The Azure Dragon is an effects rack which was designed with the primary purpose of being a flexible and mostly analogue effects rack for my Tau Hydrae monophonic analogue synthesizer.
The video presentation which goes through each module with sound demonstrations can be seen here - Azure Dragon Effects Rack
One of the several DIY instruments used by myself as Amongst Myselves - www.amongstmyselves.com
The Effects
One of the technical aims of the unit was to use as many classic analogue effects as possible. The Azure Dragon contains the following modules:-
- Valve Overdrive - this is the "classic" Matsumin Valve Caster design which is a low voltage overdrive including a pair of switchable clipping diodes.
- Auto Panner - an Arduino based LFO module controls a SSM2164 stereo VCA
- Jürgen Haible's - 20 Pole "Tau Pipe" Phasor - classic phasor module which I have left as designed
- Jürgen Haible String Ensemble / Tri Chorus - another classic sounding module with the addition of a stereo output mixer
- Oakley Sound's ADR30 BBD - high quality BBD with my addition of a complex LFO module based around an Arduino
- FV-1 - one of my standard digital units which is a Spin Semiconductors FV-1 multi effects unit
- Spring Reverb - a real tank reverb, Accutronics, with a basic driver module which includes feedback and basic tone controls
- Feedback Mixer - this allows any module to be hooked up to feedback its own signal. It includes a parametric EQ for tuning the feedback sound
In addition to these effects modules there are input and output modules which interface to the real world and include LED level meters and level controls. All the effects are connected via 3.5mm patch cables at the bottom of the unit. The output module has balanced outputs.
Given that the primary purpose for the Azure Dragon is to pair with the Tay Hydrae, the patch bay includes connections to the Tau Hydrae various control outputs like the Keyboard Pitch and Trigger signals along with the LFOs. Several of the effects modules have been made to utilise these control signals.
The Case
The case has been designed to both match and mount to the Tau Hydrae. It's made from 12 and 16mm MDF which has been painted satin white acrylic paint. The front panel was cut with my CNC router in two sections due to the router's limited cutting area. The wood pieces are held together with wood glue and positioned with biscuits placed with a biscuit joiner. The unit sits on the hardwood side panels of the Tau Hydrae and is fastened with two aluminium straps to the front.
The case does have a cooling fan as I was concerned that the valve along with several linear regulators would get a little warm without ventilation. I could remove the fan and just have vents but this can't be decided until I have used the unit a little.
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| All the boards for the different modules are mounted to the rear panel. |
The Power Supply
The power supply is a standard design of many of my projects. This is essentially the same as the MFOS - Adjustable LM317/LM337 1.5A Supply which is a transformer based +/- 15v rails. 5v is derived inside the Azure Dragon with linear regulators for two modules that require it.
It was intentionally designed to supply more than twice the amount of current needed so the unit stays cool and the components last a long time.
Like the main case, it's made from 16mm MDF with CNC routed acrylic pieces for the connection mounts and the side vents.
The transformer is a toroidal type which has a maximum of +1.5A per winding but as mentioned earlier, the Azure Dragon needs much less, running in at around 700mA on the positive rail and about 400mA on the negative.
The Panels
A method that has become standard for my designs is to use CNC (Computer Numerical Control) routed 3mm acrylic. The markings are engraved using a 0.5mm bit which is then filled with acrylic paint. Left to dry and then cleaned up with a light abrasive kitchen cleaner. Finally sprayed three times with a satin clear spray. This is the best process I have come up with that is relatively easy and cheap to get a great looking and reasonably durable result. If you don't consider the purchase of the CNC, computer and many years of trial and error.
I still use an old 2D design program called Freehand. It is quick and does everything I need. In an ideal world it would be nice to have 3D capability as I do have to take three dimensions into consideration. I have come into issues in the past but a combination of learning something new along with the simplicity of Freehand stops me doing this.
I have dabbled with OpenSCAD but only in 2D. This was very useful when doing large front panels like my Expanse project where I was able to mathematically modify sizes to make modules fit together. This could then be brought into Freehand to replace positional objects with final cutting objects.
The Modules
I thought I'd share some issues I had making the various modules.
The Chorus was the most difficult module. I purchased the PCB (printed circuit board) along with the Phaser PCB from Serge. They've taken the old stock from Jürgen Haible's estate. That was the first challenge as they're limited in numbers. The second challenge was where do I get TDA1022 BBD chips from? Thankfully a good friend has lots of them due to his hoarding nature and stripping down old organs for these, now valuable, components. I needed to find those components before I ordered the PCBs. As far as the construction of these modules, I had Jürgen's notes which are archived thanks to Serge and also Bill and Will's construction notes.
The Chorus gave me grief because I had a bad batch of TL072 chips. These are used to create the LFOs. I just wasn't getting a deep enough chorus effect which I struggled with for quite a while. I thought at first it was the CD4011 chips which I replaced with three other brands of chip I borrowed. I got there in the end.
The Phasor was pretty straight forward although I had to go beyond my usual component supplier, Tayda Electronics, to get some of the better quality capacitors.
The Oakley ADR30 was a dream to build up. No issues with this build. Though getting a BBD design that looked like it would do the job took a false start. I had previously been trying out another delay design which was a guitar pedal. This was not great quality which led me to looking into Tony Allgood's work. Alas, the BBD chips I had purchased from Cabintech were not the correct ones, so this led to another expensive purchase from the other side of the world. Oh well.
The change I made to the ADR30 was to attach a more flexible LFO. I have designed several Arduino and other MCU based LFO modules in the past. This design uses a Pro Mini Arduino which controls a digital potentiometer which I use as a voltage divider that is then fed to a buffer and bias amp to output the required 6v Peak to Peak LFO signal.
The Spring Reverb driver was another small issue for me. I'm no electronics engineer and my understanding of these things is enough to put things together but to actually design something like a spring reverb driver wasn't going to happen fast. I did find a few designs which I had tried but I wanted some tone control. What I found was a driver with a basic Bass and Treble tone control and Feedback which I have used but I am not 100% happy with it and I do have a new design ready to install. Watch this space.
The Feedback Mixer was my design with other peoples worked tacked in. I stole the parametric EQ design from Rod Elliot. He's someone who knows audio and I have used his designs and purchased PCBs when appropriate for the project. I have purchased a batch of his balance transmitter and receiver PCBs with one being used as the output stage of the Azure Dragon. The Feedback Mixer allows the output to be fed back into the input of an effect. The parametric EQ allows this feedback tone to be tuned.
The Auto Panner uses previously designed PCBs. Firstly, the LFO board is a cut down version of my TMNSD PCB. Although it's not designed as a LFO, what it does have is a high resolution DAC output, easy access to many Arduino I/O connections and some basic buffered outputs. This is an Arduino based board which controls a dual 12 bit DAC (digital to analogue converter) which in turn outputs a 0 to 10v signal. This signal is then fed into the other previous design, dual V2164 based, VCA module. The code running on the ADR30 is very similar to this code.
LFO Design
The original design for an LFO module came with the FloriVoxTron a few years back. This unit has many LFOs and using a MCU to create them seemed like a no brainer. It would be able to create any number of waveforms and do things that I am not sure an analogue LFO could do. The Expanse has a Quadrature LFO which has a Direction mode LFO built into it. This is a Square Wave LFO which changed the direction of the main LFO waveform, a very nice effect. By the way, a quadrature LFO has four outputs for the waveform which are 90 degrees out of phase to the previous output. Once again a nice effect when applied to multiple VCFs and Wave folders.
The LFO design has changed over the years. They generally have about 10 waveforms in total but are often reduced based on the LFO purpose. For example the LFO for the Auto Panner didn't really need to have both a Sine and Triangle waveform due to the less obvious nature of the effect being panning.
The two LFO designs in the Azure Dragon have a useful feature which is a single trigger function. I've not tried this in the field (jamming), but it takes a trigger input signal which will cause the LFO to only output one cycle of the chosen waveform.
