Moog Parametric EQ Graphic EQ
Last Update 07-20-2025
These two equalizers were early devices in my arsenal, I got them
from a friend as part of a purchase of his Moog Liberation.
I eventually sold the Liberation but I did keep these two
processors.
George Massenburg was the first to define the variable parametric
equalizer in a 1972 AES paper, which proposes multiple methods of
the variable peak/shape/frequency circuit. Today his GML (Geo
Massenburg Labs) company produces a couple of parametric EQ models
(I have no experience with them).
The Moog parametric EQ has three bands each with controls for
frequency, boost/cut, and width. Bob Moog and Rich Walborn (of
Norlin/Moog Music) developed this product and it was patented under
US 4,116,197 in 1979. One of the design challenges of a
parametric equalizer is independent control of any three parameters
without affecting the others. Previous designs also had
limited dynamic range and were noisy. The patented solution
was novel in that it improved the art using 1) a minimum of
components (less $$$), 2) the tuned circuit in the frequency
sensitive impedance block produces lower noise than previous
designs, and 3) the multiple feedback architecture of the
compensation circuit which performs impedance coupling at critical
points to maintain better control of the audio spectrum outside the
frequency/width settings.
This EQ is exceptional as a surgical "correction" EQ, especially
with a boost/cut of 20dB. I don't know of any other parametric
EQ with 20dB boost/cut, but when you want to notch out an offending
frequency with precision this box excels at that. I start by
setting it to full 20dB cut, width set at wide, then sweep the
frequency control until you hear the offending frequency
attenuated. Then you adjust width and cut until you get the
desired correction. One of my first applications with the
parametric was for my Kustom 88 electronic piano, notching out
certain bands for better piano tone in a band (I never did record
those settings). It was very useful in the studio for notching
out a snare drum resonance that was conflicting with the vocals, and
for notching out a honky resonance on a guitar sound.
The Moog graphic EQ is a ten band one octave equalizer with 15dB
cut/boost at fixed frequencies and widths. The top 16Khz band
is a shelf filter, the others are bandpass filters. While
nothing exotic circuit wise, this unit does have a power output
amplifier for driving 600ohm loads over long distances - not a usual
feature for graphic EQs. While this isn't the surgical EQ
talent of the parametric, I find that it has an interesting color
with boosting any band so I kept it for my studio.
These devices included a Gain, Drive, Bypass, and footswitch
control. Bypass is the clickless buffered type, footswitch
operates Bypass. Gain adjusts the output level (+/-)10dB of
the processed signal - the device can adapt to any source from low
output levels to (+)4dBu pro audio devices. Drive varies the
ratio of input to output level so that the best dynamic range and
signal to noise ratio can be attained without affecting the the
output volume - it changes the gain at input and output
simultaneously but with opposite operation. You basically
adjust the gain and drive while playing your source, and when the
OVERLOAD light indicator glows then you back them off a little
bit.
Other Moog rackmount audio processors were the 12 stage Phaser, the Vocoder (very parts intensive), and the rare
String Filter that was made to
order from the Moog Custom Shop and was not a production
device. They all have "reversible" rack ears where they can
serve as mounting to a rack, or as handles for carrying separately.
They were all suitable for stage, FOH, and studio
applications. The String Filter is an eclectic processor with
multiple fixed resonant filters that are designed to emulate the
resonance of the wood body of traditional bowed stringed instruments
such as violin, viola, cello, etc. Luthiers of the "classic"
16th-17th century era "tuned" the bodies of stringed instruments
using quarter-swan stock, bracing, controlled shaving, placement of
soundholes, and the "secret sauce" of varnish that was applied to
the wood. These luthiers had access to seasoned long growth
forest tonewoods that do not exist today. All that was done
with the skilled eyes and hands of the luthier, without the aid of
modern power tools or computers. The String Filter was
designed to emulate these wood resonances by switching in selected
filters, from any of 40(!).
Width control in the parametric EQ is an exotic part - a dual ganged
pot with 500ohm linear taper and 50K audio taper. If this
component goes bad in your unit, finding a replacement will be very
very difficult. Probably the only replacement is a ganged
rotary switch with discrete components to mimic the values of the
original pots per radial location. The other hard-to-get
component in the rack units will be the power supply SG1468 dual 15V
voltage regulator.
If you haven't already, arrange to have the dust covers on the
slidepots of the graphic EQ removed ASAP. These dust covers
are petroleum based which return to their oily form as they age,
then breaks apart in very sticky pieces that you DON'T want falling
into the slidepots! Moog used quality slidepots in their
products (apart from the Satellite or Sonic 5/6), I have had zero
problems with them.
These audio processors command serious bucks on the used gear
market, mostly because of the Moog brand. The graphic EQ isn't
worth so much, but the parametric EQ is a worthy device. I
have sold two other parametric EQs because they weren't as effective
as the Moog unit. Some unscrupulous sellers exploit the "moog"
brand and promote these EQs as having the "Moog Ladder Filter",
which is totally false.
Home
