The Enigmatic Oberheim XPANDER & MATRIX 12

By Thor Zollinger, writer/musician/engineer at large.  2022

There are a LOT of Analog synthesizers in the world, spanning from way back from the 1960’s up to today.  They have a lot of similarities, but also a lot of differences.  A friend of mine Ben, who is a toy company vice president in Canada has gotten me interested in Analog synthesizers again.  I had stepped beyond Analogs back in the 90’s.  Ben is a huge Analog synth fan, I wondered what I was missing.  I started looking at other Analog synths to see what was out there.  What were the differences (and similarities) between of all of these classic Analog synthesizers?  And then I ran across the Oberheim Matrix 12 and it’s little brother the Xpander…  They’re unique…

So what exactly is different between the Oberheim Xpander (pictured above) and everything else?  Let’s get right to the point, it’s in the internal modules that make up the synth.  The Matrix 12 and the Xpander have more of just about everything inside, and they have a couple of extras most Analogs don’t have.

Most Analog synths from the Jupiter-8 and Arp 2600 era all the way up to the modern Moog Matriarch, Arturia Maxibrute and Korg Minilogue are based on a standard recipe.  They have two oscillators with FM, one or two multi-mode filters, a mixer, and an output amplifier (VCA).  For controllers they usually have three envelopes (a PEG, FEG, and an AEG) and one or two LFO’s (PLFO, FLFO).  Sometimes one LFO can also be used as an oscillator.  Most of the time the envelopes and LFO’s are pre-assigned, you can’t apply them to something else.  If that’s all you’ve got to work with, why would you?

Oberheim ignored the recipe and added in more of just about everything when they built the Matrix 12 and Xpander, including a couple of new modules the rest don’t have.  They started with the same two FM capable oscillators, then added FIVE Envelopes,   SIX LFO’s, FOUR Ramp generators, THREE Tracking controllers for keyscaling, a fifteen mode filter, and FIFTEEN VCA’s scattered throughout the model.  They have an insane amount of programmability!  To go along with all of the extra components you can matrix all of them (in 20 slots) to any destination you can imagine.  It works more like a modular synth using patch chords, infinite flexibility.

What can you do with all of those extra components?  You can double or triple stack them to do very complex things.  Have you ever stacked an envelope onto an LFO to shape it’s warble?  Have you added an extra LFO onto a set of filter controllers with a long, slow cycle time to slowly transform the filter settings over time?  How about stacking controllers with different settings onto each oscillator, then double stacking onto the output VCA?  What about using a ramp to tone down the intensity of an effect as you hold onto the notes?  Or how about using a Tracking controller to change the intensity of a warble to create a low growl down low on the keyboard and a fast trill up high?  These are the types of controller combinations you only see on an exotic synthesizer like the Yamaha VP1.  None of these are possible on a standard recipe Analog.  And these are just a few examples.  I’m sure you can think of an entire host of crazy setups with all of these controllers to play with!

The question is, do you want these types of effects in your own patches?  I do.

Sound quality is also a huge factor.  The Xpander is a high-end synthesizer with equally high-end sound.  They didn’t even bother to put in an extra HPF for aliasing like the Jupiter 8, Yamaha CS-80, and Yamaha AN1X have, it wasn’t needed.  Multi Patches are also a big step up in lushness.  You can alter every one of the six voices to pan and widen the sound, you can detune them independently to richen the chorus, you can alter the envelopes and LFOs on each to further thicken the sound, you can add layers by mixing different patches together in different Groups, you can transition the sound across the keyboard by altering the volumes of the different patch layers, you can use the assignable controllers to create slow, generative changes in any parameter… In short, you can create fantastic sounding patches that evolve over time with a richness you can’t duplicate on any other synth.

So why didn’t the craziness of the Matrix 12 catch on when it was released…  It all has to do with price.  Most buyers are driven blindly by price, they almost always pick the lower priced item.  The Matrix 12 and the Xpander were both high dollar items.  They weren’t people’s first choice when it came time to actually fork over the cash.  Oberheim reacted to this by cutting down the number of components on all of their subsequent synthesizers to reduce the price.  They caved in and went back to the standard recipe.  Check their specs and you’ll see what I mean.  This leaves the Matrix 12 and the Xpanders as an anomaly, an anomaly well worth your time to look into. 

Next Steps - Finding A MATRIX 12

I hadn’t purchased any classic Analog synths at all up to this point, primarily due to the unreliable nature of many of them.  The insides are sometimes a complete rat’s nest of wires, making them a nightmare to work on, and I just knew I would end up having to fix something if I bought one.  Take a look below at the insides of one of the most iconic Analogs, a Yamaha CS-80 from 1977…  Yikes!


Yamaha CS-80 – Internals

 While digging around on the internet I ran across the Oberheim Matrix-12 and the Matrix Xpander, the 6 voice little brother.  I saw a photo of the insides of the Xpander… Wow, what a difference!  Take a look at the internals below.  Clean design, simple to work on, what a difference a few years makes!  It’s a beautiful piece of engineering.

Oberheim Matrix Xpander – Internals

The front panel was also cleanly designed, with the block diagram right on the front.

Oberheim Matrix Xpander – Front Panel

As an alternative to a hardware synth, there is also a VST now for the Matrix 12; the Arturia Matrix 12V.  Listening to it, it’s in the ball park.  It doesn’t sound exactly like an actual Matrix 12, but it’s really close.  At only $149, it’s a superb price for a synth this capable.  I have a copy of the VST, I’m hoping to be able to use some of the patches people come up with for the Arturia on an Xpander.  I’m also learning how to program the VST which will help a lot when I actually have a Matrix 12 or Xpander to work on. 

Arturia Matrix 12V VST

So where am I?  I’ve finally located an Analog synth I wouldn’t mind owning that can provide me with the same controller capability as a modular synth, more components to play with than ever in the model, superb sound quality, Midi control capability, and sufficient patch memory on top of that to keep me busy for a long time.  I’d love to purchase a Matrix 12, but the only one I can find a listing for is over priced at almost $30,000… way out of my price range.  The Xpanders however, are a bit more reasonable.  You can find several online on Reverb for sale from $5000 up to $8000.


Compared to a 1977 ARP 2600 or the mighty Yamaha CS-80, the Matrix Xpander is way ahead!  It adds an extensive controller matrix (it’s signature feature) ramp generators, keyboard tracking control, FM modulation, a fifteen-mode filter, and basically more of just about everything.  The differences between 1977 and 1984 are huge. 

The Xpander is a true Analog synth like the others from that era, but all of the controllers and settings are digital.  Comparing the sound of the 1984 Matrix Xpander to a fully digital Oberheim Matrix 6 or 1000, the sound of the true Analog is brighter, crisper, and an order of magnitude better than the newer digital equivalents.  The newer digital Oberheims are only a third of the price of the Xpander, but they sound muffled and thin in comparison.  Comparing the specs, the Xpander also has more components; 5 envelopes vs 3, 6 LFO’s vs 2, 4 ramp generators vs 2, etc.  Moving to digital, like most manufacturers, Oberheim reduced the number of components in the model down to a more standard set up, lowering the flexibility (and capability) of the synthesizers.  For me this is a big failure, I’d rather have more options in programming patches than a boiled down version of the internal model.  You can create far more interesting patches with more components.  I’m going to double stack modulators, use an envelope to modify the amplitude of an LFO which is adding tremolo to an oscillator or filter, or double stack LFO’s adding a long, slow modulation onto the faster warble.  You can’t do either in a cut-down synth, especially when most of the envelopes and LFO’s are pre-assigned.

The control panel of the Matrix Xpander is very well laid out, and identical to the larger Matrix 12.  On the front panel of the Xpander there is a block diagram for the synthesizer.  Each of the eight sections of the block diagram has a button that switches the center controls over to that section of the synth.  The six knobs and displays are used over and over for different parameters inside the synth, a very efficient design.  On the left are the overall patch settings and voice selection display.

Along the top center of the panel are 14 buttons for setting up the controller matrix, the key feature of the Matrix 12 and Xpander.  No other Analog synth that I know of has an extensive 20-slot controller matrix like this.  The older Analogs like the ARP 2600 only have about 5 to 7 controllers, with most of the controllers prewired/assigned.  You can’t really select where the controllers are routed on most Analogs.  This was really the deciding factor for me, I decided right then I wanted a Matrix 12 (or Xpander) over an ARP 2600, or even over the ultra expensive Yamaha CS-80.  With an extensive controller matrix and a plethora of modules you can explore all kinds of routings just like you can on a modular synthesizer!

Xpander Front Panel Diagram

Another advantage of the Matrix 12 and Xpander is the patch memory.  There are 100 slots in the Oberheim machines which can be loaded and saved through the Midi interface.  Eurorack modular synths, the ARP 2600 and most of the older Analogs have NO patch memory.  There are a few exceptions.  The Yamaha CS-80 has a primitive method of storing four patches using a set of duplicate hardware components under the hood, but you can’t transfer a patch from one machine to another.  That’s a huge disadvantage.  You have to reprogram the machine every single time you want to use a different patch on a CS-80.  Newer Analogs like the Yamaha AN1X and the modern variant of the Roland Jupiter 8 have corrected this problem.  In modern variants however, the internal models are cut down to a lower standard everyone seems to have accepted. 

The synthesizers also have a Multi Patch setting.  Each of the individual voices out of the six can be programmed independently.  Using this mode, the sound of the patch can take on a very thick, chorused sound, or it can be a weird other-worldly sound by jumping from one patch voice to another on every note.  Using this technique sparingly, you can bring a very interesting texture into your sounds, something that’s impossible to do on any other synth.

Comparison To Modern Analogs

The modern Analog synth that came to mind first was the Yamaha AN1X, I have experience with that one.  The AN1X has characteristics similar to most of the modern virtual analog synths, a familiar dual VCO setup with FM, and other common features.  A table is probably the easiest way to show the similarities and differences.  I added a couple of others into the table as well, and older Yamaha CS-80 and a modern version of the Roland Jupiter 8. 

Looking at the table, the Matrix 12 and Xpander have more basic internal modules, more types of modules, and the controller matrix has a lot more capability than the others.  For physical controllers, the CS-80 and Jupiter 8 win simply because of the sheer number of knobs and sliders on the front panels.  For Effects and arpeggios, the AN1X is the superior synth.  But, I can get these from other external sources if needed.

Also went through an online list of the Top 10 Best Analogue Synths of 2022, listed below, and compared them to the 1984 Oberheim Xpander… 

·  The Top 10 best analogue synths of 2022

Basically I’m not that impressed with the modern Top 10 selections.  Most of them have significantly fewer of everything that the Oberheim Xpander contains.  Most had the same number of oscillators, but all have fewer LFOs and far fewer Envelopes, and all had only a fraction of the Xpander’s VCAs.  None of them had Tracking (keyscaling) in any form, none had Ramp Generators, but some had two filters per channel.  The Xpander’s 15-mode filter might be able to hold it’s own though, I need to test that to see.  The modulation matrix on the Xpander is also superior in all cases, there are far more sources and destinations than in any of the new synths  (27/47).  Of course, assignable controllers IS the main strength of the Oberheim Matrix 12 and the Xpander.

The only real advantages to the new instruments were that one included a Ring Modulator (very handy) another had Reverb and other Effects (also very nice to have) and several of them had an arpeggio sequencer.  I can get arpeggios using an external Midi sequencer or the Yamaha Montage in my studio, it’s my controller keyboard of choice.  Effects also have to be added on externally.  There are lots of external Effects units anymore, or I can run the sound through the Montage.  In short, I think I can compensate for the things the Xpander lacks.  I’m far more interested in what the internal model can do with all of the extra modules. 

Overall, I’m very impressed with the Oberheim Xpander’s capabilities, it’s a great choice even by today’s standards!



Date Produced - 1985 – 1988

Audio Sources

6 Independent Velocity, Release Velocity and Pressure (After Touch) responsive analog Voices.

6 voice multi timbral   (12 for the MATRIX 12)


Analog Components:  VCOs, VCF, and VCAs

Digital Components:  Envelopes, LFOs, Lag Generator, Ramp Generators, and Tracking Generators


Per Voice Architecture

2  Voltage Controlled Oscillators ("VCOs")                                        No Ring Modulator or Reverb

1  Linear FM Modulation Generator

1  Noise Generator

1  15-Mode Voltage Controlled Filter ("VCF")                                      No Arpeggios or Sequencer

15  Voltage Controlled Amplifiers ("VCA")

5  Digital Envelope Generators

6  Digital Low Frequency Oscillators ("LFOs")                                     Don't forget the Vibrato LFO...!

4  Ramp Generators

3  Tracking Generators                                                                     Keyscaling!

1  Lag Processor                                                                              In place of Delay/Portamento



Matrix Modulation™ System utilizing 27 Sources routed to 47 potential Destinations stored in up to 20 slots per Voice.

12 Permanent ("hardwired") modulations per Voice.


MIDI Implementation


Transmit and Receive Channel select independent per Voice (MIDI MONO Mode) or per polyphonic Zone.


Mode 1: OMNI On, Poly

Mode 3: OMNI Off, Poly

Mode 4: OMNI Off, Mono


Midi Controllers

Indendent Controller Number select

Controllers ON/OFF select

Patch Change Commands ON/OFF select


Miscellaneous MIDI Features

System Exclusive ON/OFF select

MIDI Echo ON/OFF select



100 SINGLE Patch Memory Locations

100 MULTI Patch Memory Locations

"Chain" Programming Mode

Three 40-Character Fluorescent Displays

Cassette Interface - FROM (input) and TO (output) ports             

Trigger Input Requirements (selectable): +5V DC signal minimum, 1ms Pulse Width

6  CV and Gate inputs which use standard 1V/8va CV and positive gating

Power Requirements (selectable):

North America and Japan: 95 - 120 V A.C., 50 - 60Hz

Europe: 200 - 230 V A.C., 50 - 60 Hz



Xpander:    33 x 12.5 x 6 inches

Matrix 12:  38.5 x 20.3 x 6 inches



Xpander:    27 lbs

Matrix 12:  33 lbs (14.97 kg.)

I love the bright Green flourescent displays too!  Don't you?