SIGNAL PROCESSOR INPUT
1
Apply signals to be aected by GND CTRL’s signal processor here. The signal processor consists of
a manual attenuator, 7-preset gain/attenuation stage and DC bias - The signal is processed
though those stages in respective order. The nal output is then sampled by a bipolar LED
clipping indicator before buered to a voltmeter, multed normal and single inverted outputs.
7 PRESET GAIN/ATTENUATION
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Seven most commonly needed amplitude conversion ratios at your nger tips. Use this control
to conveniently interface audio and CV within your system. Settings are available to convert any
level found in audio and video systems to within a needed amplitude range. Use with the DC
bias control to convert bipolar to unipolar and vice versa. Boost external audio signals too!
Control and function reference guide
1
2
5
.
2
.
1
.
2
1
-
5
1
0
PRESET DC BIAS
INPUT
+
CLIP
0
ATTEN
+-
4
3
1
MANUAL ATTENUATOR
3
Use the manual attenuator to add precise control for custom amplitude adjustments. Fully
clockwise setting is unity and will not aect the presets. Fully counter-clockwise will completely
mute the signal.
DC BIAS
4
This control sums a DC signal with the input, after preset gain and attenuator. Center position
adds 0V DC - eectively adding nothing to the signal. +/-9V DC bias is available via this control.
BIPOLAR CLIPPING INDICATORS
These LEDs, marked “-” and “+” indicate that the signal is about to clip or clipping. The internal
5
comparators are set to ~10V and when just barely lit, they indicate your are juuust about to clip.
When fully lit you are clipping friend! The dierence between just clipping and clipping is only
within 100mV, approximately.
VOLTMETER DISPLAY
6
Very high contrast OLED meter display. The display has two modes of operation. The default
mode (shown) produces a virtual analog needle to indicate the amplitude of your signal. At high
frequencies, the display becomes a bipolar bar indicating the full range of the signal. the hash
marks represent ~1V per step. The alternate mode is a numerical display. The numerical mode
indicates the maximum and minimum voltages with oating point numbers accurate to two
decimal places. While any mode can be used, the default mode is best for quickly viewing AC
signals or for a pleasing visual appearance. Numerical mode works very well for AC and
especially well for DC signals. Numerical is the recommended mode for measuring very slow AC
and all DC signals accurately. See “VOLTMETER TIPS” on the bottom of this page.
STABILIZER
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The stabilizer control is an important feature. For some very low and sub audio frequencies, the
display may appear blank (very low freq) or react erratically with the changing signal (sub
audio). This may not produce a useful or meaningful voltage indication. The stabilizer reduces
the speed in which GND CTRL performs updating calculations as you turn the control from fully
counter clockwise to fully clockwise. This enables very low frequency changes to be perceived
and additionally causes erratic changes to settle on the maximum and minimum values. The
default setting for this control is in the fully CCW position. Adjust only as needed or desired.
VOLTMETER TIPS
When using the numeric mode, the MAX and MIN values are displayed as positive and negative respectively. If the signal
being measured is low frequency like from an LFO for instance, the current position of the voltage (positive or negative) is
displayed twice, in other words the same reading on MAX and MIN. Similarly, for DC signals the voltage is displayed twice
and diers slightly between MAX and MIN readouts. For positive DC, use the MAX value and the MIN value for negative DC.
5
8
9
11
MODE
RST
VM
STABILIZER
I/O
THRU
VM!
+ OUT- OUT
TECH SPECS
Width.............8hp
Depth.............25mm
Current Draw
Average..........+45mA
-15mA
Max................+66mA
-15mA
Disp o saves ..+11mA
VM accurate within 20mV
All inputs and outputs DC
coupled, +/-10V
Rev Polarity Protected
RoHS & CE compliant
6
7
10
VOLTMETER and DISPLAY CONTROLS
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RST - Reset. Use this button to reset the voltmeter software in the o chance that a malfunction
occurs.
MODE - This button selects between the default needle meter and numerical displays
I/O - Display ON/OFF button. Save power when not in use by turning o the display.
DIRECT VOLTMETER INPUT
9
Signals can be measured unaected by the signal processor using this jack. The signal present
here is buered and hard wired to the adjacent THRU jack to the right of this input.
PRESET FUNCTION SUGGESTED USE
.1 Divide by 10 Video & Ext Bridging
Attenuation
.2 Divide by 5 Video & CV Bridging
Attenuation
.5 Divide by 2 CV Scaling, 10V to 5V
5V to 2.5V
NORMAL OUTPUT and THRU/MULTIPLE
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The jack labeled +OUT is the post processor output. This output is buered and normaled to the
THRU jack and acts as a +OUT multiple. However, using the DIRECT VM INPUT jack will break the
multiple as indicated on the panel. If a jack was connected in the THRU output, the new signal
inserted into VM will now be present on that jack.
INVERTED OUTPUT
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This output provides and inverted version of the post processor output. Please note that the
information on the display is indicative of the +OUT only; unless you self patch the -OUT into the
VM input.
Compact Utility
Finally - a compact utility that addresses your needs. GND CTRL was designed to ll a gaping hole or should we say an - overlled hole in
the utility world. Until now, utility modules were designed with rarely more than one basic function. This often required lling up
limited rack space with attenuators, multiples and inverters -taking up space needed for that new VCO or VCF - and still, without any
convenient way to measure or even scale CVs.
Even more frustrating is that all that redundancy of function in one module is hardly necessary in a small system or for typical small to
medium sized patches. GND CTRL takes the best of utilities and couples them with the convenience of a built in voltmeter and preset
scaling unit in a compact and space saving 8hp. There is no doubt GND CTRL will make patching easier and more ecient while saving
panel resources.
Voltage Bridging
The growing variety of analog and microprocessor driven modules in Euro is great, but given the lack of standards, not all modules
produce or accept the same range of control voltages. GND CTRL’s gain presets address this issue and provide an easy way to interface
modules while getting the best range and response. Common voltages produced and utilized by the majority of Eurorack audio/video
modules are unipolar; 0.5V, 0-1V, 0-5V, 0-10V and bipolar +/-2.5V and +/-5V. The Presets address these conversion ratios. With the
visual aid of the voltmeter along with the Manual Attenuator and DC bias make this task a simple one. Dead spots and compatibility
issues are history.
Bridging External Devices
GND CTRL can be used to boost line level signals for use in the modular environment and similarly to attenuate modular signals for
monitoring level sensitive devices.
DC Voltage Source
Use the DC Bias to produce an adjustable bipolar DC voltage source. Mix the signal with modulators or use as a trigger voltage source for
pressure sensitive resistors and voltage source for boosting CV range. The currently displayed voltage is available at the +OUT and THRU
outputs as well as an inverted version at the -OUT output.
Know Your Voltages!
Knowing precise voltage levels in a patch is far more accurate than remembering a knob’s position. We all know just how subtle settings
can be.
Not only that but this knowledge provides a much deeper understanding of modular synthesis and what is happening in your patches.
1 Unity No Gain
2 Multiply by 2 CV Scaling, 5V to 10V
2.5V to 5V
5 Multiply by 5 CV Scaling, 1V to 5V
Boost Low/Ext Signals
10 Multiply by 10 CV Scaling, 1V to 10V
Boost Low/Ext Signals
CALIBRATION PROCEDURE
The calibration should be performed exactly as follows:
Using an accurate multi-meter to three decimal places.
And a stable voltage source.
1.) Start up GC and the multi-meter.
2.) Patch the voltage source to a attenuator and then
to the AUX input of GC.
3.) Patch a cable from the THRU output on GC to the
multi-meter probe leads.
4.) Using the multimeter, set the voltage from your
voltage source to 5.35 or close to that - just a value to
two decimal places that is close to 5V but not 5V exactly!
5.) Set the stabilizer pot to about 9 O'clock
6.) Using the PCB trimmer and taking the measurement
o the MAX reading - set GC MAX reading to exactly
what you get o the multi-meter to two decimal places
- as close as possible.
7.) Using the attenuator on your voltage source, cycle
through voltages from 0 to 10V and make sure that the
reading is within 10-15mV across the board or as close
to that as is possible . The reading will slightly skew
increasingly o the mark as you tend away from 5V in
both directions. But doing it this way gives the best all
round performance.
IMPORTANT!
Do not attempt to jumper the 6 pin header on the back of the GND CTRL PCB! This is for possible future voltmeter rmware updates. There are no
easter eggs or secret settings beyond the possibility of a “SURPRISE, YOU FRIED YOUR MODULE!” smoke fest. You will also void any possibilty of a free repair.
That being said, we are here to help if you ever have any problems with our modules! If you are curious and have questions just ask :)
The number one cause of damage are reversed or misaligned power connections. Always abide by the -12V aligned with the RED stripe rule for SSF modules.
We do tolerate mistakes as all our modules are reverse polarity protected but do please pay attention because not all modules have this feature!
Thank you for your purchase and as always - ENJOY!
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