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 VintageWindings Pot Core
Inductor Set for Sphere 900

Series Equalizers

Vintage Windings Sphere 900 Series Style Inductior Set

During the 1970's Electrodyne introduced a Mic-pre/Equalizer channel model 712 with a graphic style, inductor based equalizer and soon it became a favorite with engineers who used them. Eventually Electrodyne sold out but the 712 design did not die. Each time the company sold, the 712 design was expanded upon. After a couple of company sales, Sphere ended up with the design and improved it by using larger ferrite pot cores and adding two bands making a total of nine bands with two being switchable creating 11 affected band choices. The Sphere 900 was born. Vintage Windings ferrite pot cores are the same size and core material as the original Sphere 900 coils.

Sphere 900 series Inductor Data Sheet 



The Vintage Windings Sphere 900 series inductors are modeled
directly from an original 900 series unit. The same size ferrite pot
core material (still available) is utilized as are the same wire sizes
maintaining the original R values.

The Inductor Values

Coil 1 - 20.6 mH 12.8 Khz.
Coil 2 - 42 mH 5, 6.4, 8 Khz.
Coil 3 - 75 mH 3.2 Khz.
Coil 4 - 145.5 mH 1.6 Khz.
Coil 5 - 330 mH 800 hz.
Coil 6 - 586 mH 400 hz.
Coil 7 - 1.346 H 200 hz.
Coil 8 - 2.53 H 100 hz.
Coil 9 - 5.06 H 50 hz.

Sphere used pcb clamps to affix the coils to the circuit board.
The problem with that approach is that the air gap, which
determines the final inductance value in the coils, is set by
the amount of pressure holding the two core halves together.
It is next to impossible to get the gap, therefore the inductance,
just right when soldering the clamp to the pcb. This means
that the inductance values are never as close as they should
be for resonant circuits. We use nylon machine screws with
nuts to set the inductance value correctly with the help
of an inductance bridge. Mounting the coil on a pcb is as
simple as bending a small piece of wire over the top of
the coil, laying it through the screw slot and soldering the
ends to ground on the bottom of the pcb. Please see
mounting notes on the Data Sheet

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