Crate Amplifiers Rear Panel, To Eliminate Instrument Feedback, CA125 Block Diagram, Not Shown

On the

Rear Panel:

34			33	32	31	30	29	28	27
Tweeter				Line Outputs			Effects		Foot
							Loop		Switch
-6dB
-50dB	0dB	0	10
Level		Level		Gnd	Low Z	High Z	Return	Send	Reverb/
				Lift	Bal.	Bal.			Chorus

27:Footswitch. Connect the supplied two-button footswitch here for remote on/off control of the internal reverb and chorus. (When connect- ed, the footswitch overrides the front panel chorus on/off switch.)

Note: This is a STEREO jack: tip controls the chorus, ring controls the reverb, sleeve is ground. Use only a footswitch equipped with a stereo 1/4” plug.

28:Effects Loop Send. When using an external signal processor, connect this jack to the input of the effect by means of a shielded signal cable.

29:Effects Loop Return. When using an external signal processor, connect this jack to the output of the effect by means of a shielded signal cable.

30:High Z Bal. Use this jack to connect a high impedance, line level signal to a house sound board, a recording console or an external power ampli- fier by means of an 1/4” stereo plug-terminated cable. (Ring is signal +, tip is signal -, and sleeve is ground.)

31:Low Z Bal. Use this jack to connect a low impedance, line level signal to a house sound board, a recording console or an external power amplifi- er by means of an XLR-terminated cable. (Pin 1 is ground, pin 2 is signal +, and pin 3 is signal -.)

32:Ground Lift. This switch, when depressed, electronically disconnects the low Z balanced output jack’s chassis ground connection. If you expe- rience excessive noise when using the low Z balanced output jack, depress this switch.

33:Line Out Level. Use this control to adjust the output level of the line out signal. (This control works independently from the amplifier’s master level control.)

34:Tweeter Level. Use this control to adust the signal output level from the CA125’s internal tweeter. Rotating this control counter-clockwise reduces the tweeter’s output level.

Not Shown:

Power cord. Connect the end of this cord to a suitable source of line volt- age. Refer to the voltage information on the back of the amplifier for its voltage and current requirements.

Note: This is a grounded plug. To avoid the possibility of electric shock,

DO NOT defeat the ground connection in any way!

To Eliminate Instrument Feedback:

One of the most common problems encountered when amplifying acoustic instruments, especially in small environments, is feedback. Acoustic instruments typically have inherent qualities which cause res- onant feedback at specific frequencies. Instrument tone controls and sound board equalizers are helpful in getting rid of the problem, but they typically operate around relatively wide frequency bands. This almost always means the musician must sacrifice sound quality in his quest to do away with feedback. But since Crate’s feedback elimination circuit isolates only the offending frequency, instrument feedback from the CA125 can be eliminated without affecting the overall sound.

Chances are, you may not have a problem with feedback at all. In that case, leave the CA125’s Freq and Cut controls fully counter-clock- wise. However, if you do encounter feedback while playing, set the Cut control to -30dB (fully clockwise) and adjust the Freq control until the feedback is gone. Reduce the Cut to the 12 o’clock position and readjust the Freq control as needed. Continue reducing the Cut control and read- justing the Freq control until there is no more feedback with the Cut con- trol as far counter-clockwise as possible. This approach effectively elimi- nates instrument feedback without sacrificing the quality of your sound.

CA125 Block Diagram:							master
instrument
channel							effects	line out
input		filter				tones		chorus
							rev/
							effect
active	piezo						send			on
		freq	cut	gain	low	mid	cntr high	depth	rate
							peak
		phantom
vocal/aux		power					rev/
channel							effect	line out		hi-z
low-z							send
										bal.
input
			gain	effect				level
hi-z
input				return					gnd
						effect			lift
						return
aux channel							rev/
							effect
hi-z							send
input

effects send

off

low-z bal.

graphic EQ

master 80 330 1k 4k 10k

levelHz

foot

switch

spring reverb	reverb
	return

high pass	25w	hi-freq
		driver
	level
low pass		low-freq
	50w	driver
	50w	low-freq
		driver

gain