Fender Series 3000 Owners Manual - Page 16

Understanding Block Diagrams The schematic diagram of your Fender 3000 Mixer shows every integrated circuit, every resistor, every connection. This kind of detail is useful to a repair technician, but it can actually get in the way of an understanding of the operation of the Mixer from the user's point of view. A block diagram removes all the un-necessary detail from the schematic and leaves only that necessary to understand the way the Mixer operates. In a very real way, your Fender 3000 Mixer is an entire sound system made up of pre-amplifiers, line-level amplifiers, equalizers, power amplifiers and even a reverberation unit! Thus, the block diagram of your Mixer looks a lot like the block diagrams of the example systems in the back of this manual. Each section of the Mixer block diagram represents some important function. For example, the triangles represent amplifiers: pre-amplifiers, line amplifiers and power amplifiers. The rectangles represent the graphic equalizers and the reverberation unit. The jagged lines with an arrow through them are controls: pan controls, tone controls and so on. A small vertical rectangle with an arrow through it is a fader. The lines connecting all of these devices represent real wires (or traces on a printed circuit board) inside the Mixer and the vertical lines near the center of the block diagram represent the mix buses (you can always tell a mix bus because it has a large number of inputs connected to it). Additional symbols represent your Mixer's switches, LEDs, VU Meters and input and output jacks. Let's follow a signal through the block diagram. Start at the Lo-Z input. Notice that, even though your Mixer has at least six inputs, only one is shown. This simplifies the block diagram considerably but doesn't reduce its usefulness at all (all the inputs are the same anyway). Just past the Lo-Z input jack, you see a vertical line indicating the presence of phantom power on that jack. Then the signal flows through a preamplifier stage. In this preamplifier stage is the Trim control and you can now see how one Trim control can work for either the Lo-Z or Hi-Z inputs (they share a preamplifier stage). The Signal LED is also located at this preamplifier stage so that it can detect signal at either the Lo-Z or Hi-Z input jacks. From this preamplifier stage, the signal flows through the Insertion switch and, depending on the position of that switch, the signal then flows through the Input Channel Equalization Controls and then out to the Insertion jack (the "post" position of the Insertion switch) or through the Insertion jack and then through the Equalization Controls (the "pre" position of the Insertion switch). If an external device is connected to the Insertion jack, the signal will flow through it regardless of the position of the Insertion switch. Notice also that the Signal and Peak LEDs are located at the output of the Equalization Control section before the Input Channel fader which means that they are not affected by the fader. Now, the signal flows through the fader, through a "buffer amplifier" stage (not on 3106) used to isolate the fader from the Pan and Effect controls and through the Pan control to the Program Left and Right mix buses. The signal splits just before the fader to feed the Monitor 1 and Monitor 2 controls which feed the Monitor 1 and Monitor 2 mix buses. Since the signal feeds the Monitor controls before it passes through the Input Channel fader, the Monitor controls are "prefader," that is, they are not affected by the fader. The Effect control, on the other hand, comes after the fader and is therefore "post-fader" (it is affected by the position of the fader). The Monitor controls can be changed to "post-fader" by changing the location of a jumper on the printed circuit board (this modification must be performed by a qualified service technician). After the Program mix buses, the signal flows through a "summing amplifier." This summing amplifier performs the duty of mixing together the signals from all the Input Channels while keeping them from affecting each other. The Direct In jack is also connected to the input of this summing amplifier stage. Next, the signal flows through the Line Out G-EQ In jacks (and through any device connected between these jacks) and into the Graphic Equalizer. After the Graphic Equalizer, the signal flows through the Program fader which could be called the "master" fader for the entire mixer. _ After the Program fader, the signal flows through another buffer amplifier and through the Pre Amp Out Power Amp In jacks (and through any external device connected to these jacks) to a "line amplifier" (a preamplifier for the Power Amplifier) and on to the Power Amplifier. Notice that the VU Meter is connected to the Pre Amp Out jack and reads the level at this point. The Clip LED, on the other hand, reads the level at the output of the Power Amplifier. On the line amplifier is a switch labeled "AGC." This is the Automatic Gain Control circuit switch which can help you avoid clipping. After following the signal flow through the Mixer, you can see how valuable the block diagram can be. As you read the rest of this manual, we suggest that you study the various sections of the block diagram. Experienced mixer operators often keep a copy of the block diagram close at hand at all times to remind them of the way the various parts of the mixer operate and interact with each other. 14