Hi all,
I'm currently working on a project that requires the mounting of two toroids close together (one 500VA 35-0-35 toroid and another 20VA 15-15 toroid). How much care should I take to make sure they aren't too close together? How great a problem would mounting one on top of another be?
Steve.
I'm currently working on a project that requires the mounting of two toroids close together (one 500VA 35-0-35 toroid and another 20VA 15-15 toroid). How much care should I take to make sure they aren't too close together? How great a problem would mounting one on top of another be?
Steve.
Most crossover inductors work in a different way because they are either air cored or ferrite-drum cored, and thus their magnetic path is open. This involves producing strong magnetic fields around the inductor, picking up any external field produced by anything close, and interacting with ferromagnetic or conductive surfaces if they are close enough.
50/60Hz toroids are closed magnetic circuits, magnetic leakage and pickup is very low.
50/60Hz toroids are closed magnetic circuits, magnetic leakage and pickup is very low.
Toroids do have a field. You probably don't need to worry about coupling between your transformers. But if you have circuitry with gain nearby--especially circuitry that has any significant "loop area" (i.e. traces running around a PC board)--you can get some AC line freqency noise in your audio circuits.
National Semi had to shield the toroids in their reference amp using the LM4702 to get the THD+N of the amp down to the true levels of the circuit. And Douglas Self discusses it often being a problem with several designs he's worked on. Self suggests leaving extra lead length (at least temporarily) so you can rotate the transformer for minimum hum. I would expect the field from a toroid to be fairly uniform but apparently you can find "nulls" by rotating it. I personally haven't tried it as there's usually a fair distance between the toroids and gain circuitry in my amps.
National Semi had to shield the toroids in their reference amp using the LM4702 to get the THD+N of the amp down to the true levels of the circuit. And Douglas Self discusses it often being a problem with several designs he's worked on. Self suggests leaving extra lead length (at least temporarily) so you can rotate the transformer for minimum hum. I would expect the field from a toroid to be fairly uniform but apparently you can find "nulls" by rotating it. I personally haven't tried it as there's usually a fair distance between the toroids and gain circuitry in my amps.
I've had a look into a few companies that do wind transformers, but so far I've been able to source them significantly cheaper by buying each separately. If it were anything more complex, then I would definitely try harder to find a more suitable transformer, but at present having them separate doesn't pose much of an inconvenience.
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