Acoustic Energy Stereo Amplifier Contra Control Panel, Signal Flow Diagram, Preamp, Controls

Controls

Preamp

The preamp has the following controls in each channel: input level, bass, mid, treble and effects level. In addition,there is a variable frequency, selectable notch/low cut filter in each channel and a master level control that affects both channels.

Level

Phantom power

Ch 2 input, EQ and filter (same as Ch 1 below)

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 two controls are provided to allow independent control of “house” volume and “stage” volume when the unit is used as a stage monitor with a connection to a house PA. See the discussion under “Direct Out” below.

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

XLR

input

¼ inch

inputInput buffers

Combo jack

Input level

3 band EQ	Filt
	Notch Cut
	N/C Switc
Bass Mid Treble	Filter
Pre EQ	switch
outputs

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 with a maximum boost/cut of 25 dB.

Notch/Low Cut Filter

The notch/low cut filter is a fixed amplitude, variable frequency type that inserts either an 18 dB cut or a 12 dB per octave rolloff at frequencies between 30 and 800 Hz, depending on the position of the control. Approximate frequency settings are noted on the frequency control. Note that the first half of the control’s rotation affects frequencies from 30 to 70 Hz, the last half of the rotation affects frequencies between 70 and 800 Hz. This is done so that there is plenty of control in the critical low frequency range. The notch filter is used to

3

Signal Flow Diagram

Power

Phantom				Effects	Send	Notch Cut	Filter	Post	Mute
				Loop			70	EQ
									Off On
						30	800
Level	Bass	Mid	Treble	Level			Freq	Master
Input					Return	Off On			Ground
									lift	Direct Out

Contra Control Panel

4