Power Amplifiers

PrimaLuna DiaLogue Seven Tube Monoblock Power Amplifier


On the Bench

All distortion measurements were made within an 80 kHz bandwidth, at 5 volts output into 8 ohms unless otherwise specified.

At 1 kHz and 5 volts output into 8 Ohms, THD+N was 0.51% in triode mode (first graph), and 0.23% in ultra-linear mode (second graph).



Using 19 kHz and 20 kHz sine waves, the B-A peak for triode mode was 42 dB below the harmonics (first graph), while in ultra-linear mode it was 51 dB below (second graph).



IMD, using 60 Hz and 7 kHz sine waves as the signal, was 2.1% in triode mode (first graph), and in ultra-linear mode (second graph), it was 0.92%. Notice, however, that the amount of 2nd order harmonics in relation to the fundamental (1 kHz) is higher in triode mode.



THD+N vs. Frequency at 5 volts into 8 Ohms is shown below. The yellow line represents triode mode, and the red line is ultra-linear mode.


For THD+N vs. Power Output, I measured the DiaLogue Seven into 8 Ohms (first graph) and 4 Ohms, using the respective speaker taps on the rear panel. The yellow line is triode mode, and the red line is ultra-linear mode. Notice that the graphs are almost identical, which is what is supposed to happen when you match the binding post tap to the impedance of the speaker. Remember, however, that speakers are rated "nominally", which means that the impedance varies with the frequency, so you might want to experiment using the different speaker taps with your speakers.



The measured frequency response between 20 Hz and 20 kHz, shown below for triode mode (yellow line) and ultra-linear mode (red line), indicates a 4 dB rolloff below 50 Hz for both modes, and a slight rolloff above 5 kHz for the triode mode. The response at 100 kHz is down 3 dB for triode mode and 1 dB for ultra-linear mode. Note that there is a rise in response for the ultra-linear mode between 20 kHz and 70 kHz, and then it declines, to peak sharply at 160 kHz. There is also a peak with the triode mode, but it is much less pronounced.