Metrum Acoustics Forte Power Amplifier

Description

For long time Metrum Acoustics has used hybrid (triode) amps
for pleasure listening and critical evaluations. What we did not like was the
fact that triodes suffer aging problems. In simulation software, we started to
simulate triodes with fets instead. The good thing with triodes is their low
gain and a lot of bandwidth without any need for feedback. As a result we
realized a full class A high voltage fet circuirty having the right gain ,very
good open loop bandwidth  and low noise figures. A similarity is the high
voltage of 350 Volts to get this circuit running. As a result an amazing
linearity without any feedback was realized. From this point the circuit 
is driving a class A/B output section (10 watts in class A). Some little
feedback is necessary to get the right gain but also improves the damping
factor at the same time . Compared to our old hybrids, there’s no sonic
difference, just less noise and lower distortion.

After two years of prototyping and testing, we’ve now turned
this into a commercial product. The circuits are quite overdimensioned to be
sure that no errors occurs. Still we added  a lot of protection to avoid
any damage to your loudspeakers in case of malfunction. A soft start procedure
is added to charge the amazing capacity of 176000µF. This huge capacity is
available during complex and dynamic transients. As known hybrids combine tube
sound and amazing control as realized by transistor designs. Here you have the
solution. The “Forte”  power amplifier will serve you
without  problems as known with normal hybrids but still having the
holographic sound as known from good tube designs. The Forte is an addition to
our awarded Adagio digital amplifier.