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7.3
Setting Trim Pots
As discussed in sections 3.4.5 and 3.4.6, Hilo’s Line Inputs and Line Outputs can be set to Trim values of +18 dBu; +20 dBu; +22
dBu; +24 dBu; +0 dBV; +2 dBV; +4 dBV and +6 dBV. These trim positions are factory calibrated to these values within 1/100th of a
dB. Trim levels can be selected from the Hilo Home Page. These set levels will satisfy the overwhelming majority of Hilo users.
In some cases, these levels may need to be tweaked to match the reference level of gear that is not calibrated as accurately. Also, in
time and due to changes in temperature, it may be necessary to tweak trim levels to set them back to their original reference.
For this purpose, Hilo has ultra accurate, 25-turn trim pots accessible from the bottom of the chassis that can be used to or -
.5dB from the established trim level. Here are the steps to calibrate via these trim pots:
1.
Remove the plate from the bottom of Hilo. There are four screws that hold it in
place. The front-right rubber foot will need to be removed to allow access to one
of the screws. Locate the input and output trim pots on the underside of the Hilo
main board.
2.
Set the Line In and/or Line Out trim levels on the Hilo Home page to the value
closest to your desired level.
3.
It is best to use sine wave tones to adjust trims. If adjusting Input trim levels, send tones from an external device and
measure the results in either software or a scope with digital inputs. It is best to avoid analog input routed to analog output
paths for this kind of calibration. If adjusting Hilo Output Trims, send tones from a software source via the USB connection,
or tones from an external device connected to one of Hilo’s digital inputs routed to the Line Out. Make sure that the entire
signal path is set to unity gain.
4.
Adjust the trims clockwise to increase the gain on the inputs or outputs, or counter clockwise to decrease gain until the
desired reference level is achieved.
Keep in mind that this variation will also be represented in other trim levels that are selected. For instance if a trim level of +22dB is
active, and the trim pots have altered that to 22.25dB, if later a trim value of +24dB is selected from the Hilo, the resulting signal will
be +24.25 dB.
7.4
XLR Connector Wiring and Adapters
This section describes the proper wiring of cables that can be used to adapt both the Analog and AES Digital XLR connectors on the
Hilo.
7.4.1
Balanced Connections
The wiring method for balanced connections with XLR connectors to balanced TRS (¼” phone) connectors using shielded twisted
pair cable (2 wire + shield) is as follows:
XLR Pin 1 (GND) to cable shield and to the TRS sleeve
XLR Pin 2 (+) to one signal wire and to the TRS tip
XLR Pin 3 (-) to the other signal wire and to the TRS ring
1
2
3
XLR Male
or Female
2 Conductor shielded cable
Tip
Sleeve
Ring
1/4" Phone Plug
(Balanced)
