Mega Percussive Update

A big pile of boards and components ready for assembly.

I’ve failed massively at keeping the blog up to date since moving so I think an extensive update is in order. For this post I’m just going to concentrate on synth building as that’s what’s been occupying a lot of my time.

Things have been moving along steadily apart from the seasonal interruption (both financial and time-wise) of Christmas.

Rare chips arrive from Hong Kong.
Rare chips arrive from Hong Kong.

The dronesynth has been somewhat neglected, I’ve done nothing with it and I’m thinking of completely re-designing the oscillators to something which outputs a more sonically pleasing range of waveforms. Plus I’ve been distracted by starting to build a modular system.

Initially I was attracted to the world of modular by a couple of percussive circuits and the original intention was to build a series of drum voices. For a long time I’ve been using samples of percussive sounds in my music and often find myself going through loads of samples and still not being entirely satisfied with what I have. Also the act of trawling through samples to find a good sound often seems to detract from the creative moment.

LM394 supermatched transistors.
LM394 super matched transistors.

So initially the plan was to build a suitcase of drum voices to create percussive sounds as I needed them. This plan is still in effect but has grown a little. As I’ve spent more time in the synth DIY forums Muff’s Modules and Electro-Music I’ve discovered far to many interesting circuits and ideas to just stick with drums. So I’m building a full modular.

Things have been a little slow as I’ve been buying pcb’s for the projects and bulk buying components from around the world to keep costs down. It’s actually been a little dull for a lot of the autumn/winter as I’ve spent most of my time searching the internet, sourcing parts and slowly purchasing all I needed for the modules I’m currently building.

Tempco resistors.
Tempco resistors.

All that was completed by early February and since then I’ve been steadily building stuff. It’s exciting to actually get stuff finished and to finally be able to play with it.

So what have I built so far?

Power Supply.

Not the most exciting thing in the world but pretty essential as nothing works without it. Eventually as I build cabinets they will have their own power supplies and this will remain as my workbench supply.

Power supply insides.
Inside the power supply.

I found the steel rack mount case on the way home from work one day. It’s missing a proper metal front and is quite a lot bigger than my original planned case size but it was free and I like free! More money I didn’t need to spend. For now it’s got a nice plywood front, which does the job fine until I need to upgrade it.

I’ve built power supplies in the past and do know what I’m doing but I was still nervous when I’d finished wiring everything up and the time came to turn it on and see if it all worked. After double checking everything I finally plugged it in and when nothing went bang immediately gingerly tested it with my multi-meter to see if it worked.

Finished Power Supply.
Finished Power Supply.

It did, and everything was fine apart from an LED I’d stupidly soldered in backwards. After that was fixed I spent and excited 30 seconds watching both LED’s glowing. Finally I had something working.

There is only so much excitement to be gained from watching a power supply do nothing very exciting and so it was time to finish something that actually made a noise.

NeinOhNein kick drum.

This was actually the second pcb I purchased. It’s a faithful clone of the circuitry from the TR-909 drum machine. One of the classic house and techno kick drums.

NeinOhNein from the front.

As I wanted the most versatile module I could get from the circuit I spent some time searching the Internet for modifications that had been made to the original drum machine as well as the modifications recommended by the guy who had cloned the circuit.

NeinOhNein module from the back.
NeinOhNein module from the back.
NeinOhNein viewed fron the side.
NeinOhNein viewed fron the side.
Mock-up for NeinOhNein Panel
Mock-up for NeinOhNein Panel

Apart from wiring the pitch control backwards this circuit worked first time and I spent a very happy evening playing with this and my TR-707.

Demo of the NeinOhNein kick drum.

For now I’m building all these modules with plywood panels as I had a fair-sized bit I’d picked up for free. I’m designing panels which I’ll get laser cut and etched in acrylic but for now to test out the panel layouts and to get the modules working I’m sticking with wood.

Thomas Henry Mega Percussion Synth.

I left this module second as there was rather a lot of wiring involved. I spent an afternoon just creating a wiring diagram for my panel layout before starting. After the spaghetti of the dronesynth this made everything a lot easier. A day or so later wiring was complete and I plugged it in. It worked but after a bit of playing I’m pretty sure one of the voices isn’t doing quite what its meant to.

Wiring the MPS panel.
Wiring the MPS panel.

There’s been a lot of tracing signals and checking wiring and I’m pretty sure I have a duff chip in there. Luckily they’re cheap and for a couple of quid I have a replacement on it’s way.

MPS board on mounting.
MPS board on mounting.

The defective shell voice should create the main body of the sound but at present just produces tunable noise.

Assembled MPS back.
Assembled MPS back.

I’ve been playing with other parts of the circuit and am a little disappointed by the high end range of the noise generator so will try and tweek that at some point. I’ve already been playing with the decay time of the impact generator and depending on what the shell voice sounds like when it’s working will depend whether a switch gets added to switch my modification in and out.

Assembled MPS front.
Assembled MPS front.

I’ve already used this module along with the NeinOhNein kick on a track I’ve been working on.

Ian Fritz Transistor Matcher.

This is another utility module. As a lot of these circuits used matched transistors in the voltage per octave tracking circuitry (part of what keeps the voices in tune) it made sense to make this up as a permanent unit. It appears to work fine. Unfortunately I need to buy a better multi-meter as mine doesn’t measure the small signals differences needed to match the transistors. I needed to get one along with a decent oscilloscope anyway.

Transistor matching circuit.
Transistor matching circuit.

So that’s the stuff I’ve finished so far. Now we have a run down of projects which are currently under construction

4x Thomas Henry Controller LFO’s

Why four you may ask. Initially I was going to build two but the more I studied the circuit the more I realized how useful the circuit was.

In free-running mode it acts as a conventional low frequency oscillator outputting square, triangular and sine waves along with a trigger and gate signal each cycle. This in itself is quite useful for triggering events that can be modulated by the waveform outputs.

Controller LFO awaiting wiring.
Controller LFO awaiting wiring.

The real fun starts when you add a gate input. Every time a gate signal hits the oscillator it rests the wave to nothing which allows you to create for instance control voltages which fade up a sound before cutting it as a new gate signal hits.

The trigger input has a delay control on it, holding the trigger for a defined time before passing it to the next part of the circuit. Either the delayed trigger or the gate signal can then be used to control the control output. This circuit fades up the output of the LFO over a time defined by the Lag control allowing you to create for example delayed vibrato effects.

Controller LFO image
Rough design for panel.

So why build Four? I want to use at least one as a modulation source for controlling the velocity of drum sounds in my percussive suitcase. The gate and trigger outs could also be handy for creating interesting subdivisions of clock pulses to trigger sounds.

2x MegaOhm Audio VCA Rider boards

These were the first of the boards I ordered for my diy modular build. Originally designed by MegaOhm Audio to be added into other modules they can also be built as a module on their own. They’re voltage controlled amplifier. Basically a voltage controlled volume control that can be used on both audio and control signals.

vca rider boards
VCA Rider boards

These two are going to be built with all possible functions of the circuit brought out to the front panel. This will give me two extremely flexible VCA’s which I can use for a variety of tasks.

VCA Rider boards fully assembled.
VCA Rider boards fully assembled.

These boards are both assembled now and are currently waiting for panels and the controls to be wired up.

vca rider panel v1
VCA rider panel v1

Liquid Hi-Hat noise source.

The name is possible a little misleading as this module doesn’t produce a Hi-Hat sound on it’s own. Rather it is two voltage controlled noise sources, which along with signal shaping such as a voltage controlled amp and envelope generator can be used to produce a range of sounds like Hi-Hats, Cymbals and whooshy windy sound effects. It can also be combined with other voices or used with a sample and hold as a source of random control voltages.

Liquid HiHat board fully assembled.
Liquid HiHat board fully assembled.

Again this board is fully assembled and just waiting for a panel.

2x Thomas Henry X-4046 & 2x Thomas Henry 555 Voltage Controlled Oscillators

These two designs from Thomas Henry are both very versatile oscillators. Both produce a wide range of waveforms. Originally I got two X-4046 board sets as the main voices for my fledgling modular. I’ve had two old Motorola 4046 chips, the heart of this oscillator for about 20 years and as they were apparently the best make of this chip to use for this oscillator I was happy to have finally found a home for them.

X-4046 VCO boards.
X-4046 VCO boards.

Last summer Thomas Henry announced three new projects he’d been working on. The Controller LFO detailed above, a CMOS based ADSR envelope generator and the 555 VCO. Fonik who had produced the lovely red boards for the X-4046 and the Controller LFO was offering boards for this project to and how could I refuse!

555 VCO board.
555 VCO board.

I’m glad to see he’s currently working on boards for the CMOS ADSR which will be added to backlog when available.

These boards are all pretty close to being assembled. I’ve left them behind the other boards as they require a fair amount of setting up and tuning. The 555 VCO’s need matched transitors and until I get a new multi-meter they’ll have to wait.

6x Fonik Attenuverter chicklets.

I haven’t decided how to use these little utility boards so far. I may put three behind a panel together or I may put them into another module.

Single attenuverter.
Single attenuverter.

It’s a useful little circuit that can both attenuate and invert a signal. When the the control is set to 12 o’clock or half way the signal fed into it is attenuated to nothing. As you turn one way the signal goes to maximum level and as you turn the other it goes to an inverted version of maximum level. This seems more useful for control voltages at present but once I get to use these I’m sure more uses will arise.

So there you have it, that’s progress so far. There are more projects on the horizon. I really need to build some filters soon to shape the sound from my oscillators. I’ve been planning a strip-board layout for a Wasp filter, a lovely filter based on a logic chip that has a lovely sound and distorts beautifully. In fact it’s a similar chip to the one used in the fuzz pedal I built for a friend last year.

But all that’s still to come…

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