User manual

VETTA Theory of Operation………………Line 6 confidential ……………………………. Page 15 of 18
POWERAMP_MUTE *
This output signal is generated by an I/O pin of DSP #1. When low it mutes the power amps. It
is kept low from the start up of the firmware until all DSP code is downloaded and running, all
memory is cleared, and the +/- 15DEL (delayed +/- 15 V supplies) are up. This last item takes
about 2 seconds from the time the AC power is turned ON. The POWERAMP_MUTE* signal
is combined with the PS_VALID signal (see power supply PCB) by D16, R175 and R174
(page 6 of 8 of the Main PCB). This arrangement helps muting the power amp as soon as the
power supply starts to fall, and therefore limits the amount of audio thump when the power is
turned OFF.
MONO/STEREO*
This input signal is generated on the Speaker Output PCB, and is read by an I/O pin of DSP #1.
Since the VETTA Combo always runs in stereo, it is grounded and will always read low. This
signal will be used in the VETTA Head.
When the unit is running in VETTA COMBO mode (as determined by a flag stored in the flash
memory) the MONO/STEREO* input is ignored and the unit defaults to stereo.
Z_SELECT
The Z_Select line is an analog signal generated on the Speaker Output PCB. Its level indicates
the current setting of the Power Amp output impedance. Its analog voltage level versus
speaker’s impedance setting is a as follows:
4 Ohm = +15V
8 Ohm = 0V (or open)
16 Ohm = -15V (Used only on VETTA Head)
The status of the Z_SELECT line affects two parameters in the VETTA
1) It changes the gain of the power amp (see Audio System)
2) It changes the rail voltages of the power amp (see Power Supply System)
HEADPHONE_SENSE
This input signal is generated on the Headphone Output PCB, and is read by an I/O pin of DSP
#1. It is high when a jack is connected to the headphone output jack and low otherwise. When
a jack is connected into the Headphone Output (presumably a headphone), the DSP signal
going to the power amp DAC (U20) is muted.
When the unit is running in VETTA HEAD mode (as determined by a flag stored in the flash
memory) the status of this line is ignored and the mode default to “no headphone plugged in”
(= do not turn off the power amp).
LCD Temperature compensation:
Because a fair amount of heat is generated in the Vetta chassis, and because the contrast of the
U.I. LCDs is significantly affected by this heat, the VETTA implement a compensation scheme
to automatically adjust the LCD contrast setting in function of the chassis internal temperature.
To this effect, the temperature under the large graphic LCD is sensed on the U.I. Left PCB by
U11 (page 1 of 3 of U.I. left half). This IC generates a DC voltage proportional to the sensed