SPS-1 Stereo Preamp - Operating Manual
Congratulations! You have purchased the finest preamp system for acoustic instruments available today. But you already know that, so we won't bore you with the details. Suffice it to say the sound quality and versatility of the SPS-1 are unmatched, both on stage and in the studio. Since most of you would rather plunge right in and give it a listen, rather than read a novel, we've taken a different approach to explain how to use the SPS-1. If you're already technically savvy, you can head back to the Condensed Operating Instructions that precede this introduction. It is a capsule description of the main features of the SPS-1, and describes what all the buttons and knobs and jacks do in their simplest form. It should get you up and running immediately. If you need more information, or would like to learn about some of the less obvious things you can do with the SPS-1, read on.
Pickup Combinations - A Primer
Since we've been in the business of putting together preamp systems for acoustic instruments longer than anyone else, we've come across most of the configurations that players would like to use with their instruments. The bottom line is that nearly everyone wants something different, and needs a different approach to achieving it. For that reason, we've tried to incorporate as many features as you're likely to need both now and in the future. Since most players find that one pickup can't do the entire job, the SPS-1 is designed specifically for blending a pickup with something else, be it another pickup, an internal mic, or an external mic. What combination you choose depends a lot on your playing style - flatpicking or fingerpicking, playing solo instrumental music, accompanying vocals, or playing with other instruments at high sound pressure levels. Even whether you play in small clubs or with a concert sound system. The choices you make also depend on whether you're playing live or in the studio. Here are a few of the most popular combinations, and why people use them.
Two External Mics
The faint of heart need not apply! If you're a purist, and you're playing solo guitar in a studio environment, this is the combination you're most likely to use. However, it requires a pair of high quality condenser mics, and a great sounding room. Since the SPS-1 has two studio-quality mic preamps, parametric EQ and stereo output, it's the ideal preamp for going directly to DAT or digital multitrack. Perfect for recording you solo record yourself. No one would think of using this combination live, however, and expect to be heard. Unless, of course, you're doing a classical concert in a great European hall. doing a classical concert in a great European hall.
Pickup + External Mic
This is probably the ideal combination for solo acoustic performance, when you're looking for a good representation of the sound of your instrument but want some control over how 'woody' your guitar will sound. In most cases the pickup will be some sort of string-sensitive device, either a saddle or under the saddle piezo (that's pee-ay-zo folks, not pee-zo or pie-zo) transducer or a magnetic soundhole pickup. Some work better than others, some are easier to install, and some are just awful! The idea here is to use the pickup to provide the direct 'in-your-face' sound of the vibrating string, and combine it with the ambient sound of the wood vibration the external mic gives you. By varying the blend between the direct and ambient sound, you can get a very reasonable representation of your instrument. You can use more pickup in a very lively room, and more mic in a dead room. By using a single pickup or two pickup Preamp Module in one channel of the SPS-1, and an external mic in the other, you can have complete control over this blend on stage. Many players find that piezo transducers flatter light fingerstyle playing, but are harsh when the strings are hit hard. The best magnetic pickups, on the other hand, don't fold up when played hard, but are too 'round' sounding for players who prefer that 'brash' piezo sound. The choice is up to you. Check out what your favorite player is using, and see if it works for you. In addition, most studio recording of acoustic instruments also relies on using these two sound sources. During mixdown you can establish the blend of pickup and mic that gets the guitar to cut through the mix. The downside is that you have to have to stay glued to one position for the mic to be effective. This doesn't work for everyone. And, you can't use this setup with high stage levels or in a band situation, since both feedback - and more important - leakage of other instruments into the mic, will present major problems. Mic selection and placement will often help solve some of these problems, but not in all cases, or even in all rooms.
Pickup + Internal Mic
This is currently a hot combination, since it gives you the benefits of an external mic, and you can move around. There is a price to be paid, however, since a mic inside a guitar will never sound as good as a mic out in front of your guitar. It may come pretty close, and in many cases it works very well, but it's still a compromise. After all, it's is a mic in a box. All that said, it works quite well in many applications, particularly for solo players or groups where the stage levels are low. The problems encountered with external mics, namely feedback and leakage, are also problems here. Feedback problems can usually be cured by keeping the mic out of the stage monitors, which the SPS-1's monitor output allows you to do. Leakage, however is another matter. The mic is in a resonant box with a hole in it, which acts as a 'magnet' for low frequency sound, particularly drums and bass. You can roll off all the low end on the mic, but isn't that what you wanted the mic for in the first place?
A word about soundhole covers: You may think that by blocking
the sound hole, you're blocking external sounds from reaching
the internal mic. This is true, but you're also preventing air
from moving inside the instrument. If the air doesn't move, neither
does the diaphragm of the mic. Consequently, the output of the
mic drops dramatically, and sounds pretty dreadful. Venting the
cover by putting a few holes in it sometimes works, but often
the results are less than satisfactory. Sometimes you see a gauze
pad over a soundhole, which lets the guitar 'breathe'. It only
attenuates high frequency leakage though, not kick drum and bass.
If you're playing in a band, and it's loud, you can rule out any type of mic. In this case, there are a couple of options. You can get a 'woodier' sound by blending a string-sensitive pickup with a contact piezo transducer mounted to the top. Although the contact pickup can feed back, the feedback occurs at the cavity resonance of the instrument, which can easily be notched out with parametric EQ on the SPS-1. The advantage, of course is that leakage is no longer a problem. You won't get the sound of the pick or your fingers hitting the strings, but at high sound levels this isn't a great sacrifice. You will get some body noise, though - the sound of your shirt sleeve scraping against the top, or your perspiring forearm peeling off the top. Another alternative is to blend two string-sensitive pickups. A common combination is a saddle piezo pickup blended with a magnetic soundhole pickup. Here, you're getting two different tonal colors which you can blend to your liking. The piezo transducer is great for that brash, 'in your face' sound, and a biting attack. The magnetic pickup is ideal for getting harmonics out of your instrument (especially for tapping), and does very nice things for slide playing. It definitely opens a lot of possibilities.
Setting up the SPS-1
In this section we'll highlight the operation for SPS-1 and describe some of the many things you can do with it. Refer back to the Condensed Operating Instructions for the front and rear panel layouts.
Standard Set-up with a Two Pickup Preamp Module
· Start off by plugging the Two Pickup Preamp Module
into the XLR input of Channel 1. Make sure all the pushbuttons
on the front and rear panel are in the 'out' position.
Set-up for a Pickup and an External Mic
It's easy to blend one or two pickups in Channel 1 with an external mic in Channel 2. You can use the mic on your instrument, or as a vocal mic blended with your guitar sound.
· Set the Input level controls for Channel 1 and Channel
2 to 0.
Set-up for Two External Mics
Set-up for Two Instruments
The SPS-1 can also be used with two single pickup or two dual pickup instruments connected simultaneously. Each instrument is connected to its own input channel, and EQed individually. The two pickups of any one instrument are blended to mono in each input channel.
· Set the Input level controls for Channel 1 and Channel
2 to 0.
Set-up for Instruments with On-Board Active Electronics.
The SPS-1 can also be used with instruments with active electronics, with or without the preamp module. When used with the preamp module, set up as above. For use without the preamp module:
· Set the Input level controls for the Channel inputs
Set-up for Use with a Wireless System.
Although the best sound quality is achieved using a Preamp Module and a connecting cable, the SPS-1 can also be used with a wireless system:
· Set the Input level controls for the Channel input
Features of Channels 1 and 2
Input Mode Switch (1 ,1/2)
Mic Switch/ Mic Gain Trim
+48V (Phantom Power)
There are two things to note; first, the three frequency bands have considerable range (about 4 1/2 octaves) and overlap - that is, the MID band can also be used in the middle range of the LO band, and so on for the other bands. This gives you added versatility, e.g. if one band is dedicated to removing a objectionable band of frequencies, another band may be applied to access other frequencies nearby. Also note that the LO band is capable of a narrower bandwidth (larger 'Q') than the others; this is important for using the LO band to 'notch' out any objectionable low frequency resonances or feedback, particularly the instrument's cavity resonance. To put the equalizer into the signal path, press the 'EQ' pushbutton to the right of the Input control - the red LED above it indicates the EQ is on. With the level controls centered, the equalizer is inactive and you guitar should sound no different than with the EQ off. Rotating the LEVEL control to either side of the center position will boost or cut in the range selected by the frequency and bandwidth controls. Choosing a wider bandwidth will encompass more frequencies, causing a more audible effect on your guitar's sound - more like that observed with with one band of a graphic equalizer or a tone control with a 'peaking' response. With a narrower bandwidth, fewer frequencies are affected, so more boost or cut has to be applied to notice a large difference in your guitar's sound. However, the narrower bandwidth lets you be more selective about the frequency range you want to target - giving you an extremely effective way of eliminating unpleasant resonances without affecting other areas of the frequency spectrum.
We'll have a few more things to say about EQing your instrument
In this section we'll discuss the outputs available on the SPS-1, and which features you'll be most likely to use.
Master Output Section
Pan: The pan controls determine the left (ccw) and right (cw) position in the master stereo mix for Channel 1 (top) and Channel 2 (bottom). To obtain a mono blend of the two channels, set both pan controls to the center position.
Master Level: This control sets the level for the Left and Right balanced outputs on the rear panel. Set the level for the mixing board, amplifier, or tape machine you're using. The unity gain setting (+4 dbu) is 2:00.
Phase Rev: When this switch is 'in', the overall phase of the Master Outputs is reversed. Reversing the phase can be useful for feedback control.
On/Loop LEDs: These two LEDs indicate the status of the mute and effects foot switches. The 'On' LED (top) indicates that the master, monitor and channel outputs are active. The 'Loop' LED indicates that the stereo effect loop in the master output section is active. When the footswitch is not used, the 'On' LED is always lit, and the 'Loop' LED goes on when an effect device is plugged into the stereo effects returns.
Master Outputs: The two XLR-type balanced stereo outputs
are used for connecting to a snake, mixing board, tape machine,
or other balanced input. This is the output you'll normally use
to feed the 'house' sound system. Pin 2 is hot. To connect up
to an unbalanced input, use an XLR to 1/4" adapter. Or,
you can make your own adapter cable by wiring pin 2 to the 'tip'
of a 1/4" phone plug, and pin 1 to the sleeve.
Monitor Output Section
Monitor Level: This control sets the level for the Left and Right unbalanced outputs on the rear panel. Set the level for the stage monitor, monitor amplifier, tape machine or other system you're using. The unity gain setting (+4 dbu) is 2:00. The monitor level also controls the signal level sent to the headphone jack on the front panel.
Phase Rev : When this switch is 'in', the overall phase of the Monitor Outputs is reversed. Reversing the phase can be useful for feedback control onstage. Try it both ways and use the position that works best. The best setting will depend on the position of your guitar relative to the monitor speakers. So, it may change from night to night.
Monitor Source Switch (MIX / CH 1): The Monitor outputs are normally fed the master stereo mix (MIX), which is identical to the Master outputs. Press this switch (CH 1) to feed only Channel 1 directly to the monitors. This can be useful for controlling feedback in pickup/mic applications, by feeding the pickup-only signal from Channel 1 to the stage monitors. The Channel 1 signal is mono, post-EQ, post-Insert, but pre-stereo effects loop. It is turned on and off by the foot switch.
Monitor Outputs: The two 1/4" unbalanced stereo outputs are used for connecting to a stage monitor, monitor amplifier, tape machine or other unbalanced input. This is the output you'll normally use to feed your onstage amp or 'monitor' sound system. The output is assigned to the stereo mix or channel 1 via the monitor source switch.
Send Outputs and Return Inputs: Interfacing to the stereo effects mixer easy. Just connect the L and R inputs from your stereo effects device to the L and R send output jacks on the rear panel of the SPS-1. These are unbalanced, low impedance outputs that are capable of driving any effects device. Next, connect the L and R outputs from your stereo effects device to the L and R return input jacks. The Return inputs are also unbalanced. The 'Loop' LED on the front panel will light, indicating the effects returns are active. The effects returns can also be used as a post-EQ auxiliary input. It's a convenient way to combine a drum machine, synth, or to play along with your favorite CD or cassette!
Replace Switch: With the switch 'out' (the MIX mode) the stereo effects returns are blended with the dry, unprocessed signal in the preamp. In other words, the loop is combined in parallel with the unprocessed sound. Use this mode for combining reverb with the unprocessed guitar signal. - set the 'mix' control on the reverb unit to return 'wet' or 'reverb-only' signal to the SPS-1. This way, the dry signal is not degraded by the effects device.
When the switch is pressed (the REPLACE mode), the unprocessed signal is turned off and only the signal passing through the effects loop is heard. Use this mode with a compressor, stereo chorus, delay, or multi-effects processor. The blend of the 'dry' and 'wet' signals is determined by the effects device.
Foot Switch: The Foot Switch jack is used to turn your
instrument on and activates the stereo effect loop. The 'On'
and 'Loop' LEDs on the front panel indicate that the 'On' and
'Effects' switched on the Foot Switch are activated.
Equalizing your Acoustic Guitar
Comments: Before you start to equalize your instrument's
sound, it's probably a good idea to:
Main Problem Areas
·Too Much 'Boominess':Tuning the LO band to the instrument's body resonance (typically in the range of 70-140 HZ) is an extremely effective way of taming an overpowering low end 'boominess', especially with a mini-mic in the body of a guitar. To do this, set the bandwidth control fairly narrow (around 3:00) and add 12-15 db of boost. Then, lightly tap a finger on the top of the guitar behind the bridge while tuning the frequency control in the range given above (the larger the guitar's body, the lower the resonant frequency). At a certain point, the tapping will turn into a deep 'thud' as you zero in on the body resonance. (If you listen closely, you'll actually hear a series of harmonically-related resonances - tune in on the lowest frequency one.) Now, cut about 12 db, play a few chords and adjust the bandwidth and level to your liking, while using the EQ in/out switch for comparison. Cut the level and adjust the bandwidth to remove as much of this frequency range as necessary. You should be able to find a setting that effectively removes the problem without affecting the rest of the bottom end. The improvement is usually dramatic.
· Lack of 'Clarity': Often, because of the pickup's response or placement, the guitar's lower midrange overtones get exaggerated. This causes your guitar to sound 'muddy' and lack definition. Use the LO or MID band (with a fairly wide bandwidth) to cut a few db in the 400-1000 Hz frequency range.
· Lack of 'Presence': Using the MID or HI band to add a few db in the 3-6 kHz range will help your guitar stand out. Be careful though, since adding too much or centering on the wrong frequency can make your guitar sound harsh. On the other hand, some pickups tend to overemphasize frequencies in this range so you may need cut back in this region.
· Lack of 'Brilliance': Compared to the hyped-up
high end we're used to hearing on recordings, an acoustic instrument
can often sounds too 'mellow' to the modern ear. A broad boost
of the HI band above 10 kHz will give you a 'crisper', 'brighter'
tone. Applied in moderation, it can bring life to a dull-sounding
instrument. Remember, EQ is largely a matter of personal taste
and the specific needs of your instrument may be quite different
from these general guidelines. Don't be afraid to experiment
to find what sounds the best to you.
In case you were wondering, here are a few of the reasons
why the SPS-1 sounds so good!
Input(Piezo or Magnetic): 10 M, unbalanced
Notes: 0 dbu = 0.775 Vrms.
Pendulum Audio, Inc.· P.O. Box 339, Gillette,
NJ 07933.· (908) 665-9333 · www.pendulumaudio.com