A "microphonic" problem

[aron]

I have a preamp pedal that's microphonic. The weirdest thing. You can tap on it and hear the "acoustic" quality.

First off, there were 3 jacks on it (2 outputs, 1 input) and of course the input jack acted up. What do you know, the input jack was the only one not a Switchcraft. Before I changed the jack, you could "tap" on the jack and hear the circuit amplify the tap. After I changed the jack it quieted down a lot. I just can't figure out what might be the cause of microphonics. Maybe it's the ceramic cap. Pretty weird.

[QSQCaito]

I know i don't know much about electronics, but recently my dad solved a similar problem.. I've just asked him and he believes it's because of vibration, if you manage to dun know how to say in english, like cover it or make it heavier so it stops vibrating.. that could solve a bit of the ptoblem, it solved my dad's problem which was pretty similar

BYe

Dieg Andrés Cao

[RedHouse]

Microphonic jacks are an age-old problem easily solved.

Solder the inner (shield) part, to the "lug" part it is usually just crimped together there.

After being soldered even the cheapie jacks will be ok.

[brett]

Hi
I've had 2 "jumper" cables go microphonic.  They were both encased-molded designs, so they were impossible to investigate or repair.
Took me ages to find the problem the first time.

Another time I had twisted the ends of two resistors together to get the right value in series.  That pre-amp had low gain and behaved weirdly for a long time, until I realised that I hadn't soldered the joint. 

hope you have good luck finding it

[Morocotopo]

I made R.G.´s Mini Mixer with four JFET buffers on a separate board for being able to plug guitars directly into it. Volume, mute and buffer switches for each channel, master volume pot. About 99 kilometers of cable to wire everything together, and I´m not specially tidy with the wiring... The thing looked like a bombed wire factory inside...and it was so microphonic that I could lightly tap anywhere and get a nice, loud THUMP through the amp... I shortened some wires and it became much quieter. The jacks are all Neutrik (e.g. good quality), so those weren´t the cause. I think I read somewhere that the cable insulation can have an effect on michrophonics. Cable capacitance, insulation quality,  or something... True? Let the experts say...

Morocotopo

[aron]

Microphonic jacks are an age-old problem easily solved.

RedHouse, how does the jack cause the circuit to become microphonic? Is it "loose" connection between the crimped parts?

Very interesting!

[R.G.]

Most ceramic caps are slightly piezoelectric - they make voltage when mechanically stressed. That's how piezo mikes work.

Many cable insulators are either slightly piezo, or static generators, so they can make noise when connected to a high impedance circuit. I once had a guitar cord that crackled when you stepped on it , anywhere on the cable.

[brett]

Hi Aron
I suspect that deterioration in the crimping is due to eletrolysis between the dissimilar metals.  With copper and nickel in contact, the copper seems to oxidise and cease conducting.  
Under high humidity, I've seen alloy bearings lose all of their zinc and turn into porous copper because the iron shaft caused sacrificial erosion of the zinc.
cheers

[Paul Marossy]

I suspect that deterioration in the crimping is due to eletrolysis between the dissimilar metals.  With copper and nickel in contact, the copper seems to oxidise and cease conducting. 
Under high humidity, I've seen alloy bearings lose all of their zinc and turn into porous copper because the iron shaft caused sacrificial erosion of the zinc.

That's a very plausible suggestion. And since Aron is in Hawaii, that seems like a reasonable explanation. You should see what happens when you use a steel pipe from your water heater to copper flex pipe without a dielectric union installed! 

[aron]

Amazing. Also R.G.'s explanation also makes sense.

Just replacing that jack with Switchcraft seems to have fixed EVERYTHING! 

[Aharon]

HAd the same problem with my TubeScreamer,traced it to the input jack.Changed it to a high quality Switchcraft and voila!!,problem gone.
I think it has to do also with the 9v switching and the insulation between the contacts.....just guessing.
Aharon

[Paul Marossy]

Gee, I would have never thought about it being the input jack causing those sorts of problems. You learn something new every day! (Or at least you should  )