Crate Amplifiers CA125D manual To Eliminate Instrument Feedback, The DSP Section

CA125D Acoustic Amplifier

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 reso- nant feedback at specific frequencies. Instrument tone controls and sound board equalizers are helpful in getting rid of the problem, but they typi- cally 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 CA125D 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 CA120D’s Freq and Cut controls fully counter-clockwise. 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 con- trol as needed. Continue reducing the Cut control and readjusting the Freq control until there is no more feedback with the Cut control as far counter-clockwise as possible. This approach effectively eliminates instrument feedback without sacrificing the quality of your sound.

The DSP Section:

The CA125D features Crate’s On-Board Digital Signal Processing (DSP) technology that was designed specifically for use with acoustic instruments and vocals. This provides a large selection of digital reverbs, effects and delays. Select the type of effect desired by rotating the Mode control (#22). This control is divided into five sections: Small Area Reverbs (SAR), Large Area Reverbs (LAR), Special Reverbs (SPR), Delays (DLY) and Multiple Effects (Multi).

The following chart provides a list of the DSP settings along with a brief description of each effect.

SAR:	Small Room	8’ x 8’ empty room w/hardwood floor
	Small Rehearsal Hall	20’ x 40’ hall, wood floors, hard walls
LAR:	Large Hall	50’ x 100’ hall, about 50 persons
	Concert Hall	5000-seat hall, full crowd
SPR:	Plate Reverb	Simulates studio steel plate reverb
	Spring Reverb	Simulates multi-spring reverb tank
DLY:	Slapback, short	125ms delay + reverb
	Slapback, Med-short	240ms delay + reverb
	Slapback, Medium	350ms delay + reverb
	Slapback, Long	557ms delay - 630’ travel time
Multi:	Short Med. Surface	280ms delay w/21.8% regen + reverb
	Medium Hard Surface	335ms delay w/26.5% regen + reverb
	Chor-Delay	400ms delay with modulation
	Chor-Verb	Hall reverb w/modulated pre-delay
	Slap-Verb	Medium hall w/200ms pre-delay
	Instrument Doubler	Simulates second track slightly out-of-sync

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