Microphonic Erupter?

[Verne Bunsen]

Question for anyone who's got an Earthquaker Devices Erupter fuzz: is yours microphonic? I'm chasing down a wicked hum that has suddenly crept up when the Erupter is engaged and in the course of troubleshooting I noticed that tapping the enclosure or switch mechanism with the pedal engaged is quite audible through the amp. I'm honestly not sure if that was the case before, wasn't anything I noticed at any rate. I've got an e-mail in to EQD, but any input you fellers have would help me to direct my troubleshooting efforts in the mean time.

Thanks!

-VB

 

[Cagey]

I don't have that pedal, but about 100 years ago I had one of the original Univox Fuzztone units...

Man, that thing was raunchy!  (but I loved it to death at the time) Anyway, that one was good for microphonics.

Short story is: it was the input jack. New jack, no problem.*

Long story is: Distortion/fuzz devices are all about high gain, with modern units maybe having some other signal conditioning going on. But, that unit was fairly simple, and I'm pretty sure the way it worked was to amplify the incoming signal, put it across some back-to-back germanium diodes to clip the signal, then run the modified/squared-off signal though another variable amplification stage so you could blow your amp's speaker(s) after a while from having too high an average DC level that made the voice coils overheat. Yeah. Good times.

Those amplification stages were pretty sensitive because the original signal from the guitar is really small (millivolts), so any kind of hair on the incoming signal was also exaggerated (it's where I developed a deep and abiding hatred for single coils and the noise they bring to the party). But, the hair didn't always come from the guitar. Turns out a little oxidation (or other contamination) on the 1/4" input jack would make it what was effectively a loose connection. Not loose loose, like it wasn't gonna hold the plug, but electrically loose as if two wires were just touching instead of being soldered together. So, you'd get spurious noise for no apparent reason, or if you physically disturbed the box. Not really microphonic so much as vibration sensitive. So, I replaced the input jack, and it was as good as new! (which was actually a pretty low bar... :laughing7

Incidentally, in the process of learning how the thing worked, it occurred to me that if those germanium diodes weren't there, the signal would never get clipped and the pedal would just act like a massive overdrive, sans the raunch. So, I clipped those little buggers out, and sure enough - it was a beast! Actually sounded better, just overdriving the piss out of the front end of my Fender Pro Reverb. Couldn't take it too far or things got too muddy-nasty, but it was better than the fuzz tone if you wanted to sound big without having the police show up. Too much fun.

*The same thing happened again later after I'd had my first Whirlwind "Cobra" cord for a while. They used unplated brass plug ends on those things which would oxidize, and if you didn't take some steel wool after 'em to clean 'em up once in a while, they'd inject noise the same way the bum jack did.

 

[Verne Bunsen]

Cagey: Modding pedals since before modding pedals was "cool"...  :icon_biggrin:  Good story and good illustration of the "Occam's Razor" approach to troubleshooting...

I heard back from EQD and they report that the Erupter should not be microphonic. Which is what I figured. Their warranty is pretty straight forward: They'll fix everything forever. Shy of damage from mishandling. Pretty good policy! Just need to send it in.

The hum I'm getting is coming from proximity to the Pedal Power 2 mounted below the board. The Erupter is pretty much right on top of it. Interesting thing is that it hasn't always hummed. Another interesting thing: changing the load on the power supply by plugging in / unplugging other pedals changes the hum. Seems like this shouldn't be so since the outputs are fully isolated and even the transformer is (according to the marketing material) designed for individual output isolation and noise-free operation. "Now even the most sensitive pedals can be dead quiet". I've had this power supply for a long time, might just be time to replace it? I noticed the microphonics at the same time as I noticed the humming, so, while I recognize that correlation does not imply causation, I can't help but wonder if whatever malfunction is causing the microphonics is also resulting in increased sensitivity to the power supply? I'll send the pedal off to get repaired and re-assess when it gets back.

 

[Cagey]

Yeah, it sounds like maybe the output filtering/regulation of that power supply has deteriorated so instead of pure DC, you've got a ripple on it. Plus, that unit will have a transformer in it to step down the AC line voltage to a lower level to be rectified into DC. Transformers are all about magnetism - it's how they work. The more current running through them, the larger the magnetic field around them. So, as you add/subtract loads, that field will change intensity so nearby devices sensitive to that will respond accordingly. Varying loads will also change the peak-to-peak value of the ripple on the DC, making it more apparent in the operation of the devices that depend on it. Instead of the straight line DC value you need, it'll look something like this...

...with those little dips getting deeper as the load increases. Move the earthquaker device away from the power supply and put a battery in it instead of using the power supply, and much if not all of that hum will go away.

 

[Verne Bunsen]

A follow-up for anyone who is interested. I got the Erupter back from Earthquaker and they reported that they were unable to reproduce the microphonics, but that they swapped out the board for the newest version. Whatever they did seems to have done the trick, as the microphonics are gone. So, chalk it up as a win.

I was still getting the hum pretty badly, so I decided to try a new Pedal Power. To my dismay, the brand new one was significantly noisier than the old one! The noise from the new one was completely unmanageable, louder than the guitar signal. I went back and forth a couple of times to make sure I wasn't crazy, but it was consistent. I put the old one back in place and shuffled some things around on the board and the Erupter is much quieter now in its new spot. I'm not crazy about the spot it's in, but "function above form" I suppose....

Interesting thing about that new Pedal Power, can't for the life of me see why it should be so much noisier than one thats a few years old?

 

[Cagey]

If it's the same model power supply, it sounds like maybe we're learning things about Pedal Power's design or QC. For what they cost, you should be getting computer-grade power out of the thing. Maybe try one of Truetone's units, or one of the myriad others that have cropped up to take advantage of the pedalboard boom.

 

[Verne Bunsen]

I may look at some other options, my dad actually has one of those Truetone units that he has offered to lend me for evaluation. For now, since I now have two Pedal Power 2s looking at me, I'm going to see what I can do with them. I've been doing some testing and it appears that my Helix, which occupies the bigger half of my board, is not susceptible to the interference from the power supply. So I may look at re-locating the supply over to the other side of the board. Of course I'll need much longer power cables to reach the pedals from there, but what's one more hurdle? It's a good thing I enjoy this stuff.....