Tu start, one? must establish whether the
power ampliliers involved are inverting or non-
inverting, that is, do they leave a sine wave un
changed except lor amplitude or do they invert
it (turn it 180° out of phase). If you are using two
identical ampliliers in your system to power the
upper and lower sections of the Type A's, it is
likely that they are both either inverting or non-
inverting. Some amplifier manufacturers have
introduced changes in their amplifier’s circuitry
that reverse this, however, so that Iwo seemingly
Identical amplifiers built at different times may
differ. The amplifiers can be tcsled as below or
the manufacturer can be contacted with serial
numbers. Incidentally, there is no advantage
attached to an amplifier being of an inverting ur
non-inverting nature, but d the two amplifiers
used in bl-arnplng differ in this regard, the upper
and lower sections of the Type A 'will be out of
phase. The speaker wiring rnusl then be changed
lo correct the phase, as will be discussed below.
The easiest way to ascertain whether both
amplifiers fall into the same category is to hook
one channel of one amplifier to the left loud
speaker and a channel of the second amplifier
lo the right loudspeaker (normal set-up. except
for amplifiers). Place the speakers side by side,
switch the preamp lo monaural, and adjust the
preamp balance control until the two speakers
are of roughly equal loudness. While listening lo
music with substantial bass information, reverse
the speaker leads at the input ol one loud
speaker. The apparent bass output ot the pair of
loudspeakers will either inciease or decrease.
The speakers will be "seeing" the same signal
when the bass is loudest II this occurs with (lie
leads unreversed, the amplifiers are alike with
respect to inversion of the signal If the bass is
loudest wilh the leads reversed, llte amplifiers
are different. I'his information will be used in the
next stage of the sel-up.
We are now ready lo connect the two power
amplifiers to the loudspeakers as shown in figure
5. If you are converting from a single amplifier
set-up. disconnect the jumper cables that nor
malty interconnect the upper and lower sections.
Next, transfer the shorting plug on the lower
sections from the “Short for normal mode" jack
to Ihe “Short for biamp mode" jack. Add a short
ing plug lo I he “hiamp mode" jack on the upper
sections.* If you do not have an additional short
ing plug, one can be readily assembled from a
standard double banana plug and a short length
of heavy wire. Finally, connect Iho outputs ol the
high frequency amplifier to the jacks marked
“input 4 ohms" on the upper sections, and the
outputs of the low frequency amplifier to the
jacks marked "woofei input" un Ihn lower sec
tions. using speaker cables ol good quality. If
the inverting test showed the amps to he dis
similar, reverse the hoi and ground connections
at the input of both upper sections.
We now proceed to Ihe liuok up of the elec
tronic crossover (figure 4). The main outputs of
the preamplifier should be fed to Ihe inputs of
the electronic crossover. The high frequency
outputs ol the crossover should be connected lo
Ihe respective channels ol Ihe high frequency
power amplifier and the low frequency outputs
should be connected to the respective channels
ol the low frequency power amplifier.
At this point we must make level adjust
ments on the crossover lo compensate lor Ihe
differences in gain between different power
amplifiers. One power amplifier may multiply the
signal fed to it from the crossover by a factor of
30. another by a factor of 40. This is unrelated to
the rated power ol the amplifier, which is Hie
maximum amount ol power Ural Ihe amplifier is
capable of producing. An amplifier with higher
gain would send a louder signal to the section
of the Type A tfiat it powers than an amplifier
with lower gain; thus using amplifiers with dif
ferent gains in a bi-amp setup would result in an
imbalance between upper and lower sections of
the Type A's. This is corrected by adjusting the
high and low frequency level controls on the
electronic crossover. Those level controls rnusl
be set very precisely, following Ihe procedure
outlined below, using a signal generator and
VOM of high quality. Refer to Figuie 6.
Connect Ihe signal generator lo an auxiliary
input of Ihe preamplifier, pul tire preamp into
monaural mode, and set Ihe tone controls to flat.
Turn all the level controls on the electronic
crossover lo their maximum positions, but leave
(tie preamplifier volume control fully down.
Select a 4000 Hz tone on the signal generator
and conned Ihe probes ol the VOM to the left
channel high frequency power ampliliei output
terminals. Slowly turn up the preamplifier volume
control {and the signal generator volume control
if necessary) until the VOM reads exactly 1.5
volts. Now connect the VOM probes to the tell
channel output terminals of the low frequency
power amplifier and select a 40 Hz lone on the
signal generator. If the VOM reads greater than
1.5 volts, reduce the left low frequency level
control on the crossover to give a 1.5 volt read
ing. being careful not to change the* position of
lire preamplifier or signal generator volume con
trols. If the 40 Hz VOM reading was Initially less
Ilian 1.5 volts the preamp volume control must
be increased until 1.5 volts is reached. This will
ol course increase the high frequency output as
well, so you must once again select 4000 Hz arid
reduce Ihe high frequency level on the crossover
until the high frequency power amplifier VOM
reading is back down lo 1.5 volts. Once again
take a low frequency power amplifier reading at
40 Hz and a high frequency power amplifier read
ing at 4000 Hz lo double check that both read
1.5 volts un Iho VOM Finally, repeal Ihe onlim
procedure for the right channel.
’WARNING: Never connect Hit* shorliny plug lo Ihr? upper
section "bianip mode" lack unless using an clechomn ciosr,
over which has Ihe correct crossover spocHiealions and is
approved by Snell Acoustics. Damage rosulling Irani Ihe
above conslilnles misuse mid may void ihe vmrumly
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