BILL POSTERS Posted February 25, 2012 Share Posted February 25, 2012 (edited) [quote name='flyfisher' timestamp='1330197345' post='1554122'] I'm not convinced that a battery and bulb would reveal anything that a DVM wouldn't. [/quote] If youd spent as much time as I have trying to make sense of the wierd readings you sometimes get if you try to take measurements on long, O/C or high resistance or floating cable runs, or where there are strong AC or RF fields using a DVM, then you might. My trusty old 20,000 OPV AVO 8 with its 15V battery gives much more reliable readings under those circumstances than my Fluke, with its test voltage across the probes of less tha 0.5V, which is sometimes less than the induced voltage. Also, using meter with a lower OPV, or a continuity tester, or [i]even[/i] a battery and bulb, will draw a little current through any poor cpnnections, and so will be much more likely to show them up. A bit like when like using the continuity tester on a DVM, if the probes are not pressed together well, you can hear the buzzer 'rattling' , Just speaking from personal experience mind, others might well have, and are welcome to, different ideas.. Edited February 26, 2012 by BRANCINI Quote Link to comment Share on other sites More sharing options...
Jungle VIP Posted February 26, 2012 Author Share Posted February 26, 2012 Cool. Everyone's starting to go over my head now but unfortunately I don't have any spare bulbs or 15V batteries. I re-ran the test with the multimeter set on 200 and took a reading from the bridge to the earth pin of the kettle lead. It's about 00.5/00.6. Does this help? For Brancini as well, yes there are those sorts of things in the house but I made sure that there weren't any on my floor. The only dimmers are 2 floors down and I unplugged everything else to try and get rid of it already Quote Link to comment Share on other sites More sharing options...
icastle Posted February 26, 2012 Share Posted February 26, 2012 [quote name='BRANCINI' timestamp='1330214065' post='1554303'] If youd spent as much time as I have trying to make sense of the wierd readings you sometimes get if you try to take measurements on long, O/C or high resistance or floating cable runs, or where there are strong AC or RF fields using a DVM, then you might. My trusty old 20,000 OPV AVO 8 with its 15V battery gives much more reliable readings under those circumstances than my Fluke, with its test voltage across the probes of less tha 0.5V, which is sometimes less than the induced voltage. Also, using meter with a lower OPV, or a continuity tester, or [i]even[/i] a battery and bulb, will draw a little current through any poor cpnnections, and so will be much more likely to show them up. A bit like when like using the continuity tester on a DVM, if the probes are not pressed together well, you can hear the buzzer 'rattling' , Just speaking from personal experience mind, others might well have, and are welcome to, different ideas.. [/quote] Like most test equipment usage it really depends on interpretation of the results and an understanding of what you are likely to find based on experience. Quote Link to comment Share on other sites More sharing options...
icastle Posted February 26, 2012 Share Posted February 26, 2012 [quote name='Jungle VIP' timestamp='1330033076' post='1551905'] Although after that I thought I would try my friends guitar for a laugh... Mmm. I don't know where Snap is but I've found Crackle and Pop! Guess it's not the bass. Weird... [/quote] Right. If you're getting the same effect using your friends guitar then you can pretty well rule out the bass being at fault. That leaves your amp, leads and mains supply. [b]AMP:[/b] Ask your friend with the guitar if you can borrow his amp. [b]LEADS:[/b] Try your friends lead whilst trying his amp - if that's working OK then substitute his lead with yours. [b]MAINS SUPPLY:[/b] If there's an issue with mains supply then, going from what you've said, it's going to be something related to the ring main earth and that's going to need an electrican to trace and fix the defect. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 26, 2012 Share Posted February 26, 2012 [quote name='icastle' timestamp='1330253019' post='1554529'] Like most test equipment usage it really depends on interpretation of the results and an understanding of what you are likely to find based on experience. [/quote] Precisely, thats why I suggested that the OP might be better using a continuity tester or a battery and bulb rather than a DMM. a few ohms aint really gonna make much difference, so he should be looking for either a high resistance or an open circuit. Quote Link to comment Share on other sites More sharing options...
icastle Posted February 26, 2012 Share Posted February 26, 2012 [quote name='BRANCINI' timestamp='1330256820' post='1554610'] Precisely, thats why I suggested that the OP might be better using a continuity tester or a battery and bulb rather than a DMM. a few ohms aint really gonna make much difference, so he should be looking for either a high resistance or an open circuit. [/quote] Well, as the OP is getting the same problem using a mates guitar, the scope of where the potential fault resides is getting smaller now and it's going to be a really easy fix or something beyond a DIY solution... Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 26, 2012 Share Posted February 26, 2012 (edited) [quote name='icastle' timestamp='1330260633' post='1554711'] Well, as the OP is getting the same problem using a mates guitar, the scope of where the potential fault resides is getting smaller now and it's going to be a really easy fix or something beyond a DIY solution... [/quote] As I said early on, I'd try it at a different address. Cant see it being the amp itself, , so its either dodgy earthing in the house, or coming from something else. We dont know the whole story, He might live under a 132kV pylon, or next to a Vodafone mast, plus RFi from a cheapo switched mode PSU or mains induced buzz from dimmers could be coming from a few doors away, let alone from the floor below which is probably using the same earth.. Edited February 26, 2012 by BRANCINI Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 26, 2012 Share Posted February 26, 2012 Mains wiring can sometimes act a bit like an aerial, effectively carrying or transmitting interferece from equipment connected to or earthed through it. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 26, 2012 Share Posted February 26, 2012 [quote name='Johnston' timestamp='1330267687' post='1554858'] If it happened when playing through his phone then he wasn't connected to or earthed through the mains. [/quote] Mains wiring can sometimes act [u][i][b]a bit like an aerial,[/b][/i][/u] effectively [u][b][i]carrying or transmitting interferece from equipment connected to or earthed through it. [/i][/b][/u] Ever tried using an AM radio near a TV or laptop PSU ? Quote Link to comment Share on other sites More sharing options...
flyfisher Posted February 27, 2012 Share Posted February 27, 2012 (edited) [quote name='BRANCINI' timestamp='1330256820' post='1554610'] Precisely, thats why I suggested that the OP might be better using a continuity tester or a battery and bulb rather than a DMM. a few ohms aint really gonna make much difference, so he should be looking for either a high resistance or an open circuit. [/quote] Well, I agree that a battery and bulb will give an approximate indication of continuity to within a few ohms but if I was looking for ground-related faults I'd want to verify that the ground connections were good to within [u]milli[/u]-ohms. The introduction of resistance/impedance in supposedly-grounded circuits is a classic recipe for induced interference and a few ohms could make all the difference. Edited February 27, 2012 by flyfisher Quote Link to comment Share on other sites More sharing options...
flyfisher Posted February 27, 2012 Share Posted February 27, 2012 [quote name='BRANCINI' timestamp='1330262164' post='1554751'] As I said early on, I'd try it at a different address. [/quote] Given the results so far, that's sounding like a pretty good idea. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 27, 2012 Share Posted February 27, 2012 [quote name='flyfisher' timestamp='1330377671' post='1556575'] Well, I agree that a battery and bulb will give an approximate indication of continuity to within a few ohms but if I was looking for ground-related faults I'd want to verify that the ground connections were good to within [u]milli[/u]-ohms. The introduction of resistance/impedance in supposedly-grounded circuits is a classic recipe for induced interference and a few ohms could make all the difference. [/quote] Next time you get the chance, try measuring between 2the earths of two sockets in the same buiding but some way apart with a DMM. Then put it on a low AC volts range and measure that. usually it will read a few volts, this is normal with a high impeadence meter. It will often read some volts whether the earth cable is intact or not, and voltage between the probes will reult in an inaccurate reading. So, you see, ohms measurements in those circumstances are not going to be true. As I said, a continuity tester, or [size=5][i]even [/i][/size]a bulb and battery [size=5][i]may be[/i][/size] more use, as they are harder to foo, and the OP is not experienced in using a DMMl. This is based on personal experience of sorting hum and other interference problems with rs485 and CCTV in an industrial envoironment. Which I did for about 15 years. Quote Link to comment Share on other sites More sharing options...
flyfisher Posted February 27, 2012 Share Posted February 27, 2012 Well, I only worked in electronics for 27 years, including 10 years as chief engineer on some of the largest video switching and distribution systems in the country and I never found any need for a bulb and a battery in my test equipment armoury. Sure, a battery and a bulb will tell you there is some sort of circuit continuity but it won't tell you the indicated resistance in the circuit, or the voltage, or the current. So I'm struggling to understand just what it would tell you, apart from the fact that there is enough, albeit, unknown voltage/current to light up a light bulb - which basically says nothing about the 'quality' of the connection. And, when it comes to eliminating noise-related problems, it's the ground connection 'quality' that is usually the key. I'd much rather an inexperienced person gave me results from a DVM than just saying that a light bulb has lit up. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 28, 2012 Share Posted February 28, 2012 (edited) No [quote name='flyfisher' timestamp='1330382199' post='1556704'] Well, I only worked in electronics for 27 years, including 10 years as chief engineer on some of the largest video switching and distribution systems in the country and [i][b]I never found any need for a bulb and a battery in my test equipment armoury.[/b][/i] Sure, a battery and a bulb will tell you there is some sort of circuit continuity but it won't tell you the indicated resistance in the circuit, or the voltage, or the current. So I'm struggling to understand just what it would tell you, apart from the fact that there is enough, albeit, unknown voltage/current to light up a light bulb - which basically says nothing about the 'quality' of the connection. And, when it comes to eliminating noise-related problems, it's the ground connection 'quality' that is usually the key. I'd much rather an inexperienced person gave me results from a DVM than just saying that a light bulb has lit up. [/quote] Nor me, but then I know what I'm looking at, the OP probably doesnt. I only said that [i][size=5]even [/size][/i]a battery and bulb would do as a sort of figure of speech, but actually, it would be sufficient to check continuity between his Bass and the mains plug. it wont be milli ohms though, the lead alone will be a couple of ohms probably. Using his DMM to measure between his radiator and his amp or his mains earth would be pointless, as he wont get a true reading on an ohms range anyway. As engineering manager for a national security electronics company, I couldnt help but notice how engineers tend to look for complicated problems and overlook the obvious simple solution. And I think thats probably whats happened here tbh. I know he says he's turned everything off, but I bet that doesnt include everything. Intruder alarm, etc will still be on, [size=5][i][b]Possibly [/b][/i][/size]radiating etc, same with SMPSUs for a PC monitor, Telephone, lots of things, I dont need to tell you. For all we know he might live under an electric pylon and has a Vodafone mast on his roof. Its all guesswork till he tries the kit at a different location though isnt it ??. Edited February 28, 2012 by BRANCINI Quote Link to comment Share on other sites More sharing options...
flyfisher Posted February 28, 2012 Share Posted February 28, 2012 [quote name='BRANCINI' timestamp='1330393038' post='1556862'] Nor me, but then I know what I'm looking at, the OP probably doesnt. I only said that [i][size=5]even [/size][/i]a battery and bulb would do as a sort of figure of speech, but actually, it would be sufficient to check continuity between his Bass and the mains plug. it wont be milli ohms though, the lead alone will be a couple of ohms probably. Using his DMM to measure between his radiator and his amp or his mains earth would be pointless, as he wont get a true reading on an ohms range anyway. [/quote] A DMM may or may not give an accurate ohms reading but a battery and bulb won't give ANY sort of reading - thus such a test is of almost no value when trying to find a noise problem because it gives little indication about the 'quality' of the mains earth connection. Thus it's the battery/bulb test that is pointless, not the DMM measurement. So, yes, the OP may live next door to a mobile phone mast or other sources of interference but if he has a bad quality mains earth connection then this will make his rig more susceptible to pickup. It may seem like a pedantic point but I wouldn't want to encourage the view that a bad earth connection - which would pass a battery/bulb test - is OK. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 28, 2012 Share Posted February 28, 2012 [quote name='flyfisher' timestamp='1330418378' post='1556956'] It may seem like a pedantic point but I wouldn't want to encourage the view that a bad earth connection - which would pass a battery/bulb test - is OK. [/quote] I'm not suggesting it is. But in practice it would make a quick, simple check good enough for whats needed here. A measurement with a DMM is [b]not[/b] the correct way to check mains earthing either, as it draws so little current. Earth loop resistance checks are not for DIY, and not done with a DMM anyway, I'm not a sparks and wouldnt try to advise the OP how to check the safety of his mains supply. This could go on forever at this rate and isnt going to help the OP with his problem. Quote Link to comment Share on other sites More sharing options...
flyfisher Posted February 28, 2012 Share Posted February 28, 2012 Fair point about testing mains earthing for safety purposes, but that's a high current application whereas noise currents are relatively tiny so different considerations apply - not that they should override safety considerations of course. But you're probably right that we've done this to death now. Good discussion though. Quote Link to comment Share on other sites More sharing options...
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