DC Filter

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robomatique

Well-known member
Joined
Jun 6, 2004
Messages
145
Location
London / UK
As I understand it, a DC filter could eliminate mechanical hum from transformers. I recently built a power supply for my Musical Fidelity headphone amp, and I got a small hum in the torroidal that I want to get rid of.

While searching on the net I found this commercial module:
dcfilterdia.gif

Which is bassically a capacitor and a 4.3V bipolar tranzorber... but... what is a tranzorber and what should I look for? I am not interested in the aux output, just the thru circuit.

Do you think a circuit like this would help me (would also help if I use torroidals for my mic preamps)

Robert
 
a "transorb"(brand name..) is a transient suppression device(we call them TVS in power design). it has a specified threshold voltage that when gone over it conducts, usually placed between Line and Neutral. kinda like a super fast zener but this one is bidirectional.

now when you say DC filter, do you mean filtering DC from the input/output of your toroid? Is the toroid mechanically humming or causing hum in the circuit?

usually mechanical hum is a couple of things:

the toroid is not properly bolted down.
it's being asked to supply too much current.


check both. is the toroid getting warm to the touch?
 
[quote author="Svart"]
now when you say DC filter, do you mean filtering DC from the input/output of your toroid? Is the toroid mechanically humming or causing hum in the circuit?

usually mechanical hum is a couple of things:

the toroid is not properly bolted down.
it's being asked to supply too much current.
[/quote]

There is a mechanical hum in the torroidal. I am quite sure it is bolted down correctly and it is very much overrated, so that shouldn't be a problem. I have only read that mechanical hum can come from DC on the input (from the same company who sells the above module...) but I know nothing about these things.



Robert
 
I have only read that mechanical hum can come from DC on the input
For a conservatively designed toroid, yes, a likely source of mechanical hum is a DC offset on the primaries. This can come from the AC line being unbalanced in the building. One guy accidentally unbalanced the AC in his house with diode pellets voltage reducers for his garage lights, which were only on at night. His hifi toroids hummed at night, not in daylight. That was a tough one to find.

The unbalance can be a few volts and cause hum in some toroids.
 

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