11
Nagra –
VPA
Selecting the right speaker impedance
The Load Match Meter was specially designed to help you match your
amplifier with your speakers. The Nagra VPA’s output stage features a
custom hand-made Nagra transformer that offers 3 different output
windings for 4, 8 and 16 Ohm speakers.
Start by verifying the nominal impedance of your loudspeakers, either
from their technical specifications or on the rear of the speaker. Then
connect the “+ve” speaker cable to the correct terminal on the VPA.
The modulometer features two pointers, the red pointer indicates the
peak cathode current and the black pointer indicates the peak anode
voltage of the output tube. They will allow you to know if the
impedance match is right.
When playing music (main selector in the
ON
position)
Needle position
What is happening
Solution
Red needle > Green
needle*
Output impedance is
too high
Choose a lower
output (8 or 4 Ohms)
Green needle > Red
needle
Output impedance is
too low
Choose a higher
impedance (8 or 16
Ohms)
Needles follow each
other
The match is perfect
Enjoy your music
* as shown on the picture
NB the two needles will almost never superimposed one above the
other, but should not be too far apart, this is subjective; spend a little
bit of time to know how to “read” the needles.