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The Gollihur Music Blog

Learn How To Play Your Amp!! (Part 3)

In Part 1 of this series we talked about basic amp controls and specific methods for learning their effects. In Part 2, we went over the all important topic of "Gain Staging," and discussed some of the tools relevant to that. This final article, Part 3 covers the additional features that amps and external preamps may have that affect your sound, including parametric EQ's, Notch Filters, and more.

As always, I encourage you to spend time with each one to analyze what they can do for you. The better we learn our amps, the more instinctive it will become to reach for the right knob to tweak when the need arises.

semi-parametric
          equalizer example; Genz Benz 9.2A (Semi-) Parametric Equalizer (EQ) is form of tone control, like the "Bass/Mid/Treble" knobs covered in Part 1, but it can be a much more precise tool than a conventional tone control or even a graphic equalizer. As illustrated in a piano image from part 1 of this series, an amplifier's regular Bass tone control, for example, affects a wide swath of notes, or frequencies. A Semi-Parametric Equalizer adds a knob (or multi-position switch) to choose the center frequency of the group of notes affected. You -- not the amp designers -- decide which notes are boosted or cut, as to better sculpt your tone.

parametric equalizer
          example; DTAR EquinoxA full Parametric Equalizer adds a third knob, which is used to adjust the bandwidth (sometimes called "Q"). This lets you choose how many notes on each side of that center frequency are affected by the control - from a big wide "scoop" to a small slice. As with other tone controls, I'd suggest learning what these do by listening -- but you can always reference actual bass note frequencies at our FAQ on FREQUENCIES: What are the frequencies of bass notes? I love these equalizers for the incredible flexibility they bring. They're great for correcting flaws, such as frequencies that are louder in some performance spaces, as well as more precisely enhancing midrange presence and detail without sounding like you're playing through a telephone.

Visit the Blog Page for the rest of this article!


Learn How To Play Your Amp!! (Part 3, continued)

Notch Filter: A Notch Filter is similar to a Semi-Parametric Equalizer, but it's usually a tool that is mostly used to "cut" the response of a very narrow band, like a single note. While the parametric EQ is designed specifically to alter your tone, the notch filter allows you instead to fix problems without making a dramatic change in your tone. So, if your bass "favors" a particular frequency with extra response, or there is a specific frequency that excites your bass into feedback, you can dial in a reduction on just that frequency (note) to tame its response -- without screwing up the neighboring notes and your overall tone. There are some units that have more than one filter, so if you identify more than one problem frequency, you can address them as well. Most units will also allow you to boost that narrow band to help out with a note or range of notes that are weak. In most cases a Parametric Equalizer can be utilized as a Notch Filter, by simply specifying a very narrow bandwidth of frequency, and cutting it.

High Pass Filter - aka Low (Bass, Sub-Bass) Cut Filter, Subsonic Filter, Depth Control - The counter-intuitively named "High Pass" Filter is so-called because it lets high frequencies pass and, like the black knight, stops undesirables (in this case, boomy and muddy low frequencies) from passing, starting at the frequency where you adjust the knob or slider. This feature is a popular and very useful one, particularly for upright bass players, as it can get rid of low frequency rumble, and surprisingly, even subsonic sounds beneath the range of notes your bass can play. While we know a low E is 41.2Hz and a low B is 30Hz, it's best to set this control by ear, because it isn't a sharp cutoff but gradual reduction at the frequency you select. Using this control properly can reduce "mud" and power-robbing, bass vibrating lows that make your sound flabby... and encourage feedback. That satisfying thickness on stage may mean your audience is just hearing rumble, and while that rich maple syrup tastes good, it's no fun to swim in it. Whether you need to use one -- and where you'd set it -- will depend on your instrument and pickup, as well as the stage and setup (like whether you're stuck in a corner).
Want to know more? Check out our FAQ about High-Pass Filters.

Enhance, Shape, Contour are a sample of labels you'll find on some amp knobs, most of which change the tonal character of your signal by boosting high and low frequencies and cutting midrange. In my experience they seldom help the sound of upright bass -- which in my opinion needs those midrange frequencies to help define its character in a live performance mix -- and they often impart an "electric bass" or otherwise generic tone. Switches or buttons like Deep, Bright, etc. will also apply a specific tone shape, which can sometimes be kind of radical for upright. Learn these tools by setting all of the amp's tone controls at neutral, and try each of them using the techniques discussed in Part 1 of this series.


These last few common amp features are not specifically involved in tone, but it's good to know what they do:

Phase Switch: When a signal is "in phase", a note you play pushes air from your bass into the room, and the vibration of your amp's speaker also pushes air out into the room. A Phase Switch (also called an "Phase Reverse", "Invert Switch," etc.) reverses the signal's phase, so when you play a note the speaker is "sucked in." Reversing phase may or may not result in a big change to your sound. But since it it is opposite from your bass' vibrations, it doesn't make your bass vibrate more, because it more or less pushes air "in" while your bass is pushing out. In practical use, the use of reverse phase may help you gain a little more volume before feedback, but don't expect a miracle. Another use for a phase switch is when one is using two pickups, or a microphone with a pickup. Different devices can be inadvertently wired in or out of phase, and if the phase is not the same it will usually rob you of bass response. Noise-cancelling headphones use this principle by reproducing what they hear (on built-in microphones) in reverse phase, thus cancelling the sound in your headset. If you suspect this condition, switch the phase on one channel and listen to the result. The Euphonic Audio Doubler has a Phase Knob, which changes phase gradually from one extreme to the other, for more precise adjustments.

Effects Loops are a feature for inserting various devices, typically pedals, into your bass signal. They come in two flavors, series and parallel. Series interrupts the entire bass signal and sends it through the device, so none of the original, unaffected bass sound remains. Parallel gives you a signal to affect but places it alongside the original signal. Usually you'll have a control that lets you choose how much of the affected signal to mix in with your original bass sound. If you don't know which you have, plug an unused cable into the Send jack while you're playing; if you can no longer hear your amplified bass from the speaker, it is a series effects loop. Many players choose to put their effects boxes, or sometimes tuners, between the instrument and amplifier input, where it acts as a series loop might. It's best to experiment to see which method works best for your specific purposes.

Direct Out, or DI is usually a XLR jack that is designed for sending your bass signal to a PA system or recording board. There can be various controls and switches associated with this, such as the ability to send the raw, unprocessed signal (often labeled Pre-EQ) or sending it after it is filtered by your tone settings (Post-EQ). If you tend to fiddle with your on-stage tone and volume settings it will be best to send the Pre-EQ signal to the board, because your sound engineer may throw a rock at you because they will have to make adjustments at the board to compensate for your changes. For help with these settings if you are in a performance or recording session requiring the use of the Direct Out jack, talk with the person running the system — always make friends with these people because they can make you sound really good... or really bad.



Learn How To Play Your Amp!! (Part 2)

In Part 1 of this series, we talked about basic amp controls and specific methods for learning their effects. This article, Part 2 (of 3) covers 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 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 preamplifies (multiplies) to a medium signal level that is at a high enough level to feed the power amp.
  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.

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 not so "hot" that it overloads the input and causes distortion. Our friend on the left demonstrates the signal levels as you play bass; he's a 6'4" foot guy in an eight foot room. Just as you play notes, he jumps, but if you play a note that makes him jump higher than the amplifier's ceiling (maximum level)... well, it's 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 experimenting 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,
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.
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 percieved overall volume.

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 your preamped, 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.

(this blog continued on the Gollihur Music Blog page)


Learn How To Play Your Amp!! (Part 2, continued)

(continuation of part 2)

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 worthwhile.

Compression, Limiter: An Upright Bass, when we pluck it enthusiastically, can put out a huge burst of sound. Compressors and Limiters soften and minimize that peak so it doesn't overload the amp and/or annoy your bandmates. A Compressor can usually do it more gracefully than a simple Limiter (depending on its design), but a compressor's primary role is to squeeze the dynamic range of the notes you play, so the quietest are a little louder, and the loudest are a little quieter. You'll notice compression being used when you watch a TV show -- where if the whispers were at their original, actual volume, they would be hard to hear, and an explosion in an action scene would make you jump out of your chair. Amp makers may include simple single knob compressors, or less often, a more comprehensive unit with up to four knobs for precise control. Compression is not something generally needed for upright bass gigs, except in special situations, such as for taming the impact of rockabilly slap. Using compression well would take up an entire article on its own -- so Study user manuals, and experiment extensively before using.  Rule #1: If you can "hear" the compressor working (a "pumping" sound) it isn't set right. Subtle = good.

A final word on Too Much Bass Disease: Yes, I know you are playing a bass, but don't automatically turn up the bass or push the deep switch! If you've read my other writings, you know this is a pet peeve of mine. This is due to the many upright and electric bass players I've heard, or tried to hear, only because they are so far down in the bassment that their all their cool musical activities are buried in rumble. And dammit, so many can't take the constructive criticism or objective advice from their band members or another bass player. "This is the way I play," or some similar justification makes for the ugly status quo. And yes, I am like one of those reformed smokers, because I remember my own past self-defeating leanings towards the Deep Dark Side.

So check out these features (if available) on your amplifiers, perhaps it's time to adjust these controls and carefully listen to the results, so you are familiar with the tools at your disposal. All of these are potential ingredients in creating your Reference Sound. It may be time to revisit Part 1 and go back to the drawing board for some tweaks.

Coming soon: Part 3 - Parametric EQ, Notch Filters and other useful features!


One might ask...

Genz-Benz...after over ten years with just two amplifier companies, why have you added Genz•Benz to the mix? As usual, it comes down to the same reason I first began to use, and then sell Acoustic Image and Euphonic Audio's stuff. My never-ending "in search of" philosophy brought me to another amplifier company, one that has some gear unlike what we currently have, as well as some options for lower priced amplification solutions for you, our customers.

I don’t know about you, but my pattern for gear adoption has usually been driven by gig needs. Lately, electric bass gigs have been mostly the blues on electric five string, leading me to look for a more "tubey" sort of sound, not unlike the legendary Kern IP-777 tube preamp I used to pair with a power amp a dozen years ago... but lighter and more compact. I should mention that its replacement, the Euphonic Audio iAMP800, was to meet the need for a more articulate yet still warm sound that could better cut through a dense mix, the primary gigging needs at that time, and something I still admire and need.

A Genz•Benz Streamliner 900 will sit atop my new Euphonic Audio NL-210 (coming out in late October 2011) 2x10 speaker cabinets, as my electric bass guitar (and very loud URB/EUB) rig. The Acoustic Image Contra (now Coda Series 4) remains my favorite for low to medium volume upright bass gigs, and my compact EA Doubler (or Streamliner)/EA Wizzy 10 rig will also still see service for small electric gigs and some URB/EUB stuff. Just like having two upright basses set up for different sorts of gigging duties, having multiple rigs is also a good thing if you have the resources to do so.(Yes, there are advantages to owning a music store as well as having kids that are well past their college years.)

But back to the Genz•Benz gear... The Genz•Benz Streamliner amps have three 12AX7 preamp tubes utilizing six gain stages, so it is definitely very Old School Tone Land. Their other amps, and most other “tube preamp” rigs on the market, have but one tube in the preamp section, so the result can be far less “tubey.” In fact, many of those amps seem to use their single 12AX7 tube more effectively in the marketing of the amp than in the actual circuitry, but the Genz•Benz are not in that category. I should also mention that all the Genz•Benz amps have tube preamps with solid state power amp sections, and some even have circuitry to lend a tubey tone to the power amp's limiter, so doesn't go splat when you hit the wall.

Amps with tubes can have characteristics that can make them desirable... or unacceptable. You have to decide what you want your amp to do for, or to, your bass tone, and also recognize that all do not offer the same characteristics. The perceived benefit of a tube in the preamp section is a desired coloration of the sound, and varying the level of tube involvement and gain level of the circuit can take it from mildly warm, somewhat fat, or all the way to overdriven nastiness... if the amp maker includes that ability. My personal goal was more “heft,” with more body in the higher register, with a subtle smoothness and softening of the overall bass signal. The price you pay by going in this pillow-ish tonal direction can be the loss of some of those edges to the note that help it overcome a dense mix, as well as some jagged overtones that exhibit the distinctive character of your bass.

Of the Genz•Benz lineup, the Streamliner’s three-tube preamp definitely can deliver more of the pillowy, rich sort of old school goodness, but can also get pretty intense and driven as you advance the tube gain control. The Shuttle and ShuttleMax single-tube preamp offers a slightly less intense tube experience, not as thick or dense, but still pretty satisfying, and is probably a better choice for players who want to play on both sides of the fence. The Genz•Benz ShuttleMax 9.2 is in a class by itself, offering both a tube and FET (solid state) channel that you can mix for a little sharpness in your cream, or move between tube and clean channels depending on the gig or song. I have been swaying back and forth between the Streamliner and ShuttleMax, as the surgical fine tuning ability of the latter is quite attractive, similar to the Euphonic Audio iAMP800 (now iAMP Pro) I have used for the past several years.

In any case, one does have to step back and evaluate their personal amplification goals. None are wrong, all are valid, and admittedly, the differences can be quite subtle... especially in the mix. We are indeed fortunate to have the variety of such highly capable and precise bass amps and cabs from which to choose.

I should also say how thankful I am that Class D amps and Neo speaker cabs arrived just in time for the decline of my ability to carry the heavy stuff. What a wonderful world!

Bob

This blog preempted "Making Friends With Your Amp (Part 2) ", but it will be published shortly.




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