I just finished assembling the PCB for my homemade op-amp based synthesizer and am having a bit of a weird problem. Almost every time after operating the device, if I touch something grounded like the case of my power supply, I will get a static shock. The circuit is provided with 3V DC, which is stepped up to 6V using a charge pump IC (ADM660).
I think it might have something do with the switches I installed for my oscillators, since when I touch them I can hear small pops in the audio. I'm using a metal DPST toggle switch, which connects the oscillator either to the amplifier (ON) or to nothing/floating (OFF), like so. Is this bad practice? My guess is that somehow the switch is becoming charged from the floating output of the oscillators when they are switched off, and by touching them I'm charging myself. Should I tie them to ground instead of leaving them floating in the off position?
I've never experienced anything like this before, so any help is appreciated. Thanks!
I think it might have something do with the switches I installed for my oscillators, since when I touch them I can hear small pops in the audio. I'm using a metal DPST toggle switch, which connects the oscillator either to the amplifier (ON) or to nothing/floating (OFF), like so. Is this bad practice? My guess is that somehow the switch is becoming charged from the floating output of the oscillators when they are switched off, and by touching them I'm charging myself. Should I tie them to ground instead of leaving them floating in the off position?
I've never experienced anything like this before, so any help is appreciated. Thanks!
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I have you tried grounding the switched case?
Pot and switch cases should be ground as they provide a static shield just as they do on the inside of a guitar's control compartment as they are grounded, as well as the string so you don't get such noises. 😉
jer 🙂
Pot and switch cases should be ground as they provide a static shield just as they do on the inside of a guitar's control compartment as they are grounded, as well as the string so you don't get such noises. 😉
jer 🙂
Where is the 3V DC coming from? A wall wart perhaps?
Have you measured AC and DC voltages with a meter where you touch things at the same time and get a shock? It may not be static electricity, it may be a more serious leakage and or grounding problem. A meter should be used to check. Depending on what you measure there may be some other things to check for safety.
The power is provided by a variable bench power supply, though I've never had problems with it before.
I've not measured them but I'll do so tonight...
Sorry if I was unclear in my initial post, but the times I've been shocked I was never touching two things at once. More like, I mess with the circuit for a bit, stand up, and then touch something metal and get zapped. It's identical to the shock from carpet and a doorknob. I'm starting to question if it's even possible for the circuit to cause this. Even if the surface of the metal switches were (for example) inductively coupled to the current flowing through them, that surely wouldn't be enough energy to cause a shock right? Maybe it's just a coincidence with the cold weather? It did happen 4 times in a row though.
As a side note, I did end up connecting the floating terminals of the switches to ground. Though, I can still hear small pops when I touch them.
If you can confirm its static, then that's good. Several kV can be involved even though current is very low. It might be the high voltage sparking that is affecting the circuit more than the associated current.
Any chassis grounds such as those shields and such should be tied to the earth ground via single connection to the main box, make sure that after all the shield are connected together to ground make sure that when each one is Not connecting another one twice forming a Groundloop somewhere inside and before the connection to the chassis, as this will/can render noise getting picked up with in the box itself an, shielding can get tricky with a bunch of different stuff added along, it is easy to miss something.
But one scenario I can give you is that one time when I had my recording system all set up I had one noise I just could not get rid of and tried everything I could do with Twp P4 Dells on line in the mess with a 16-track and all of my effects and devices...........
I finally got it down to moving one power cord around would make it fade in and out.
Before that nothing would work until I unplugged the whole mess and made sure that All of the power plugs Polarities were going in the socket the right way and not reversed, and that helped a lot up to that point, I had to remove a few covers just to verify that right way.
After moving the mess again, with one of those Dells I could not get the ground noise from it to go away no matter what I did as the PS was bad in That one and later failed.
Also just a note ......................
If All of your circuits are common grounded inside the case and you add a circuit with a shielded wire and ground "both" ends of that cable in side the chassis then you have caused an internal ground loop creating a Huge Noise Antenna sitting in your rack.
I have a slight noise issue in my system as I need to go and cut 32 ends of shield of off the cables to the 16 track as those were unbalanced !
And, I did make them correct in the First place with both ends connected, but this causes a short section the shield not having any effect on the signal path as the chassis of the tape deck and the chassis of the Mixer are ground tied at the wall so what I have is 16 channels of in/out that are unshielded because of this.
It is Measurable but hasn't caused to much of an issue for me since 1994 when I built the system as long as the gain structure is set properly.
Turn it up a bit and you can hear it, float the ground on the tape deck it goes away, but you can't do this with tape, the machine must be grounded to the wall due to static discharge.
Get my drift ?
It took me a very long time to figure this out when even when Mr Mackie himself in 1994 could not tell me why I was getting noise from the mixer everytime I hooked his Little mackie mixer up to the snake via unbalanced or Balanced and all that Switching noise from the panel display never went away when every time I hit the Play Button on the Tape machine as the ground level on the displays would spike and end up on the on almost every recording I have done..........
And, he tried to tell me that the displays weren't switching types, Liar!!
Does any of this relate to you?
I hope my little Adventure around the ground loop race track can help give you some idea's as what to look for in the long run. 🙂
Cheers !!!
jer 🙂
P.S. on those cables I have to cut the shields on, The shields are tied on one end as they are supposed to be for unbalanced, the mistake I did is the Both of the red and black wires are connected and the shield on one end is proper, but the signal does not need be grounded in this case in order for current to flow from the out/in and VS, with the shield connect the red wire is shielded and ground is established through the Chassis as mentioned, and connect the black wire on both end as well and this makes a ground loop there, and introduces the noise I have been combatting ever since 1994 when I got the thing. 😉
But one scenario I can give you is that one time when I had my recording system all set up I had one noise I just could not get rid of and tried everything I could do with Twp P4 Dells on line in the mess with a 16-track and all of my effects and devices...........
I finally got it down to moving one power cord around would make it fade in and out.
Before that nothing would work until I unplugged the whole mess and made sure that All of the power plugs Polarities were going in the socket the right way and not reversed, and that helped a lot up to that point, I had to remove a few covers just to verify that right way.
After moving the mess again, with one of those Dells I could not get the ground noise from it to go away no matter what I did as the PS was bad in That one and later failed.
Also just a note ......................
If All of your circuits are common grounded inside the case and you add a circuit with a shielded wire and ground "both" ends of that cable in side the chassis then you have caused an internal ground loop creating a Huge Noise Antenna sitting in your rack.
I have a slight noise issue in my system as I need to go and cut 32 ends of shield of off the cables to the 16 track as those were unbalanced !
And, I did make them correct in the First place with both ends connected, but this causes a short section the shield not having any effect on the signal path as the chassis of the tape deck and the chassis of the Mixer are ground tied at the wall so what I have is 16 channels of in/out that are unshielded because of this.
It is Measurable but hasn't caused to much of an issue for me since 1994 when I built the system as long as the gain structure is set properly.
Turn it up a bit and you can hear it, float the ground on the tape deck it goes away, but you can't do this with tape, the machine must be grounded to the wall due to static discharge.
Get my drift ?
It took me a very long time to figure this out when even when Mr Mackie himself in 1994 could not tell me why I was getting noise from the mixer everytime I hooked his Little mackie mixer up to the snake via unbalanced or Balanced and all that Switching noise from the panel display never went away when every time I hit the Play Button on the Tape machine as the ground level on the displays would spike and end up on the on almost every recording I have done..........
And, he tried to tell me that the displays weren't switching types, Liar!!
Does any of this relate to you?
I hope my little Adventure around the ground loop race track can help give you some idea's as what to look for in the long run. 🙂
Cheers !!!
jer 🙂
P.S. on those cables I have to cut the shields on, The shields are tied on one end as they are supposed to be for unbalanced, the mistake I did is the Both of the red and black wires are connected and the shield on one end is proper, but the signal does not need be grounded in this case in order for current to flow from the out/in and VS, with the shield connect the red wire is shielded and ground is established through the Chassis as mentioned, and connect the black wire on both end as well and this makes a ground loop there, and introduces the noise I have been combatting ever since 1994 when I got the thing. 😉
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Well, it is winter and in the colder parts of the country the humidity can get quite low, which makes static charge a much bigger problem.
Generally when the RH is above 40-50 %, static charge doesn't accumulate much because it's naturally dissipated by the moisture in the air.
Below that, it builds up and will discharge as you experience.
To verify, you can get a simple RH meter for about $15 and if it's low, consider a humidifier.
As you probably know, static discharge can damage many types of electronic components / circuits, so it should be taken seriously.
In winter here in the North East I've seen the RH below 10% and static charges over 30 kV can occur.
Static control and elimination has always been an essential part of my job in several industries.
Generally when the RH is above 40-50 %, static charge doesn't accumulate much because it's naturally dissipated by the moisture in the air.
Below that, it builds up and will discharge as you experience.
To verify, you can get a simple RH meter for about $15 and if it's low, consider a humidifier.
As you probably know, static discharge can damage many types of electronic components / circuits, so it should be taken seriously.
In winter here in the North East I've seen the RH below 10% and static charges over 30 kV can occur.
Static control and elimination has always been an essential part of my job in several industries.
Static dissipates when the RH is high due to the presence of water molecules on every insulator's surface. The lower the RH the less densely surfaces are covered in water molecules, until the point where they don't touch enough to leak charge around. Water molecules can exchange protons (hydrogen ions) readily which is why it can carry charge around easily.
In winter the heating of the outside air in buildings causes its RH to drop - so static is typically an indoors problem in winter.
In winter the heating of the outside air in buildings causes its RH to drop - so static is typically an indoors problem in winter.