Description:  Mattson Mini-Modular Voltage Controlled Mixer

Here is a MOTM-ized Mattson VC Mixer!  From the Mattson website:

The VC Mixer consists of 4 channels.

Each channel has an associated gain control and control voltage input.

There are two outputs; Normal and inverted.

The control inputs respond to a 0-5V control voltage input. 0V is fully attenuated and 5V will produce a 100% output level.

The Level control attenuates the channel level.

The control inputs are cascaded. 5V is applied internally to the Control input for the channels and cascaded from channel 1 to channel 4. This allows the module to be used as a 4-channel mixer with no control voltage input to the Control in jacks.

When a Control input is plugged into a channel Control in jack, it interrupts the 5V from that channel through channel 4 allowing the gain for that channel, and all subsequent channels to be controlled by the new control voltage. New control voltages applied to the subsequent channels will interrupt the preceding channel control voltage for that channel and be applied to the remaining channels.

The trim pots on the circuit board are labeled with the associated CV gain adjustment and are set for a 1:1 input to output ratio. They can be trimmed to provide additional gain to utilize the mixer as an amplifier, if so desired. The gain will clip the original signal and can be set to overdrive the signal into a square wave peaking at the positive and negative power supply levels.
The mixer will work with both audio and CV inputs.

Construction

I used a Front Panel Express Panel of my own design, based on the MOTM jack grid like other recent panels I’ve been making.  This grid allows fitting more pots into a smaller area.

Bracket parts

The Mattson PC board is just a tad too wide to fit on a Bridechamber 3-jack bracket.  I made an adapter bracket out of thin aluminum stock I got at Lowes.  The adapter bracket mounts onto the Bridechamber bracket and then the board to the adapter bracket.  This photo of the bracket shows the bottom side that attaches to the Bridehamber bracket.  I matched the holes up to existing holes in the BC bracket, drilling out to 1/8-inch to work with some old PC motherboard standoffs I had.

Wiring up a Mattson DIY board is easy if you purchase the corresponding wiring kit.  All I had to do was to trim the wires and connect them to the panel parts.

Description: Mattson Mini-Modular Quad Buffer

I took Mattson’s DIY Quad Buffer board and added four attenuator pots to turn it into a quad buffered attenuator.  I call it a distributor, because each channel has two independently buffered outputs.  The board supports cascading the channels by providing a third buffered output for the first three channels that can be connected to the third lug on a switching jack.  I designated the four channels A-D, and decided to cascade A into B and C into D.  The pot on the first channel impacts both.  In other words, the A pot affects the A outputs and the B outputs.  Likewise the C pot affects the C and D outputs.  The B and D pots only affect their respective outputs.  There is a 1% voltage drop on the cascaded channels, due to the use of 100K pots and the 1K output impedance of the buffer.  (Note that when wired as intended the Mattson module doesn’t have any voltage drops along the cascade, because the input impedance of the buffers without pots is very high.)

What’s it for?  Quite a few modules in my system have control voltage or signal inputs without attenuation.  My other buffered attenuators (Oakley Multi-Mix, and Blacet Mixer) are bipolar and don’t have a good zero setting.  The Blacet mixers do have a center detent pot and a trimmer to null the center, but a small signal can still penetrate.  My own DIY Mixer-Comparator has only one channel. So I really wanted more zero-off buffers.

Construction

I used a Front Panel Express Panel design of my own, again using the MOTM jack grid like I did for the CGS Super Psycho LFO and Slope Detectors.  This is a compact design that essentially allows fitting more pots onto a panel.

The tricky bit is mounting a Mattson PC board onto a Bridechamber 3-Jack bracket.  The bracket isn’t quite wide enough.  I had to make an adapter bracket.   See my post on the Mattson VC Mixer for all the details.

Wiring up a DIY Mattson module is relatively easy.  Mattson DIY boards are assembled and tested.  I purchased the corresponding wiring kit with all necessary wiring pre-fitted to connectors.  All I had to do was to trim the wires to fit.

Quantity: 1 in a 1U-wide panel

From Ken Stone’s website:

This module is a much expanded version of the Psycho LFO, featuring six free-running oscillators, each variable between LFO and audio ranges, two of which can be switched to have triangular wave outputs. Each oscillator can be switched between low and high ranges, as well as off, and also has a rate LED, to allow visual determination of the frequency at which it is running. As per the original, there are also level and glide controls.

This module can be used to create a range of pseudo-random modulation voltages that can be used to generate unusual sequences, control VCFs or or VCAs etc. When run at higher frequencies, it can be used as a series of audio drones, or to generate complex sounds by frequency modulation a VCO.

Panel:

This is the second module I’ve built using the 8×2 MOTM jack spacing and small pots and knobs. You can download this Front Panel Express Panel.  This format works perfectly for the Psycho LFO, which I had never built because I did not wish to devote 2U of panel space to it, which would be required if standard 1-inch diameter MOTM knobs were used.

Modifications:

There wasn’t room on the panel for Triangle/Square switches for the two oscillators with triangles, and because the triangles impart an undesirable DC offset when switched off, I chose to omit the triangle option and make all six oscillators use square waves. I substituted 2K2 resistors for the specified 1K for the LED current. I could have used 5K6, because the LEDs came from an original Blacet Miniwave. They’re too bright! I’ll probably change them.

Circuit comment:

How many modes of operation does the Super Psycho LFO have?  It has six identical oscillators, each of which can be Off, Low Frequency or High Frequency.  Do the math:  There are 21 different combinations, I think, between one Low Frequency oscillator on to one High Frequency oscillator on.

Here’s the construction. The LEDs are not glued, but are held in place by the wiring harness.

The empty spot on the lower right of the PC board is where the IC for the triangle waves is omitted.  You can  see the two jumpers hard-wiring the square wave option.

Here’s how it looks in the cabinet with the Blacet Miniwave on the left and the CGS Slope Detectors in the same panel format to the right, next to the MOTM-650.

The slope detector is an event-driven gate/trigger generating device. It monitors a control voltage, and responds according to what that voltage is doing. If the voltage is rising, the slope detector gives a “gate” output (approx. 5V) on its “rising” output. Likewise, if the voltage is falling, the slope detector gives an output on its “falling” output. The duration of this gate signal depends on the incoming CV and the setting of the sensitivity pot. When the CV is remaining constant, the “steady” output activates.

These gate signals can be used to fire envelope generators dependent on the action of the CV, for example opening a filter when a melody is rising in pitch, and closing it when the melody is falling in pitch. It can also be used to generate gate signals from LFOs, envelope generators, to advance sequencers etc.

The sensitivity pot allows the slope detector to work with either relatively fast events, like the edges of a square wave pulse train, or very slow events, such as the sine output of an LFO being used to drive filter/phaser sweeps.

This is a dual module, housed in a Front Panel Express Panel of my own design. It’s the first of four modules planned in this style, which has sixteen equally spaced positions (8 x 2) where pots, jacks, switches, or LEDs can be placed. The vertical spacing between components is one inch and the horizontal 0.85 inches, which is the same as MOTM jack spacing. The use of 16mm Alpha pots and 3/4-inch Alco knobs allows the placement of pots anywhere. This is the design insight and also the main compromise. The Slope Detector has one pot, three LEDs and four jacks, perfectly fitting two of them into a 1U panel.  The red LED comes in a chrome bezel, Lumex PN: SSI-LXR4815ID.  SSI-LXR4815YD and SSI-LXR4815GD are yellow and green. I use green to indicate positive voltages, so I chose it to indicate Rising.

Modifications:  I changed the voltage divider resistors on the outputs to be 3K3/1K8 instead of the original 1K8/1K to reduce current draw.  I use these values for all of my digital outputs.  RLED is 2K2 ohms.

The 3-jack bracket from Bridechamber allows mounting the PC boards adjacent to each other.  (Two additional holes need to be drilled.)

Here it is in the cabinet, next to a standard MOTM format module. The most unusual thing is the LEDs located in what’s normally the jack region. I think the smaller knob fits in well.

• Mackie 802-VLZ3 8-input mixer
• Lexicon MPX-1 Multi-effects processor
• TC Electronics Desktop Konnekt6 Firewire Interface
• TASCAM SS-R1 Compact Flash MP3 recorder
• A pair of FMR Really Nice Compressors

Of the many potential ways to hook this stuff together, I’ve come up with this patch.  Have a look at this block diagram.

I’ll describe how this works with the Mackie features to get flexible signal routing.  The first thing to look at is the Matrix Mixer in the upper left.  This is my own Matrix Mixer module.  It can mix up to six signals coming out of the modular and has stereo outputs.  (Most of the arrowed lines on the diagram indicate stereo connections.)  Note how the output of the Matrix Mixer tees off, one branch straight into the Mackie on channels 3-4, and the other going through a compressor and the Lexicon in series into channels 5-6.   Both the compressor and the Lexicon are stereo units, and each has a bypass switch.

Moving down the diagram, note the mono Aux Send output.  This is not pre-patched.  I use it to send signals into the modular for any purpose, but usually to patch modules as effects.  The MOTM-410 filters, Blacet Time Machines, and Blacet StonZ Phaser make very good effects processors.  The outputs from whatever I’ve chosen are then returned to the Mackie channel inputs 1-2, which have equalization and also the ability to mix back into the aux send bus for feedback!

Next, notice how the firewire interface is fed from the Alt Outputs of the Mackie, and is returned on channels 7-8.  I have to explain the alt outputs.  Each input channel on the Mackie has a Mute-Alt button.  In the normal position, the channel signal is routed to the main mixing bus, headed ultimately to the tape recorder and the studio monitor speakers.  But when the Alt button is engaged, the channel is routed to the alt out bus.  The channel fader still controls the level, but now on the alt out.  This means I can mix to the computer any of the three sources:  from Matrix Mixer, from Lexicon effects, and from modular effects.

Remember that each Mackie channel also has an aux send pot that mixes into the Aux Send bus.  (Selecting the ‘pre-fader’ option sends the signal to the aux bus before it reaches the channel fader.)  Are you getting the picture now?  Possibilities include:

• Three parallel effects:  Lexicon, Computer, Modular.
• Lexicon and/or Computer effects followed by a Modular effects.
• Modular effects followed by Computer effects.

A few things I can’t do, such as routing the stereo output of the computer to the stereo input of the Lexicon.  (I have to mix channels 7-8 to the aux send and patch the mono aux send into the Matrix Mixer for that routing order.)  This setup has flexibility that I could have used even before I got the firewire, if only I had thought of it.  I hope this information may be useful to you.  And please add comments!

This version uses the dual Pulse Comb Filter from Audio Mulch that I’ve been playing around with lately.  It’s the same mulch patch as the other pulse comb stuff posted here, but with different settings (there’s a lot of settings to play with!).

This version uses two additional effects.  The MOTM-410 sweeps the sound with two bandpass filters, resulting in a stereo effect.  And the MPX-1 Double Delay.