Van Alstine rev 2 ABX Switch Manual - page 2
Up to three sets of speakers connect to the left most 6 dual banana jacks. Right and left C speaker, right
and left B speaker, and right and left A speaker. Black is common ground throughout the ABX switch.
Up to two power amp outputs connect to the right most 4 dual banana jacks. Right and left B amp and right
and left A amp. Extreme care should be used to ensure correct cable polarity, as a dual banana plug
flipped around between the ABX switch and the amplifier output will connect ground to the positive
amp output which could result in catastrophic amplifier damage.
Subwoofer support is available in the form of left and right line level output to a subwoofer “plate” amp
through 2 RCA connectors. Usually, the subwoofer volume tracks the regular volume setting, but it can be
set differently if desired.
Up to two line level sources connect to the left most 4 RCA connectors on the right side of the ABX Switch.
Right and left B source in and right and left A source input.
Up to two line level outputs to power amps connect to the right most 4 RCA connectors on the right side of
the ABX Switch. Right and left B output to amp and right and left A output to amp.
Left and right volume is shown on the display located on the left side of the front of the unit. Volume can
be set from “99” (maximum volume) down to “00” (minimum volume). For the most part, the display
increments are 0.1 db. So a volume of “92” would be .1 db less than “93”. This small difference is
inaudible to humans but can easily be measured on test equipment. The ABX switch has no gain and can
only attenuate the line level input signal from the source. It is important to keep the ABX switch volume set
to a high number. Internally there is a limit to allowable signal swing. This limit can be exceeded if the
ABX volume setting is set low and the source is “cranked up” to get reasonable listening levels out of the
ABX switch. When this permissible signal swing is exceeded, the signal is clipped and a large amount of
distortion is generated. The insertion loss of the switch, set to maximum volume, is about 1 db. Therefore
from volume “99” down to volume “10” represents an attenuation of about 1 db to 9.9 db in 89 steps. From
volume setting “09” down to “00” the full range of the attenuation circuit is used which translates into about
3 to 4 db per step. Volume “09” is about 13 db down, volume 08 is about 16 db down. This continues
down to volume “01” which is 42 db down , and finally “00” is 63 db down. Volume settings of “09” to
“00” should never be used unless necessary to get equal volumes on the A and B sides when the “quiet” side
has the volume set to maximum. The only reason to need a volume setting of “09” to “00” is if testing an
extremely “hot” source against an extremely “quiet” source, or an extremely efficient speaker against an
extremely inefficient speaker.
Green LED’s are used for A source, A amp, and A speaker. Blue LED’s are used for B source, B amp, and
B speaker. A red LED is used for C speaker.