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[GTx-PRE-JC120-Bass.jpg]
The Bass control is a low pass shelving filter
operating at 80Hz. Again, far more cut than boost
is available.
[GTx-PRE-JC120-Mid.jpg]
The Middle control provides much more cut than
boost. The cut is in the region of -14dB whereas
the boost is only about +4dB.
[GTx-PRE-JC120-Treble.jpg]
The Treble control is interesting providing a large
cut in high frequencies starting at 600Hz and
sliding off until 10kHz where is drops off sharply.
However, it also boosts frequencies between 100-
600Hz in order to keep the curve between the bass
and treble balanced. Boosting the treble provides
only a very very minor increase in treble above
300Hz, with it most noticeable in the 300-4kHz
region, with a peak at 1.5kHz. However, it also
cuts the bass frequencies below 300Hz ever so
slightly, and the mid-scoop is now centred on
approx 280Hz, rather than 600Hz.
[GTx-PRE-JC120-Presnc.jpg]
The Bright control adds an interesting combination
of boosts and cuts. The 40-150Hz region has been
cut slightly, and the 500Hz to 3kHz is region is
slightly boosted with the boost centred on 1.5kHz.
There is a more significant boost to signals above
10kHz. The Presence control provides exactly the
same boosts/cuts as bright. This therefore gives
you an adjustable 'Bright' control if you like.
[GTx-PRE-JC120-Spkr.jpg]
Turning on the speaker simulator significantly
changes the sound. There is a drastic cut high-
pass filter cutting frequencies below 150Hz. The
150-700Hz region is boosted and there is a
significant scoop in level between 700Hz and
4kHz with the lowest level shown at 2kHz, It then
dips again between 4kHz and 6.5kHz before
entering a sharp dropping low-pass filter at
6.5kHz.
[GTx-PRE-JC120-Gain.jpg]
The gain/volume controls work in combination.
The gain provides the rough setting and the
volume control the fine. The low gain provides a
deep mid scoop, this scoop lessens and lessens
until at very high gain a crunch is apparent and the
frequency response has flattened off. The gap
between low-middle is greater than that of middle
to high. Indeed, Middle + volume increased to 100
is not far from High, volume 60.
© Copyright 2000-2002 Barry S. Pearce et al.
Section 14
Clean TWIN
[GTx-PRE-CleanTWIN-Ref.jpg]
The Clean TWIN is similar to the JC-120, with its
mid scoop. However, the Clean Twin accentuates
this by boosting the Bass and treble significantly.
So what you get is a bandpass boost between 20Hz
and 200Hz centred somewhere around 60Hz
(approx 60Hz/Q1/+7dB), a mid cut between
200Hz and 1.5kHz (600Hz/Q2/ -9dB), another
boost
between
5kHz/Q1/+5dB) and thereafter a significant drop
off with a low-pass filter.
[GTx-PRE-CleanTWIN-Bass.jpg]
The Bass control provides much more cut than
boost. 10-60Hz shows a slight boost with the 60Hz
peak the same as normal. 150-800Hz is boosted
and the trough of the scoop sneaks up from 600Hz
to 800hz Cutting, cuts below 70Hz greatly and
between 70-300Hz is a slight linear shelf. The cut
also boosts the 450Hz to 4kHz region slightly in
order
to
maintain
Interestingly enough the mid scoop has effectively
disappeared here.
[GTx-PRE-CleanTWIN-Mid.jpg]
The Middle control again increases the 600Hz/Q2
cut by a further -6dB. Cutting also seems to
produce a small cut in level at all frequencies.
When boosting the frequencies above 3kHz are all
boosted quite a bit. Even at full boost the scoop is
severely lessened but the mid levels never equal or
exceed the bass or treble.
[GTx-PRE-CleanTWIN-Treble.jpg]
The Treble control cuts high frequencies above
800Hz in a quite drastic manner bringing it down
to an almost flat response from 800Hz upwards,
until about 5kHz where it then drops off to 22kHz.
The scoop has effectively disappeared and
frequencies between 450-800 are boosted slightly
to ensure a smooth curve. When boosted a
significant boost above 350Hz is available, but this
is also combined with a reduction between 15Hz
and 350Hz. The 60-350Hz region suffers a cut
because of the shift in mid-scoop centre frequency
from 600Hz to about 250Hz.
[GTx-PRE-CleanTWIN-Presnc.jpg]
The Bright control increases treble, by boosting
600Hz and above, The Presence control again is
basically adjustable bright. Except bright contains
a slightly higher boost in the 600Hz-3.5kHz
region.
[GTx-PRE-CleanTWIN-spkr.jpg]
Preamps
1.5kHz
to
13kHz
(approx
the
curve
smoothness.
69
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