Acoustic Image Contra R 411 BA Manuel du propriétaire - Page 3

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Operation

Power

CAUTION: TO REDUCE THE

AC Input

RISK OF ELECTRIC SHOCK

DO NOT REMOVE COVER.

115/230 VAC

NO USER SERVICABLE PARTS

INSIDE. REFER SERVICING

50/60 Hz

TO QUALIFIED PERSONNEL

250 Watts

CAUTION: TO REDUCE

RISK OF FIRE, REPLACE

FUSE WITH SAME TYPE

3A-250V SLO BLO FUSE

Power Switch

Contra/Coda Rear Panel (the New Yorker rear panel is similar).

Plug the detachable AC power cord into the receptacle on the back of the amp

and into a wall receptacle. A power switch next to the AC connector turns

on power to the pre- and power amps, illuminating a "power on" indicator on

the front panel of the amp. A 3-amp slo-blo fuse is mounted on the back panel.

To replace this, remove the AC cord and twist out the fuse holder. A spare

fuse is included with this manual.

AIl combos will work with either 115 volt, 60 Hz AC or 230 volt, 50 Hz AC power.

A switch located on the rear panel selects the appropriate voltage. Note that

the correct AC power cord must be used for connection to the appropriate wall

plug. If you do not have the right cord, you can buy one from an electronics

or computer store. Be sure the switch is in the correct position for the intended

application. Operation at 230 volts with the switch in the 115 volt

position will damage the unit.

Preamp

Refer to the signal flow diagram (shown for the Coda R--the other models have

the same signal flow for the features equipped) and the control panel drawings

for more information.

Inputs

The Contra, Coda and New Yorker all have an instrument channel with high

(10 megohm) and low impedance (1 megohm) inputs, accessible using

standard 1/4-inch plugs. The option is given in order to get the best sound from

piezo pickups. Both inputs have the same gain through the amp. Which

impedance is most appropriate for your particular instrument depends on

pickup design. To decide, listen to the bass/treble balance as you change

inputs. Typically, terminating in the higher impedance will raise the relative level

of the bass frequencies. Magnetic pickups normally sound best with the low

impedance input. Don't be afraid to experiment to find the best sound

for your ears. There are no set rules as to which input is best to use.

If your preamp has two channels, the microphone channel is accessed using

a standard XLR connector. Phantom power is available through the connector

for powering a mic or outboard preamp and can be activated using the push

button switch located next to the connector. To avoid an audible "pop", set

the mic input level control all the way off when switching on the phantom

power.

Fuse

Voltage Switch

Speaker Output 2 min

115/230 V

The two instrument inputs are separately buffered. This allows you to plug two

instruments into your amp and play them separately or together. This feature

is useful when you are doubling on two instruments with different impedance

requirements (for example, electric and acoustic guitar or bass). Plug the

acoustic into the high Z input and the electric in to the low Z input. You can then

play each instrument as needed without having to plug and unplug instruments.

With the Coda models, the mic and instrument channels can be blended to mix

a mic and pickup for best sound from one instrument or to mix vocals with an

instrument. An adaptor can be used to convert the XLR input to a 1/4 inch input

if a second instrument channel is desired. However, when using an adaptor,

the resulting input impedance is fairly low which limits the use of the channel

to magnetic pickups. Using a piezo pickup with such a low impedance will likely

result in poor sound quality.

Controls

The preamp has the following controls in each channel: input level, bass, mid,

treble, brite and effects level. In addition,there is a variable frequency,

selectable notch/high pass filter and a master level control. Note that the New

Yorker does not have the effects level control or the filter capability.

Level

The input level controls the level of the signal at the input stage of the preamp.

The master volume controls the level of the signal at the output of the preamp

(at the input of the power amp). Set the master control at "12 o'clock" and the

input level at zero. The input level should then be used to control the overall

output of the unit.

The maximum volume at which the system will play is limited by the capability

of the speaker system. A 10-inch driver in a small cabinet has a limitation in

how loudly it will play. If more volume is needed, use a Contra EX extension

cabinet or take a feed from the Direct Out jack to a PA system or another

amplifier.

Tone

Each tone control has a center detent at the flat position. Experiment with

settings to achieve the frequency balance that sounds best to you. In general,

small values of boost and cut are best. The amp is designed with flat frequency

response so only minor corrections should be required to compensate for room

effects or "peaky" pickups in order to maintain the balanced response desired

for acoustic instrument amplification. To minimize electronic noise, avoid

operating all controls simultaneously at their maximum settings.

The bass control is a shelving-type that affects frequencies below 250 Hz and

with a maximum boost/cut of 15 dB. The mid control affects frequencies

between 300 Hz and 2000 Hz and has a maximum boost/cut of 15 dB. The

treble control is also a shelving-type that affects frequencies above 1000 Hz