W W W . G O L D E N A G E P R O J E C T . C O M
II
CIRCUIT DESCRIPTION
The main signal path in the EQ-73 MKII
consists of two gain stages that uses
three transitors each and a few resis-
tors and capacitors. So, all in all, the
complete signal chain only contains six
active elements. 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.
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.
The EQ-73 MKI was designed to be used in combination with a unit
with low level, unbalanced connections, saving the cost for the
classic transformer based in- and output stage. The MKII retains
the insert jack connection but an IC-based IO with balanced con-
nections and the st 4dBu operating level has been added
as an option. This makes it possible for the EQ-73 MKII to operate
as a standalone 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-73 MKII uses, cannot match the low
distortion 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.
USING THE EQ-73 MKII
Using an equalizer is not rocket science. Here are some points
though to help you getting the maximum out of the EQ-73 MKII:
- Connect the cable from the power supply to the AC 24V connec-
tor at the back of the EQ-73 MKII. Power on the unit with the front
panel POWER switch.
- Select the operating mode with the LINE IN/INSERT switch on
the back panel, pressing the switch engages LINE IN mode. Con-
nect the signal source to the LINE IN Combo jack and one of the
OUT jacks to the next unit in the signal chain.
- INSERT mode is activated with the switch in its outer position.
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 suitable unit that the EQ-73 MKII will to be used together
with. “Tip” of the TRS is the input and “Ring” is the output.
The two OUT jacks will output the signal also in this mode and
can then be used as an alternative output with a different sound
character.
The EQ-73 MKII in INSERT mode will now be inserted in the signal
path of the PRE-73. If you are using the EQ-73 MKII together with
one of the PRE-73 DLX models, you must engage the INSERT
switch to activate the EQ-73 MKII.
- The best way to learn how to set the controls of the EQ-73 MKII 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 MKII from the signal path.
- There is a Ground Lift jumper inside the unit close to the input
jack. The jumper should normally be in place. If the EQ-73 MKII 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. You can then try removing the Ground Lift
jumper which will lift the circuit board ground from the cabinet of
the EQ-73 MKII.
PLEASE NOTE:
- The maximum boost and cut varies somewhat with the selected
frequency.
- Inserting the EQ-73 MKII 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 MKII are sensi-
tive 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 MKII is mounted above or close to a unit that contain a
power supply with a mains transformer.
WARRANTY
The EQ-73 MKII is built to last. But as in any electronic device,
components 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 MKII!
I hope it will serve you well and that it will help you in
making many great sounding recordings.
Bo Medin
Vintage character
for modern ideas
