Aphex 1788A Premium Eight Chan Mic Pre - Manual (Page 21)

Page 20
MICROPHONE PREAMPLIFIER
Page 21
Instruction Manual
4. FUNCTIONS IN DETAIL
Sample Rate
The RATE button toggles through the three available sample rates of 32, 44.1, 48, or
96KHz when running the 1788A on internal clock only.
4.4 MONITOR BLOCK
Channel Select
Repeatedly pressing the CHANNEL SELECT button toggles through all eight
channels which will be displayed in the General Status Readout. The audio
of the displayed channel is sent to the headphone jack. It is only possible
to monitor one channel at a time. When the unit is in remote control, the
Channel Select button is still functional.
Volume Control and Phone Jack
The VOLUME control sets only the headphone volume and does not affect the mic pre or
line output gains. Any headphone with a 1/4” stereo or mono phone plug is suitable. With
stereo headphones, both ears hear the same signal.
TIP: Turn down the volume control before plugging in phones to avoid ear damage.
4.5 TEST BLOCK
700Hz Test Tone
A 700Hz test tone is provided for adjusting the system levels and checking the
full function of each 1788A mic channel. Why 700Hz? Because it sounds nice
and you won’t mistake it for other test tones. When the test tone is activated
for any given channel or group of channels, several things happen. First, a low
level tone is substituted for the mic input jack. Second, the preamp gain is reprogrammed
to the precise level necessary to achieve the calibrated output level. This checks the
function of the whole amplifier chain from the mic input back to the line outputs. Also,
two precisely calibrated output levels are available for system setup. When the tone is
stopped, all the original gain programming is clicklessly restored.
This puts two extremely useful tools into your hands. First, you have a complete confidence
check of all preamp channels of your 1788A, as well as the optional A/D converters.
Second, you have a definitive system level reference for matching the 1788A’s output level
to any following equipment. By using the tones for level calibration, you can guarantee
the highest signal to noise ratio and that MicLim will absolutely protect your system
downstream from overload.
Two tone levels are available: -20dB and 0dB.
The dB reference is the maximum level before clipping of the preamp and the A/D
converters. So, the 0dB tone represents the maximum undistorted output level available
and maximum digital level. The -20dB tone represents the 20dB headroom point and