Hey, I'm just wondering what I should do with the oscilloscope ground clip when measuring audio from my PC, DSP and amplifier. Is it safe to just connect it to 3.5mm/RCA ground on all devices without shorting anything? I guess a local ground would give me less noise for measurements.
Also, I've seen a lot of posts telling you to not "float the scope (remove earth)" but in this case I can't really see any dangers if I'm just connecting it to aux "-" outside my PC, it's not like I'm opening up a PSU here. Is that a good idea?
I have a SDS-1104x-e, so not battery or USB powered.
Also, I've seen a lot of posts telling you to not "float the scope (remove earth)" but in this case I can't really see any dangers if I'm just connecting it to aux "-" outside my PC, it's not like I'm opening up a PSU here. Is that a good idea?
I have a SDS-1104x-e, so not battery or USB powered.
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Yes typically just connect to signal ground. However beware some loudspeaker outputs that may be bridge-tied (most class D outputs are like this for instance).
Simple test, connect the probe to what you think is ground (the tip, not the clip), and if it shows as 0V on the 'scope it should be safe to connect the 'scope probe ground clip to. For loudspeaker outputs do this test with a signal present. And with x10 probes always use the x10 setting unless there's a good reason not to.
Simple test, connect the probe to what you think is ground (the tip, not the clip), and if it shows as 0V on the 'scope it should be safe to connect the 'scope probe ground clip to. For loudspeaker outputs do this test with a signal present. And with x10 probes always use the x10 setting unless there's a good reason not to.
This seems to be generic advice "all over internet" - but what would be the main reason for doing so?
X10 does a couple things. Mainly it adds a 10X voltage divider in front of that scope front end offering additional protection. Probably less important for audio is generally the 10X probe mode has higher bandwidth. On mine, 1X is I think 35MHz whereas the 10X is 350. So big difference in high frequency response.
Thanks! I could also use a DMM from oscilloscope ground clip to where I want to ground on the board to see if it's 0V too right?
I usually just use 10x probe too. I assumed 1x was less safe due to 10x the voltage but more precise.
Also, in what cases should I be careful with the scope earth clip? I've seen many posts suggesting isolation transformers, but isn't the PSU already one? If I want to measure anything in my PC relative to something else I could always just connect clip to ground with your method (check voltage), then use the differential mode A-B with two probes right?
I'm a noob and usually learn stuff by just trying random stuff all night but here I want to be really sure I don't kill anything 🙂
I'm a noob and usually learn stuff by just trying random stuff all night but here I want to be really sure I don't kill anything 🙂
For best "waveform quality", it´s not always irrelevant where you fix the probe ground. The grounded case for example will work, but sometimes with some noise. Some sensitive measuring require the so called "pin barrel" or "tip barrel" grounding.
https://electronics.stackexchange.com/questions/221292/tip-barrel-test-of-oscilloscope
https://electronics.stackexchange.com/questions/221292/tip-barrel-test-of-oscilloscope
@Hardi: Right, so for audio signals I should put the earth clip on "-" for the least amount of noise? Is there anything I should be careful about when probing my PSU powered dsp and amp then as long as I check for 0V before attaching earth clip? DSP is connected to my pc's pcie soundcard via 3.5mm to rca adapter.
I sometimes also connect my PC to DSP via USB to program it. I have a WONDOM APM2. Thanks again!
I sometimes also connect my PC to DSP via USB to program it. I have a WONDOM APM2. Thanks again!
With power off you can check if what you are going to use as ground is connected to mains earth with an Ohm-meter. Sometimes a piece of equipment does not have a mains earth so this is usually OK for your scope ground.
Don't float your scope, trouble is = its easy to forget its floated weeks later (no mains earth) and it becomes a safety hazard.
Another way is to connect the scope ground to what you would like to use as your audio ground via a 100K resistor, then use two scope probes to measure your signal by measuring the difference voltage between them ie A - Inverse of B
Don't float your scope, trouble is = its easy to forget its floated weeks later (no mains earth) and it becomes a safety hazard.
Another way is to connect the scope ground to what you would like to use as your audio ground via a 100K resistor, then use two scope probes to measure your signal by measuring the difference voltage between them ie A - Inverse of B
@richgwilliams, how'd checking if it's connected to mains ground while powered off work here? Couldn't there (theoretically?) be a relay or transistor between that's only open when powered on, hence not shown when measuring while powered off?
Also the 100kohm method seems useful, ty
Also the 100kohm method seems useful, ty
So in short, as long as I know it's ground it should be safe to connect the oscilloscope earth pin to any place powered by a smps like my pc, dac and amp?
Relay in the earth connection is very unlikely - people don't usually mess around with earth connection - just connect it because its there for safety. That said good idea to have a good look at the wiring by visual inspection.
Hard to give a rule for every situation, its experience gathered over time.