MAKE FRIENDS WITH YOUR AMP - Gollihur Music

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P age | 4 Now we move on to advanced features that you’ll find on many amplifiers and preamps and how they can further help your sound… Let’s cover the tools (and concepts) for managing preamp gain, as well as some of the features which can have an effect on preamp gain, like compression and alternate inputs. PREAMP (INPUT GAIN) AND MASTER VOLUME CONTROLS These are two different controls entirely, and how you use them can have a big effect on your sound. This brings us to the important topic of… “Gain Staging” Instrument amplifiers have separate preamplifier and power amplifier circuits, and most have a volume (gain) knob to adjust the levels of each. The way these knobs are adjusted can help — or hurt — your sound. What the preamplifier and power amplifier do is pretty simple; they each multiply the bass signal. 1. The Preamplifier takes the relatively low level signal of your instrument and pre-amplifies (multiplies) to a medium signal level that is at a high enough level to feed the power amp efficiently. 2. The Amplifier then takes that stronger signal and multiplies it to an even higher level to power your speaker. Generally speaking, if your instrument and/or preamp signals (volumes) are too low and your Master (power amplifier) level is too high, you’re likely to have extra noise (usually “hiss” or “static.”) This is because the percentage of good bass signal is low, so the preamp increases general background noise in the signal along with the bass. On the other hand, if your instrument level and/or preamp signal (volumes) are too high, they can cause distortion, and other ugly sounds, as they overwhelm the input capacity of the power amp. Make Friends With Your Amp – by Bob Gollihur Courtesy of Gollihur Music • www.GollihurMusic.com • ALL MATERIAL ©COPYRIGHT 2012 BOB GOLLIHUR
P age | 5 The trick to setting these controls properly is to find the “window” where the incoming signal has sufficient level to provide adequate volume without excess noise, but is not so “hot” that it overloads the input and causes distortion. You can draw an analogy to the limits of a person’s jumping height inside a room with a ceiling. Our friend on the left demonstrates the signal levels as you play bass; he’s a six foot tall guy in an eight foot tall room. As you play notes he leaps; the louder you play, the higher he jumps. If you play a note that makes him jump higher than the amplifier’s “ceiling” (maximum level)… well, let’s just say it’s going to get bloody. Some amplifiers provide assistance: Peak, Overload, or similarly labeled lights, or a meter, are designed to tell you when you have reached the preamp’s or amp’s design limit. There is no “standard” (or if there is, nobody abides by it), so experience or experimentation should tell you just how ugly things get if that light flashes too much or stays on. To set my amp’s input gain/volume control, I will play my lowest note at the loudest instrument preamp and/or volume control level (play hard and continually) and adjust all the knobs to a point (all the way up on my bass guitar) and adjust the input gain control on my amp so that little light only flashes a tiny bit. That way you’ll know you shouldn’t distort, but still have a strong signal that will have a full sound. Listen carefully for distortion, because those lights and meters are calibrated differently depending on each amp’s design, so you will know what works best for your particular amplifier. Note: Depending on the amp, turning up any tone controls (bass, in particular) may also increase the effective preamp volume and can put you back into that distortion place, so compensate by reducing the amp’s input volume/gain control if necessary. You can also use this to your benefit: if you are at the limit and still need more volume, roll off some bass and then turn up a little; lower notes take more amplifier power to reproduce than the highs and mids, and while you won’t have quite the “bottom,” it may increase your perceived overall volume. The Straight Dope: if an amp has a power rating of 300 watts, even if you add more preamplification (gain) to try to make it louder — well, that’s like trying to put 400 gallons in a 300 gallon septic tank. The brown seeping over the 300 watt limit represents the brown sound; let’s say it sounds like something brown. The bottom line is that an amplifier cannot get louder than it is designed to get, at least not in a “pretty” way. High/Low and Passive/Active are just two examples of labels you may find next to input jacks. Usually, the two different jacks allow for two different fixed levels of gain (see above) – one for the higher level of output for instruments with active preamplifiers or other electronics, and the other for lower-gain “passive” pickup arrangements. Unfortunately, there are no industry standards, but you’ll find when you plug into one of them your bass will be quieter. That is the jack to use if you use an external preamp, or if one is built into your bass, meaning it is “active.” The other is for basses with passive (no preamp) instruments, so it is “louder”, offering more gain (volume). It is important when considering Gain Staging, above, so that the pre-amped, and therefore usually louder, signal does not overload the preamp inside your amplifier. Some amplifiers have only one input jack but may have a switch or button to decrease the input sensitivity; like with the jacks, your ears should tell you which to use. Drive, if included, is usually a knob alongside the input gain control. The design goal is to add character to the sound, such as a tube saturation or mild to wild intentional overdrive, which can add thickness and/or distortion to your bass sound. Some amps include preamp tubes (aka “valves”) or tube emulators, and in that case a gentle dose of drive can add heft to your notes. “Off” is usually a good position for these controls if you want a pure upright bass tone, but as with these other controls, experimentation is certainly worthwhile. Make Friends With Your Amp – by Bob Gollihur Courtesy of Gollihur Music • www.GollihurMusic.com • ALL MATERIAL ©COPYRIGHT 2012 BOB GOLLIHUR
Page 1 and 2: MAKE FRIENDS WITH YOUR AMP A HANDY
Page 3: P age | 3 TURN THEORY INTO PRACTICE
Page 7 and 8: P age | 7 MOVING ON: OPTIONAL SPECI
Page 9 and 10: P age | 9 Effects Loop This is a fe

MAKE FRIENDS WITH YOUR AMP - Gollihur Music

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