How can I take advantage of a multi-effect pedal?
Jul 9, 2009 Pedals
It’s more a question of not getting carried away. Your modern multi-effects can typically produce as many as five or six effects simultaneously (or even more). So it’s easy to start piling a plate reverb on top of a chorus effect plus some EQ, a little compression and maybe a speaker simulator and . . . well, in many cases, the sky’s the limit.
As an example, Digitech’s GNX4 will not only produce a superb tonal palette, but it also includes things we never dreamed of even a few years ago, like 8-track digital recording (at 24-bit resolution, no less), USB connectivity to your computer, a built-in drum machine and even a mic preamp with phantom power. And all at the unbelievable Sweetwater price of just $599.97 ($799.95 list)! And no, that’s not a misprint.
For a lot less cash, you can still tap into an incredible boatload of sophisticated processing with units like the Boss ME-50 ($295.97) or even the budget-priced, yet amazingly powerful Alesis GuitarFX Pedal ($69.97). Almost all the gear made today is capable of delivering a wide range of effects with very low signal-to-noise ratios. In fact, most guitars cannot claim to be as quiet as the majority of today’s multi-effects.
Even the curent crop of amp modelers, like the PODxt ($299.99) and Vox ToneLab ($449) include a wide range of effects that can be used individually or in a chain, either pre or post amplifier.
Speakers: Does size matter?
Jul 9, 2009 Amplifiers
For this discussion, we turn our attention to simple physics. Smaller speakers can produce higher frequencies than larger speakers, which is why a tweeter is small and a woofer is large. So in the real world, a 10-inch speaker will generally produce a better “top end” than a 15-inch speaker. There is also a difference between an open-backed cabinet and a closed-cabinet design. Which is why certain amps, like a 4×10 Bassman with an open back will sound different than a 2×12 Bassman with a closed cabinet.
Many blues players swear by those old open-backed 4×10 Fender amps, as they can produce a range of tones from smooth to searing. If you want to sound like Jimi, you’ll likely want to plug your Strat into a Marshall with a dual 4×12 cabinet design. One well-known guitarist preferred four 4×12 cabinets, which may explain his current hearing problems – yikes, 16 12-inch speakers will definitely play loud, but the overall frequency response, if charted using sensitive laboratory gear, will be totally different than that of our 4×10 example. Today manufacturers can custom tweak their amps by combining a certain size cabinet with a certain size set of speakers.
Amplifier Output Classes explained (A, AB, B, C, D & H)
Jul 9, 2009 Amplifiers
Class A - In CLASS A operation, the output stages of an amplifier are arranged to have a quiescent current more or less equal to their full-load current. This results in a very linear mode of operation, but is wasteful of supply power. This power wastage results in continuously high thermal dissipation, is is generally only used where very high quality (low harmonic distortion) performance is required, with the minimum of negative feedback for correction of non-linear distortion. Class A amplifiers can be either single or double ended.
Class B – Class B differs from Class A in that there is no (or very little) current flowing when the output devices are under no-signal conditions. Class B can really only be useful in a push-pull (double-ended) configuration, and in this configuration, the output stage consists of two amplifiers, one handling the positive excursion of the waveform, the other handling the negative.
For audio use, pure Class B is rarely recommended, because of the large amount of feedback required to correct “cross-over distortion” . This distortion is due to the non-linearity of the “near-zero” part of the output waveform as the output stages switch over, positive to negative and vice versa.
Otherwise, the Class B amplifier has the advantage of approaching 100% efficiency in terms of power transfer to the load, consuming virtually nothing under no-signal conditions.
Class AB – This is a mode which is intermediate between Class a and Class B.
Basically, it is constructed using a push-pull Class B configured output stage, which is then biased into a small amount of conduction, which vastly reduces the amount of negative feedback required to eliminate cross-over distortion.
This class of power amplifier is the most commonly met linear amplifier, and represents the most acceptable compromise of performance.
CLASS C – Class C amplifiers are generally single-ended, and may be likened to half of a Class B amplifier. They are not used in quality audio, and are mainly used in high frequency applications, where simple tuned circuits can deal with the huge amount of distortion inherent in this class design.
Class D – Class D amplifiers are really switch-mode power supplies. They are supremely efficient in their semiconductor incarnation, because the output devices are either off or on, so, there are no “resistive” losses in them.
This “binary” mode of operation led to Class D being dubbed “digital” … this is entirely incorrect … these amplifiers generally work by employing Pulse Width Modulation (PWM), Pulse Density Modulation, or Delta-Sigma Modulation, and there is no digital coding of the signal.
A high frequency pulse generator is modulated by the above methods, and the resulting signal then passed through a filter which blocks the high switching frequency, leaving the modulating information available at very low source impedance for the output.
Until recently, Class D amplifiers were not used for high-end audio, but there are designs by the likes of B&O which are very comparable to AB amplifiers, but are very much smaller, power for power.
Class H – If an amplifier has more than one voltage rail (DC voltage delivered by the power supply), then it is designated Class H. This is a very efficient type of amplification. The output transistors of an amplifier have to dissipate, in watts, the difference between the rail voltage and the voltage across the speaker terminals multiplied by the load current. So, there is a low rail voltage for use during periods of low volume, and a high rail voltage for use during high volume. The output devices don’t have to dissipate very much power when the volume is low. This causes less drain on the power supply and makes it possible to build a very lightweight design. The drawback is distortion at mid-volume when the amplifier has to go back and forth between the two (or more) rail voltages, which effectively constitutes a secondary cross-over distortion.
There are several additional classes of power amplifiers, but these are mainly modifications to, or derivations from the above.
