Moog Taurus I Bass Pedal Synthesizer

pic of Taurus pedals
pic of rear of Taurus pedals

Update 06-14-2014

The Moog Taurus I is a self-contained synthesizer famed for its earthquake-inducing bass timbres.  It does one thing, and does it well... BASS.  It was originally designed as one of a trio of synths for the Moog Constellation system, which consisted of the Lyra (a monosynth that never made production), the Apollo (the Polymoog prototype), and the bass pedal synth which became the Taurus.  The Lyra and Apollo currently exist in the Audities collection in Calgary Alberta Canada but the prototype bass pedal synth is long gone.  Like the Minimoog, the Taurus stands as the standard against which all other bass pedals are measured.

I had wanted a clean set of Taurus pedals for a long time.  Most of the ones that show up on auction sites or in stores had been well gigged, were ratty, or needed repair.  The market value for Taurus pedals was $2,000 and climbing - higher than a vintage Minimoog.  Pretty absurd prices for a synth that does little other than bass sounds.  I was checking out one of my regular jaunts, a vintage guitar store that sells vintage Fenders, Gibsons, and PRS guitars. On occasion they have a synth or combo organ.  They had an excellent condition Moog Liberation a few years prior with a fairly high price tag, it took them over a year to sell it.  This store had also sold vintage accordians, and I spotted an oversize accordian case in an inconspicuous place. 

My curiousity was aroused.  "That's an awful big accordian".

Popped the case open and inside was a pristine set of Taurus pedals.  They weren't even on display!  Spotless case, no broken pedal keys, missing the window/bezzle over the controls.  On the handle was a price tag.  On disbelief I took the case to the counter to confirm the price.  The price they were asking was less than half the market value!  They had belonged to an employee of the store.  After doing a quick run-over of the pedals, I immediately bought them. This was a lucky find, as this was a reputable store that sells vintage guitars and has net connections so they can check auction sites and other stores for current values.  You would think that after selling a 1959 sunburst Les Paul Standard at market value (yes they have had them in that store) that they would know the value of Moog Taurus pedals...!

The case was a factory polymer molded case with stiff foam supports inside.  A peek at the old Moog Music price lists shows that the case was offered only for a couple of years, last in 1976.  The inspection tag inside the pedals dates it to 1976, a year after they were introduced.  The pedals were so clean that I don't think they have ever seen a stage.  I called around and Mike Bucki had NOS bezzles and could make the window assembly.  I got them in a couple of weeks and the window looks like the original, even the VARIABLES label looked authentic.  I only had to add magnets so that the window would stay closed when I moved them.  Many Taurus pedals are missing the window/bezzle because they were friction fit to the case and they often worked loose.  I had to secure them from the inside using RTV, worked like a charm.

According to Bob Moog, the Taurus I pedals were designed not by Bob but by Dave Luce, who also designed the Polymoog.  Dave copied the Taurus filter from the 904A low pass filter module of the Moog modular systems.  Dave Luce's name appears on the three US Patents for the Taurus pedals (further reading on Don Tillman's site).

The 13 note Taurus has three preset sounds, plus a fourth "variable" which is a user configured sound using the controls in the middle of the panel.  Encompassing the control panel are a pair of foot controlled slidepots, one for volume, the other for filter cutoff.  These work for all the sounds and are useful for varying the presets.  Above the pedalboard are footswitches - four for the presets, then glide, decay (release actually), and octave.  The presets are labeled "Bass", "Tuba", and "Taurus".  "Bass" is a dual VCO synth bass sound with a rapid decay transient that begs to be sequenced or be played by hand.  "Tuba" is a single VCO sound that has better use when processed, IE stereo chorus.  That single VCO is one solid bass sound though.  "Taurus" is the famed sound favored by prog rock groups like Genesis, Yes, Asia, UK, and Rush as well as Motley Crue and The Police (Andy Summers had a set, Sting had a pair in front of him).

The control panel defines the "variable" sound - you are given control over footage from lo-mid-hi (shared with both VCOs), VCO A/B mix, VCO B frequency (little over an octave), VCA Attack/Decay (actually Release), VCF Attack/Decay, VCF Cutoff, Emphasis, and Contour Amount.  These controls do not affect the presets, they are set by fixed resistors.  Three other controls - Glide, Beat, and Tune - work on all the presets.  Beat is like a master detune control for the VCOs. The VCOs are rising ramp waveforms only - they are not falling ramp as illustrated in the Taurus user/service manual.  There is a SUSTAIN LEVEL control grouped with the VCA Attack/Decay but it is not the traditional SUSTAIN parameter associated with the industry standard ADSR EGs.  It is actually a volume control for the "variables" preset, similar to the contour amount for filters.  The VCA EG is A/R with full sustain, the VCF EG is A/D with zero sustain.

Bass is the Taurus pedals' forte. Below are samples of some sounds under the "variable" palette.  These are best heard/felt with subwoofers or headphones, you won't hear that deep bass with generic PC speakers.  None of these sounds have any processing or EQ.

Deep Bass
Growl Bass
Angry Bass
Deep Resultant Bass
Filter Sweep

Shoes make a difference playing the Taurus pedals.  Hard flat soles work the best, long accepted by organ players in churches and theaters.  Sneakers don't work as well, particularly when using the footswitches.  There is too much "sponge" in soft sole shoes and you don't get the firm playing tactile response you do with hard soled shoes.

I own other Moog keyboards - Memorymoog, Minimoog, Source, Polymoog, Liberation, Voyager.  The Source was my primary bass keyboard since 1985.  They could hold their own against the Taurus, but the Taurus has that indefinable oomphTM that separates it from the rest.  It is true that the Source can emulate the Taurus pedals as I have copied the sound, but something was still missing.  The sound of the famous "Taurus" preset opens with a throaty growl, then settles to a pleasant distinctive purr as the filter cutoff decays.  The growl and filter decay was easy to emulate on the Source, but that purr wasn't quite the same.

The "Tuba" preset demonstrates how massive and solid just one Taurus VCO can sound.  None of my other Moogs sound this big.  I use Rane line mixers with no EQ so there is no question of EQ differences.  I could get the growl and filter decay of the "Taurus" preset on the Source but it didn't have the mass of the Taurus VCO.  What was missing?

There is a myth that the Taurus is fatter because of the linear v/hz VCOs.  An exponential VCO, used in Minimoogs and just about every other synth, contains a linear voltage to exponential current converter followed by a ramp generator based around a charged cap with reset pulse.  A study of the Taurus VCO reveals the same circuit minus the exponential converter - giving it a linear v/hz response yet with no difference in the audio sonority in the ramp generator.  My first gigging synth was a PAiA 4700 modular with linear v/hz VCOs and these were far from the obesity of a Taurus VCO.

So why do Taurus pedals sound so big?  One answer is the coupling between the VCF and the VCA.  The service manual states that the AC coupling between the VCF and VCA was designed so that the RC product would increase the bass at a corner frequency of 20hz.  There is a bass boost built into the Taurus pedals!  According to Bob Moog, Dave Luce simply lifted the filter design right out of the modular - the 904A low pass filter module is one mighty big sounding filter so there is no question about that.

The other element of the bigness of Taurus I pedals is distortion in the waveshape.  This is due to two factors 1) the filter is driven pretty hard which introduces harmonics 2) the filter feedback recovery amp and the VCA are CA3080 OTAs which are NOT high fidelity devices, they actually introduce subtle distortion.  This changes the timbre to the point that the fundamental is emphasized.  This also introduces a compression effect via overdriving the filter.  This is also why Taurus I pedals do not suffer from phase cancellation of dual detuned VCOs as the timbre animation cycles around.

So that "bass boost" is the "purr" that is missing from the Source.  Therefore the Taurus bass sound remains unique.  Many analog synths need a 10-20 minute "warm-up" period for the VCOs to come in tune - the reason is that the expo converter has a temperature factor that affects its conversion.  When power is applied the components heat up over time, settling at an operating temperature higher than ambient temperature.  During this "heating period" the expo converter will be inaccurate, which means the VCOs will not be in tune.  Once operating temperature is reached, the VCOs are in tune.  Because the Taurus is lacking the expo converter in its linear v/hz VCOs, there is no warmup time needed to wait for the VCOs to tune - they are ready to play when you turn them on.

Why do the Taurus use linear v/hz VCOs?  One, it is a one octave pedalboard therefore octave switching is trivial.  Two, no modulation of any kind (pitch bend, mod wheel) is needed for a bass synth.

The "Taurus" preset doesn't suffer from phase cancellation of dual detuned VCOs, which led to the myth that the Taurus pedals contain some kind of compression - not true, say the schematics.  What the schematics DO reveal is that the mix level of the VCOs are not equal on the "taurus" preset - if you turn down the level of one of the VCOs, the phase cancellation is minimized while you can still hear the timbre animation.  This is a trick I have been using on the Source since I bought it back in 1985.

You haven't heard justice done to Taurus pedals until you play them through a proper PA system.  I have a two way PA system consisting of a pair of JBL SF25s (2x15 plus titanium tweeter) and two pairs of EV S-181 subs with 18" speakers.  This is a big sounding system, hall-caliber quality.  Those subs got a workout with the Taurus pedals, they have some serious BOOM that you won't hear on small studio speakers.  I never felt such subsonics in my life.  Now I know what a Genesis or Rush concert experience would have felt like (I never caught either in concert).

The Taurus I pedals were in production from 1974 to 1981.  From 1982 to 1985 a second version called the Taurus II was released which is an 18 note pedalboard with the synth "brain" module suspended at playing height via a pole.  The electronics of the Taurus II is identical to the compact Rogue synthesizer with the exception of the keyboard CV circuit.  While this model has more features, it is a pale imitation to its predecessor.  It does not have the big bass sound of the original Taurus I. There was also rumor of a Taurus III.  No such device by that name was ever made, it is likely confused with the Taurus Controller which is the Taurus II pedalboard minus the synth "brain" module - it has trigger and CV outputs, but no synthesizer circuits inside.

The achilles heel of Taurus I pedals are the pedal key contacts.  They are exposed to the floor and the elements which leaves them vulnerable to collecting dust and debris.  The contacts are also silver plated which can tarnish and render a key to malfunction.  If a range of keys from high C below stops working, it is dirty contacts.  The best way to clean them is to remove the circuit board containing the contacts and apply Tarn-X tarnish remover with a pipe cleaner.  Any tarnish remover will work but Tarn-X is a strong cleaner.  WARNING - use Tarn-X in a ventilated area, the fumes are mighty noxious!

If you tire of cleaning dirty key contacts once a year, Kevin Lightner makes a replacement key contact PC board that uses high reliability leaf switches in place of the silver plated spring contacts.  This is a complete circuit board which is a direct drop in replacement.  I bought a set and have been very happy with them.

Another foible of Taurus I pedals is failing frequency divider trimpots.  These do not age well and will cause the pedals to go out of tune when you move them.  The service manual has a procedure for replacing them with standard trimpots and resistors.  The lubricant in the slidepots can dry out and make them sticky.  Mike Bucki tells me that petroleum jelly can be used to re-lube them but I would recommend Dow Corning 7 lubricant as anything containing petroleum distillates or byproducts will damage the bushings making them swell up.  I also question whether a petroleum-based lubricant would have a corrosive effect on the resistive element of the slidepot.

The pedal keycaps can break.  The best way to prevent that is to use the Taurus on a rug or a small remnant.  Lowrey and Moog were both owned by Norlin back in the 70s so Lowrey supplied the pedalsets used in the Taurus.  If you need keycaps they can be scavenged from Lowrey home organs, however the keycaps on the current Lowrey organs are not the same.

There is a great big cap plug on the rear panel of the Taurus I pedals.  This was supposed to be a connector to an external accessory box that allowed external control of the "variables" controls.  There were connectors on the Taurus circuit board ready for this accessory, which according to the user manual was available from the Custom Engineering department of the original Moog Music.  Mike Bucki worked in the Custom Engineering department and he has never seen this accessory box, ever.  David Kean of Audities tells me that Dave Luce had planned this interface to work with the Polymoog (carrying some design proposals from the original Moog Constellation), but that feature never came to fruition - too many engineering changes to the Polymoog prevented any development on it.

Although Mike Bucki has never seen the accessory box, I spotted a web site that had pics of a set of well-worn Taurus pedals belonging to Genesis.  There is a box laying on the pedals (highlighted in pics below) with a circular multipin connector at its cable end.  The box appears to contain slidepots of similar model and layout of the Taurus control panel, and the cap plug on the rear panel is replaced with what appears to be a mating connector.  This may a very rare example (maybe the only one) of the optional accessory box for the Taurus Pedal.

pic of Genesis Taurus front
pic of Genesis Taurus rear

Adding MIDI I/O to a Taurus I is not trivial as there are no interface I/O jacks.  Kenton used to offer a decent MIDI interface that is long out of production.  You need a CV converter that generates a v/hz CV signal, not the more common v/oct.  You'll have to drill some holes for jacks.  There are a few companies that offer suitable converters.  I'm not happy with the current solutions - the aforementioned Kenton Taurus MIDI kit was the best solution.  It avoids calibration issues with CV trimming, includes a MIDI out that the others do not, and activates the footswitches in response to MIDI controls.  Since I want to add MIDI to my Taurus pedals, I am planning a homebrew MIDI interface patterned after the Kenton solution using a PIC controller.  Since the Taurus circuit board was ready to accept an external accessory box, I may attempt to access those points using MIDI CCs converted to CV control.

Can the Taurus I pedals be cloned?  The circuit uses standard parts, but the keyboard circuit used a custom integrated resistor array that is no longer available and the CA3080 OTA is becoming a member of the endangered species list.  The Taurus I case itself would be expensive to reproduce and a pedal set would not be cheap.  A faithful reproduction of the Taurus I pedals would have to be an accurate clone of the voice circuits as the sound is critical.  One could clone the Taurus I synthesizer circuit in a tabletop or module form and use an aftermarket MIDI pedalboard to get the same function (less the footswitches), and it would cost less than a faithful reproduction.

Fortunately, Moog Music has reissued the Taurus pedals in the form of Taurus 3, which is a faithful reproduction of the Taurus voice with added bells like MIDI and programmability.  A limited run of 1000 units proved so popular that they built past that - serial numbers are approaching 1500.  Moog has just announced the Minitaur which is a tabletop synth with the Taurus voice but with some features stripped to make it more affordable.

Why is there a big appeal for the Taurus I pedals?  Why do people pay over $3,000 for a used set, even ones that are broken?  Why do vintage synth dealers have a waiting list of customers wanting Taurus I pedals?  One attribute is the sound - they possess the beefiest most solid bass sounds I've ever heard.  One user claims to have witnessed chairs moving on the hall floor when he was testing his Taurus pedals at a soundcheck.  Another memorable auction description describes the Taurus pedals as "so fat you'll have to put your studio on a diet".  A second attribute is the package - the layout of the Taurus controls is optimized for operation by foot.  It is easy to change the sound without using your hands, which is important for bass and guitar players.  A third attribute is it just looks so cool - I'm particular to traditional hardwood like the cases of Minimoogs, but the Taurus pedals just looks right with that aluminum trim, dark grey casing, and protruding legs by the pedal keys.

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