ACG EQ-02 Preamp
Alan Cringean (of AC Guitars) has teamed up with John East from East UK to produce a filter based pre-amp.
This new pre-amp is available in several different configurations. This includes a single pickup version, two Jazz plate versions and 3/4/5 knob versions. The Jazz plate version will fit into a standard Jazz Bass control cavity including the battery. Same easy installation as other East Preamps with all connections made using screw terminals so no soldering required.
How it works
If you are used to the normal cut and boost type of EQ using the ACG pre-amp will require
a different approach in order to get the most from it.
First a few notes on the principals behind the design and then a few suggestions on how
to get the best from it.
Note: With regard to knob rotation:
ACW = Backing a knob off or turning it anti-clockwise
CW= Turning a knob up towards maximum or turning it clockwise.
The volume of the instrument is controlled by the upper ring on the stack while the lower
ring controls the mixing of the outputs from the two pickups. Turn ACW for the bridge
pickup alone and CW for the neck pickup. Intermediate settings allow a mix of the two
pickups. The indented centre click gives an equal mix. In several configurations the volume
and blend are on individual pots.
The main element in the pre-amp is the filter stacks.
BASS FILTER STACK
First, a filter lets some parts of the frequency spectrum through and not others. The type of
filter determines which part it lets through. Also, the amount of cut-off is important. If it has
a sharp or steep cut-off, it is more dramatic.
There is a LOW PASS FILTER where the frequency is variable over quite a broad range;
from just allowing the very deepest sounds through, to allowing upper midrange frequencies
of 3kHz. As the frequency control is adjusted, sound ranges from very deep to a much
more open sound, taking in more midrange as the control is increased. As it's a low pass
filter, the very low bass is always there, but the high frequencies can be progressively
This aspect of the pre-amp is controlled by the lower ring on the filter stack. Fully ACW giving
you a very full deep bass sound. As the knob is turned CW, more of the higher frequencies
are let through the filter.
The upper knob of the filter stack controls the overshoot peak. This means that some
resonance can be added at the frequency of cut-off to which the filter is tuned. This has
the effect of making the sound much richer at the point of the filter frequency. So if the filter
is set to a low frequency on the neck pickup, and the overshoot peak is increased, you get
a massive reggae style of sound as you're giving resonation to the more fundamental frequencies.
If the filter is set higher, it accentuates the harmonics. To give you an idea, if you
rotate the filter control up and down when the peak is turned up, it sounds very much like a
The upper ring on the filter stack sets the peak level. Fully CW is maximum gain (boost)
and when turned ACW the gain is reduced.
TREBLE FILTER STACK
The treble stack is there to address the top end of the spectrum as the filters cut off below
the very highest frequencies you can get from roundwound strings. Here we're talking
about the high end 'sizzle'. The frequency control also goes well down into the upper midrange
around 1kHz. This is another filter type, a HIGH PASS FILTER in the treble signal
path. This sets the frequency above which the treble spectrum is allowed to pass through.
The upper knob controls the gain (boost) applied to the treble frequency while the lower
ring controls the frequencies which are allowed through. Turning the frequency ACW allows
more of the lower treble spectrum. Setting more CW allows only the higher frequencies
of the treble spectrum to pass.
In the 4 knob J plate version and the 5 knob version there is the addition of a passive tone
control. The dual passive tone pot and two capacitors are connected directly to the pickups
in order to create a passive roll-off via direct interaction with with the pickups.
The pre-amp also has some internal control options.
There is a separate gain control for each pickup input.
The main use for this control is to allow you to use two different types of pickup but still
have a balanced volume from them both.
This would also allow you to use say a Musicman style pickup with a Jazz style pickup and
still be able to balance their respective volumes.
---> Installation Instructions