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#1
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Mains interference on power amp
Hi,
this really is driving me nuts now. I have a EV P3000 that is intermittently going into protect. I think I have established why. Mains spikes are getting into the amp. A lot of them. I can make the amp trip every time by switching off my soldering station slowly and making its mains switch arc. This is putting over 10 volts of HF hash onto the amp chassis, PCB earth traces and power supplies. The trip circuit runs on the unregulated -26 volt supply that feeds the -15 volt audio circuit, the +26 volt supplies the +15 audio. When I do the soldering iron switch arc thing, the up to 10 volts of hash appears on both the ground and the -26 volt supply, and even the amp chassis. This immediately trips the circuit, muting the amp for 2 seconds before resetting and carrying on fine. Note this 26v supply isn't very clean, it has around 2 volts of ripple to start with. (I have compared this to another amp which has the same ripple). I have tried 0.1uF caps on the -26v rail on the protect switching transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help. I have also tried a 0.1 uF X cap accross the mains live and neutral, still getting 10 volts of hash. All these are stilll in place, except the one on the switching transistor. The mains plug earth to chassis reads good. Switching ground lift on and off has no effect. (just disconects signal input ground I guess). Both existing X caps on the mains input read OK. Not sure where to go from here. Any ideas? Am I barking up the wrong tree thinking this is the problem? Cheers, Gareth. |
#2
Posted to rec.audio.tech
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Mains interference on power amp
"Gareth Magennis" wrote in message ... Hi, this really is driving me nuts now. I have a EV P3000 that is intermittently going into protect. I think I have established why. Mains spikes are getting into the amp. A lot of them. I can make the amp trip every time by switching off my soldering station slowly and making its mains switch arc. This is putting over 10 volts of HF hash onto the amp chassis, PCB earth traces and power supplies. The trip circuit runs on the unregulated -26 volt supply that feeds the -15 volt audio circuit, the +26 volt supplies the +15 audio. When I do the soldering iron switch arc thing, the up to 10 volts of hash appears on both the ground and the -26 volt supply, and even the amp chassis. This immediately trips the circuit, muting the amp for 2 seconds before resetting and carrying on fine. Note this 26v supply isn't very clean, it has around 2 volts of ripple to start with. (I have compared this to another amp which has the same ripple). I have tried 0.1uF caps on the -26v rail on the protect switching transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help. I have also tried a 0.1 uF X cap accross the mains live and neutral, still getting 10 volts of hash. All these are stilll in place, except the one on the switching transistor. The mains plug earth to chassis reads good. Switching ground lift on and off has no effect. (just disconects signal input ground I guess). Both existing X caps on the mains input read OK. Not sure where to go from here. Any ideas? Am I barking up the wrong tree thinking this is the problem? Cheers, Gareth. If you're seeing a spike on the 26 Volt line AND on the ground of the amp, then your scope is not seeing what the amp sees. You might need to float the scope ground, grounding it only to the amp, or use it in differential mode, putting one probe on the chassis. But... It doesn't seem likely that a spike could get across the power supply -- not if it's a very short one. You should probably start at the protection circuit, and try to see what it sees. Or... Try disconnecting all cables, speaker, audio, antenna, ground wires -- absolutely everything except the power cord (no scope leads either - nothing), then do your soldering switch thing and see if it still trips. It may not, indicating that it's not sneaking into the power supply. Keep everything else the same; don't even move any cables. Ground-induced high-frequency noise can be the culprit, but rarely gets looked at. -- Earl |
#3
Posted to rec.audio.tech
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Mains interference on power amp
In article ,
"Gareth Magennis" wrote: Hi, this really is driving me nuts now. I have a EV P3000 that is intermittently going into protect. I think I have established why. Mains spikes are getting into the amp. A lot of them. I can make the amp trip every time by switching off my soldering station slowly and making its mains switch arc. This is putting over 10 volts of HF hash onto the amp chassis, PCB earth traces and power supplies. The trip circuit runs on the unregulated -26 volt supply that feeds the -15 volt audio circuit, the +26 volt supplies the +15 audio. When I do the soldering iron switch arc thing, the up to 10 volts of hash appears on both the ground and the -26 volt supply, and even the amp chassis. This immediately trips the circuit, muting the amp for 2 seconds before resetting and carrying on fine. Note this 26v supply isn't very clean, it has around 2 volts of ripple to start with. (I have compared this to another amp which has the same ripple). I have tried 0.1uF caps on the -26v rail on the protect switching transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help. I have also tried a 0.1 uF X cap accross the mains live and neutral, still getting 10 volts of hash. All these are stilll in place, except the one on the switching transistor. The mains plug earth to chassis reads good. Switching ground lift on and off has no effect. (just disconects signal input ground I guess). Both existing X caps on the mains input read OK. Not sure where to go from here. Any ideas? Am I barking up the wrong tree thinking this is the problem? Cheers, Gareth. It doesn't make much sense that a little soldering station would produce so much electromagnetic noise. I suspect that your amp prone to oscillating and that's what's showing up everywhere on your scope. Is the HF hash still strong if the amp is off while you arc the contacts on your soldering station? -- I will not see your reply if you use Google. |
#4
Posted to rec.audio.tech
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Mains interference on power amp
Gareth Magennis wrote: Hi, this really is driving me nuts now. I have a EV P3000 that is intermittently going into protect. I think I have established why. Mains spikes are getting into the amp. A lot of them. I can make the amp trip every time by switching off my soldering station slowly and making its mains switch arc. This is putting over 10 volts of HF hash onto the amp chassis, PCB earth traces and power supplies. The trip circuit runs on the unregulated -26 volt supply that feeds the -15 volt audio circuit, the +26 volt supplies the +15 audio. When I do the soldering iron switch arc thing, the up to 10 volts of hash appears on both the ground and the -26 volt supply, and even the amp chassis. This immediately trips the circuit, muting the amp for 2 seconds before resetting and carrying on fine. Note this 26v supply isn't very clean, it has around 2 volts of ripple to start with. (I have compared this to another amp which has the same ripple). I have tried 0.1uF caps on the -26v rail on the protect switching transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help. I have also tried a 0.1 uF X cap accross the mains live and neutral, still getting 10 volts of hash. All these are stilll in place, except the one on the switching transistor. The mains plug earth to chassis reads good. Switching ground lift on and off has no effect. (just disconects signal input ground I guess). Both existing X caps on the mains input read OK. Not sure where to go from here. Any ideas? Am I barking up the wrong tree thinking this is the problem? How does this hash appear on the GROUND ? Do you mean Chassis or '0V' btw ? Graham |
#5
Posted to rec.audio.tech
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Mains interference on power amp
"Earl Kiosterud" wrote in message news:B6sak.197$713.167@trnddc03... "Gareth Magennis" wrote in message ... Hi, this really is driving me nuts now. I have a EV P3000 that is intermittently going into protect. I think I have established why. Mains spikes are getting into the amp. A lot of them. I can make the amp trip every time by switching off my soldering station slowly and making its mains switch arc. This is putting over 10 volts of HF hash onto the amp chassis, PCB earth traces and power supplies. The trip circuit runs on the unregulated -26 volt supply that feeds the -15 volt audio circuit, the +26 volt supplies the +15 audio. When I do the soldering iron switch arc thing, the up to 10 volts of hash appears on both the ground and the -26 volt supply, and even the amp chassis. This immediately trips the circuit, muting the amp for 2 seconds before resetting and carrying on fine. Note this 26v supply isn't very clean, it has around 2 volts of ripple to start with. (I have compared this to another amp which has the same ripple). I have tried 0.1uF caps on the -26v rail on the protect switching transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help. I have also tried a 0.1 uF X cap accross the mains live and neutral, still getting 10 volts of hash. All these are stilll in place, except the one on the switching transistor. The mains plug earth to chassis reads good. Switching ground lift on and off has no effect. (just disconects signal input ground I guess). Both existing X caps on the mains input read OK. Not sure where to go from here. Any ideas? Am I barking up the wrong tree thinking this is the problem? Cheers, Gareth. If you're seeing a spike on the 26 Volt line AND on the ground of the amp, then your scope is not seeing what the amp sees. You might need to float the scope ground, grounding it only to the amp, or use it in differential mode, putting one probe on the chassis. But... It doesn't seem likely that a spike could get across the power supply -- not if it's a very short one. You should probably start at the protection circuit, and try to see what it sees. Or... Try disconnecting all cables, speaker, audio, antenna, ground wires -- absolutely everything except the power cord (no scope leads either - nothing), then do your soldering switch thing and see if it still trips. It may not, indicating that it's not sneaking into the power supply. Keep everything else the same; don't even move any cables. Ground-induced high-frequency noise can be the culprit, but rarely gets looked at. -- Earl Thanks, I have just gone back and noted that if I probe the ground of the scope some hash is there, so this is indeed a misleading reading, the probe must be an aeriel. With the probe removed from the scope there is still a small amount of hash. Maybe this explains why putting caps on the power supplies has no effect - there may not be any hash on the power supplies at all. I now have a second P3000 from the same guy with exactly the same symptoms. It is here on my bench unopened. It has nothing connected to it, and when I arc my soldering station this too goes into protect. He has brought me these amps because they trip randomly at different venues, and I am assuming now it is spikes on the mains that are the trigger. I am also assuming that the amps should be able to tolerate an arcing mains switch without jumping into protect. Ah, while writing this I have just realised that it may not be going into protect at all - it may be going into its power up cycle, which behaves exactly the same as a momentary protect/reset. (The 2 protect LEDs light, and the fans go full speed). There are 3 relays on the power supply input side, 2 for soft start, a third for protect. These are situated within the mains input/fusing part of the PCB. It could be that these mains spikes are triggering a tired relay somehow and starting the power on cycle? I've been looking at hash on the power supplies that probably isn't there, this is starting to make a little more sense. Cheers, Gareth. |
#6
Posted to rec.audio.tech
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Mains interference on power amp
"Eeyore" wrote in message ... Gareth Magennis wrote: Hi, this really is driving me nuts now. I have a EV P3000 that is intermittently going into protect. I think I have established why. Mains spikes are getting into the amp. A lot of them. I can make the amp trip every time by switching off my soldering station slowly and making its mains switch arc. This is putting over 10 volts of HF hash onto the amp chassis, PCB earth traces and power supplies. The trip circuit runs on the unregulated -26 volt supply that feeds the -15 volt audio circuit, the +26 volt supplies the +15 audio. When I do the soldering iron switch arc thing, the up to 10 volts of hash appears on both the ground and the -26 volt supply, and even the amp chassis. This immediately trips the circuit, muting the amp for 2 seconds before resetting and carrying on fine. Note this 26v supply isn't very clean, it has around 2 volts of ripple to start with. (I have compared this to another amp which has the same ripple). I have tried 0.1uF caps on the -26v rail on the protect switching transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help. I have also tried a 0.1 uF X cap accross the mains live and neutral, still getting 10 volts of hash. All these are stilll in place, except the one on the switching transistor. The mains plug earth to chassis reads good. Switching ground lift on and off has no effect. (just disconects signal input ground I guess). Both existing X caps on the mains input read OK. Not sure where to go from here. Any ideas? Am I barking up the wrong tree thinking this is the problem? How does this hash appear on the GROUND ? Do you mean Chassis or '0V' btw ? Graham See my reply to Earl - the hash is being picked up by the probe acting as an aeriel. Doh! Cheers, Gareth. |
#7
Posted to rec.audio.tech
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Mains interference on power amp
"Kevin McMurtrie" wrote in message et... In article , "Gareth Magennis" wrote: Hi, this really is driving me nuts now. I have a EV P3000 that is intermittently going into protect. I think I have established why. Mains spikes are getting into the amp. A lot of them. I can make the amp trip every time by switching off my soldering station slowly and making its mains switch arc. This is putting over 10 volts of HF hash onto the amp chassis, PCB earth traces and power supplies. The trip circuit runs on the unregulated -26 volt supply that feeds the -15 volt audio circuit, the +26 volt supplies the +15 audio. When I do the soldering iron switch arc thing, the up to 10 volts of hash appears on both the ground and the -26 volt supply, and even the amp chassis. This immediately trips the circuit, muting the amp for 2 seconds before resetting and carrying on fine. Note this 26v supply isn't very clean, it has around 2 volts of ripple to start with. (I have compared this to another amp which has the same ripple). I have tried 0.1uF caps on the -26v rail on the protect switching transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help. I have also tried a 0.1 uF X cap accross the mains live and neutral, still getting 10 volts of hash. All these are stilll in place, except the one on the switching transistor. The mains plug earth to chassis reads good. Switching ground lift on and off has no effect. (just disconects signal input ground I guess). Both existing X caps on the mains input read OK. Not sure where to go from here. Any ideas? Am I barking up the wrong tree thinking this is the problem? Cheers, Gareth. It doesn't make much sense that a little soldering station would produce so much electromagnetic noise. I suspect that your amp prone to oscillating and that's what's showing up everywhere on your scope. Is the HF hash still strong if the amp is off while you arc the contacts on your soldering station? No, the amp is not oscillating. I think I know what the problem is now. The 3 relays that do the soft start and the protect switching are on the same PCB as the protection circuitry. I removed all 3 and the PCB underneath was not too clean. Since the relays switch mains voltages, it is not beyond the realms of possibility that mains voltage and any hash will make its way over to the circuitry via the dirty PCB. The main protect line runs along all 3 relays, only 5mm from the relay coils. I have also established beyond doubt that the protect circuitry is actually being pulsed on briefly via this protect line. I'm going to fit 3 new relays tomorrow and clean it all up, and hopefully the nightmare will be over. I might even re-route that protect line. Cheers, Gareth. |
#8
Posted to rec.audio.tech
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Mains interference on power amp
"Gareth Magennis" wrote in message ... "Earl Kiosterud" wrote in message news:B6sak.197$713.167@trnddc03... "Gareth Magennis" wrote in message ... Hi, snip Gareth. If you're seeing a spike on the 26 Volt line AND on the ground of the amp, then your scope is not seeing what the amp sees. You might need to float the scope ground, grounding it only to the amp, or use it in differential mode, putting one probe on the chassis. But... It doesn't seem likely that a spike could get across the power supply -- not if it's a very short one. You should probably start at the protection circuit, and try to see what it sees. Or... Try disconnecting all cables, speaker, audio, antenna, ground wires -- absolutely everything except the power cord (no scope leads either - nothing), then do your soldering switch thing and see if it still trips. It may not, indicating that it's not sneaking into the power supply. Keep everything else the same; don't even move any cables. Ground-induced high-frequency noise can be the culprit, but rarely gets looked at. -- Earl Thanks, I have just gone back and noted that if I probe the ground of the scope some hash is there, so this is indeed a misleading reading, the probe must be an aeriel. With the probe removed from the scope there is still a small amount of hash. Maybe this explains why putting caps on the power supplies has no effect - there may not be any hash on the power supplies at all. I now have a second P3000 from the same guy with exactly the same symptoms. It is here on my bench unopened. It has nothing connected to it, and when I arc my soldering station this too goes into protect. He has brought me these amps because they trip randomly at different venues, and I am assuming now it is spikes on the mains that are the trigger. I am also assuming that the amps should be able to tolerate an arcing mains switch without jumping into protect. Ah, while writing this I have just realised that it may not be going into protect at all - it may be going into its power up cycle, which behaves exactly the same as a momentary protect/reset. (The 2 protect LEDs light, and the fans go full speed). There are 3 relays on the power supply input side, 2 for soft start, a third for protect. These are situated within the mains input/fusing part of the PCB. It could be that these mains spikes are triggering a tired relay somehow and starting the power on cycle? I've been looking at hash on the power supplies that probably isn't there, this is starting to make a little more sense. Cheers, Gareth. OK, if nothing (absolutely nothing) is connected to the amp, and it still trips, then it's almost certainly coming in the mains cord, not from other cables acting as antennas putting HF currents through the PCB, where they can cause havoc (radio stations get picked up, etc), a not-too-uncommon problem. And if it's doing a power-up sequence, then perhaps it's falsely sensing something that triggers that. You have 2/2 units doing it, so it may be a known problem. Probably the first thing to do is either a Google search, or contact EV. Failing that, there are HF filters for mains you can get that might help. -- Earl |
#9
Posted to rec.audio.tech
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Mains interference on power amp
Gareth Magennis wrote: I think I know what the problem is now. The 3 relays that do the soft start and the protect switching are on the same PCB as the protection circuitry. I removed all 3 and the PCB underneath was not too clean. Since the relays switch mains voltages, it is not beyond the realms of possibility that mains voltage and any hash will make its way over to the circuitry via the dirty PCB. The main protect line runs along all 3 relays, only 5mm from the relay coils. I have also established beyond doubt that the protect circuitry is actually being pulsed on briefly via this protect line. I'm going to fit 3 new relays tomorrow and clean it all up, and hopefully the nightmare will be over. I might even re-route that protect line. Did I ever mention you chat with Bruce at Shuttlesound ? He's very helpful. Nice bloke. Graham |
#10
Posted to rec.audio.tech
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Mains interference on power amp
"Eeyore" wrote in message ... Gareth Magennis wrote: I think I know what the problem is now. The 3 relays that do the soft start and the protect switching are on the same PCB as the protection circuitry. I removed all 3 and the PCB underneath was not too clean. Since the relays switch mains voltages, it is not beyond the realms of possibility that mains voltage and any hash will make its way over to the circuitry via the dirty PCB. The main protect line runs along all 3 relays, only 5mm from the relay coils. I have also established beyond doubt that the protect circuitry is actually being pulsed on briefly via this protect line. I'm going to fit 3 new relays tomorrow and clean it all up, and hopefully the nightmare will be over. I might even re-route that protect line. Did I ever mention you chat with Bruce at Shuttlesound ? He's very helpful. Nice bloke. Graham Yes I have spoken to Bruce about this a few times, he did give me some good tips generally, but didn't seem to have come across this before. Cheers, Gareth. |
#11
Posted to rec.audio.tech
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Mains interference on power amp
Gareth Magennis wrote: "Eeyore" wrote How does this hash appear on the GROUND ? Do you mean Chassis or '0V' btw ? See my reply to Earl - the hash is being picked up by the probe acting as an aeriel. Doh! Worse things have happened at sea ! ;~) Graham |
#12
Posted to rec.audio.tech
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Mains interference on power amp
Gareth Magennis wrote: "Eeyore" wrote Did I ever mention you chat with Bruce at Shuttlesound ? He's very helpful. Nice bloke. Yes I have spoken to Bruce about this a few times, he did give me some good tips generally, but didn't seem to have come across this before. OK, well, worth trying anyway. I've seen 'something' a little like this once before on a Chinese amp but I'm damded if I can remember what it was now. Marginal stabilty perhaps, causing 'RF' breakthrough into the protection. Shouldn't happen on an EV though. Graham |
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