How much space between input transformer and eq inductor?

[BluegrassDan]

How much physical space do you think there should be between a 1:10 mic input transformer and an EQ inductor?

 

[ruffrecords]

If the transformer has a mu metal screen then I would say not very far. In the latest version of the Poor Man's Tube Mixer plug in mic pre there is an EQ inductor not three inches from the mic input transformer. Seems to work OK.

Cheers

IAn

 

[JohnRoberts]

+1 it depends on shielding... Back last century at Peavey I had to design background music amps with mic input transformers and 100V audio output transformers for constant voltage speakers systems all inside the same compact chassis.

Mu metal shielding is your friend.

JR

 

[BluegrassDan]

I have laid out this PCB where the nearest EQ inductor is about 1.25" away from the input transformer, which will be a shielded Cinemag. The inductors are Cinemag too.

 

[Bo Deadly]

Coupling between low current magnetics should be a total non-issue. H field intensity depends on loop area, current, frequency and of course distance. So if the magnetics are wound sloppily, the current is high, the frequency is low and the distance is small, the more coupling you'll have. But these particular magnetics are probably wound pretty well, mic transfomers and even inductors are relatively low current scenarios and the distance is enough that there should be basically zero coupling even if they were placed right next to each other.

Now 60 Hz mains power is a completely different story. The H field impedance of mains power at 60 Hz is very low even (fraction of an ohm) even at a significant distance and so it is very difficult to shield. So it would be far more important to position any kind of power supply handing mains to be far enough away that the 60 Hz hum is below the noise floor of the main amplifier. In practice this is nearly impossible and there will always be a little mains component. Especially in circuits with a lot of magnetics. This is one of many reasons why I prefer a properly implemented SMPS based supplies. With SMPS the frequency much higher and small amplitude such that it is almost always possible to achieve and completely 60Hz-free signal path.

 

[CJ]

you will notice that Pultec uses a can to house the inductor and caps,