I've decided to include the latest and archive blogs from Amongst Projects where my music electronics and filming gear is stored.
|TMNSD - The Final Unit !|
The TMNSD is short for ? Actually I've totally forgotten what it's short for. Never mind. My friend Bernard asked me to build this unit for him to his needs for his modular synthesizers. This unit is three independent Control Voltage controllers each with a built in arpeggiator designed to control modular synthesizer systems Voltage Controlled Oscillators or any other voltage controlled input device.
The user can simply play single notes or use the arpeggiator to cycle through the chosen notes in a variety of patterns and also over a larger range of octaves. The arpeggiator has several Play Modes. There's Up, Down, Up/Down and Random. It also has a AsPlayed Off and On mode which means the notes will play in the order that they were selected. The Latch control will hold the notes on when first pressed and turn off when pressed again.
Each module has an external trigger input located on the left side of the unit. On the right hand side each module has CVA and CVB outputs. These are control voltages set at 1V per octave to control the VCOs (Voltage Controlled Oscillators) pitch. The outputs have an accurate range of 12 octaves. There are three trigger type outputs - Trig, Gate and Aux. The Trig outputs the trigger signal and naturally the Gate outputs a gate signal. The Aux output has several output options. The only link between the three units are an internal sync connection. They are synced to the previous module. By this I mean that module C will sync to B, B to A and A to C. This way most combinations can be achieved.
|Top view of the completed TMNSD|
The front panel controls consist of a potentiometer for controlling the arpeggiator speed when in independent mode. It also acts as an time offset control. More on this later. There are 12 touch sensors which represent the 12 notes of a chromatic octave which have 12 associated RGB LEDs and four function controls. These controls are FUNC which takes the unit through several setup screens. ARP which puts the module into arpeggiator play mode. LATCH which will latch the notes off and on and finally MODE which is another setup screen relating to the arpeggiator controls.
The FUNC key takes the unit through 3 different modes. When lit green the unit is in PLAY mode where notes can be selected. When RED the unit is in the INPUT and OUTPUTS setup where the clock source can be changed, what is output on CVB is changed along with what the Aux output will be outputting. During this mode the ARP SPEED potentiometer also changes to control the timing offset of the Trigger output which will range from 0% to about 90% offset to the next trigger. This also affects the Gate signal. When FUNC is BLUE the note keys represent a divisor of the clock speed whether internal or external. This starts from 1/1 up to 1/12 on the B note.
The other function is when the MODE key is GREEN. During this mode the notes have several different functions which include the play direction of the Arpeggiator, the octave range of the arpeggiator and also a transpose function which takes the arpeggiator down by up to 2 octaves.
Each module is made up of two PCBs. There's the CPU board and the Panel board. The CPU board contains an Arduino Pro Mini which controls a MCP4922 dual channel 12 bit digital to analogue converter via SPI. The two outputs of this converter are processed through an op amp to change the output voltage range of 0 to 5v to -6 to +6 volts. The opamps have 10 turn trimpots for tuning the output voltage offset and range to generate an accurate 1 volt per octave output. The trigger outputs are generated from 5v digital outputs on the Arduino which are buffered through a TL074 quad op amp. The trigger inputs are processed through a diode and transistor to clamp voltages over 5v as to protect the digital inputs on the Arduino. This schematic came from the wonderful Electro Druid web site. As can be seen below, the AMP trimpots from CVA and CVB have been removed. For this project I decided it would be easier to fix the feedback resistor of the op amp channels and use software to correct any error. I could have done similar with the Bias trimpots as well.
|TMNSD CPU Board vD - note the capacitors across the resistors and the lack of AMP Trimpots|
The front panel is made up of 16 daisy chained WS 2182 RGB LEDs which I've used before and have down pat though I have to admit that I wrongly used two different purchases of LEDs to find that the second batch had a different LED order. Thankfully these are all together on separate modules. The touch sensors were using a new discovery, the BS818 chip which is an eight channel capacitive touch sensor chip. I've previously used TTP-223 chips which are single touch switches but I needed to find a multi-switch version for this project. The potentiometer is also mounted to the front panel board for ease of construction. The touch sensors themselves are neodymium magnets. I'd previously used drawing pins for touch sensors but they needed complicated electrical connections in the way of single sockets.
|Front Panel Board - front side - populated|
The boards were made by Seeeds Studio in China and they are very good quality. I've had 10 made of the CPU boards and 5 of the front panel boards. Due to the numbers I decided to make the CPU boards a little more generic. The board has provision for MIDI and via the serial port which includes a jumper location to change between the programming port and the MIDI port and an I2C for a LCD screen. I have a number of previously made MIDI interface boards which could be used. This way the module could potentially be used to create an LFO module or any other number of music related projects. The I2C connection could be used to connect another Arduino which in turn would have provision for multiple potentiometers or data encoders. The options are there.
|Close up of a LED bezel shows the countersinks for the magnet and bolt|
|Front Panel with all the acrylic pieces in place and the white paint infill completed|
The case was another milestone for me. It's made from hardwood in particular Tasmanian Oak which is a plantation wood. It is quite hard, as the name suggests, and takes a considerable amount of time to cut on the router but after many attempts I managed to make a finger joint using this wood. Previously I have used MDF and plywood but neither of these woods worked to form a clean finger joint. I think this is something that I will be using more into the future. The input and output panels are 3d routed from 3mm black acrylic and filled with white acrylic paint as I have done in many projects.
The power for the system runs from a 18v plugpack. This in turn is converted to 5v via one step down converter and another buck converter creates the -12 and +12 volts needed by the opamps.
All the discs are made and I'm getting ready to mail out to all the radio programs around the world.
So Hostbaby is closing down and has been taken over by Bandzoogle. I have to say that it's all looking good so far and easy to edit. There are some caveats with formatting but I personally like some limitations.
I'm "streaming" through my Amongst Projects blog here as well which is a little out of date but its purpose is to log my electronic projects I design and build for music and film related areas.
|The Transport Controller - this unit does the transmitting - well used already !|
A while back I made up a simple transport controller so I could remotely, well a few metres away, control my two main audio software packages, Cakewalk Sonar X3 and Sony Vegas Pro 13.
This unit is made of two parts. There is the remote battery powered transmitter and the receiver unit which has a MIDI output on it to connect to one of my MIDI interfaces. The transport controller transmitter simply has seven switches which are monitored by a Arduino Nano which when pressed transmits the a value to the receiver. The receiver gets these values and puts out an appropriate MIDI controller value to the music computer.
The radio setup in both units are nRF24L01+ 2.4Ghz ultra low powered transceiver modules which are cheap and work a treat. Several libraries exist for the Arduino making coding simple. I used mirf. The radio modules communicate with the Arduino via the SPI interface.
I wanted to also try out something different for the controller buttons. So I went with touch sensitive buttons. This uses a small module called the MPR121 capacitive touch sensitive breakout board containing a Freescale MPR121 chip that interfaces with the Arduino using the I2C interface. I became aware of them via Julian Illets youtube videos for his penny touch organ. The module has 12 touch sensitive electrodes in total. I am only using 7 for this project. The buttons themselves are drawing pins as it seemed the simplest way of getting a neat electrical connection from the front of the panel to the pins on the MPR121 board.
Another challenge was to use WS2812G RGB leds as indicators for each button. These I mounted onto the rear of some routed 6mm opal acrylic bezels to help diffuse the light. In turn these bezels where mounted through holes of the transport controllers front panel. The front of these pieces of acrylic had the basic transport control symbols routed into them and filled with acrylic paint. This has a nice effect of backlighting the symbols. When the unit is running each of the symbols are lit with a washout colour but when the button is pressed it goes to full saturation.
The power for the transport controller comes from an 18650 3.3V LiPo battery. The battery is charged via a micro USB connector which is mounted on the TP4056 based battery management board which takes care of charging the LiPo battery. From the outputs of the TP4056 there is a step up voltage board which takes the voltage of the 3.3v LiPo battery to 5v which powers the Arduino Nano. In hindsight I should ave used a 3.3v based Arduino as it would have saved using this step up board as all other parts in the transport controller can run from 3.3v.
|The receiver unit showing the USB power socket, MIDI connections and Joystick socket on the top.|
The receiver is a simple Arduino Nano with a nRF24L01+ attached. Pretty simple. One of my standard MIDI I/O boards is also mounted in the receiver case to transmit the incoming radio signals to the MIDI output and eventually controlling the software. Once again I used the Forty Seven Effects midi library.
|The joystick controller|
I have recently made an addition which is a joystick controller that sends out MIDI controller values for the X and Y positions of the joystick. This is something I wanted to control certain VST plugins within Sonar. One VST in particular which is a granular effect emulates a joystick on its own screen which I was able to attach to my new joystick controller. For this I made one of my acrylic cases to house the joystick with a 4 core cable running back to the transport controller receiver. The two signal lines from the joystick for X and Y are connected to two analogue voltage inputs on the Arduino and their values are converted into MIDI controller values. I found I needed to add a bit of smoothing via a couple of 100nF capacitors across the analogue input pins as the power coming from my USB 5v power supply which powers the receiver was a little noisy and affects the incoming joystick values.
The unit works well when doing recording mostly. I have the controller sitting on the keyboard I am using and with a simple setup with either audio package I can record and do other operations.
|The Therematron NOT - current model|
So the original Therematron design was based around MFOS Soundlab Mk2 designed by the late and great Ray Wilson. Along with this wonderful 2 oscillator synth I was to use Ray's Echo Rockit digital delay unit and the icing on the cake would be the PAIA Theremax theremin. What a wonderful machine it was. In theory anyway.
It was quite a while ago that I started the original Therematron. I started this back in August 2014 or possibly earlier. Looking back at my daily log I read that it wasn't until February 2016 that I finally got back to trying to make the Therematron work. I had got the Theremax working inside the case but there was something wrong with the Soundlab. The wiring of Ray's boards isn't easy. I fully comprehend that he designs his boards to be as small as possible but in the process most potentiometers and switches don't have their terminals next to each other and can often be part of a chain of wires to get them all connected hence the wiring of a single board synthesizer is quite messy. Add to this the limited space inside the case and problems become quite difficult to solve. Hence I appear to have put off getting this unit running considering it was in late 2014 that I had made the case up.
Moving along to March 2016 and several other distraction projects later, I was battling with getting the VCOs to be stable. The issue was and still is to a degree, an amount of the envelope generators LFOs coming through. It must be something to do with the earth line as far as I can tell. I'm not working on solving this issue as I'm happy with where it is. Someday I may come back to this.
I made this funky light display on the rear of the Therematron as just something to do and it also affects the power supply but to a greater degree that I can't use it. I could possibly try putting in a power regulator on the light display to help alleviate any affect it has on the other parts of the power circuit. Since this is only seen from there rear I think I will just put a 9v battery inside to run it when I use it live. Seems the simplest solution to me.
|Rear panel atom animation|
It was during this period of finalising the Therematron that I could not get the Pitch on the Theremax working when installed in the case along with all the other electrical noise. I could get a reduced output from the Volume antenna. Quite disappointing. I was also disappointed by the quality of the Echo Rockit. I knew that it was "lo-fi" but it was lower fi that I was happy with. So there Therematron went back on ice and then we moved to the country. It was February 2017 before I started what would become the Therematron NOT !
Having moved into the new house and setup a new studio I returned to where I left off back at the Blackwood Studio and started work on the Therematron NOT! in the new Wahroonga Studio. I decided that I would remove the Theremax and replace the Echo Rockit with an Experimental Noize module. Quite a bit of work but I wanted to get this machine working. The Theremax may still appear in a new case later down the track.
This upgrade couldn't be simple could it ? Oh No. I designed an effects chain which not only had the EN SKRM module but in addition the module contained an analogue feedback path which, for extra variation in sound, includes a VCF and a LFO for VCF modulation. The idea being to emulate to some degree what the Echo Rockit could do and more.
The EN-SKRM module was mostly straight forward as I had already made the UM-XN1 guitar effects unit. Where the Therematron version differed was the addition of a feedback path which routes the output of the unit back to the input but via a VCF. This VCF can also be moved within the signal path. It can be changed from being in the Feedback path to being at the start of the effects unit. Reasonably straight forward in theory.
So a LFO. I wanted to make a LFO based around an Arduino controller and a MCP41100 digital potentiometer. These potentiometers have a 256 level 100k pot which are controlled simply using SPI from a microcontroller. So the idea came to me to use the Arduino to create several different waveforms as a CV to output as a modulator. A fellow electronics nut and musician, Abram Morphew, had done all the work already. Abram had created what I was after as far as the waveform creation using interrupt timers on the Arduino. Some small modifications to his code made the digital pot do all the work.
The LFO has another Arduino which controls the selection and display of waveforms on the front panel. The EN-SKRM module also has a similar Arduino panel controller. I decided to use a simple serial protocol to have the panel Arduino talk to the LFO Arduino which appears to work well after some initial problems. I originally had the serial communications working over the Software Serial library, which is a software method of creating a serial line on any Arduino digital connection but the downside of this is there is no UART with a data buffer. Hence, if you do not monitor the software serial connection you may miss something. The hardware serial ports on the Arduino have a buffer where data is stored until read or until it's full. This way you don't have to be as concerned about servicing the serial port.
The VCF I wanted to be cheap and dirty. I chose a design Ray Wilson had in his book, "Make: Analogue Synthesizers". It was based around a single LM13700 chip. The only problem was it was too dirty. Aghhh ! Now I need to find space and another design. I was getting bored by this stage. I trawled through links to find the YuSynth site. Here I found a Steiner VCF that was not only a good sounding VCF but there was also a single sided PCB design. So I set out and cut myself a slightly modified version of this VCF. I moved the power connectors around and change the ins and outs to suit my connectors.
|The new VCF, LFO and Effects section|
So now I had a good sounding setup. I needed to create a new bottom panel for the Therematron. Like usual I spent a good day in Freehand moving things around on the screen and realised that I had some spare real estate now that the Echo Rockit has been replaced. "Let's put in another module !" - I heard my evil twin shout. But what ?
I had been playing around with some simple circuits from my copy of Nicolas Collins, Handmade Electronic Music, is recent months and I remembered where he describes using a 4017 at audio speed. A 4017 can be used as a divider. It's in reality a decade counter. So it gets me thinking about using a 4017 to make a sub-oscillator. Why stop there. A 4017 puts out a nasty square wave so I put a variable filter after the 4017 and now I have switchable 1 or 2 octave sub-oscillator with a low pass filter on it. That fits quite nicely into the front panel.
|My rather messy schematic for the Sub Oscillator (note power input is +/- 5v)|
It all fits quite neatly. Don't lie ! It's a mess inside there. Do not enter without a guide. It's not perfect as the whole VCF switch around on the effects doesn't quite work but for now I am happy. I've programmed the SKRM module with a basic set of reverbs, echos and modulation effects for now and I can always come back and change these later. The top front panel still has the Theremax controls but the Theremax is no longer contained and the aerials for the Theremax are still there and act as nice handles. Now I just need to use it to make noises !
But the main question is whether this is the end for the modifications after all there's the front space where the Theremax controls were ?
|The full rear panel|
|The Flatman and Ribbon - Dual Ribbon CV controller|
The main focus is making a controller for modular synth units hence it needed to put out a control voltage relative to the position on the ribbon. Going to my trusty supply of Arduino Pro Mini processors you may know there is a lack of voltage output control. There is a method of creating a voltage output using a resistor ladder and several digital outputs but we wanted something a little more accurate and less output hungry. So I chose the MCP4922 dual 12 bit digital to analogue converter (DAC) primarily because Chip used this one in his ribbon controller project. This digital to analogue converter was cheap and has two converters on it. So it was the dual converters on the DAC that allowed this project to easily have two ribbons.
|The botched job of the MCP4922 Digital to Analogue converter can been seen at the bottom left of the printed circuit board.|
|Showing the back side of the controller unit. The overkill power supply with it's 6 x 1000uF electrolytic capacitors|
I went a little overboard with the power supply. It's based on Ray Wilson's (MFOS) design which I have used before. The Wall Wart Bipolar Supply is a simpler way of getting a dual rail power supply as it avoids dealing with mains wiring. This is because it uses an external 12v AC plugpack or wallwart. I don't think anyone really likes plug packs but working with mains wiring is less appealing plus there is the added cost of the associated hardware. Using Ray's schematic, I replaced the 7812 and 7912 in the design with 7809 and 7909 regulators to give me 9v which is more than adequate for the output voltages needed. If I used 12volts I would be pushing the Arduino's own power regulator to its limit which I didn't want to chance.
|Showing the front panel with the outputs down the left side and the lcd with menu buttons on the right|
Next to the output sockets I've put a rgb led associated with each output. These rgb leds are my favorite led at the moment - the WS2812. What makes this leds nice is you can simply string several together and the library courtesy of Adafruit makes them easy to control. I highly recommend you support Adafruit. I would more if the freight costs to Australia were more affordable. These leds reflect the state of the outputs. The control voltage leds do a colour wheel effect based on the ribbon position. There was a small issue when it came to the software. I use have used one of the processors interrupt timers when running the sample/hold mode but alas the Adafruit library gets upset with me doing this thus during this mode the leds do not function correctly.
The unit includes a MIDI In and Out. Since the Pro Mini has a standard serial interface it makes sense to include a MIDI interface. The unit will act as a MIDI merger allowing all MIDI information coming on the In connector to be thru putted on the Out socket. With the addition of the information from the ribbons. In addition there is a MIDI function which monitors the MIDI in for a MIDI clock and converts this into a pulse on the Aux Output.
The outputs on the controller box are Control Voltage A, Trigger A which are associated with the top ribbon. Control Voltage B, Trigger B which not surprisingly are associated with the lower ribbon and Aux Output. Depending on what mode you are running the unit in depends on what the different outputs do.
|The underside of the controller panel lid. Shows the LCD at top with it's I2C daughter board, button board at the bottom, the rgb leds and output sockets to the right.|
There are various parameters within the menu system. For both ribbons we have:-
- U Lo Volt - sets the lowest voltage value
- U Hi Volt - sets the upper voltage value - note this can be made a low value and the U Lo Volt can be a high value thus creating a reserve direction ribbon
- U Trigger - whether the trigger output is Trigger or Gate - trigger will simply pulse when the ribbon is first pressed whereas Gate will hold the trigger pulse high until released
- U Hold - set this On and the control voltage output will be held at the last value otherwise it will revert to the U Lo Volt value
- U MIDI Ch - this is the MIDI section and this value sets the output midi channel
- U MIDI CC - this is the controller value that this ribbon will output on
- U MIDI low - the minimum value to output
- U MIDI high - the maximum value to output
|The USB end of the ribbon platform which I am very proud to have made work and look good|
|This the Cut2d shaded preview of the USB end of the platform. The pcb was made to the same shape as the large internal cutout but less 0.5mm in size so that it was a tight fit.|
|These two pieces were routed from 3mm black acrylic and adhered on their joining edge.|
|Florian Vox - View from the front|
I got interested in voice synthesis one day partly due to being in the Kraftwerk cover band, Uber Ding, where I had given myself the task of creating some synthesized voices for some of the tracks. Hence the name Florian Vox being a reference to Florian Schneider, founding member of Kraftwerk.
I came across the Emic 2 Speech Synth module which was an easy to use and somewhat more advanced sounding than other voice synthesis. One nice thing about this module is it will allow singing at specified notes which I thought could be fun to play with.
So the project was to be a standalone unit which accepted MIDI as a controlling device. The idea being that I could create programs on the unit which were controlled via midi notes or controllers. Allowing the press of a key to say a word, phrase or even sing something at a given pitch. The unit would also need a few other items like an audio output as well as some simple buttons for various operations.
The unit is powered via the USB which is also the programming port of the Arduino Nano. This is the first project that I have done where I have used the standard hardware serial which is normally used for programing the Nano. I've placed a toggle switch on these ports because the MIDI interface which is connected to them during a run interferes with the USB interface and hence causes issues while programming the Arduino.
The Emic module has a speaker output with a small audio amplifier. I made the mistake of connecting the audio output to this connection. There is a 3.5mm jack on the Emic module but for some reason I thought this was also a speaker connection. It is actually a line level output. I modified my board to accommodate this error.
|Florian Vox - View inside the case - the Emic2 module on the left hand side - one of my standard MIDI interface boards on the right.|
The hardware side of things was quite straight forward apart from a couple of small errors. The other small error I made was regarding the toggle switch. I designed and made the printed circuit board before I had the pcb mounted switch in my possession. Unfortunately I had placed the pin holes in the wrong place and the outcome was the switch would not be mounted on the board but to the case. The angled toggle switch that I purchased at great cost was not used in this project.
I had some fun with the case. I took a vector graphic of Kraftwerk in fan recognised standing pose and then routed and paint filled it on the top panel. The case is one of my standard and now familiar cases. This is also the first case where I have replace the standard philips head screws with hexagon bolts as I think they have more of an industrial feel that I like.
The bad news though is that it can't really be used as a real-time instrument. The Emic module operates by receiving serial codes. There is a quite a substantial delay from sending this code to getting a response from the synthesizer. Simple problem really. So alas I use the unit to make the sounds and then sample these to be used in the band. Of course that doesn't mean the unit couldn’t be used in a less structured music type of way but I've left the unit programmed to simply receive serial via the Arduino IDE. Something to ponder for future development.
|Florian Vox - Rear view showing the MIDI in and Out alongside the USB power and programming port|
|UM30 Mixer - Art View|
What is the UM30 Mixer's purpose - let's step back in time first
The UM30 Mixer came from an origin idea to make a new and larger matrix mixer which would replace the UM13 Matrix Mixer. So it made sense to do a bit of a log of the UM13 Matrix Mixer.
I've not done a log of the UM13 Matrix Mixer design and construction but this unit is based around a 3 stereo inputs and 6 stereo outputs. The purpose of this matrix mixer is to allow me to connect various effects units to my modular analogue equipment. So there are three input channels which each have five sends which lead out to effects sends. The sixth send is a main fader which sends a dry signal to the output of the mixer. What makes the mixer a little different is that the effects returns are also matrix input channels which can be send on again but only to other effects channels and only one at time. What this gives you is the ability to chain effects together and manually change them at any time during a performance. All input channels are stereo throughout.
This mixer is built into a rack, which I did log, which also contains my PAIA 9700 modular synth and the Music From Outer Space Weird Sound Generator and 10 Step Sequencer. What it also contains is a Kawai RV4 which is a quite nice but basic quad stereo effect processor. This RV4 is what is connected to four of the effects loops on the UM13. The other effect loop is connected to a Line6 Pod which gives some nice distortions. The WSG (Weird Sound Generator) and the UM13 share a common dual 12v power supply.
|UM30 Mixer - Front View - Note that I have used a simple single character to label what the pots function|
UM30 Mixer - an extension of the matrix mixer
When I only have a few pieces of gear, the three input channels was sufficient but of course like most people's setup, it starts to expand. Hence the need for more input channels.
The UM13's printed circuit boards are veroboard and the schematic design is overly complex - there's no real need for stereo input channels or sends. Both combine to make a noisy unit which is difficult to repair and has had ongoing wire connection issues which have only recently been fixed. One of the original design fails was using make before break wafer switches which caused a large thump when changing these switches. Replacing these with break before make switches has solved the thumping.
So the initial idea for the UM30 was a 8 input channel and 6 effects channel matrix mixer. I based the schematic design on the UM13 Matrix mixer but I wanted to make it more modular by way of having individual duplicate boards for the input channels and effects sends and returns. I also wanted to reduce the circuit components which meant going back to mono input channels. But it soon become clear that it was going to be too complex for me to make my own single sided printed circuit boards. I make my own printed circuit boards with my CNC router.
The result was that I would compromise the design and utilise the UM13. It was decided to treat the inputs on the original UM13 matrix mixer as effects input from yet another mixer. I know it's a little complex but it is the best option.
So the design has the following:-
- 8 mono input channels
- Each channel has a gain stage, 4 mono pre-fade sends, pan and level output
- 4 stereo effects returns
- Master output level
Each input channel of this unit is a separate printed circuit board which is held in place via the board mounted front panel potentiometers. The first three effects sends go to the UM13 with a spare effects send for another effect unit.
Many of my designs are based around someone else's design. Often I will base audio circuits on Rod Elliot's work. His designs are very good as far as I can tell. I've supported him in the past by purchasing some of his pcb's that he sells for his designs. I also cross reference with Ray Wilson of Music From Outer Space's designs. One of the new additions to the input channels was a comparator based led for the level indicator. I put in an dual opamp to make this circuit work. The circuit is simply a under voltage and over voltage setup where the green led will turn on at a set level as does the red led. The led used is an RGB led which I had in stock. These had a couple of 10 turn pots on them so I could calibrate them once the unit was completed. For no real reason I setup the red led to start flashing when the preamp on the input channel was about -6db from distortion. The green led starts up at around -28db. This seems to work well so far.
One of the stipulations of this new unit was for as little wiring as possible. Wiring not only adds places of noise and signal degradation but also makes for a slower construction. This started with the idea that the input channel boards would have all the pots mounted to the board and in turn the board would be mounted to the front panel via the mounted pots. So I have eight boards which are identical which are the input channels. The first board had a few design issues but I managed to modify this original board and still use it in the final project.
|UM30 - Inside view of the Input Channel boards - note the worrying power distribution board with the heatshrink|
All the panel sockets have boards behind them as well. The boards still have wiring to access power and join them up to their different busses but this is done using jumper leads.
I decided to build the power supply into a separate unit which in turn is powered from an AC plug pack using one of Ray Wilson's, rest his sole, wall wart regulator units. This is a cheaper way of powering a low power unit like the mixer. Otherwise I would have needed a more expensive 240vac transformer and associated regulation electronics. There is certainly no measurable noise from the power supply in this unit.
The unit is very quiet which is good as the matrix mixer is not overly quiet. But the noise levels are fine considering the use of these units within my analogue synthesizer setup which isn't overly quiet.
The case I designed and made up using my cnc router. It's about the largest I can do on my router and I actually cut the bottom piece of wood by hand. I used 16mm plywood because I had some in the shed and I wanted to use it up. The case is all glued together without nails or screws. The pieces are held together using the Mortise and Tendon join. This is where one piece of wood has male extension which fits into and is glued into a female cut. This diagram should help (picture needed here !!!!).
|UM30 Mixer - shows the front panel mounts. The side pieces is screwed to the side piece of wood whereas the front square tubing is mounted into the side piece and glued at the same time as the front piece of wood.|
The front panel is 3mm acrylic which was cut to size by hand and the routed with the cnc router. It was finished off by painting on white acrylic paint to fill the routes. This panel is held in with screws which screw into angles aluminium which are routed into the side pieces of the wood to make for a clean finish.
What I feel I achieved with this project was a method whereby I have managed to create printed circuit boards which avoid as much wiring as possible. My layout method was very accurate to allow for the pot holes to line up with the mounted pots on the printed circuit boards. The audio quality is very good due to a low number of components.
|UM30 Mixer - View from the rear showing the hole where the DC power connects|