User manual

VETTA Theory of Operation………………Line 6 confidential ……………………………. Page 7 of 18
Diodes D3/D4 and D5/D11 protect the op amp U10 from overdriving and electrostatic
discharges. R44/R170 and R43/R169 attenuate the FX Return signal from the maximum
specified 20Vpp to 5Vpp. R44 and R43 also protect the input of the CODEC ADC in case the
voltage would exceed +/-2.5V. C14 and C15 allow the signal to be DC biased at +2.5V by the
ADC input. D8/D7 and D10/D9 are not installed on the PCB. The ADC output of CODEC U16
feed DSP#2.
FX Send:
The differential outputs of CODEC U16 DAC are amplified and low pass filtered (31KHz) by
U11_A and B. U11 outputs feed the FX Loop ¼” jack (20Vpp max)
On the Power Amp PCB:
The differential inputs at connector P1 feeds the two power amps. Notice that the gain of the
power amp is conditioned by the status of the Z-Select line. This allows for setting the
maximum power amp output swing, and power, in function of the current load impedance (4 or
8 Ohm). Notice also that the power amp can be muted by the POWERAMP_MUTE* signal
(0V = muted, above 3V = un-muted)
On the Speaker Output PCB:
The function of SPLIT switch on the Speaker Output PCB is described in the VETTA User
Manual. The wiring of the ¼” jack J9 is such that if no jack is plugged into it, the split switch
SW2 default to the Split OFF position. This was designed so that if no external speaker is
plugged in the LEFT speaker output jack the split switch will have no effect on the speaker
signals routing.