Pultec inductor based equalizers are legendary. Many audio engineers find that the sound of an LC EQ is smoother than other types, mainly due to the minimal phase shift throughout the audio bandwidth. The EQ-1 passive filter was designed by the engineers at Western Electric's Bell Labs. Pultec licensed the design from WE and added a tube gain makeup amp, later to be replaced with a discrete solid state API 2520 Op-amp. The early EQP-1's used two toroid coils, one 100 mH and one 50mH which were switched in and out of the circuit in various combinations to make the required values. Most Pultec EQP-1A, EQP-1A3 models used a single tapped inductor to get the values needed for the hi-frequency section of the EQ. The VintageWindings EQ-1A Complete Filter Unit is a ready to use EQP type filter
assembly housed in a quality shielding can.

Description:


The Vintage Windings EQ-1A Complete Filter Unit has the entire
Pultec EQP type filter circuit conveniently pre-assembled into one
high quality shielding can. A Vintage Windings EQ-1A Toroid coil
is included along with all of the capacitors and resistors needed for
the passive filter section for the Pultec EQP type equalizers. All that
is needed to complete the filter section are the pots and switches that
are mounted on the front panel. The EQ-1A Complete Filter Unit
does not include a gain make-up section which can be vacuum tube
or solid state. The wiring guide for the EQ-1A Complete Filter Unit
can be found Here.  


The Vintage Windings EQ-1A Complete Filter Unit uses a Molyb-
denum Permalloy Powder toroid core inductor coil suitable for use
in the passive equalizer section of the Pultec EQP-1A, EQP-1A3
tube and solid state equalizers. The core material formulation was
chosen to compliment this application specifically. The coils are
vacuum baked and potted, then they are mu shielded.

The taps:

29.9mH
31.4mH
48.2mH
67.5mH
87.9mH
156mH

High quality polypropylene and polystyrene capacitors are used
throughout the filter unit. The unit is housed in a quality metal
shielding can with a baked enamel finish (original Pultec
dimensions: 3" x 2.5" x 3.375"). Mounting screws are
provided.

This unit is also available in tightly matched pairs. Typically they
are matched to under 1%.

EQ-1A Data Sheet 
 
A free paper describing the use of the Vintage Windings Complete
Filter Unit in a DIY Pultec EQP-1A3 SS type EQ is posted Here.

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