How close can inductors be placed to one another (MEQ-5)?

[soapfoot]

Hey there, building a pair of MEQ-5s. The capacitors I used are rather large, so my filter enclosure is rather cramped quarters.

Will there be any issue placing two of the inductor coils (by vintage windings) essentially stacked flat against one another (perhaps separated by a 1/8" thick nylon washer)? Will that cause any issues or unintended interactions that I should be aware of?

Thanks in advance!

 

[ruffrecords]

Depends if the inductors are shielded or not. If not then they will definitely interact. I know this from personal experience when designing a mastering EQ. I has several inductors side by side on a PCB to make a tapped inductor. I expected the total to be just the sum of the inductors but because of interaction it was not. I replaced them with shielded ones and it worked as expected.

Cheers

Ian

 

[gyraf]

Agree.
And you'll probably always want magnetically shielded inductors anyway - these are very prone to noise pickup otherwise. Think non-humbucking gtr pickups..

/Jakob E.

 

[soapfoot]

Thanks for the input!

These will be housed together in a shielding can per the original Pultec form factor, so I should probably find another mounting solution to keep interaction between them to a minimum.

Thanks again

 

[gyraf]

for inductors that are meant to "work together" anyway, I wouldn't bother isolating them. The original(s) were even on same core..

/Jakob E.

 

[emrr]

The CBS console EQ's from the '60's have 5 pairs of toroidal inductors stacked pretty tightly, and all side by side with no spacing.  FWIW. 

 

[abbey road d enfer]

for inductors that are meant to "work together" anyway, I wouldn't bother isolating them. The original(s) were even on same core.

Actually, in that case,  the strong interaction is taken into account in determining the number of turns.
Since the inductors are submitted to the same signal, the only interaction is coupling, which just changes the resulting value of the compound inductor.
A 100mH inductor may take 500 turns. Two in series without coupling will make 1000 turns for 200mH. A 200mH wound on the same core will need only 707 turns.
It is quite possible to take into account the coupling between different coils and alter them in order to compensate.
So, to answer the OP, it is possible to mount the inductors very close, knowing it may alter the global inductance if they are both connected at the same time. Mounting them at 90° eliminates coupling almost completely.

 

[soapfoot]

I found a solution wherein I was able to mount them all inside the can, but not stacked. I'm going to call that good.

 

[Gus]

IIRC there was an Audio Amateur or Speaker Builder article years ago about inductor interactions in speaker cross overs and how to place them.

IIRC a cool test is drive one of the coils and connect the other to a scope or amp to look and/or listen to the interaction.

 

[abbey road d enfer]

IIRC there was an Audio Amateur or Speaker Builder article years ago about inductor interactions in speaker cross overs and how to place them.

The problem with passive x-overs is that the currents in the inductors are not the same, so the interaction is not simply that of changing the value, but actually changing the frequency response, and possibly creating spillage between sections.