User manual

VETTA Theory of Operation………………Line 6 confidential ……………………………. Page 1 of 18
Engineering
CONFIDENTIAL
VETTA Theory of Operation M.D. / G.S December 20, 2001
- The * sign next to a control signal name indicates that this control is active low
The Vetta Combo electronic circuitry is distributed across 8 PCBs:
- Vetta Power supply PCB
- Vetta Main PCB
- Vetta Power amplifier PCB
- Vetta U.I. (User Interface) Left PCB
- Vetta U.I. Right PCB
- Vetta Guitar Input PCB
- Vetta Headphone Output PCB
- Vetta Speaker Output PCB
Power supply system:
On the Power Supply PCB:
The main components of the power supply system are located on the power supply PCB. This
is a switch mode power supply. Directly connected to the AC input is the line filter. The line
filter limits the noise that the power supply injects into the AC line. L1 and L2 are common
mode inductors, which work with “Y-caps” C6, 7, 43, 44, 45 to filter common mode noise.
Common mode noise is on both the line and neutral. A Y-cap is connected from line or neutral
to the chassis. The chassis should be connected to earth ground. There are two X-caps - C3, 43
which are connected from line to neutral and they filter differential noise. Service note: Both
X and Y caps go through special testing from the safety agencies and should only be replaced
with approved parts.
The fuse F1 provides protection in case of a failure in the primary circuit. Service note: It is
very unlikely that this fuse will blow without a catastrophic failure. Never replace the fuse and
apply power before repairing any failed components.
The negative temperature coefficient (NTC) thermistor RT1 limits inrush current when the unit
is cold.
D1, C1, and C2 comprise a full-wave, or voltage doubler rectifier circuit. If a jumper is
installed across J5, the unit is in voltage doubler mode and the nominal AC input range will be
100 to 120VAC. If no jumper is present the range is 200 to 240VAC. When the jumper is set
properly for the available AC, the DC voltage across C1, C2 is a roughly constant 350VDC.
Service note: If no jumper is installed (240VAC mode), and the unit is operated at 120VAC, it
will function but it will not be able to output full power. If the opposite condition is present
(jumper in 240VAC) the unit will get damaged (350V across 200V caps). Obviously, great
care should be taken to avoid this condition.
The power converter is a flyback topology (The correct term for the magnetic element in a
flyback converter is a coupled inductor but it is commonly referred to as a flyback transformer.