HARDWARE OPERATION
How to adjust the preamplifier controls for the lowest noise
Start with the Gain and Output knobs centered, and the Pad switch in. This provides about 20dB of gain.
Increase the Gain control until the Clip LED in the meter just barely comes on during the loudest peaks in
level, and then back off the control slightly from that point. (The Clip LED should come on occasionally at
most.)
If there is not enough level with the Gain control set fully clockwise, back off the gain to 12 o’clock and place
the Pad switch in the out position. Adjust the gain control as above.
Adjust the Output control until the -10 LED is on most of the time during loud passages.
Increasing the input gain and decreasing the Output level control adds more tube warmth.
Remember, that the Clip LED looks at both the preamp input and output peaks, whereas the -10, -20, -30
LED indicators only look at the preamp output level which feeds to the A/D converter.
How to set the Output Level switch (on the rear panel)
Setting this switch correctly can lower the noise in the output signal chain by optimizing the operating levels
between the Tubeopto 8™ and external gear.
One way to determine how this switch should be set is to send audio to the Tubeopto 8™ from an ADAT
digital interface and run the audio outputs into a line input on a mixer or signal processor. Check the meters on
the mixer or signal processor to see if the level appears to be too high (clipping) or too low (barely showing any
indication on the meters). Set the Output Level switch so that the level meters in the external gear do not
indicate excessive clipping yet still provide good full-scale (or near full scale) deflection.
Changing the sample rate
The D/A converters always sync to the incoming ADAT data stream. The front panel display and switch apply
to the A/D converter sample rate and sync source. Pushing the Sample Rate switch (or holding it down) cycles
through the various settings.
The settings marked 44.1K and 48K select the internal crystal based clock generator. Selecting the internal
clock generator makes the Tubeopto 8™ the timing master for your digital system. In this case you would set
the rest of your system and software to sync to the Tubeopto 8™. When 48K mode is selected, both Green
LEDs are lit to make it easier to read.
The ADAT sync setting selects the incoming ADAT data stream as the timing source for the Tubeopto 8™. In
this case the Tubeopto 8™ would be the slave in terms of timing.
Note: If the signal at the ADAT input jack is not present or has errors, the ADAT LED will flash. This applies to
ALL sample rate selections.
The Wordclock selection synchronizes the A/D with the signal present at either of the BNC jacks. This is the
mode that should be used when you want to have an external Wordclock generator set the master system
timing, allowing for multiple devices. This LED will flash if Wordclock mode is selected AND the incoming clock
signal is not present or out of lock range.
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