GA Project EQ-81 User manual

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Vintage Style Equalizer
EQ-81
INTRODUCTION
Congratulations on choosing the Golden Age Project EQ-81 Equalizer!
The class-AB circuit used in the EQ-81 is similar to the eq section in the classical 1081 module, without the
high and low pass filters.
The sound character is warm, punchy, sweet and musical. These classic characteristics have been heard
on countless recordings through the years and it is a versatile sound that works very well on most sound
sources and in most genres. The essence of this sound is now available at a surprisingly low cost, making it
available to nearly everyone.
The EQ-81 has stepped frequency controls that offers a wide selection of frequencies from 33 Hz to 15 kHz.
The BASS and TREBLE frequency bands are switchable between shelving and bell and the MID frequency
bands is of the bell type with a switchable Hi Q setting.
The control range is +/- 18dB. All four bands can be set in an off mode.
The EQ-81 is not intended to be used as a standalone EQ. It is designed to be used together with one of the
Golden Age Project models that has an insert jack. It can also be used with some other product that has a low
level (about -18 dBu to -10 dBu) unbalanced insert connector.
Combining one of our PRE-73 units and an EQ-81 and using a UNITE rack kit to mount them together, one will
get a 19-inch 1081-style unit at a low cost and with a great sound!
FEATURES
- Vintage Style electronics. No intergrated circuits in the signal path
- 4-band with inductor based mid frequency bands
- Stepped frequency selection
- A wide selection of frequencies from 33 Hz to 15 kHz
- Control range up to +/- 18 dB
- Each band has an off mode
- Tantalum capacitors in the signal path
- Designed to be used together with one of our models with an insert jack
- TRS jack for in-and output connection, the nominal working level is around -18 dBu
- Selectable ground lift switch
- External power supply to avoid interaction with the audio circuits
- Great sound that suits most sound sources and genres
- A solid build quality that will last many years of normal use

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CIRCUIT DESCRIPTION
The main signal path in the EQ-81 con-
sists of four gain stages, one for each
each frequency band. Each gain stage
uses five transitors and a few resis-
tors and capacitors. So, the complete
signal chain contains a small number
of active elements. Compare that to the
big number of transistors that are usu-
ally used in one single integrated circuit! The filter circuits uses
additional passive components.
The mid bands uses inductors and capacitors for a classic LC-
style eq circuit.
By designing the EQ-81 to be used with a unit with a low level
insert jack, the unit did not have to be fitted with an input and
output stage, reducing the cost of the unit.
MODERN VERSUS OLD
It is true that there are some great IC´s available today that
achieves very low levels of static and dynamic distortion.The
simple circuits that the EQ-81 uses, cannot match the low distor-
tion specifications of modern IC´s.
It is the distortion components that imparts a sound character
to the audio signal and, if the distortion components are of the
right sort, this is a good thing since it makes the recorded voice
or instrument sound “better”, more musical, more pleasing to
the ear. This is one reason why vintage style units are so popular
today.
This is not to suggest that modern, transparent sounding audio
circuits is a bad thing, sometimes they are prefered over colored
ones. It´s all about taste and it depends on the genre. For most
modern music styles, color and character is definitely a good
thing.
And doesn´t it feel good to use audio components built according
to the old, minimalistic approach where one can follow the signal
from one discrete component to another?
USING THE EQ-81
Using an equalizer is not rocket science. Here are some points
though to help you getting the maximum out of the EQ-81:
- Connect the cable from the power supply to the AC 24V connec-
tor at the back of the EQ-81. Power on the unit with the front panel
POWER switch.
- Connect the supplied stereo TRS cable between the back panel
TRS jack and the insert jack of one of our PRE-73 models or any
other unit that the EQ-81 will to be used together with. “Tip” of the
TRS is the input and “Ring” is the output.
- The EQ-81 will now be inserted in the signal path of the PRE-73.
If you are using the EQ-81 together with a PRE-73 DLX, you must
engage the INSERT switch to activate the EQ-81.
- The best way to learn how to set the controls of the EQ-81 is to
experiment with different settings on different sound sources. The
four bands and the different frequency selections will give you
many possibilities for shaping the sound.
- The BASS and TREBLE bands are of the bell type but can be
switched to a shelving type, ie, it will affects all frequencies below
(Bass) and above (Treble) the selected frequency. The eq action
gradually starts above (Bass) or below (Treble) the selected fre-
quency and increases up to the maximum boost or cut.
The MID bands has bell curves, ie, a cut or boost centered around
the resonance frequency. They can be switched to Hi Q mode
meaning that the eq action will be more narrow around the center
frequency and the maximum boost/cut will be higher.
- By setting the frequency switches to OFF, the eq action of each
band is removed for comparions between eq and no eq.
Using the INSERT switch in the PRE-73 DLX, one can instantly
bypass the complete EQ-81 from the signal path.
- There is a Ground Lift switch on the back panel. It should nor-
mally be in the OUT position. If the EQ-81 is mounted in a UNITE
rack kit together a PRE-73 and / or mounted in a rack where other
units are also mounted, ground loops can give rise to problems.
Try engaging the Ground Lift switch which will lift the circuit board
ground from the cabinet of the EQ-81.
PLEASE NOTE:
- The maximum boost and cut varies somewhat with the selected
frequency.
- Inserting the EQ-81 in a PRE-73 will result in a small gain
change.
- Clicks can arise when the controls are operated, This is normal
and a consequence of the used circuit design.
- The inductors and the filter circuits in the EQ-81 are sensitive to
electromagnetic fields. If you have a problem with hum or noise,
try moving the unit to another physical location in your studio.
One situation where this problem is most likely to show up is if
the EQ-81 is mounted above or close to a unit that contain a power
supply with a mains transformer.
WARRANTY
The EQ-81 is built to last. But as in any electronic device, compo-
nents can break down.
There is a slow blow fuse located inside the unit. If the unit dies,
please check this fues. If it has blown, replace it with a new one
with a rating of 1A, You can also try with another 24V AC adaptor if
you have one available.
If this doesn´t help, or if the unit has another problem, it will need
repair and you should then contact the reseller where you bought
the unit.
The warranty period is decided by the Distributor for your country.
The Distributor will support Golden Age Project resellers and end
users with repairs and spare parts.
REGISTRATION
You are welcome to register your unit at our website:
www.goldenageproject.com
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I would like to thank you for chosing the EQ-81!
I hope it will serve you well and that it will help you in
making many great sounding recordings.
Yours,
Bo Medin
Create music
– Be happy!