I just broke down a triamped system that ran nearly dead quiet. With the active crossover removed running one EL84 amp I noticed a humm. Lifted the cables with amp off, still humm. Disconnected cables from amp. Still humm! Pulled speakers two feet from any device (tv,cable, etc...) still humm!!!! This is the craziest thing I have ever seen. Cables are all sheilded and twisted pairs either PVC or Teflon can't remember at the moment. Any thoughts would be much appreciated. I think I tracked it to the inductors which are quite large (16mh). Disconnecting speaker cables removes humm but leaving cables in place and disconnecting coils does too.
JN
JN
It seems like a Mains hum is being induced into the 16mH inductors from possibly a power transformer that is 'on' somewhere in your kit or elsewhere.
It does sound like an inductive fault from your description.
C.M
The humm remains with the speaker cables disconnected from the amp! No source, no amp. Just cables leading from the terminals. The crossover for the LF is a simple 1st order coil and cap. Xover for HF is just a cap. That's it! It remains when I drag the speaker as far from the tv as space will allow. About two feet
What kind of inductor is on the woofer; you said 16mH? Is it air core?
You could try re-orienting it. If that helps you could try a cored inductor which would present a smaller pick up aperture. I am surprised that this is happening particularly with the amp connected as it puts a pretty low impedance across the speaker terminals at audio frequencies.
You could try re-orienting it. If that helps you could try a cored inductor which would present a smaller pick up aperture. I am surprised that this is happening particularly with the amp connected as it puts a pretty low impedance across the speaker terminals at audio frequencies.
It appears you have some very strong 60Hz magnetic fields where you are located. This is the only way you could hear a hum without any electronics connected. You may want to borrow or purchase a Gauss meter to check your surroundings.
You could shield the crossover, but you will need heavy iron/steel plate or thick aluminum. If you use steel or iron, you will need to keep the inductors away from the metal or it will change the values.
I believe the pitch placed on inductors is to keep the coils from vibrating. The vibration can induce harmonic distortions in the output.
Here is a link to a cheap EMF meter which will give you a ballpark measurement of your ambient fileds.
https://www.amazon.com/ElectroSensor-Electro-Magnetic-Field-Detector/dp/B000G82KLI
You could shield the crossover, but you will need heavy iron/steel plate or thick aluminum. If you use steel or iron, you will need to keep the inductors away from the metal or it will change the values.
I believe the pitch placed on inductors is to keep the coils from vibrating. The vibration can induce harmonic distortions in the output.
Here is a link to a cheap EMF meter which will give you a ballpark measurement of your ambient fileds.
https://www.amazon.com/ElectroSensor-Electro-Magnetic-Field-Detector/dp/B000G82KLI
Potentially stupid debugging ideas - when all else fails try the simple stuff:
1) Tie the speaker leads together - still hums?
2) Try simple minded speaker leads like zip cord?
3) remove speaker leads - no Hum?
4) Still hums with all external leads removed? Try putting 8 ohm resistor across terminals - and/or move speakers into various
positions/places - trying to find an active LF field here...
Once you've eliminated the obvious suspects - then move on to Soviet-level debugging beginning with the revanchist, neo-manichean inductors.
You might not find the problem. but at least the firing squad will get some practice.
Cheers
Jim
1) Tie the speaker leads together - still hums?
2) Try simple minded speaker leads like zip cord?
3) remove speaker leads - no Hum?
4) Still hums with all external leads removed? Try putting 8 ohm resistor across terminals - and/or move speakers into various
positions/places - trying to find an active LF field here...
Once you've eliminated the obvious suspects - then move on to Soviet-level debugging beginning with the revanchist, neo-manichean inductors.
You might not find the problem. but at least the firing squad will get some practice.
Cheers
Jim
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Thanks all for the ideas and the levity. Now I'm thinking that brain cancer might be the more pressing concern. I will certainly get that meter! I had read that sheilding inductors can shift their values. The irony is that I went to a passive system to minimize the influence of decaying components in my Sony TA4300f crossover. Cest la vie.
Iron cored inductors can be sensitive to interference. Distance can help, both from other inductors and the amp. Can you use longer speaker cables?
If your amp is the only concern and you don't want to move it then shielding the amp makes sense, being the source of the problem, and of course rotating it too.
A 16mH air cored inductor can be large. One of the issues could possibly be interwinding capacitance but if this is for a woofer then you may not have an issue, otherwise use two in series.
If your amp is the only concern and you don't want to move it then shielding the amp makes sense, being the source of the problem, and of course rotating it too.
A 16mH air cored inductor can be large. One of the issues could possibly be interwinding capacitance but if this is for a woofer then you may not have an issue, otherwise use two in series.
One other off-the-wall thought - I've seen cases where relatively stiff pleated surround main drivers (specifically EV Wolverines) could actually mechanically resonate with hum from components like Microwave oven transformers or commercial Auto-chlor machines.
So your spiked speakers with good mechanical ground could be sweetly humming along with the heat pump that's energising the crossbeam over which they sit.
Trust me - this stuff falls into the non-obvious hair-tearing category...
Cheers
Jim
So your spiked speakers with good mechanical ground could be sweetly humming along with the heat pump that's energising the crossbeam over which they sit.
Trust me - this stuff falls into the non-obvious hair-tearing category...
Cheers
Jim
Jim that's a good point however this is an electronic humm with a slight buzzing. I have heard it often with my failed attempt at DIY interconnects with their attendant sloppy solder joints. I may post this on YouTube as it is s curiosity. Will link it if I get around to it and if the mic picks it up.
Love it! No snow falling here today but a great day for skiing!
Do you have easy access to the crossover?
Can you disconnect if from the speaker to see if the hum persists?
I assume that the setup is:
open leads>>>>>>>>crossover>>>>>>>more wires>>>>>>>speaker in box
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