Greg Hanks Design BA-660, Руководство по эксплуатации и обслуживанию

Страница: 15 / 24

BA660.doc 01/01/97 12 of 25
∆
Set the output trim so
that when metering
output, approximately "0"
is obtained
.
•
Power switch
Provides balanced switching
of the incoming power line,
pre-fuse.
Overview of Operation
Setting the input level
The input selector provides gain in 10 dB stepped increments, from -
65 to +14. At the lower extremes, the unit has 2 gain stages and an
input transformer. With higher gains the 2nd gain stage is switched
out. At even higher gains the input transformer is switched out, and at
the highest gains a pad is inserted in the signal path to further lower its
amplitude and along with that the 2nd stage gain is set to unity. In the
lower gain configurations, the equivalent input noise goes up so the
signal to noise ratio suffers. The signal should be close to "0" but with
>30 dB of headroom, this is not really an issue nor is it that important.
Our only real concern is being able to control the gain with the
dynamics that we find audibly pleasant as well as having the output
level be within reason. (It is real easy to start pumping out a nominal
+26 signal level, and not even notice that you're SMOKING the next
piece of gear in line!.
Be careful, for you can develop in
excess of 100 volts peak to peak signal energy
.
Monitoring levels.
The LED's around the threshold knob are two audio meters in one.
The bright dot is indicating "VU" levels with ANSI ballistics. The solid
bar is indicating peak level at 10 dB per division. The input monitor
position of this meter looks at the signal level at the output of the 2nd
stage as it appears at the gain cell input. (This is the same point as the
insert return). The output monitor position is just prior to the mute
relay on the output. "0" indication on the meter is calibrated to +4 dbv
ref. 600
Ω
, or 1.23V. The maximum indicated signal level is +34 dbv,
and the minimum is -56.