18
Solution 3:
Floating ground on signal cable, chassis connected via a separate wire
to the chassis ground.
The input sensitivity (or level) is 1V for 200W. This level was chosen to be compatible with as
many other manufacturers as possible.
OUTPUT STAGE
The MPA is equipped with a class AB push-pull output up to 250W maximum power per
channel. The output stage uses low level of feedback including static and dynamic limitations.
The advantage of such an output stage allows the MPA to accommodate a wide range of
loads (capacitive, inductive, or varying resistance) without the risk of oscillation or
intermodulation.
As an example, “WATT Puppy” speakers from the WILSON Audio specialities deliver an
excellent performance despite their impedance variation between 1 Ohm and 16 Ohms. Even
when connected to Quad electrostatic speakers the MPA is capable of delivering remarkable
music reproduction.
A short circuit on the loudspeaker terminals or disconnection of the loudspeakers for a short
duration will not damage the MPA in any way.
PROTECTIONS
Static limitation on the output stage starts at a current drain of 17 App (Peak to Peak).
Dynamic limitation on the output stage starts at a current drain of 25 App after approximately
150 ms.
If during a period of minimum 1 second a DC current of more than 200 mV appears at the
output, the output stages are powered off and the protection led switches on.
This happens also if the MPA is switched on without the speakers connected.
In one of the above cases, switch off the MPA by the main switch at the backside and wait for
approximately 30 seconds until the internal led is turned off. Verify that the speakers are
correctly connected and switch on the MPA. If the led lights up again, contact your nearest
dealer.
The same phenomenon can also happen if the main AC has a micro interruption. In this case
repeat the previous paragraph.
The internal red led can be seen through the holes of the deck plate towards the front right
side of the MPA.
CHASSIS
Opening the chassis of the MPA is reserved strictly for qualified specialist engineers. Inside,
all the smoothing capacitors are designed to completely discharge in 15 minutes after the AC
mains power cable has been disconnected.
