A-143-1 Vactrol Mod

A simple modification to allow voltage control of the attack and decay times of Doepfer's Complex Envelope Generator/ LFO.

Despite its size, I love the A-143-1 for its natural sounding envelopes. The only thing it lacks is voltage control. I considered buying Doepfer's A-101-9 Universal Vactrol module, but reckoned it could be more fun and cheaper to hack one myself. This involved repurposing my A-180/ Quad Slew once again.

The circuit is simplicity itself. The tip of the cable/ jack carries the CV, which travels through the vactrol's LED and back via a resistor to the jack's ground connection. The hard part is gaining access to the potentiometer pins on the A-143-1 to apply the vactrol's resistance. As a lazy hacker, I opted to modify only the lower section of the A-143-1. This meant I didn't have to dismantle the entire unit.

The vactrol is connected to the attack and decay pots via switches. As I only used one vactrol, switching both in effectively connects both pots too. This means the manual pot settings affect the overall resistance of both time constants. It's a kludge, but it works!

See this thread for more A-143-1 mods.

WMD PDO Demo

Audio examples and review of the WMD Phase Displacement Oscillator. A sequel to this post.

The WMD PDO is a timbral oscillator with a twist. Three of its outputs can be discretely shifted in phase relative to the first. It can be used as a quadrature LFO, but the real fun starts when modulated at audio rates. This yields results similar to linear FM, but as the PDO’s creator William Mathewson says in one of his promo videos, phase modulation “gives you more”. Here it is in action:


The sounds in the multi-tracked demo track were generated by modulating the PDO either by itself, for wave-shaping, or an external VCO for PM effects. Buy the EP to access the full set of unprocessed demos (10 recordings, 30 mins duration).

As you can hear, the PDO is capable of a wide variety tones: deep acid basses, bright bells, wooden klonks, scraping steel strings, rasping super-saw/ PWM sounds, even digital noise. As with the Zeroscillator, panning two phase shifted outputs hard left and right can result in stunning stereo effects.

I found I could push the PM index harder and get brighter sounds than with either the analogue ZO or digital Hertz Donut. Like thru-zero linear FM, when the PDO is modulated with a bi-polar signal, its sign, or direction, changes. However, modulating the phase rather than the frequency results in less pitching artifacts.

That's not to say the PDO is artifact-free. At slower modulation rates I thought I could see/ hear the PDO 're-calculating' the phase offset, resulting in a mild siren effect. I asked William about this and he explained that this was the nature of phase modulation; what I was hearing was similar to the Doppler effect where moving the phase forward increases the frequency. At higher audio rates this was not apparent, but it might have an effect when using the PDO as an LFO. The digital wave-shaper means aliasing is apparent and the sound can break up at extreme frequencies or when FM-ed hard. However, I took this to be part of the PDO's character and, as you can hear in the demo track, it means you have another set of timbres to play with. I thought the saws and pulses were not as beefy as an analogue VCO and that it was a shame that one can't affect pulse width and phase simultaneously for 'shonky beats'. However this can be addressed by routing a shifted output to the reset input via a clock divider.

These are minor points given the wealth of sounds and possibilities packed into the PDO's 10HP. In fact, that would be my biggest criticism: it's pretty cramped! I'm sure I'm not the only one who'd gladly devote more rack space to a larger PDO, possibly with an onboard sine modulator and index VCA. As it is, the list of modules the PDO could replace in my system is shocking - it's perfect for a live set-up or desert island suitcase.

There is one last thing to consider: at almost €400 the PDO is in the same price category as the SynthTech E350 and Cylonix Cyclebox, which both offer increased fidelity. Whether they offer the same depth of phase modulation and character is something I look forward to testing in a future post.

Thanks to William for taking the time to answer my questions and for a great module!

Video Synthesis Premiere for Basic Electricity

Stan Stencil will be joining Koma Elektronik onstage at Basic Electricity #3 this Friday.

"The backbone of Stencil's Eurorack system are modular analogue video synthesisers combined with audio waveform generators. The result is a mesmerising visualisation of sound synthesised entirely from audio signals and creating an incomplete visual artefact of the original audio."

Check out his videos here. Three days to go!

Basic Electricity #3 Reminder

The lads from Koma Elektronik play Basic Electricity #3 next Friday, April 27. Details are here or on the Basic Electricity homepage.

BE-EP1 has been updated, adding two tracks featuring mono-poly on his monster Malekko/ Wiard rig and our mystery Japanese guest on guitar.



If you haven't done so already, please download the EP and join our mailing list. Look forward to seeing you next week!

New Basic Electricity Website & Gigs

Richard Scott and I have a new website for our Basic Electricity nights in Berlin:

https://flavors.me/basicelectricity



It's a flavors.me site, so it aggregates our blog and Bandcamp pages:

http://basicelectricityberlin.blogspot.de/
http://basicelectricity.bandcamp.com/

You can download the EP to join our mailing list for gig & release info.

We're proud to have the lads from Koma Elektronik, Ian Boddy, and Franz Schuier & Lu Katavist lined-up for our next thee gigs.

Look forward to seeing you in Berlin!

PotD - Swings & Roundabouts

How to patch a thru-zero frequency shifter with two quadrature VCOs and ring modulators.



I love my Cwejman FSH-1 for its wide range and smooth analogue tone. The one thing it lacks is thru-zero capability. At slow settings, frequency shifters yield beautiful spatial effects. Thru-zero is the icing on the cake as it allows the up & downshift channels to 'swap sides'. Heard in stereo, this can sound great - or disconcerting, depending on the amount of shift!

So, how to go about patching one?

James Clark's Nord Modular tutorial on spectrum shifting explains the workings of a frequency shifter but stumped me on the need for all pass filters/ Hilbert Transformers. A post by Matt Jones at the Synthedit Yahoo Group offered the necessary clue:

"Out = (Input) * (Sine oscillator) + (Input shifted by 90 degrees) * (Cosine oscillator)
Changing the + sign to a - switches the amount of the shift from up to down …"

Here's the proof of concept:



In the recording you can hear me manually sweeping a DC voltage from positive to negative, biasing the modulator and causing the shifts to move from left to right.

My patch (see below) has three caveats: one, you need a Zeroscillator or similar to provide the thru-zero shifts (!). Two, unless you have the means of generating a cosine from your complex input signal, you're limited to simple sines. Three, it's fiddly and not 100% precise. That said, the results sound great:



The patch details: the ZO is used as the modulator. Set its bias to zero and patch the 0 & 90 degree outputs to the CV inputs of two ring modulators (e.g. A-133). I used the Doepfer A-143-9 QLFO as my signal as it provides the necessary outs. The 0 & 90 degree outputs were patched to the respective ring mods. The Toppobrillo TWF can be used to generate a cosine from another source, but I wanted to keep the patch as simple as possible.

To generate the upshift, I mixed the result of the 0 and 90 degree multiplications. To get the downshift, I subtracted the 90 from the 0 degree via an external inverter. The Cwejman VCA-4MX was used as the output to my final mixer. It's perfect for this task as it allows you to independently tap the mix of channels 1&2 and 3&4, which you can then pan left and right.

The fiddly bits: to bias the ZO correctly in both directions, I had to tune two voltages (+ve & -ve, Maths or Fonik's mh-01) and send them to the linear FM input via a sequential switch. It would have been easier to use the pulse output of the clocking LFO, but this didn't give me equal positive and negative bias i.e. the side-swapping effect was compromised. You can hear this in the first recording where I apply the bias manually. The second detail you have to watch is the mix/ subtraction balance to ensure clean up & down shifts, but this isn't too tricky. Just use your ears for both.

The ZO makes this patch possible. With zero bias, the oscillator comes to a stand-still. Any voltage you apply to the linear input will cause it to jump into action. Reverse the bias voltage and the ZO changes direction causing the shifts to swap sides. You could use a second A-143-9 as modulator, but would then lose this ability. Still, two QLFOs, an A-133 and mixer/ inverter offer an inexpensive single-sideband-modulation patch.

Buy Swings & Roundabouts.

Patch Tips #23 - PEG Burst Generator

How to patch the 4ms PEG for use as a synced burst generator.



I love the burst output of the Wogglebug but sometimes want the pulse streams to be in time and on command. The PEG makes this easy:



Patch your master clock to the Ping input on one PEG channel. Send your gate - or 'on' command - to the QNT input. I used the T-Gate output of Pressure Points in the example.

Using the QNT input means the PEG will only fire when told to, thus avoiding the need for extra AND logic. It also means it will repeat/ loop its envelopes at a rate set by the div/ mult.

Keep the curve linear and set the skew clockwise for an instantaneous attack time. The EOR now becomes your timing pulse, which you can use to trigger another envelope.

With the basic patch set, use the EOF to trigger a random generator like the Wogglebug. Patch its stepped output to the PEG's div/mult CV to get random but in sync bursts.

If you have an SCM and Expander, you can try a similar patch using the mute and rotate inputs.