7
Amplifiers & Preamplifiers
INSTALLATION (cont'd)
CONNECTING THE PA640
I When making connections to the PA640 be sure the power cord is unplugged. Proceed as follows:
Stereo Mode Connections
1. Using good quality RCA type patch cables, connect the L
and R OUTPUT jacks of the driving preamp to the CH1,
CH2, etc. LINE INPUTS jacks on the PA640. Do this for
each amplifier pair. Refer to Fig. 6.
2. Slide the BRIDGED/STEREO switch to the STEREO
position.
3. Using good quality speaker wire, connect the individual
speaker leads to the 4-terminal "SPEAKERS" connectors
on the PA640 as shown.
4. Even though the PA640 is 2-Ohm safe in Stereo Mode,
make sure the impedance presented to the speaker
terminals by the speakers (or any combination of speak-
ers) is 4-Ohms minimum.
5. Be sure to observe correct polarity by connecting the "+"
and "–" terminal from each channel on the PA640 to the
corresponding "+" and "–" terminals on each speaker.
This will ensure correct "phasing". See Fig. 6 and Speaker
Phasing below.
Since the connectors are removable, you may unplug
them for ease of lead assembly.
6. As a rule of thumb, use 18 gauge speaker wire for speaker
runs up to 30', 16 gauge up to 70', and 14 gauge up to 150'.
The 4-terminal connectors accept wire sizes up to 12
gauge max.
7. Strip the insulation back about 1/4" and twist the strands
on each lead to prevent fraying.
CAUTION: After lead ends are inserted and the screws
tightened down, be sure there are no free strands that
could cause shorting!
Speaker Phasing
To obtain stable imaging and full bass response, it is imperative
that stereo speakers be connected "in phase" with each other.
You can verify this as follows:
1. If the "+" (positive) and "–" (negative) terminals on your
speakers are correctly marked, and visible, and you have
wired the system as shown in Figs. 6 and 7, then the
system will be "in phase". No further action is required.
Most manufacturer's identify the positive terminal with a
red binding post, a "+" sign, or a red dot.
2. If you are unsure of the markings, you can verify the
phasing. Using a mono sound source, such as AM radio,
alternately reverse the leads to one of the speakers. Pick
the connection that delivers a solid center image between
the speakers along with best bass response.
Fig. 6 STEREO Mode Connections
C H 1 C H 2
BRIDGED
STEREO
LEVEL
LINE INPUTS
VIDEO
AUDIO
L
R
1
RCA Type
Patch Cords
Preamp Outputs
ZPR68, etc.
PA640 Input Panel
PA640 Speakers & AC Panel
+ – – +
C H 2 C H 1
PROTECTION
S P E A K E R S
+ –
B R I D G E D
–
+
Be sure speakers are
connected with correct
polarity as shown.
Wall speakers,
shelf speakers, etc.
Left
Right
Set
BRIDGED/STEREO
Switch to
STEREO position
1V
.2V
3V
–
+
PA640
