About, Mods, Repair

Contour Boost

This is a true clean boost that emphasizes low distortion and high output level. It also features a convenient "contour" control for adding a small tone change appropriate to boost and amp driving. This type of boost can push a tube guitar amplifier (and others) into much deeper distortion without distorting itself. Like the classic MXR Micro Amp, this is an IC based boost, very clean, but more modern, more hi-fi, with even more output. A common complaint is that the MXR seems to have too much bass and treble when used. Psychoacoustically, louder sounds will seem to have more bass and treble. Or, when the boost increases distortion, too much bass and treble may cause feedback, bass mud and more hiss. Midrange boosts the "body" of the sound and is most effective at increasing apparent sustain. If desired, an internal trimmer allows directing the Contour control to also boost some treble. Options are available to best suit the application. Uses Hammond small 1590B cast aluminum enclosure, finish is clearcoat over sanded aluminum. Feedback on the first batch was very positive: "love it", stands up against others, studio applications, "it's perfect for boosting up my Single Coils to HB level. Very 'neutral' boost". click photos to enlarge

SOUND SAMPLES / applications
Please note: clean boost sound samples make no sense unless you listen primarily for the RELATIVE change.
se1_h-powertubesschb.mp3 (232 KB) Full volume power tube distortion demo. Single coil unboosted, then boosted, then switch to humbucker (Multibucker "Fast Track 2" and series humbucking). SE-1 #002.
se1_fb-bigmuffdemo.mp3 (376 KB) "Big Muff Demo": buffering effects are shown using Full Bypass Contour Boost set to minimum driving a "tone sucking", "partial bypass" black made in Russia Big Muff Pi distortion pedal. First, Muff is off and boost is switched in and out to restore the signal. Then, Muff is on and has typical fuzzy sound, then more detailed with boost unloading the pickups. Finally, boost is turned up pushing the Muff further, and the Muff is turned off at the end. SE-1 #003.
se-1h_basichumb.mp3 (236 KB) Basic contour/boost of humbucker-crunch demo. #002 Hard electronic switching, deselected and reengaged twice during clip.
se-1h_chopleadish.mp3 (122 KB) Thickening of single coil: high contour, low boost of humless single coil sound (Dimarzio "Chopper" section of Multibucker). Deselected in middle: #002 hard electronic switching.
se-1h_various1.mp3 (321 KB) Boost with tone turned down, going into unboosted single coil crunchtwang, into heavy chords using same pickup contour boosted. SE-1 #002.
contourboost1.mp3 (138 KB) #001 Soft switching, humbucking (old strings though). Boost comes on about 4 seconds in, and off during last note.
... use "Save Target As" to download instead of just play ... enjoy or pardon the guitarplaying as applicable ;) ...
=> All w/ Ibanez RG-550 guitar (bridge Multibucker), through my old prototype 15W tube amp in preamp distortion (except first)... perhaps an odd choice but it is a neutral, basic amp (three 12ax7 stages with about 20 dB total interstage attenuation some EQ in preamp, 6V6s). Through Cele V30s (2x12), EV N/DYM 257A, Porta2 as preamp (flat as reasonable), soundcard. Should have also sampled one through a Legend A30 hybrid amp (HV tube distortion, otherwise solid-state) also when it was here, because the results were surprisingly good and it really needed the extra gain. 64 Kbps Mono MP3s.

Boost Pedal Uses

Boost pedals are most often used to drive the input of an amplifier into deeper distortion. Gain beyond the normal capabilities of the amplifier is possible, while maintaining the desirable sound quality of the amplifier. Or a boost pedal can be used as additional means to control amp gain. As an alternative to turning the amp higher and using the guitar's volume control, noise is reduced and control is improved.... If the amplifier is set clean, turning on the boost will increase volume and possibly cause distortion. If the amplifier is set to distort substantially, the boost will increase distortion further and cause only a small increase in volume. It must be emphasized that a true "clean boost" does not distort within itself, it increases distortion due to increasing drive level to another device. Some amps may require considerably more gain or not respond so favorably to high input levels, in which case a boost with overdrive controls might be preferred. To produce maximum drive to an amplifier, if other effects are used then boost is normally placed last in the chain in order to avoid overdriving the other effects.

Another use of a boost pedal is to raise the signal level of low-output pickups to a level comparable to high-output pickups. In this case the boost pedal may be placed at the beginning of an effects chain to help make all the effects work better.

Some boost pedals include some type of tone control function. While not as flexible as a graphic equalizer, simpler circuitry tends to result in better audio quality. Any effect placed before high gain distortion needs to have the lowest possible noise.

Yet another use of a boost pedal is as a volume switch. In the case of an amplifier being used for distortion, a volume switch must be placed in the amp's effects loop if a change in the amount of distortion is to be avoided.

Contour Boost Technical Information

About 1 to 27 dB of flat-response boost plus 0-8 dB of contour (boost-only) is provided. Of course, the output level of your guitar pickups will determine the maximum gain beyond which any boost device will distort. The Contour Boost is built around an OP-amp integrated circuit with "rail-to-rail" output capabilities, which means that it will deliver to your amplifier almost everything a 9 volt battery will put out. This is a better match to pushing the first stage of a tube amplifier into significant distortion than lower output boosters, without the extra trouble of requiring two batteries or other problems. For example, if you turn the knobs very high and play loudly, momentary distortion will occur following each pick attack, but the output level will be high enough to incur some distortion of almost any guitar amplifier on the market (including a Fender Twin) regardless of setting. Moderate boost will really open up most amps, however, some may require considerably more gain or not respond so favorably to high input levels, in which case a boost with overdrive controls might be preferred. When high gain boost or volume increase is desired and other effects are used, boost is normally placed last in the chain in order to avoid overdriving the other effects and deliver full signal to the amplifier. A lower boost level can be effective in front of other effects however.

The contour function is a wide midrange boost centered slightly below the middle of the spectrum which I have found useful for adding sustain and a slightly thicker sound appropriate to higher gain. The boost extends to the fundamental tones of the highest notes on the guitar without adding to feedback problems which tend to occur just slightly higher in frequency; when this is applied prior to distortion, sustain of this range is improved without causing excessive midrange overall (midrange can also be reduced slightly on the amp). This is somewhat like using a wah pedal set just below middle, but much more subtle and controllable. Since regular wah users may not have need of this effect, and there are surely other ideas for a desirable tone shift, the circuit is designed to be modified for other contours (inquire). The depth of the contour effect may also be completely dialed out with the front panel control, and an internal trimmer control provides a treble boost option (normally I set this low to reinforce the thicker sound of the contour).

Switching Options

True Bypass: is a good system favored by many players. In bypass, the effect is completely out of circuit with a short handwired signal path.
Electronic switching: is particularly advantageous here because the circuit is so simple. Deselection simply removes the boost-setting components from affecting the circuit when the effect is deselected, resulting in a buffer with unity gain. The result is quiet switching with no signal interruption and consistent output characteristics at all times, with yet only a fraction of the signal degradation of the multiple buffers in many other effect units. There is no possibility of a drop-out when switching, not even for a split-second, because the signal chain is never interrupted. The always-buffered output is capable of driving long cables, and possibly even reducing noise or lossiness of following circuits (due to low output impedance). Electronic switching comes in two flavors: "Soft switching" which results in a slightly gradualized transition in and out of boost over about 1/2 a second and minimal impulse. This avoids a jarringness to the transition and feels luxurious to use. This might be seen as undesirable if a sudden transition is desired, but in practice this is not often a problem, because the boost will come on faster than the initial attack of a note subsides, leaving no lull. (Soft switching is not intended for volume switching of high levels in a completely clean environment as there can be some transitional distortion, but in the intended application this is unnoticable.) "Hard switching" is also available, which uses a simple switch in the amplifier circuit instead of a transistor for instantaneous switching, non-dropout/high reliability (including redundant contacts), and always-buffered operation. However, since the footswitch itself passes audio, switching noise is only slightly lower than with True Bypass. All switching options use a "click" type footswitch as this simplifies circuitry, provides decisive operation, and retains the last used setting, but the electronic switching uses a switch with a softer "click".

These options allow the player to weigh various factors, such as expected switch usage and system "buffer budget".

All standard Spencer Amps effects use components and construction chosen for excellent audio quality, ruggedness within industry standards, and also for affordability and value. Normal options and modifications are available at reasonable prices, depending on availability, as well as more extensive custom work: please inquire. Do note that these effects are largely handmade and some cosmetic imperfections may be visible upon close inspection.

Ordering Information

Availability:
True bypass $60 starting/$70 BIN, $19 ship/handle/restock fee, see Ebay (posted 4/28/08):
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=250242389086&ssPageName=STRK:MESE:IT&ih=015.

-- Gallery -- First of the cast aluminum case versions. SE-1 #001 -- larger case style, Soft electronic switching (see above). This is an earlier version all-handmade Boost which I have used for over 10 years. Uses momentary footswitch (yeah it's plastic) with very soft Non-bypass electronic switching.