Oberheim Matrix 6R Patching

I bought an Oberheim Matrix 6R used a music store in uptown Minneapolis back in the late 1980's for $500.  The Matrix series consists of 6 voice polyphonic analog synthesizers including the Matrix 6 keyboard version, the Matrix 6R rackmount, and the Matrix 1000 with 1000 preset patches.  I was original looking for a Matrix 1000 but the salesperson talked me into getting the Matrix 6R because it was programmable from the front panel.

My first impressions were not overly favorable, I think I was hoping for a Moog sounding filter and the filters at high resonance sounded very harsh.  It did have some classic Oberheim sounding horns which I liked, their was an oscillator sync patch called "Ai-Ai" which was really good but generally I was not overly impressed with the sound.

The real problem with the synthesizer was the programming interface, which was done completely through panel buttons and not a single knob or slider on the entire panel.  After awhile I got pretty fast at it though.

I began using it less and less, it was a bit too big to take out to a gig, I think I brought it to one gig.  After one of my studio rearrangements I didn't bother to even hook it up.

So now it has probably been about 10 years since I last used it and have been looking at the new polyphonic analog synthesizers on the market and longing for one when I thought I would give the M6R another try.  This is really a very interesting synthesizer.

Besides the standard features you might expect on any analog synthesizer, the M6R has a bunch of features that make it really interesting.

• 2 DCOs (Digitally controlled oscillators)
• 1 VCF Lowpass
• 2 VCAs
• 3 Envelopes
• 2 LFOs
• 2 Ramp generators
• Portamento
• Tracking generator
• Lag processor
• 10 point Matrix

So far, so good, a nice analog synth very similar to many others.  But since this is polyphonic there are six identical copies of all of these features.  The M6R can also play poly timbral with two different patches playing on the keyboard at the same time.

Next I want to look at the components in a little more detail.

DCOs

There has been quite a bit of complaining about the DCOs on this  synth, since it has DCOs instead of VCOs.  I don't have a problem with these oscillators.  They have a lot of functionality and they tune automatically which was one of the main reasons for them being digitally controlled if I am not mistaken.

There are actually three types of waveforms, pulse, saw, and both.  The pulse width can be modulated, the saw can produce a decent saw when set to 0 or triangle wave when set to 63, the triangle wave is actually almost a sine wave.  Both combines both waveforms together.

DCO1 can be synced and DCO2 can be detuned.  DCO2 can also be set to respond differently to the keyboard so you could actually have it fixed and not change at all.  The sync has three different settings from soft to medium to hard sync.

There are a number of preset connections, LFO1 is set up to modulate the pitch of the DCOs and oscillator 2 is set up to modulate the pulse width of the DCOs.  These can be routed manually in the matrix.

Both oscillators can also produce a click sound and DCO2 can also produce white noise.

There is a Unison mode where all 12 oscillators play at the same time.  Unfortunately they digital tuning is so effective that you can't really tell that there are 12 oscillators playing.  It would have been extremely cool if you would have been able to all of the oscillators.  Unison mode does seem to change the tone of the oscillators but I need to put them on a scope to see exactly what is happening.

VCF

So originally I really disliked the VCF.  I think I was expecting a Moog ladder sound and it was not like that at all.  Especially when you crank the resonance all the way up or get close to self oscillation it sounds particularly harsh.  It is a 4 pole lowpass only filter but sounds to me more like a two pole.

Listening to this with a little more maturity I like it much better.  I don't think polysynths sound that great at really high resonance anyway.  Back off on the Q and you can make some nice smooth pads with lots of motion.

One unique feature of the VCF is the ability to do a type of frequency modulation with DCO1 as the modulator and the VCF as the carrier.  This can be used to add some bell like sounds to the voice.  I need to spend more time experimenting with this to see if it can produce some more interesting effects.

VCA

Not too much to say about this.  I don't notice any noise or anything.  One VCA just takes a straight number for volume and the other is tied to envelope 2.

Tracking Generator

The tracking generator basically reshapes a control source in a way similar to wave shaping.  This is a feature not found on your typical analog synth (of course you can probably get on modulars).  For instance instead of having a triangle wave for the LFO you could make it into sort of a house shape.  Instead of having the keyboard increase the pitch in single steps you could have go up then down.  Applying this to an envelop could give you a much more complex envelope shape.  This was hard for me to understand at first but now that I look at it I can see it could be extremely powerful.  On the other hand, I have not really tried to mess around with it yet so I could be off base on its capabilities.

Portamento

There is a portamento feature (glide) that enables you to slide between the pitches.  It has three settings, linear, constant time, and exponential.  You could set the synth in Unison mode to have a gliding monosynth if you wanted to but mono's do this better so don't bother.  It does a nice polyphonic glide.

Envelopes

The ADSR envelopes also have a delay section at the beginning to delay the start of the envelope so they are actually five stage envelopes.  It can also be set to DADR mode delay, attack, decay, release.  There is also a free run mode that lets the envelope finish its full cycle, basically generating its own gate once it is triggered.

LFO

The LFO has the waveforms triangle, saw up, saw down, square, and random (noise sample and hold), noise, and sample and hold.  The LFOs have a lag processor so you can take the edge off of a square wave.  The sample and hold mode can sample another modulation source.

Matrix

The matrix is a virtual patch system which can handle up to 10 interconnections between the synthesizer elements.

The 20 control inputs are: Envelope 1-3, LFO 1&2, Vibrato (a special LFO), Ramp 1&2, Keyboard, Portamento, Tracking generator, Keyboard gate, Velocity, Release velocity, Pressure, Pedal 1 & 2, Lever 1-3.

The 32 destinations are: DCO Fqc, PW, Wave shape, (x2) Mix, VCF FM, Fqc, Q, VCA Volume (x2), Env Delay, Atk, Dec, Rel, Amp (x3), LFO speed, amplitude (x2), Poramento rate.

System Start Up

I powered up the system and after sitting for all those years most of the patches were gone messed up.  I think it is probably due for a new battery.  At first when I was using the system it was generating random errors and locking up.  I opened up the case and vacuumed out the dust and rubbed a dry paint brush over some of the circuits to clean them.  I couldn't see anything else wrong with it so I put it back together.  It seems to be working fine now but will probably put a new battery in it next time I do a Jameco order.  It looks like Jameco has battery clips that should fit on this board.

I created a number of patches which I will try to share here.  I created a template for recording patches since I don't have a computer with a MIDI connection near this system.

Here are a couple of patches:

Rig with Motif Pulse and MPC

I have been attempting to make a psytrance song lately.  This is a picture of my keyboard rig.  The wood ends on the Pulse make it much more control friendly.

The MIDI connection is as follows:

Motif MIDI In <- MIDI Out of Computer
Motif MIDI Out -> MIDI In of Computer
Motif MIDI Thru -> Pulse MIDI In
Motif Local Control = Off
Reaper is Running on the computer with a track set to:
  I/O = MIDI Out
  Record enabled
  Record input: Audio or MIDI
  Monitor enabled
  Input = MIDI In (All Channels)

That way I can play the arp on the Motif (Note the Motif arp can be set to a different MIDI channel than the regular MIDI channel!) and either record it to Reaper or listen to it on the Pulse.

MPC is not connected in this photo.

Very Bizarre Filter Revisited

A while ago I came up with a design for a very bizarre filter which attempted combine a fuzz distortion with resonant low pass filter.  Unfortunately the prototype did not pan out.  This is a second attempt at a bizarre filter.  The idea is not to create a certain type of filter but to deliberately introduce distortion into a filter. 

This design is based on the new filter Ray Wilson is using on his Noise Toaster.  The Noise Toaster is an excellent sounding box which gives you a lot of options in a small space.  I was looking for a simple filter design so that I could try out some experiments without using a whole pile of chips.  The advantage of this filter is that it uses only one op amp.  I had been experimenting with Ray's Weird Sound Generator filter since it is very simple.  This new filter is an improvement over the WSG filter.

The first modification I decided to try was putting in some diodes.  I found that putting a diode and a potentiometer that could be switched on and off in the resonance section allowed for a lopsided resonance which should give some unique character to the sound.

The second modification I wanted to do was to subtract a low pass signal from the resonant low pass signal. That should result in just the resonance from the signal.  Next I wanted to add some hard edges to the signal so I passed it through the an op amp at high gain.  Finally I added another resonant filter at the end to reintroduce resonance on the newly created peaks.  Leaving in all of the controls gives nine different controls for messing with resonance and distortion.

The left trace shows Ray's original filter, the next trace shows the diode modified filter, the next trace shows the clipped resonance signal and the next image shows the re-filtered signal.

I have not built this device yet, I will have to wait to see if it works out.  If I build it I will post a video.  I am hoping to add a filter to a NAND synth so I may use this one.

Heavily Modified APC

This is a heavily modified Atari Punk Console.  Modifications include pitch and mod Cv inputs, resonant low pass filter from the Ray Wilson's Weird Sound Generator, dual low frequency oscillator with cross feedback, selector knob for up to six different capacitor pairs ranging from control frequencies to high pitched oscillator frequencies.

 The circuit for this is on the bottom right:

Analog Sequencer

I finished an analog 10 step sequencer based on one of Ray Wilson's designs with some modifications.  For one thing I made it based on 9V so I could use my standard power supply.  I used a 555 for the clock instead of Ray's clock.  I ended up leaving most of the gate generating part which I later regretted but I would need to add a daughter board to fix it.  I used ten different colored LEDs on this device.  The 10 knobs control the voltage sent to the left output.  The knob by the left output controls glide, the knob by the right output controls step time.  The right output is supposed to be a gate but it only works if you have every other switch up and down.

Another issue is that it outputs a voltage from 4.5 - 9 V rather than 0 - 9V or -4.5 - + 4.5 etc which is problematic with most other synths.  In the next revision I would try to change that as well as a few other things.

Anyway, not too bad for a first prototype.  The videos demonstrate how it sounds:

And another:

Accompanied by a Yamaha CS01 analog synthesizer using a breath control to modulate filter cut off and processing both through a Lexicon Vortex.  The sequencer is modulating  a modified Atari Punk Console that is part of the Thing 2 device.  That device also has a NAND synth, noise generator and starve features.

I added a resonance knob to the CS01 as can be seen in the video.

Here are some pictures of the sequencer in progress.

Thing 2 vs. Steam Drone

In this video I do an improvisation using my Thing 2 NAND/APC/Noise drone box and Steam Drone box.

The Steam Drone is on the left.  The system combines a NAND synth with a resonant low pass filter based on the LM13700 OTA.  The LEDs use two transistors and capacitors to do flashing lights (yellow and red). The knobs control the frequency of the three NAND oscillators as well as the level of audio sent to the filter.  It turns out the filter performance depends somewhat on the input level.  the next set of knobs include Q, filter cut-off, and output volume.  The knob on the far left is a potentiometer that the input voltage passes through.  When this is all the way to the right it passes the voltage unaltered.  As you move it to the left the input current has to pass through more and more resistance essentially starving the circuit of voltage.  Starve is one of my favorite effects because the circuits get into a mode where they don't behave like they are supposed to, before they shut down completely.  Three of the switches control are used to link the NAND oscillators directly to the output, the other switch turns on the power.

The box on the right is the Thing 2 system.  This is a board I made by combining the following circuits: NAND synth, Atari Punk Console, low pass filter, zener diode noise source, blinking light circuit.  I had a bunch of layouts drawn up so I decided to combine all of these on a single board.  The noise part of the circuit was not making any noise so I kept increasing the resistor value over the op amp to increase the gain but it still would not make noise for me.  I noticed however that the whole circuit was producing noise so I settled for that.  This box has additional inputs for the control voltage of the 556 which basically controls mod and pitch.  I also added an input for the filter to process an external signal since the noise wasn't working.

Something interesting occurs on the Thing 2 when you starve the circuit.  The noise starts to become enhanced and the LEDs start having a big impact on the sound.  I was originally disappointed with the flashing light part of the circuit because the flashing of the lights is not related to the sound the device makes.  As you starve the circuit though, each time the lights flash they make a sound.  So I ended up really liking this circuit.  It was sort of a whim to combine all of these circuits on one board but I like the results a lot.  I ended up with two other indicator LEDs, yellow and green, in addition to the flashing ones, blue and red.

I had photo cube from Michael's which was big enough to hold the circuits and the knobs and I had used a photo cube for the Thing 1 device.  I came up with the idea to cut pieces of Fresnel lens and mount them on the inside surface of the photocube.  This gives a really cool effect when the lights are out.

Hadronistics

Hadronistics involves the study and application of Hadristors; gravitational devices which which play an essential role in FTL (Faster Than Light) transportation.

Took this one down.

This piece was done by improvising four different long sounds using home made boxes including the Thing 2 device depicted in the image.  The Thing 2 device combines an Atari Punk Console, a NAND Synth, an Odd Filter and a noise source in a single box with four LEDs, two of which are blinking.  The walls of the box are covered with fresnel lenses to give the impression of something which look larger on the inside than it does on the outside (TARDiS).  Other instruments used are an APC expanded with a capacitor array and odd filter used as input to a Bass++ drum trigger for rhythm patterns.

The Thing 1 noise source, NAND Synth 1 and 2 with VCF LPF 1, some signals were processed through a Motif with chorus, reverb, phasing and delay.  The entire sound was processed in Reaper with Apple reverb and Voxengo Elephant for compression.

Thing 2 and Steam Drone

This video demonstrates my Thing 2 device with a Steam Drone device.

Phaser, echo, reverb, and chorus added with a Motif.

Steam Punk Drone/Noise Box

I found this box at a thrift shop a while ago and was trying to come up with a circuit to put in it.  I finally decided on a circuit made from a NAND synth combined with resonant low pass filter.  The controls are as follows:

Top row (left to right) Power on, NAND Osc 1 to output, NAND Osc 2 to output, NAND Osc 3 to output

Middle row (L to R): Starve (10 kOhm Pot on supply V), Q, Fco, Output volume

Bottom row (L to R): NAND1 Fqc, NAND2 Fqc, NAND3 Fqc, NAND input level to filter.

Back (not shown) Ext. Audio Input, Fco Cv input, Output.

Note: Below the glass plate are a couple of blinking diodes.

The control voltage mix op amp is to the left.  It turns out this section did not function because apparently I forgot to tie some stuff to ground and -V.  The NAND gate chip is on the right.  In the middle is the VCF based on LM13700.  This is the filter schematic.  Note this has an error the transistors on the right need to be grounded.  I think there is another error too.  (The NAND synth section is not shown)  The TL972 I am was using did not seem to work in this application.  I am replacing it with a TL082 in future versions.  Not quite sure why.

Updated circuit diagram and PCB layout.  IC pin spacing should be .1".

Salen-Key VCF

This is a voltage controlled low pass filter with three control voltage inputs and three audio inputs.  Designed for 9V but could be higher.  This design has not been tested so use at your own risk.

Chaotic Circuits

Ian Fritz has a number of chaotic circuits on his page that look really interesting.  I thought I would start with one of the simpler ones.  This is my drawing of the Driven Damped Well chaotic oscillator.  Unfortunately this does not seem to make any sound when I power it on so I need to trouble shoot it.

Update: I did some trouble shooting but it still does not behave as expected. (chaotically) it seems to be passing the original sound to the output.  I am monitoring the NL output so I think I will switch over to the X output.

Update 2: I did more trouble shooting and switched the output to X and now it does indeed behave chaotically although in a not very usable fashion at the moment.  One thing I love about chaotic systems is that they depend on prior initial conditions.  So as you turn the knobs the circuit may not be making any sound, then you pass a point and here a blip, as you tweak around the blip you gradually bring it into oscillation.  Suddenly the oscillation goes away and you get silence again.

I have been feeding the output of an Atari Punk Console in to drive this circuit.  At some settings it has been making some overtones and clicks but they are difficult to find.

Current DIY Projects

 These are some pictures of some current DIY synthesizer projects.  This first one is a 10 step sequencer with a 555 clock.  I used different colored LEDs for each step (not sure if this will mess up functionality yet).

The next one is my DACPOD.  This will be mounted in a case and combines a simple resonant VCF with an Atari Punk Console and my blinking light circuit to give it two flashing LEDs.

 This circuit is supposedly a snare drum but it needs a couple of capacitors and a transistor yet.

This is a Rossler Attractor chaotic oscillator circuit.  Should have put some caps on the outputs for this one.

This circuit combines (left to right) a control voltage mixer, a voltage controlled resonant low pass filter, and a NANDsynth oscillator as well as blinking LEDs along the top.  This circuit ended up as my Steam Drone box.

MFOS Alien Screamer

Ray Wilson has come out with a new circuit the MFOS Alien Screamer:

I really like the sound of this thing and possibly more importantly I like how such a complex sound can be generated by such a simple circuit.  Ray has done a great job of extracting the most functionality out of the fewest components here.  The only thing missing is an appropriate filter to go with it.  I have been working with a couple of VCFs including Ray's Odd Filter from the Weird Sound Generator but I think for this one a LM13700 filter is more appropriate.

Atari Punk Console

This is my layout for my Atari Punk Console.  This is about as compact as you can probably make this device without going to surface mount.  The + and - go to a switch to the battery.  The P+ supplies the positive voltage to the two pots (right side), the PP goes to the wiper of the Pitch Pot, the PM goes to the wiper of the Mod Pot, CvR provides a voltage to the two control voltage RTS 1/4 jacks and should connect to the ring of both jacks.  This will allow you to use an expression pedal to sweep pitch or mod.  Note the resistor presents too much current from flowing if you short out the connection.  The CvP goes to the tip of the pitch control voltage quarter inch, and the CvM goes to the tip of the mod control voltage quarter inch jack.  The output goes to the tip of the 1/4 right of an audio pot 10k-100k.  The wiper goes to the tip of quarter inch jack.  The sleeve of the jacks should all be connected together and grounded.

This design makes use of both modulation connections on the 556 chip so you can modulate pitch and wave shape.

This setup has the following additional components:

2 stereo 1/4 inch jacks for control voltage or expression pedal input
1 mono 1/4 inch jack for output
2 500k - 1M linear taper pots (either work) for pitch and wave form modulation
1 10k-100k audio taper pot (either should work) for volume
1 SPST toggle switch for on/off
1 battery clip or 9V supply connecter (or both)
1 case of some type, a lot of options here but I like the "Really Useful Box" series from Office Depot because they are easy to drill holes in.

Here is a video demonstration of this device:

You can use this to make a PCB.  You will have to scale to the correct size.  The spacing between the pins on the chip should be 0.1 inch.  The output will be the contact on the far right.