VTL 225W Deluxe monoblock power amplifier Measurements
Sidebar 3: Measurements
The VTL 225W monoblock clipped at 178W into 8 ohms (22.5dBW), and 208W into 4 ohms (20.2dBW), which is good for a tube amplifier. When driving 2 ohms, they did not increase their power output at clipping, indicating that they are current-limited. Frequency response featured a slightly rising HF response above 10kHz, reaching +0.2dB at 20kHz. When driving a capacitive load (2.2µF in parallel with the load resistor), this HF rise started at a lower frequency and reached a greater amplitude. At 20kHz, the response into this load was up nearly 2dB, which will be audible.
Output impedance was 0.86 ohm at 20Hz, dropping to 0.67 ohm at 20kHz. This is typical for a tube amplifier, and together with the peakiness into a capacitative load, suggests that the 225W's signature will to some extent be dependent on the loudspeaker with which it is coupled.Robert Harley