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CIRCUIT DESCRIPTION
The main signal path in the EQ-73 con-
sists of two gain stages that uses three
transitors each and a few resistors and
capacitors. So, all in all, the complete
signal chain only contains six active ele-
ments. Compare that to the big number
of transistors that are usually used in
one single integrated circuit! The filter
circuits uses additional passive components.
The first gain stage handles the LF and HF bands and the second
gain stage handles the MF band. By designing the EQ-73 to be
used with a PRE-73 with an Insert jack, the unit does not have to
be fitted with an input and output stage.
The MF band uses two inductors and capacitors for a classic
LC-style eq circuit. The first inductor has a several taps to achieve
suitable Q-values (ie, the shape of the curve) for the different mid
frequencies from 350 Hz to 10 kHz. The second inductor has a
higher value and are used for the two lowest mid frequencies, 160
Hz and 240 Hz.
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-73 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-73
Using an equalizer is not rocket science. Here are some points
though to help you getting the maximum out of the EQ-73:
- Connect the cable from the power supply to the AC 24V connec-
tor at the back of the EQ-73. 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 the PRE-73.
- The EQ-73 will now be inserted in the signal path of the PRE-73.
If you are using the EQ-73 together with a PRE-73 DLX, you must
engage the INSERT switch to activate the EQ-73.
- The best way to learn how to set the controls of the EQ-73 is to
experiment with different settings on different sound sources.
There are a number of frequencies added to the original design,
expanding the possibilities for soundshaping.
- The LF and HF bands are of the shelving type, ie, it affects all
frequencies below (LF) and above (HF) the selected frequency. The
eq action starts gradually above (LF) or below (HF) the selected
frequency and increases up to the maximum boost or cut. The MF
has a bell curve, ie, a cut or boost centered around the resonance
frequency.
- By engaging the OUT switches, the eq action of each band can be
easily removed for quick comparions between eq and no eq. Using
the INSERT switch in the PRE-73 DLX, one can instantly bypass
the complete EQ-73 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-73 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-73.
PLEASE NOTE:
- The maximum boost and cut varies somewhat with the selected
frequency.
- Inserting the EQ-73 in a PRE-73 will result in a small gain
change.
- Clicks can arise when the controls are operated, especially on
the HF band. This is normal and a consequence of the used circuit
design.
- The inductors and the filter circuits in the EQ-73 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-73 is mounted above or close to a unit that contain a power
supply with a mains transformer.
WARRANTY
The EQ-73 is built to last. But as in any electronic device, compo-
nents can break down.
There is a fast blow fuse located inside the unit. If the unit dies,
please check this fues. If it has blown, replace it with a new one.
You can also try with another 24V AC adaptor if you have one avail-
able.
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-73!
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!
