Solid State Power Amp Reviews

Sidebar 2: Measurements

The Carver Silver Seven-t was the most powerful amplifier I have ever measured, exercising my dummy-load resistors to their limits. Maximum power output at clipping (1% THD) was a whopping 608.4W into 8 ohms (27.8dBW), and 878W into 4 ohms (26.4dBW). I could not, however, measure the Silver Seven-t's clipping point into 2 ohms because the amplifier became unstable and oscillated when driven even moderately into this low impedance. An input voltage of 50mV (a very low value) caused the amplifier to oscillate when connected to a 2 ohm load. In addition, a spurious signal subsequently appeared on top of the 1kHz sinewave when driven by more than 35mV into 2 ohms. (It is possible that the stress of the clipping power test had caused something to fail.) Note that Carver rates the amplifier at 1000W into 2 ohms.

Frequency response, measured at 1W output into an 8-ohm resistive load, showed a flat LF response with a slight peak in the treble, dropping to 0dB at 20kHz. Interestingly, this HF peak disappeared when the amplifier drove a capacitive load of 2.2µF in parallel with the load resistor, a combination regarded as being typical of an electrostatic speaker. The response was down about 0.5dB at 20kHz into the capacitive load.

Output impedance was the highest I have measured, whether tube or transistor, at 1.24 ohms at 20Hz, dropping to 1.16 ohms at 20kHz. Presumably, the tubed Silver Seven also has this extremely high output impedance. This probably accounts for the sluggish nature of the bass I noted. Typical solid-state amplifiers have output impedances of about one or two tenths of an ohm.—Robert Harley