst because they have no humbucking. Why you guitar peaks while its near the pedal is most likely an oddball Theremin effect.

 

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A Theremin works on the principal of circuit feedback to generate a tone (oscillators) The unit contains an amplifier like your pedal does.

The proximity of the hands near the two antennas creates a feedback loop between the transmission antenna and the receiver antenna, much like you'd get with a mic too close to a speaker. Except in this case its a magnetic field which is being allows to circulate from the transmitter to the receiver through the hands and body which is actually a pretty good conductor when you consider the blood is mostly salt water which conducts electricity, especially static electricity very well.

 

The thing your pedal doesn't have is an actual oscillator so its obviously not going to sing like a Theremin, but it does have AC hum coming in on the signal wire which is apparently varying in intensity with the positioning of the guitar near the box and is having its waves multiplied when they are in phase.

 

Truly none of this is no big mystery for anyone who experiments in building radio gear. Its actually the stuff that got me interested in electronics as a kid back in the 60's I used to build crystal/fox hole radios which you could use to hear radio stations without any amplifier. It only takes and antenna, diode and coil to bring in a strong station on headphones and I thought it the coolest thing ever when I first built one.

 

later as I experimented more I learned how one coil in close proximity to another would allow the radio waves to jump across with no electrical connection and virtually discovered how a transformer worked before I even knew what it was. After that I connected a tape recorder amplifier to the circuit and could hear everything clear as a bell. The wires from the tape head lead to several preamp stages and can boost the crap out of a weak signal.

 

After that I learned how the antenna could be manipulated in all kinds of ways to change the signal. A person coming close could amplify the noise or null it depending on the specific wiring and conditions. Leaned all about AC static too. I had a small electronic shop in the basement and went through great pains shielding it against AC hum by wall papering it in aluminum foil.

 

By the age 10 I had already made my own guitar pickups and installed a crude one in an acoustic guitar. Used that tape recorder to produce fuzz tones. Hummed like an SOB too. I eventually read a book on Faraday (there were only books and magazines back then) and learned about the Faraday cage. Then I eventually had some adult electronic techs recognize my aptitude and they wound up donating several decades worth of electronic magazines. I in fact reread most of them on line recently.

 

There were a bunch of them like these, https://www.rewindmuseum.com/electronicsmagazines.htm

 

And these https://www.amateurradio.com/popular-electronics-1954-1982-available-as-pdf-downloads/

 

Anyway, that's getting off topic a but it is fun stuff to learn about. many of the issues that do come up in audio are often pretty simple faults but troubleshooting and eliminating them can be tough at times. You have to be a Sherlock Holmes to get enough details gathered and the person who's having the issue may or may not even realize when they say something which rings a bell.

 

You did help to conform my suspicion the components in the box are likely causing a field effect within the box simply by it being a mini box which is going to place the components much closer and because the board is suspended by the jacks and switch its allows to vibrate freely.

 

My best advice is to pull the unit out and simply dampen the circuitry and/or box with hot glue. Its not that much different then potting a pickup in bees wax to prevent the metal cover from vibrating in front of the pickup coil and acting like a diaphragm. The wax however wouldn't be the best choice for a full circuit the same as it would be for a pickup coil. Hot glue should do the job well, or you could just squeeze a bunch of silicone glue or even epoxy to form a brick inside and kill the microphonics. The solution will need to be mechanical because you haven't got allot of room to work with moving components to kill the resonance.

 

I'm just curious. What is the box made of and who makes the booster.

I own several of them, even really cheap ones and have none of the issues you're having. I suspect its one of the cheaper imports given its a mini.

 

 

I used to have big problems with the old Electro Harmonix pedals because they used stainless steel enclosures which sucked at blocking AC hum. If you set them on an amp over the power transformer they would hum like a bastard.

 

Many of the pedal enclosures are either aluminum, Die case aluminum or potted white metal which contains zink, tin, iron alloys. Aluminum has to be fairly thick - like 2mm to block hum well. It has a hard time blocking low frequency noise like AC. Stuff coming out of the orient is often made of recycled tin cans and other low quality metals which may be magnetic and therefore microphonic or they might be a low Mu metals which doesn't block hum very well. Yours seems to be both magnetic and low MY due to the hum problems.

[1001gear]

It's an Ammoon Kokko booster. I don't know if it's a Suhr rip but I wouldn't be surprised if it uses the basic circuitry. The one I have opens with a 5, maybe more db increase in level, which I kinda like since it's primarily for goosing stuff. Does so admirably I might add.

[1001gear]

Found this.

https://www.reddit.com/r/guitarpedals/comments/59dp33/kokko_booster_pedal_super_cheap_gutshots/

 

https://imgur.com/a/lc3LB

 

Ahmma guess that brown cap is the doorbell.

 

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Also looks like those 5 pins on the right connect to th socket on the lower board?

 

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[WRGKMC]

It says Amoon on the outside but has Nux stamped on the boards.

 

I bought one of those NUX amp simulator pedals. Its one of the worst pedals I've ever bought. It loaded with SS components and its supposed to be an amp emulator pedal but what a total piece of crap that thing is. I couldn't get a single usable sound out of it. I figured I paid $12 so it wasn't worth the cost of shipping it back. I'll likely use the case at some point for another project.

 

I'm not seeing anything obvious in those pics that can be microphonic. The best guess I have is the op amp and transistor near the LED come close enough to the case where their high gain may cause a field effect between the case and op amp. The vibration of the case may be disturbing the field around the op amp and generating an audible signal. Its not that much different then tapping on a preamp tube and having it ping except the case itself sets up the disturbance.

 

I'd apply hot glue to the components on the top of the board Maybe even put a few drops between the boards then squeeze them together like an Oreo cookie to deaden any vibrations.

 

If it winds up being the switch or connectors there really isn't anything you can do about those besides try others, and thay likely cost more then the entire pedal does to replace. .

[1001gear]

Ordered another one so once that gets here I can proceed into the techie darkness. Hopefully I can isolate the part and get by with glopping just that.