Logic is you want EMI as low as possible. Bruno Putzeys puts it in nice words why toroids, especially standing ones, aren't a serious option:
Amplifier Implementation and High-Frequency EMI Performance
At these frequencies, there are no mathematical tricks to minimise the problem. The designer has to insure as little as possible high-frequency energy is generated and as much as possible is stopped leaving the amplifier. Only diligent work on the hardware will do.
I noted earlier that output filters don't do much at 100MHz. That is to say, the output coil has turned itself into a capacitor and the output capacitor has become inductive. The only way around is to reduce these parasitic components. It turns out to be more fun, though, to discuss the ways some manufacturers manage to actually increase them.
Toroidal inductors : Toroids are said to have no stray field, because each winding's stray field is cancelled by that of all the other aggregated windings. That's fine as long as the windings are evenly distributed along the circumference. The need for getting wires to and from it makes a gap necessary, as does the mounting clip. There goes the nice theory. Also, the winding also forms one large parasitic winding along with the toroidal choke. Fancy that, sending the output current from the switching power stage around a 1" loop? I thought not. Note the latter problem is mitigated by laying the toroidal inductor flat on the PCB with ground plane underneath it.
But I'm digressing. We were talking about parasitic parallel capacitance. The toroidal core, although said to be resistive, is fairly conductive, and helps to capacitively couple all windings together. If there were means to ground it, the core would actually be a bonus, but there isn't, so it isn't.
If you see toroids in the output filter, shudder. If it's mounted upright, shudder once more.
Amplifier Implementation and High-Frequency EMI Performance
At these frequencies, there are no mathematical tricks to minimise the problem. The designer has to insure as little as possible high-frequency energy is generated and as much as possible is stopped leaving the amplifier. Only diligent work on the hardware will do.
I noted earlier that output filters don't do much at 100MHz. That is to say, the output coil has turned itself into a capacitor and the output capacitor has become inductive. The only way around is to reduce these parasitic components. It turns out to be more fun, though, to discuss the ways some manufacturers manage to actually increase them.
Toroidal inductors : Toroids are said to have no stray field, because each winding's stray field is cancelled by that of all the other aggregated windings. That's fine as long as the windings are evenly distributed along the circumference. The need for getting wires to and from it makes a gap necessary, as does the mounting clip. There goes the nice theory. Also, the winding also forms one large parasitic winding along with the toroidal choke. Fancy that, sending the output current from the switching power stage around a 1" loop? I thought not. Note the latter problem is mitigated by laying the toroidal inductor flat on the PCB with ground plane underneath it.
But I'm digressing. We were talking about parasitic parallel capacitance. The toroidal core, although said to be resistive, is fairly conductive, and helps to capacitively couple all windings together. If there were means to ground it, the core would actually be a bonus, but there isn't, so it isn't.
If you see toroids in the output filter, shudder. If it's mounted upright, shudder once more.
good shielding is what you want. you don't need or want overly thick cable; that will just make building harder than it needs to be.
I like having copper shield as well as a foil wrap, but you may not need such extreme measures.
you can also try twisted pair and see if that's enough. a neat trick is to make your own. take 2 wires and secure them in a vice on your bench. walk down to the end of your room with the free ends of those 2 wires and secure them in a cordless drill and DRILL THEM to twist them. its fun, actuallydon't go too far, but twist them enough and keep tension on the pair so that it stays twisted. if your cables are not very long, often the twisted pair trick is enough.
more important, though, is to keep inputs away from power and outputs. power and outputs can 'mix' but keep inputs away, physically, from other things.
thank you! anyway, i saw that in your project you used what i think is a shielded cable to interconnect amp input to the input socket. is this good?
https://it.aliexpress.com/item/26AW...69.html?spm=2114.13010208.99999999.269.KWvFGw
i found this wire with not less than 2 cores + shield. eventually how should i solder the wire? one core goes to the hot pole, the ring should be connected to the shield or to the 2nd core?
as for the amp output to the speaker output plugs, is this good? https://it.aliexpress.com/item/2x-3...lack-Flexible-Wonderful-Gift/32244528581.html
thank you!
Could you give an example?
I have looked up the dielectric constant of teflon and pvc and the pvc is 3 while the teflon is 2 or 2.1.
This would result in more capacitance if the pvc (relative to teflon) were used in coax...close to the return path (ground)
I have also looked up the loss factor for both and the pvc is much higher ( around 600) and the teflon is relatively lower at 2.
But again wouldn't this be significant only if the dielectric was the only element between the conductor and signal return (ground)?
If the wire is in "air" wouldn't these looses be less significant?
At what source impedance and frequency would this affect become measurable?
DUG,
Thank you for challenging these "myth". I have heard that comment in "audiophile circles" before where teflon insulation is best and PVC is bad". When I asked why (being curious about the facts behind it), no one can gave a "real" answer.
Just to be clear, I have no disagreement with someone says teflon insulated wires sounds better to their ears as compare to the PVC ones, that's a personal thing.
Hope to run into you at TAVES next week!
Regards,
Just seeking enlightenment.
I have no disagreement when someone says they like " anything " better.
Just like technical explanations whenever possible.
TAVES will probably be Sunday.
p.s. I use teflon because I have some leftovers (lots) from work...
and the insulation does not melt when soldering...
and it stays formed - being rather stiff.
I have no disagreement when someone says they like " anything " better.
Just like technical explanations whenever possible.
TAVES will probably be Sunday.
p.s. I use teflon because I have some leftovers (lots) from work...
and the insulation does not melt when soldering...
and it stays formed - being rather stiff.
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I'm old enough to have a bag full of stories and 'myths'. Cables, always confused me.
We came to a digital era, and cables... well, the discussion continued...
I have a hard time believing a cable is so much better than the other to a point that justifies spending +600USD on a mains power cable that represents only the last 1-2m on several kilometers power line transmission...
We came to a digital era, and cables... well, the discussion continued...
I have a hard time believing a cable is so much better than the other to a point that justifies spending +600USD on a mains power cable that represents only the last 1-2m on several kilometers power line transmission...
