Audioplex QUADTROL Installation Manual - Page 2
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Print PageThe first 8 attenuation steps of this control are 3 dB each. For each 3 dB of attenuation, the
impedance of the load (speaker) on the control is doubled as reflected to the driving amplifier. Thus if an
8 Ohm speaker is connected to the control output and the control is moved one position CCW from its
maximum output setting, the attenuation will be 3 dB (X2), and the 8 Ohm speaker will appear to the
amplifier as a 16 Ohm load.
If the speaker was 4 Ohm in the example above, it would appear as 8 Ohms to the amplifier. It is
apparent that if the amplifier were limited to a minimum of 4 Ohms load, TWO 4 Ohms speaker/control
pairs could be operated simultaneously if the OPTIMATCH (TM) controls were operated at the -3 dB
position as a maximum setting. With 8 Ohm speakers, 4 pairs could be operated simultaneously, or 8
pairs of 16 Ohm speakers could be used in the same circumstance. The control can be operated safely
through 11 of its full range of 12 positions with a remaining attenuation range of 31 dB.
Operating the control CCW one more position to -6 dB doubles the impedance once again from the
previous position above, so that the speaker impedance is now multiplied by 4 (X4). Thus if the control is
limited to a setting of 2 positions less than the maximum, a 4 Ohm speaker would appear as a 16 Ohm
load, and 8 Ohm one as 32 Ohms, or a 16 Ohm one as 64 Ohms. This would allow simultaneous safe
operation of up to 4 pairs of 4 Ohm, 8 pairs of 8 Ohm, or 16 pairs of 16 Ohm speakers. The control will
still have 10 positions remaining, with a 28 dB attenuation range.
The above progression repeats for each additional switch position CCW. At 3 positions down (-9 dB)
the impedance is doubled again, multiplying the load impedance (Z) by 8 (X8) with a remaining control
range of 25 dB in 9 steps. The next position would be -12 dB, doubling the load impedance again so that
it will be multiplied by 16 (X16), leaving a control range of 22 dB in 8 steps. This progression can be
continued, although the need to do so is highly unlikely.
The above characteristics can be achieved in a foolproof manner by use of the simple adjustable stop
mechanism furnished with the control. If impedance matching is not a consideration and the full range of
the control is desired, the mechanism need not be used. However if matching is a requirement,
adjustment is accomplished easily observing the following instructions.
The mechanical stop provides an additional function, it may be used to set a maximum volume limit in
a room or location were low level sound is desired to protect either the ears or the speakers. If this is
done, be sure to set the stop at a point where the maximum setting is lower than that required for a safe
impedance match.
Wiring the system is done identically to the manner of hooking up standard attenuators. The controls
are installed ONE PER SPEAKER PAIR and in parallel. Wiring may be such that one wire pair from the
amplifier feeds the system with each control connected across like lamp sockets in a 120 volt AC house
wiring system. Another common approach is the "home run", where the wires from each control are
individually brought to the amplifier, or a junction box (such as the MJ-1 Terminator ) and then to the
amplifier. Either method works well, although line losses may be slightly less with the "home run"
system. DO NOT CONNECT CONTROLS IN SERIES! They will not operate properly.
HOW IT WORKS:
INSTALLATION: