Mackie M1200/M1400 owner manual Meters, You may wonder why we didn’t use just one stereo

So what are the pros and cons of these two approaches? The reason some amplifier manufacturers use the constant gain ap- proach is because the noise specification looks better. It’s a fact of physics that as the gain of the amplifier increases, the circuit noise is amplified and increases too. By main- taining a constant gain, the noise spec for an 800W amplifier can look as good as the noise spec for a 100W amplifier. The downside to this is that you have to crank up your mixer level feeding the input of the amplifier, losing headroom and possibly increasing the noise level from the mixer (unless you have a Mackie mixer with low-noise VLZ circuitry!).

Conversely, constant sensitivity demands that as the power increases, so must the gain. Yes, the output noise of the amplifier will increase, but you maintain the critical head- room available from your mixer. The addition- al noise is generally not a problem in live sound reinforcement situations. If it is, you can turn down the GAIN control a few clicks to find a happy compromise between noise floor and headroom available (see “Optimiz- ing Sound System Levels” in Appendix D). As an added benefit, you can drive multiple amplifiers with the same signal and get the maximum power available from all of them.

Mackie subscribes to the philosophy of constant sensitivity. Our amplifiers can be driven to full power with an input level of +4 dBu (1.23V rms).

tion or sound check, then leave them alone, using your signal source (usually a mixer) to control listening levels as you work. Or play.

You may wonder why we

didn’t use just one stereo

control to control both sides.

That’s in case your applica- tion requires a left/right

imbalance (due to an irregularly shaped room) or if you’re using the two sides for completely different purposes (monitor in channel 1 and side-fill in channel 2, for instance). Besides, they look cool.

METERS

The M•1200/M•1400’s meters indicate the relative output level of the amplifier refer- enced to full power. The numbers next to the meter’s LEDs are in dB below full power.

Ideally, the M•1200/M•1400’s –20, –9, –6, and –3LEDs will flicker at normal signal levels, while the OL LED may flicker occasion- ally during peak moments.

OL is short for Overload. Overloading, or clipping, occurs when the output voltage no longer linearly follows the input voltage and simply stops. This causes a sine wave to “square off,” or get “clipped off.” Thus, the term clipping. Fear not — this scenario is quite un- likely. Even with the GAIN controls fully up, the M•1200/M•1400 amplifiers easily accept professional “+4 dBu” operating levels.

				FULL SYMMETRY DUAL DIFFERENTIAL						HIGH CURRENT DESIGN
CH	GAIN/dB						GAIN/dB			CH	CH	CH
1		3v		OL		OL		3v		2	1	2
	18	20	22	–3		–3	18	20	22		INTERNAL STATUS
			2v						2v
16			24	–6		–6	16		24			PROTECT
14			26	–9		–9	14		26			SHORT
8			28	–20		–20	8		28		TEMP STATUS
			30						30			CH
	00						00					1& 2
			1v						1v
											COLD	HOT
SENSITIVITY			1.23v (+4dBu)				SENSITIVITY		1.23v (+4dBu)
				SIG	SIG

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