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Interference on sub woofer amps
My subwoofer picks up. Mobile phones, radar pulses, clicks and bangs on the
mains and occasionally short wave radio. The very short speaker wires from amp to speaker in the box appear to be the culprits for the higher frequencies, and the input leads the way in for the rest, except The mains borne crap. It has a three core mains lead of the iec variety, but its only been doing these things since it had a new bridge rectifier fitted a while back. I am suspicious that some capacitors may have been damaged when the bridge went down, but I'd have thought this would just result in hum. The amp is built on pcbs maounted on the heatsink which effectively forms the back of the cabinet beside the port. Any ideas? Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! |
Interference on sub woofer amps
"Brian Gaff" wrote in message m... My subwoofer picks up. Mobile phones, radar pulses, clicks and bangs on the mains and occasionally short wave radio. The very short speaker wires from amp to speaker in the box appear to be the culprits for the higher frequencies, and the input leads the way in for the rest, except The mains borne crap. It has a three core mains lead of the iec variety, but its only been doing these things since it had a new bridge rectifier fitted a while back. I am suspicious that some capacitors may have been damaged when the bridge went down, but I'd have thought this would just result in hum. The amp is built on pcbs maounted on the heatsink which effectively forms the back of the cabinet beside the port. Any ideas? Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! I'll preface this by saying that it's hard to diagnose at long distance, but by your description I would look at the following first:- Assuming a conventional power supply, not switch-mode, 1) Any mains filtering before the mains transformer may have been damaged by excessive current due to the rectifier failure 2) Any high frequency filtering i.e. small capacitors across the rectifier and/or smoothing capacitors may have been damaged by excessive voltage due to rectifier failure. 3) Check also the main reservoir capacitors as they too may have been damaged, but I agree that hum is the more likely result of damage there. Good luck. S. |
Interference on sub woofer amps
In article , Serge Auckland
wrote: "Brian Gaff" wrote in message m... My subwoofer picks up. Mobile phones, radar pulses, clicks and bangs on the mains and occasionally short wave radio. The very short speaker wires from amp to speaker in the box appear to be the culprits for the higher frequencies, and the input leads the way in for the rest, except The mains borne crap. It has a three core mains lead of the iec variety, but its only been doing these things since it had a new bridge rectifier fitted a while back. I am suspicious that some capacitors may have been damaged when the bridge went down, but I'd have thought this would just result in hum. The amp is built on pcbs maounted on the heatsink which effectively forms the back of the cabinet beside the port. Any ideas? Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! I'll preface this by saying that it's hard to diagnose at long distance, but by your description I would look at the following first:- Assuming a conventional power supply, not switch-mode, 1) Any mains filtering before the mains transformer may have been damaged by excessive current due to the rectifier failure 2) Any high frequency filtering i.e. small capacitors across the rectifier and/or smoothing capacitors may have been damaged by excessive voltage due to rectifier failure. 3) Check also the main reservoir capacitors as they too may have been damaged, but I agree that hum is the more likely result of damage there. I'd agree with the above comments. However I am also wondering why anything related to the PSU would then cause the amp to become sensitive to things on its signal input leads. Who changed the diodes, and what else did they do? I also wonder *why* the "bridge went down". Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Interference on sub woofer amps
In article , Brian Gaff
wrote: Now I know its easy to convince oneself that you can hear something, but this morning on turning it on, I think I heard the hum reduce a lot slower than it used to do. What "hum" do you mean? So, I'm thinking, a capacitor which is slightly leaky might still be in the circuit. If any reservoir caps are leaking dc to a sigificant extent they'd certainly need replacing. But if they leaked enough to cause hum I'd hope they'd quickly blow a fuse! Otherwise you may have a safety problem. And large electrolytics won't really be capacitors at RF, say, above a few MHz. No other work was done other than fit a new bridge, so I'm thinking, it might be wise to get the guy to change out the caps as well, or measure what the supply drain is off load. You should perhaps also ask "the guy" if he changed/removed any small RF caps across the original bridge. Also find out *why* the old bridge failed. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Interference on sub woofer amps
"Brian Gaff" wrote in message m... My subwoofer picks up. Mobile phones, radar pulses, clicks and bangs on the mains and occasionally short wave radio. The very short speaker wires from amp to speaker in the box appear to be the culprits for the higher frequencies, and the input leads the way in for the rest, except The mains borne crap. **Use sheilded cable for the speaker leads. It's a long shot, but I've found that it can work with very high feedback, poor stability amps. It has a three core mains lead of the iec variety, but its only been doing these things since it had a new bridge rectifier fitted a while back. I am suspicious that some capacitors may have been damaged when the bridge went down, but I'd have thought this would just result in hum. **Not necessarily. Most high feedback designs have prodigious PSRR figures. Loss of one cap can go almost unnoticed, unless you test it on the bench. The amp is built on pcbs maounted on the heatsink which effectively forms the back of the cabinet beside the port. Any ideas? **A dedicated mains circuit would probably solve most mains issues. Other than that, a complete redesign might be in order. -- Trevor Wilson www.rageaudio.com.au |
Interference on sub woofer amps
On 20/01/2010 10:12, Brian Gaff wrote:
My subwoofer picks up. Mobile phones, radar pulses, clicks and bangs on the mains and occasionally short wave radio. The very short speaker wires from amp to speaker in the box appear to be the culprits for the higher frequencies, and the input leads the way in for the rest, except The mains borne crap. It has a three core mains lead of the iec variety, but its only been doing these things since it had a new bridge rectifier fitted a while back. I am suspicious that some capacitors may have been damaged when the bridge went down, but I'd have thought this would just result in hum. The amp is built on pcbs maounted on the heatsink which effectively forms the back of the cabinet beside the port. I'd look closely at the supply decoupling electrolytics for the final stage amplifier, be it an integrated module or discrete components. If it's a module it could be possible that it's been used without much bandwidth limiting (as per use in other applications that are full bandwidth) relying instead on upstream low pass filtering for the function of your subwoofer, and this is where interference is getting in. Are any caps showing signs of bulging / dome'ing? -- Adrian C |
Interference on sub woofer amps
Brian, if the change in behaviour coincided with work on the amp perhaps the
earth is no longer connected to all the pieces of the case, effectively removing the shielding. Best of luck Dave "Brian Gaff" wrote in message om... Hi again, Yes, the bridge was perhaps a littlelow on margin, but I was thinking along similar lines. Just because it powers up and works does not mean its OK. Now I know its easy to convince oneself that you can hear something, but this morning on turning it on, I think I heard the hum reduce a lot slower than it used to do. So, I'm thinking, a capacitor which is slightly leaky might still be in the circuit. No other work was done other than fit a new bridge, so I'm thinking, it might be wise to get the guy to change out the caps as well, or measure what the supply drain is off load. Its one of those old chicken and egg things. As far as picking up stuff, no it certanly was not apt to do this, but the earth seems connected OK from the lead, and I'm not into any of Russes mains leads either! There are, I'm told some smaller capacitors scattered around, but they surely would bbe much higher voltage devices. The new bridge is slightly bigger than its predessor, and thus there is more wire connecting it to the pcb. As I say, I can more or less tell what is there, but my sight precludes me investigating personally. I'm desperately trying to remember the maker. Starts with an E I think. Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! "Jim Lesurf" wrote in message ... In article , Serge Auckland wrote: "Brian Gaff" wrote in message m... My subwoofer picks up. Mobile phones, radar pulses, clicks and bangs on the mains and occasionally short wave radio. The very short speaker wires from amp to speaker in the box appear to be the culprits for the higher frequencies, and the input leads the way in for the rest, except The mains borne crap. It has a three core mains lead of the iec variety, but its only been doing these things since it had a new bridge rectifier fitted a while back. I am suspicious that some capacitors may have been damaged when the bridge went down, but I'd have thought this would just result in hum. The amp is built on pcbs maounted on the heatsink which effectively forms the back of the cabinet beside the port. Any ideas? Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! I'll preface this by saying that it's hard to diagnose at long distance, but by your description I would look at the following first:- Assuming a conventional power supply, not switch-mode, 1) Any mains filtering before the mains transformer may have been damaged by excessive current due to the rectifier failure 2) Any high frequency filtering i.e. small capacitors across the rectifier and/or smoothing capacitors may have been damaged by excessive voltage due to rectifier failure. 3) Check also the main reservoir capacitors as they too may have been damaged, but I agree that hum is the more likely result of damage there. I'd agree with the above comments. However I am also wondering why anything related to the PSU would then cause the amp to become sensitive to things on its signal input leads. Who changed the diodes, and what else did they do? I also wonder *why* the "bridge went down". Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Interference on sub woofer amps
Apparently there is nothing obvious, but its back together again. However I
think the slight hum going away in seconds is getting worse, so I am a bit worried, Do they still go bang like they used to, though it has to be said none seem warm at all. I do not really want a speaker coated in lots of gunge. Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! "Adrian C" wrote in message ... On 20/01/2010 10:12, Brian Gaff wrote: My subwoofer picks up. Mobile phones, radar pulses, clicks and bangs on the mains and occasionally short wave radio. The very short speaker wires from amp to speaker in the box appear to be the culprits for the higher frequencies, and the input leads the way in for the rest, except The mains borne crap. It has a three core mains lead of the iec variety, but its only been doing these things since it had a new bridge rectifier fitted a while back. I am suspicious that some capacitors may have been damaged when the bridge went down, but I'd have thought this would just result in hum. The amp is built on pcbs maounted on the heatsink which effectively forms the back of the cabinet beside the port. I'd look closely at the supply decoupling electrolytics for the final stage amplifier, be it an integrated module or discrete components. If it's a module it could be possible that it's been used without much bandwidth limiting (as per use in other applications that are full bandwidth) relying instead on upstream low pass filtering for the function of your subwoofer, and this is where interference is getting in. Are any caps showing signs of bulging / dome'ing? -- Adrian C |
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