The following features and functions are common to nearly all SWR® amplifiers. This guide is a reference for players who are new to SWR or who are looking for deeper understanding of the features of their SWR amplifier. If you require information on a specific feature not included in this guide, please refer to the owner's manual for your model. Other resources for SWR feature and technical information include the SWR FAQ, Glossary and Manuals.
Both input jacks accept a standard 1/4" phone plug; both inputs can be used simultaneously. Since both inputs are independent, no loss in volume or tone will occur when using two instruments simultaneously. The main reason for having two separate input jacks is their difference in level—the "Passive/Active" input has five times the gain of the "Active" input. In other words, it's not necessarily intended as a "submixer" for two instruments, even though no harm will result from plugging in two instruments at once (although phasing problems can sometimes be caused by characteristics of the instruments being used).
Instrument Input (Passive/Active)
The "Passive/Active" input jack (sometimes labeled "Hi Gain" on vintage SWR models) is found on all SWR amplifiers. It's the most commonly used input jack and is the recommended starting point for most SWR users. Connecting your instrument to this jack with a shielded instrument cable will send the signal from your instrument to the preamp section of your amplifier, where it can be adjusted before being sent to the power amplifier section and then to your speakers.
In this instance, "passive" refers to an instrument that doesn't have a built-in preamp and doesn't use a battery. Although labeled "passive," this input jack will work with all instruments having a maximum output of one volt RMS or less. Many professional instrument pickups use batteries and will work perfectly with this input, as will most professional instruments with active electronics. If you're using an active instrument in this input and you hear a small amount of distortion in the signal, try using the "Active" instrument input.
Instrument Input (Active)
Although found on most SWR models, the "Active" input jack (or "Low Gain Input" on vintage SWR models) is generally the lesser-used connection. It's for use with instruments with an on-board preamp that will produce a signal of one volt RMS or greater, and instruments that have "hotter" pickups. The "Active" input jack is attenuated to accommodate such instruments, resulting in a quieter signal compared to the "Passive" input jack. Connecting to this jack with a shielded instrument cable will send the signal from the instrument to the preamp section of your amplifier, where it can be adjusted before being sent to the power amplifier section and then to your speakers.
In this instance, "active" refers to an instrument that uses a battery-operated preamp for gain and/or tone controls. Although labeled "active," this input jack will work with all instruments, even those that don't have active electronics. Using the "Active" instrument input with passive instruments may result in loss of high-end transients. Players who roll off high frequencies starting at about 2kHz or prefer a "darker" sound may find this input more to their liking.
Gain Control adjusts the volume of the preamp section. Since this control resembles a "pad," a small amount of signal may be heard even when the Gain Control is rotated fully counter-clockwise (especially if the Master Volume Control is set to a position other than minimum). To properly use Gain Control, first adjust all tone controls (bass, mid, treble, Aural Enhancer™) to taste, then raise the Gain Control level until the peak clipping indicator LED barely flashes when striking your loudest note. This will ensure maximum signal-to-noise ratio and prevent unwanted clipping of the preamp section.
Gain Control can also serve as an effects send level adjustment when using the side-chain effects loop (a feature available on most SWR amplifiers). If your external effects device input is being overdriven by the incoming audio signal, turn down the Gain Control and readjust your Master Volume for overall loudness.
Preamp Clip LED
The LED generally found directly above the Gain Control is the Preamp Clip LED. This will illuminate whenever the preamp, tone section or output buffer is driven to clipping (i.e., runs out of headroom, exceeding the maximum undistorted signal level). Most players will generally want to have a clean signal at this point in the chain, so decrease the level of the Gain Control if the Preamp Clip LED illuminates.
The Aural Enhancer has been a feature on nearly every SWR amplifier since the company's inception in 1984, and is a trademark part of the "SWR Sound" people have come to know and love. It was developed to help bring out the fundamental low notes of the bass guitar, to enhance high-end transients and to reduce certain frequencies that help mask the fundamentals. The result is a more transparent sound, especially noticeable when slapping and popping, and it can give a passive bass an "active" quality when set at two o'clock" or higher.
The Aural Enhancer works as a variable tone curve that changes depending on how you set it. As you increase the control clockwise from the "MIN" position, you're elevating a whole range of sound (lows, mids and highs) at a variety of frequency points selected specifically because they're different than those selected for the individual tone controls.
This remains true up to about the two o'clock position. This position—a favorite for many users—brings out the low-end fundamentals and crisp highs. At the same time, it adds a little lower midrange to help cut through the band. If you go further clockwise past the two o'clock position, however, selected mids will start to drop off; specifically, a group of frequencies centered around 200Hz. At this point and beyond, the effect becomes much more pronounced, but the curves involved here are gentle as opposed to the extreme curves you can create by boosting or cutting the active tone controls (EQ).
Most significantly for basses, the Aural Enhancer will help bring out the fundamentals of your lower registers without masking them with overtones, as is possible when using the Bass control only. It also opens up the sibilance characteristics of all instruments without being harsh.
Obviously, numbers and curves and circuits mean nothing compared to what you hear with your own ears. Play a chord, a repeated lick or a harmonic, and adjust the Aural Enhancer to various points to hear the effect for yourself. As always, your ears are the best judge when it comes to settings that affect the tone of your instrument.
The Bass Control found on all SWR models uses a shelving-type circuit that boosts or cuts the bass response plus or minus 15dB from about 30Hz to 100Hz. Adjusting the Bass Control clockwise from the 12 o'clock position boosts the bass response; adjusting it counter-clockwise from the 12 o'clock position cuts the bass response.
Midrange frequencies are integral to the character of your overall tone. SWR offers several different midrange control feature sets that differ with regard to their degree of control—everything from the simple boost/cut single control (found on our LA and smaller Workingman's Series models), to full-blown semi-parametric and paragraphic sections on the more esoteric Professional Series models. As this is one feature area that differs greatly by model, please refer to the individual product owner's manual for specific information.
The Treble Control found on all SWR models uses a shelving-type circuit that boosts or cuts high frequencies and their octaves plus or minus 15dB from about 2kHz to 14kHz. Adjusting the Treble Control clockwise from the 12 o'clock position boosts the treble response; adjusting it counter-clockwise from the 12 o'clock position cuts the treble response.
The Limiter is an electronic circuit designed to prevent distortion of attack transients or peaks. It can be used as an effect to give your tone more "punch," and is also useful in preventing speaker damage. In most SWR models, the limiter circuit is located after the Master Volume and before the power amplifier section, thus being driven by the Master Volume Control. The Limiter threshold (starting point) is preset by the factory so that the user can get maximum overall apparent volume without overdriving (clipping) the power amplifier.
The Limiter LED illuminates in green when your signal has reached a preset starting point to indicate that the Limiter circuit has been activated. It's often confused with the Preamp Clip LED, but your amplifier and/or speakers are not being harmed when this LED illuminates or remains lit.
Effects Blend Control
The Effects Blend Control works in conjunction with the Effects Loop (found on the rear panel of most SWR amplifiers and consisting of an "Effects Send" and "Effects Return") and allows you to blend the signal sent from your instrument with the signal coming from any effects units in the loop. The Effects Blend circuit is similar to that used on professional recording consoles, with the Effects Loop on a "side chain" to the normal circuit. Unless the control is set to the fully "Wet" position, you will always get the full sound of your instrument and get the diversity an effects unit offers. This circuit is also effective, due to its location after the gain stages in the preamp, in reducing noise generated by effects units.
The Effects Blend functions only when the Effects Loop is being used. It is activated when a 1/4" phone plug is inserted into the Effects Receive jack. When the Effects Blend Control is set to the "Dry" position (fully counter-clockwise), no signal from the effects unit will be heard. As you adjust the Effects Blend control clockwise, more of the effect will be heard in the overall sound. When the Effects Blend Control is set to "Wet" (fully clockwise), no true or unaffected signal is heard other than what your effects unit provides. If your effects unit has a similar control, it should be adjusted to its full "Wet" position. This should avoid any possible phasing problems.
The signal at the Effects Loop is line level. Units such as effects pedals (designed to be inserted between your instrument and the preamp input) may be overloaded or incur signal loss when used in the Effects Loop. If you have a rack effect with a switch for setting the input level, it should be set for 0dB or +4dB.
Master Volume Control
The Master Volume Control adjusts the signal level being sent to the power amplifier section, therefore controlling the overall volume and output of the amplifier. Adjusting the control counter-clockwise reduces the overall level; adjusting it clockwise boosts the overall level.
Note that the Master Volume Control never affects the level present at the various audio output jacks on the rear panel—it only affects the level being sent to the power amplifier and, subsequently, your speaker outputs only. Also note that losses caused by external effects units can be recovered by increasing the Master Volume Control.
Power On/Off Switch
Setting the Power On/Off switch to the "On" position activates the electronics as indicated by either the switch body or the power LED illuminating (depending on the model). Setting the Power On/Off switch to the "Off" position deactivates the electronics.