Operating Instructions
VM Operating Instructions
Using the Front Input
To view a signal, connect a patch cord from your source to the V IN jack on the front of the VM module. VM will detect that a jack has been inserted and perform a light show indicating that it has switched to the front input. VM will then display the voltage using the display mode you have selected.
If you are monitoring a signal that needs to continue on to another module, the bottom THRU jack offers a buffered version of the input signal. Note: while VM is capable of displaying voltages that are outside the power supply range, the buffered output is limited to about +/-10V (on account of it’s buffered).
It is not recommended to leave other modules connected to the THRU jack if there is nothing plugged into the input as the input’s sense signal gets passed through to the THRU jack. It won’t hurt anything, but it might be kind of annoying.
Selecting a Display Mode
If you want to change display modes, press the button on the front of the module (display mode can only be changed while using the front input). It will cycle through the following modes:
- Bar Mode: All LEDs up to and including the indicated voltage light up.
- Dot Mode: One LED lights at a time, indicating voltage to the nearest volt.
- Precision Bar Mode: Like bar mode, but one of the LEDs flashes to indicate tenths of a volt.
- Precision Dot Mode: Up to two LEDs light at a time. The solid one indicates volts, and the flashing one indicates tenths of a volt.
VM will remember the selected mode, even after being powered off.
Using the Rear Inputs
To monitor the voltages coming into the power supply connector on the rear of the module, remove the patch cable from the front input. VM will detect that there is nothing plugged into the front input and switch to one of the rear inputs.
While in rear-input mode, you may use the front panel button to cycle through rear voltage sources. VM will display a light show indicating which input has been selected.
- +12V Power Supply: All red
- -12V Power Supply: All blue
- +5V Power Supply: All magenta
- CV Bus: Top half build red
- Gate Bus: Bottom half build red
The display will then show the voltage present on the selected bus. VM remembers which input you’ve selected, even after the power has been turned off. It will return to the selected input whenever there is nothing plugged into the front input jack.
When displaying power supply voltages, VM uses color coding so that you can easily tell which supply you are looking at:
- +12V = Red (unless something is broken and it goes negative)
- -12V = Blue (unless something is broken and it goes positive)
- +5V = Magenta (so you can tell it apart from +12V)
Since the supply voltages should always be fairly close to specific voltages, when these inputs are selected, the display will always be in the precision version of whichever display mode you have chosen (if you’re in bar, the PS inputs will use precision-bar. If you’re in dot, they will use precision-dot).
The CV and Gate busses could conceivably swing either positive or negative, so they could be any color. These inputs don’t force the display into precision mode.
Reading the Display
The display indicates the voltage present at the selected input by lighting one LED for each volt (bar mode) or a single LED that is determied by the number of volts (dot mode). The numbers to the left of the LEDs indicate how many volts are being displayed. No LEDs lit indicates 0 volts.
In one of the precision modes, a single blinking LED will indicate tenths of a volt. The numbers to the right of the LEDs represent voltage tenths. For example, if 5 LEDs are lit solid and the eighth one is blinking, then the meter is displaying 5.8 volts. No LEDs blinking indicate 0 tenths (.0). If the same LED is indicating both volts and tenths of a volt, then it will blink between dim and bright instead of completely on and off.
If the incoming voltage is positive, then the LEDs will light red. If the incoming voltage is negative, then the LEDs will light blue.
Overvoltage
VM only has enough LEDs to indicate voltages up to +/- 12.9 volts. If the input voltage goes beyond that, then the entire meter will flash to indicate the error. It also starts subtracting 1 LED per volt from the bottom of the display, so you can actually read voltages up to +/- 16V.
Fast Signals
VM is primarily designed to provide a visual indication of steady or slow-moving signals. The voltage sample rate isn’t fast enough for audio signals, and there is some filtering so the display doesn’t sit there and flicker back and forth if your signal is right on the edge between two voltages. While VM was never designed to be a VU meter, it does have some features that make monitoring fast-moving signals a bit more useful.
When the input frequency hits approximately 1.5Hz, VM disables the tenth-volt indication if it was enabled, since it would move too quickly to be of any use. It also disables the signal filtering so the voltage indication is more responsive. The module also grabs the peak positive and negative voltages and displays them as solid dots superimposed on top of the fast moving signal display (red=positive, blue=negative). In this mode, you can still get an idea of how your signal is moving, but you don’t lose the peaks because they’re going by too quickly.
At right about the point where the input frequency reaches the audio range, the meter stops trying to keep up with the signal and enters peak hold mode. Only the peaks are displayed, one for positive and one for negative. The peaks are displayed in their standard red/blue colors, and are shown as magenta where they overlap. Keep in mind that the module’s sample rate isn’t really high enough for audio signals, so peak hold mode will be more accurate for a periodic signal (where it has multiple chances to grab the peaks) than it will be for a random one.
Display Blanking
Regardless of which input you are monitoring, you can blank the display by holding the button for about 1 second. This is useful if the meter’s display is being too distracting or you want to hide your signals from prying eyes. Pressing the button again will bring the display back.
