SWR Sound 750x - Manual (Page 19)

RACK MOUNTING INSTRUCTIONS
To preser ve the beauty and reliability of your amplifier, we recommend that you install your amplifier in a
rack case. The 750x is completely ready to be rack mounted and needs no additional par ts or accessories
other than the rack screws and the case itself.
The 750x takes up three full rack spaces. If the rack in which you mount your 750x requires that the rubber
feet on the bottom of the chassis be removed, please remember to keep the screws handy in case you
wish to reattach the rubber feet at a later date.
The 750x should be mounted as close to the bottom of the rack case as possible. If you must mount the
750x in an area of the rack other than the bottom space, a piece of wood or similar solid material should
be installed between the bottom of the rack case and the bottom of the amplifier to prevent flexing of the
amplifier’s chassis. Severe or constant flexing of the chassis can damage the amplifier and is not covered
under the warranty.
Please do not neglect your amp after it has been installed in a rack case. Continuous transpor tation and
vibration can cause screws to become loose, both on the 750x and with your rack case rails. We recom-
mend that at least once a month you remove the 750x from the case and tighten all outside screws and
wipe off the outside of the chassis with a damp cloth. Then check all the connections in your rack case and
reinstall the unit.
A FEW WORDS CONCERNING HEAT
One of the most asked questions about our amplifiers is why they tend to get warmer than other amps. The
chassis of your amplifier can get quite warm during normal usage. This is especially true if you are operat-
ing your 750x at the minimum 2.6 ohm total impedance. This is because these low impedances are intro-
ducing the least efficient condition of the unit (in terms of power drawn from the outlet in relation to power
produced in the speakers). The difference in these two figures can be as high as 300 watts. This would be
the equivalent of putting a 300-watt light bulb inside a metal box, which would obviously get quite hot.
Most musical instrument amplifiers on the market today use steel for their chassis, which does not conduct
heat as well as aluminum. The 750x uses an all aluminum chassis and front panel because it has less
impurities than steel, is less susceptible to rust, and is a better conductor of heat. This results in the chas-
sis acting as an additional heatsink, drawing heat away from heat-producing components inside and thus
extending their life. In this manner, we feel we have produced a more reliable amplifier, but at the same
time, the outside of the 750x will get warmer than cases made out of steel.
The one condition you should be aware of is if one or more of the power amplifiers in your unit becomes
“over-biased.” This condition can be recognized by turning your amplifier on and letting it sit “idle” (without
speakers plugged in and without playing it). If your unit star ts getting hot under these conditions, it may be
over-biased. This situation should be attended to and can be easily remedied in about 15 minutes by a
qualified ser vice technician. A power amp can become over-biased through continuous vibration or by any
large jolt received in shipping, etc.
FINAL ENGINEERING SUMMARY
The two preamp gain stages utilize a specially-selected 12AX7A. The tone controls incorporate I.C.’s, and
the power amp is designed with extremely high quality bi-polar devices. Each type of device was chosen for
its per formance and reliability in the application used. The front panel and chassis of the 750x are com-
prised of aluminum, because of its superior electrical and thermal characteristics and light weight. All prima-
ry electrical components are U.L. approved, and SWR uses Beldon Cable for all shielded wire. All units are
assembled by hand and individually soundtested in the USA at our factor y in Southern California.
750x OWNER’S MANUAL • 17