OPERATION
The slopes of the low boost and cut and high cut sections are 6 dB per octave which is very gentle
and smooth. The slopes become slightly steeper when the combination of boost and cut is used. Few
console EQs are this gentle- not even on million dollar desks. The section marked "high boost" could
be considered mid to high boost with the frequencies ranging from 1.5 kHz to 16 kHz. There is a bandwith
control that is roughly equivalent to "Q" on parametric EQs but the range is less and tends to be both more
subtle and musical.
One other bit of Pultec trivia - the circuit was designed to help make telephone lines sound better
- even acceptable for music (Western Electric remember!). That is why the EQ arrangement is the way
it is. It was designed to "fix" less than perfect transducers and lines. It is not surprising to us that this circuit
helps low cost mics and digital recordings. Contrary to many claims - too much gear today still sounds
just a bit better than telephone quality.
5
The Langevin EQP1-A is another variation of the Pultec EQP1-A. Manley Labs is the only
company today with permission from Eugene Shenk (founder of Pulse Technologies) to use the original
Western Electric passive EQ circuitry that Pultec licensed and were given Eugene's personal blessing
in the endeavor. We have improved on the circuit by increasing the number of frequencies and by using
an all discrete solid state 10 dB make-up gain amplifier / line driver. We also use much better quality
parts and manufacturing techniques than was available back when Pultec was in production. The Pultec
EQs are one of the few pieces of professional audio equipment that has stood the test of time and is
usually one of the three top choices of engineers when asked to name their favorite EQs. It is because
the circuit has a musical transparent quality often missing in modern designs. We believe the reason for
this is that the EQ has no active circuitry and is based only on a few capacitors and inductors along with
a few resistors and pots. Hard to beat sound-wise. There is one disadvantage to vintage passive EQs.
The type and range of controls is less than what may be found in most modern EQs. While parametric
EQs may be more versatile for removing some types of problems, they may be the wrong choice for
a general every-day "tone" controls. The old Pultec EQs are famous for the drums, bass and whatever
could use some extra "cruch" with that big low bottom end, but the Manley/Langevin are clean enough
to use on anything.
The most common question from those only familiar with parametrics is "Why both a boost and
cut for the lows- couldn't you just have a single control with cut & boost". Three reasons - In the circuit,
the controls are in different places and each has its own associated parts. #2 - we did not design this
circuit - we are not about to change the basic design of something that works this well. #3 - Almost every
Pultec user finds the combination of both boosting and cutting gives not only the best results but results
that are almost impossible with parametrics. The curves of the boost and cut are not symetrical and don't
cancel each other out as might be expected. Instead some of the lower mid is cut when both controls are
used. In practice, usually more boost than cut is dialed up and the result tends to look approximately like
this:
20 Hz
1000 Hz
20 kHz
Flat
