Bleeps & Bloops Reimagined

A fun experiment, applying events that might be clichéd in the modular context to preset sounds. Inspired by the CV to MIDI compositions of Konstantine, the piano playing of Quentin Tolimieri and rediscovered due to this forum thread.



Recent discussion of a piano module reminded me of something I did a few years ago where I used a simple Clavia G2 patch to control a Yamaha QY10. It’s a small MIDI notepad from the 90’s that has a rubberised keyboard, sequencer and PCM sounds … drums, piano, double bass, horns, strings etc. In other words, the antithesis of the timbres we know from the modular synth. Here’s what it sounds like ‘sequenced’ by a stream of random MIDI events:



The Patch uses the G2’s MIDI modules to send both keyboard and random notes to the QY10. Flicking through the MIDI channels on the Yamaha itself causes hanging notes and weird stuff.



It’s all quite entertaining - the above recording was played live and edited for brevity. If you want to hear music made by someone who does this properly, check out Konstantine aka Paranormal Patroler. He knocked us out at his Basic Electricity concert with his CV to MIDI set using Doepfer and ADDAC conversion.

Thru-Zero FM Explainer

How to get the best results from your analogue thru-zero linear FM oscillator. An explainer in response to questions about the Doepfer A-110-4, but which is also applicable to other TZ-FM VCOs.



The A-110-4 seems to be more prone to pitching artefacts than other thru-zero (TZ) VCOs. That might partly be due to the specific design, but general considerations like the tolerances and sensitivities of analogue designs also play a role. Another issue might be perception, e.g. when certain modulation depths make it hard to discern the original pitch of the carrier.

DIGITAL FIRST

Ignoring the actual implementation (frequency- or phase-modulation), the reason digital FM is easy is because it’s clean. There are no DC offsets or pitch instabilities to ruin the result.

Here is an example using the Clavia Nord Modular G2. The carrier is always heard and only the modulator is enveloped. The frequencies of the two oscillators are fixed but the FM amount is manually increased: 01-TZ_clavia-digital

The carrier was tuned to B3 and the modulator D#5. I chose these pitches by ear to show an effect which might be confused for pitching at higher mod depths. When the modulation recedes, we get a sound similar to guitar feedback. This shows that it’s possible to find combinations of frequency relationships and modulation depths that will sound ‘wrong’ even when patched digitally. In an analogue system, frequency drift or tracking inconsistencies can worsen the problem.

DIRTY SIGNALS

But weird C:M ratios are not the main problem. The real enemy of dynamic linear FM is asymmetry caused by DC offsets. If the modulating wave is not centred about zero, the sound will churn. Here’s the same G2 patch, this time with some virtual DC offset added: 02-TZ_clavia-digital_virtual-dc-offset

To avoid this, some FM inputs are AC-coupled - the signal is filtered by a capacitor. But this is not a magic bullet. If the offset is large enough and being swept dynamically, the capacitor will have a hard time eliminating it. The most likely cause for DC offsets are the modulating oscillator itself, or more precisely its wave-shaping circuitry. I have had best results with Doepfer’s A-143-9 Quadrature sine-core oscillator.

SCIENCE, SWITCHES

Analogue TZ-FM involves switching to generate ‘negative frequencies’. No matter how finely timed, there is a moment of indecision which may be audible as a growl or rumble. DC offset makes this worse as it shifts the switching point. Lower initial frequencies (aka Bias, Symmetry or LFreq) allow more modulation and brighter sounds, but the cost is lower accuracy and more ‘bum notes’.

THE A-110-4

The Doepfer TZ-VCO switches between two oscillators. This method has pros and cons. If the two VCOs do not respond equally to modulation, the resulting FM will sound ‘off’, even if the modulator is clean and the switching point is accurate. This cannot be trimmed by the user. To mitigate pitching artefacts at the point of switching, calibrating the TZ transition can help.

WHAT IS IT?

As Cynthia Webster says in her humorous video showing the difference between thru-zero and normal linear FM, without TZ “half the modulation is gone”. As you’ll hear, the frequency relationship between carrier and modulator also plays a role.



The first VCO you hear in the next two examples is the Zeroscillator, then the A-143-9 which I have modified for standard linear-FM.

If the carrier’s initial frequency is high enough and/or the modulator is higher in frequency than the carrier, the tonal result is very similar:
03-TZ-high-initial-freq_ZO-A-143-9

The real difference between thru-zero and normal linear FM is apparent when the modulator is slower. As you can see above, instead of adding gentle folds, the modulator pushes and pulls the carrier through zero. TZ allows deep levels of modulation, even when the carrier’s initial frequency is low. When this is the case, there is a big difference between normal and TZ linear FM in the possible tonal result: 04-TZ-low-initial-freq_ZO-A-143-9

One last thought on this as the Zeroscillator video is much quoted when the question “what is thru-zero FM?” is raised: toggling the “Through Zero” switch on the ZO does not yield ’typical’ linear FM; normal linear FM does not sound like this: 05-TZ-not-typical

PATCH TIPS

I have concentrated on the audio effects here, but VCOs that can go thru-zero have other uses when they themselves are used as modulators. For an idea, try this patch for a thru-zero frequency shifter and listen to your sounds swap stereo sides.

I hope this explainer helps you with your TZ-FM experiments. The files folder is here. If you’re not sure about the analogue results you’re getting and need a digital ’control’, download the Clavia Nord Modular G2 demo. If you’re on a Mac and 10.7 or higher, you can run the demo under Wine. There is info here or an installer here.

A-147 LFO Wave Skew Mod

A simple modification to gain voltage controllable wave shapes from Doepfer’s A-147 VCLFO. Learn how to turn this old stalwart into a morphing modulator with just a couple of resistors.



The A-147 is a triangle/square-wave oscillator built around the pairing of an integrator and comparator. They work in a loop with the one feeding the other, back and forth. You can see them in action here.

The result of integrating a square wave is a triangle. But if we independently change the rate at which the integrator charges and discharges, we can skew the waveform from a rising to falling sawtooth via a triangle. Because the integrator and comparator are related, the square wave becomes a variable width pulse.



The easiest way to achieve this is to hijack the square-wave on its way to the integrator, split its path with two diodes and then set the balance with a potentiometer. You can see this manual arrangement in Ray Wilson’s Variable Skew LFO or Ken Stone’s Utility LFO.

To get proper voltage control over this ‘re-balancing’ might take a considerable amount of extra active circuitry, more than I felt the effect is worth, especially given the digital options available today. Here’s my simple kludge:



The idea is to massively reduce the size of the square wave going into the integrator so that the injection of an external voltage is enough to shift the bias of the square and hence alter the shape coming out of the integrator.

Resistor R14 (15k), which is to the left of the quad opamp (TL084) forms a voltage divider with the 1k resistor which also marked in yellow in the picture above. The output of this divider goes to the CA3080 OTA for integration. I found that swapping the 15k for a 1M resistor was enough to allow the bias to be shifted with a +/-5V CV. For the CV input I ended up using two resistors in series to give me 670k rather than the 1M in the picture.

Reducing the amplitude of the square wave to the integrator also reduces the overall frequency of the LFO, so I also swapped the 0.1uF capacitor C2 for a smaller 15nF to bump up the speed.

Below is how it looks and here are some construction pictures.



I like simple mods - minimum change for maximum effect. Skewing the wave shape with this method also changes the frequency of the LFO, which you might not want. There is a way to compensate for this, but again, I decided it wasn’t worth the extra circuitry as I like the effect of the LFO slowing down as it changes direction, almost like a thru-zero oscillator. But you could try the following schemes. One is relatively simple, the other might need an expander module to provide space for the extra PCB. Neither is perfect.

The idea here is to inject a fraction of the skew CV to the A-147’s FCV input. For example, given a skew CV of 5V I found I needed about 5-600mV FCV to correct the frequency. You can use the attenuator on the module for this or send your skew CV via a ca. 560k resistor to the output pin of the 50k FCV potentiometer (ahead of the FCV buffer). The ‘gotcha’ with this method is that it only works for positive offsets as we always need to speed up the LFO when skewing.

What is needed is an active full-wave rectifier to ensure that the compensation voltage is always positive. This is a simple enough circuit to add but for the lack of space behind the panel. If you want to try this, have a look at Jim Patchell’s Ideal Diode Tutorial hosted at René Schmitz’ Schmitzbits site.

The usual DIY disclaimers apply - you do this at your own risk. Have fun but take care of your module and yourself!

Thank you Tim Stinchcombe for identifying the relevant parts and for your thoughts and suggestions.

Funkhaus Fun + Ribbon Tales

Thanks to everyone who came to see the concerts in Saal 2 of the Funkhaus on Friday night of Superbooth. Wolfgang Seidel, Hillary Jeffery, Hainbach, Frank Bretschneider and I had a great time. Thanks also to Andreas Schneider and especially Adam and his team for the wonderful sound and light.



Our trio’s set was improvised but Wolfgang and I did have one ‘get to know you’ musical session, during which I noticed he uses not one but three Doepfer R2M ribbon controllers! I had tried one of these years ago, when Schneider bundled them together with an Analogue Solutions MS-20 filter/ VCA and Doepfer VCO - the Jimi-Box, named for Hendrix.



But the ‘widdle’ wore thin pretty quick so I passed on the analogue version of the ribbon controller. The R2M, of course, can ‘speak’ both analogue and digital. It’s a good partner for the MIDI-equipped Clavia Micromodular, which has only three knobs and no keyboard. For its part, the Micromodular, with its familiar environment and patch recall, is the perfect accompaniment to an analogue modular when playing live. You can see me using them in the second picture above.

Here are two patches from that concert. One is inspired by Peter Grenader’s iconic ribbon video from a few years ago. Note position determines pitch, panning and also speed of the clocking VC-LFO, pressure adds modulation.



I wanted to use a voltage controlled radio during our set at the Funkhaus, the former East German broadcasting house, but was unsure of whether I’d get any reception. The answer was to mimic the random bursts of noise and music fragments with this second patch. Three comparators provide an on-off switch for the virtual radio, tonal and frequency changes.



You can download the patches and R2M preset info here. Let me know how you get on!

Doeper/ Serge VCS Expander Schematic

A description of the method I used to add Hold, Burst and EOR functions to the Doepfer A-171-2. An update to this post. The module is a licenced version of the Serge/ CGS DUSG/ VCS, so these mods will work on them too, although the pins may be different.

You can download the schematics and Fritzing file here. I wish I had done this at the time in spring as I've had to retrace my thoughts from incomplete notes. It's been fun but I might have some things wrong and I’m sure some aspects could be done better. So, please continue the discussion and post corrections and improvements to this circuit in this forum thread. I will update this post accordingly.

HOLD



The idea behind the Hold circuit is simple: interrupt the integrator. If you wanted to go no further and keep this mod passive, all you would need to do is cut one trace and hook up a switch. On the A-171-2, I found a convenient place between pin 7 of the TL084 quad opamp and the 8k2 resistor (R39).

If we want to automate this, we need an analogue switch. Transistors can be fiddly and the common CD4066 won’t process all signals, so I used a DG201. This switch is ‘normally closed’, so with no gate on the command input, drain and source are connected and the integrator’s loop is closed. Pulsing it breaks the connection.

EOR

Referring to Tim Stinchcombe’s VCS analysis and comparing with the Doepfer layout, pin 4 of the LM3900 is high during the attack phase. The ‘not attack’ gate, which will become part of our EOR gate, can be found on pin 5 of the LM3900. If you observe this output with an oscilloscope you’ll notice we need to process it as the ‘not attack’ gate remains high until the next attack phase is initiated. This can have its uses, but it’s not what we’re after if we want an EOR/ variable length gate that can be used to ping filters etc.



This is where we have to get creative and ‘patch with ICs’: we use another switch on the DG201 to operate a logical AND function. The signal which chops our ‘not attack’ gate down to the right length is the EOC gate. We can tap this signal from the End Out jack on the A-171-2. As the EOC gate is ‘high’ at the wrong time, we want to flip its activity.

The need for a logic inverter conveniently also answers the question of how to buffer the inputs for this mod. I used an HCF4049UBC Hex Inverter. As the supply voltage also determines the logic threshold for this chip (lower voltage = lower threshold/ faster response), I chose to run it off 5V, supplied by a 78L05A regulator. I sent the new EOR signal from pin 15 of the switch to a jack and an LED.

BURST

Now that we have the means to process logic, the burst function is relatively simple. It’s a circuit adaptation of the classic Maths Trills patch where we used a logic gate to interrupt the loopback of the EOC signal to the trigger input. As with the EOR gate, we use a switch to function as a logical AND gate. The DG201 is ’normally closed’, so we need to keep the switch open when there is no burst command present. To do this, we use a spare inverter to flip the activity of the burst input. Looking at the schematic on Ken Stone’s site, the trigger and cycle inputs are OR-combined by diodes, so the VCS can be triggered and burst/ cycled at the same time.



The DG201 is powered from +/- 12V. Filter the supply as usual and add 0.1uF bypass caps for the ICs. The burst and hold inputs were conditioned by cutting negative voltages. The schematic says 4001, but I used 4148 diodes.  I added a manual gate by tapping 5V and sending it via an ON-ON switch to either the burst or hold jack’s switching contact.

It sounds more complicated than it is. Once I’d thought it through, I built it on stripboard on the fly, without the need for a detailed schematic. Lesson learned on that score! I hope these notes help and look forward to your comments and improvements.

Thanks to Dieter Doepfer and Chrisi & Erik at Koma Elektronik for their help on the subject of switches.

The usual DIY disclaimer: do this at your own risk, take care and have fun.

A-171-2 VCS Expander

Adding gated hold & burst functions and an End of Rise output to Doepfer’s Serge VCS. An update to this post.



A recent forum thread about the Serge 1973 envelope got me thinking about whether it would be possible to add its hold function to the VCS. Once I’d understood what was needed, a burst and EOR pulse were obvious additions.

Both Burst and Hold can be activated manually or by an external signal. Hold freezes the envelope in its tracks. It’s different to patching via a S&H as the envelope continues where it left off. Burst simply cycles the envelope at will.

Audio examples: Hold (cycling VCS FMs a VCO, button pressed to hold), Burst (first manual, then activated by 2nd row of sequencer).



The EOR is needed for quadrature functions with two envelopes (the other fires at the End of Cycle). Conditioning the pulse required some creative thinking, a case of patching with ICs! Its width can be varied, so it can be used to ping filters or delays.

These modifications are simple to implement with switches and logic inversion (schematic to follow). The additions borrow from my favourite envelopes and make the A-171-2 close to ideal. Yes, I could have just bought a Function but it wouldn’t have been as fun or educational!

Serge VCS Modification

Modifying the Doepfer A-171-2 Serge VCS for more extreme non-linear curves and more manual control over rise and fall times.



The Serge Voltage Controlled Slope is a classic design and an integral part of many modular musicians’ systems. The Doepfer A-171-2 is a faithful recreation of the original circuit. It works just like the Bananalogue VCS that has been in my case since pre-Maths times. That’s good, and bad.

The VCS easily allows one to set different contours for its rise and fall phases. But its non-linear curves are not as extreme as those possible with Maths. Setting times on the VCS is harder, as the useful range is limited to about 20% of the potentiometer’s throw. It’s these differences between these two similar function generators that this modification tackles.

The feedback that generates non-linear shapes is pre-wired on both the VCS and Maths. Calibrating the VCS output voltage from 5V to 8V has only a marginal effect. But if one patches the VCS envelope output to its ‘Both CV’ input with VC Rise + Fall set to linear, the Serge yields the desired curves. This suggests the internal CV feedback loop is capped.

Indeed, if we look at the left of the schematic, at switches SWF & SWR we find 330K resistors limiting the amount of feedback to the CV mixer to about 30%. If we lower this resistance we’ll get more feedback. I desoldered and replaced the 330K resistors with 200K but you could also try soldering another value in parallel e.g. 150K (= ca. 100K, 100%) or 470K (=ca. 200K, 50%).

This part of the modification helped clear up an oddity about the VCS: namely, why making the curves more exponential actually increases the overall envelope time. Negative feedback should make it shorter, and vice versa.

If we study the same part of the schematic again, we can see -12V across a 1M resistor feeding the summing points. Given the gain ratio set by the 100K resistor, this offsets the rise and fall rates by +/-1.2 volts. I find this counter-intuitive, so I removed both 1M resistors.



Both my Doepfer and Bananalogue modules are fitted with logarithmic potentiometers to manually set the rise and fall rates. This means, when using the VCS as an envelope or slew limiter, changes in the first 50% of the pot’s throw are imperceptible. Typical envelope settings lie between about one and three o’clock. Tapering the A50K potentiometers on the A-171-2 with a 5.6K resistor between the CW/ ‘hot’ lug and the wiper solves this. The useful range now spans from nine to three o’clock.



To solder these in place, you’ll have to unscrew the jacks and remove the board from the faceplate. I tape Gaffa around the ends of my pliers to avoid scratches. While you’re there, you can measure the output between the A50K wipers and the subsequent 82K resistors to understand how the log pots choke the voltage. I did try an S-curve taper with two sets of resistors but the quasi-linearization suggested here by Daverj worked best.

So, what does it sound like? Here are two recordings:

feeback mod: exp-fall, unmodified, 0:08 modded, exp-rise, 0:16 unmodified, 0:23 modded.

pot taper mod: cycling, rise = zero, fall manually altered. Stock VCS then modded at 0:39

These simple changes have given my VCS more whip and made it easier to use. Thanks to Dieter Doepfer for helping me read his PCB layout, Ken Stone for publishing his schematic, Tim Stinchcombe and Dave Jones.

If you’d like to try this yourself, take the usual precautions to avoid damage to yourself or your module. I will not be held responsible. If in doubt, ask Doepfer or your technician to carry out the modifications for you.

A-143-9 Lin-FM & Buchla Saw Modification

How to add a linear FM input to Doepfer's quadrature oscillator and get the weird waveshapes of Buchla's 258 VCO.



The A-143-9 quadrature oscillator is a favourite for FM. Its sine wave is pure and the DC-offset is minimal. This makes it the perfect choice as the modulator in dynamic FM patches. It's a shame then that it itself doesn't have a linear FM input. Fortunately, the fix is simple and the result sounds great, especially in quadrature 'stereo':

A-143-9_linFM.mp3
A-143-9_stereo-linFM.mp3



Most analogue VCOs are linear at heart. To get the response we need for musical pitches, CVs need to be translated. If we bypass the part of the circuit that does this - the exponential converter - we should be able to modulate the VCO in a linear fashion.

This depends on the actual circuit design but, happily, this 'dodge' is possible with the A-143-9. I asked Dieter Doepfer and he identified pin 6 of the top quad opamp (TL084) as the target (see A-126 connection PDF for board layout). A resistor determines the modulation depth. Dieter suggested 100K but I ended up using 68K to allow for some over-modulation.



There is one caveat with this simple modification, but it's a limitation that can also be used to musical effect. Pin 6 is also connected to -12V via R8 (270K). This provides the current needed for the oscillator to work. If the modulation voltage 'robs' the VCO of this current - i.e. at 0V - the oscillator will stop. This is good and and bad: at low audio-rates, over-modulation could sound choppy. On the other hand, we gain the ability to gate the VCO/ LFO on or off, similar to a track-and-hold.



The reason FM-ing the A-143-9 sounds so good is that there's no waveform converter messing things up. Even with the best schemes, the sines on triangle- or saw-core VCOs show their heritage by being either brassy or buzzy. So, a sine-core makes sense if clean FM is a priority. Question is, what do you do if you also want a saw or square?

The latter is easily generated with a comparator. For the saw, we can take inspiration from the Buchla 258's 'funny waveshapes'. We can use a triangle-to-saw converter circuit or a patch:

Patch the sine (0) output of the A-143-9 to a mixer. Patch a multiple of the sine to another mixer (e.g. mh01). Set the channel to 50%. Mix in a 2.5V offset and patch the result to the signal input of a polarizer or DC-coupled ring modulator like the A-133. Patch the cosine (90) to a comparator (A-167, Sport Modulator etc.). Set its threshold to 0V. Patch the comparator's output to the CV input of the A-133 and send the result to the first mixer. Now balance the amount of original sine to get the shape you want. Altering the comparator threshold will yield other shapes. Here's how it can sound when modulated:

A-143-9_buchla258saw.mp3

It's not thru-zero, but the quality of the A-143-9's sine-on-sine linear FM is clean and stable. Given the right C:M ratio it can cover some of the sounds generated by wave-folding. With a little more circuitry to provide a permanent saw/ square output, a pair of these quadrature VCOs could form the basis of a budget timbral VCO.

Nord Coast - Micro Modular Patches

Performance patches created on the diminutive yet powerful Clavia Nord Micro Modular.



I'd seen these odd shaped and coloured boxes lying round in studios gathering dust before. But it wasn't until I saw Rastko Lazic's inspiring video that I took the Micro Modular seriously. Here is a collection of patches, driven solely by the Micro Modular's three knobs:



Yes, it sounds digital and you need to jump through hoops to get the editor to work on a modern Mac operating system, but it's worth it. I've used the G2 demo for years to try out ideas, so I was used to the workflow. The NM engine doesn't have some of the conveniences or modules of the G2. But, as ever, there are workarounds. If you get stuck, consult the Nord Modular Book, edited by James Clark or Rob Hordijk's workshops.

In his video, Rastko uses a new Faderfox controller to play his patches. The two make a perfect pair, but I didn't want to be tied to a USB host i.e. computer. The older FF controllers are less flexible when it comes to custom assignments, so I built my own. I used a Doepfer Pocket Electronics kit and a perspex sandwich. The joystick is a small, game controller type.



With that built (and an old Faderfox controller now bought ...), I've realized that the beauty of the Micro Modular is its simplicity. With some canny patching you can get a lot of mileage out of three knobs! Download the album to access the patches and try them yourself.

Here is a link to Clavia's sound-bank. If you're using a Mac, the V3 Editor will run with varying degrees of stability and frustration under emulation. I have both Win XP and 10.6 versions running under VMWare Fusion on a 10.8 system.

Super Sawtor Demo

A review of Happy Nerding's Euro-format sawtooth animator.



As the name suggests, the Super Sawtor is designed to produce the sort of multi-oscillator unison sounds known from certain Roland synths and dance genres. Feed it a single saw, triangle or sine to get a dense, buzzing cluster. Too Trance for you? Have a listen:


The two tracks should give you an idea of the Sawtor's sonic scope. If you want to hear more, pay as-you-like to download the source files (10 tracks, @ 25 mins).

The Sawtor is solidly built and simple to use - the only parameters are the dry/ wet mix and the amount of spread. Its internal LFOs change speed in response to the incoming signal's pitch. That keeps the amount of spread even for most of our hearing range. The result is rich, vibrant and less prone to the phase-cancellations I know from my Roland Super Jupiter. Indeed, although it is analogue, the Sawtor emulates the beating of a digital super-saw.



It's this 'intelligent' modulation that sets the Sawtor apart from Doepfer's sawtooth animator and draws a parallel to Cyndustries'. It also limits its use. The only parameter you can affect is the 'spread' i.e. the number of stages. Once activated, the saw-multiples are constantly in motion. They can't be 'stopped' and spaced statically to produce new waveforms as is possible with Doepfer's A-137-2. To improve audio fidelity, the Sawtor is AC-coupled. This rules out certain CV-processing tricks.

So, does that make it a one-trick pony? Yes, but only in the sense that spring reverbs or fuzz boxes are too. Because you can't independently influence the modulation speed, the choice of input becomes important. Gated, sync'd, FM'd or even polyphonic sounds can make interesting fodder if you want to go beyond the Hardcore Hoover. But maybe that is to miss the point of the Super Sawtor: it makes one VCO sound like many and does so without fuss.

Many thanks to Igor for the module and for answering my questions.

A-143-1 Modification

Adding voltage control and a combined trigger output to Doepfer's Complex Envelope Generator. An update to these posts (1, 2).



The A-143-1 is king of the shonky rhythm. There's something about the swing generated by its four chained envelopes and comparators that is hard to replicate with a VC-LFO and sequencer. This modification provides two features I wanted when using the A-143-1 as a wonky clock: a combined pulse stream to control other modules and an automated means of influencing the rhythm.

For the latter, I chose to add simultaneous voltage control to the threshold of all four comparators. For me, this is the parameter that makes the A-143-1 tick. It means a single CV can be used to stretch and shrink the rhythm without affecting its inherent groove. Think 'Funk Soul Brother'. Just as importantly, the modification can be accommodated on the original panel.

The Comparator outputs are chopped down to 1ms pulses, so they can easily be mixed without the need for a 'proper' logic circuit. They are also hot enough to ping filters. Add a Sample & Hold to grab values from the A-143-1's bipolar mix out and the results can sound like this:

a-143-1_mod.mp3



The star of this mod is the H11F1 Photo FET Optocoupler. It may not have the cachet of a VTL5C3, but this vactrol alternative might make a better choice for some synth mods. It's smaller, cheaper and, most importantly, has a fast, linear response.

The circuitry used in this mod is simple. The difficulty arises out of the need to quadruple the parts. You can download my build-notes here (the usual DIY disclaimers apply!) to see how I went about it. See this thread for more A-143-1 modification ideas.

To close, today's Patch of the Day offers a musical example of this modification:



The patch uses just two envelopes, sometimes chained, sometimes running as LFOs. The new combined trigger was multed to ping a Cwejman RES-4 and trigger a S&H and CTG-VC envelope. The A-143-1's mixout was sampled by the S&H and sent to the RES-4's FCV and CTG-VC's Attack CV-in. The RES-4's audio output was sent to a VCA-4MX and multed to an A-199 Spring Reverb. The 100% wet signal was sent to a second VCA/ mixer channel and opened by the CTG-VC's envelope. Altering the threshold changes the timing and also the CV that is sampled from the mix output.

A-162 CV Mod

How to add voltage control to Doepfer's dual trigger delay without vactrols. Another chapter in my A-162 mod saga.



Having changed the timing caps for delay and length, there's just one thing left: voltage control over those parameters. Vactrols are an easy, if expensive option. Ray Wilson has a cheaper solution.



Using a FET as a variable resistor is not without its difficulties, but Ray's circuit works with the A-162. It's not precise, but the object was just to get some automated variation.



The floating perf-board is held by a combination of resistors, shrink-wrap and single-core wire. It weighs next to nothing, so should be ok. There was just enough room for the jacks.

Vactrols slew and need 2V before they get going. Transistors operate as resistors only within a limited range. Next time I'll tell you how I added VC to my A-143-1 quad AD envelope using a combination of the two.

Basic Electricity - Concert Today!

A reminder about tonight's gig with Derek Holzer, Vanessa Ramos-Velasquez and JenaMu6. The venue is the Kino on Kastanienallee 77, 10435 Berlin Prenzlauer Berg. Doors at 21:00, music at 22:00 sharp.



I won't be playing, but had some fun with this patch last night:



Inspired by the sound of Japan's Gentlemen Take Polaroids, it features a Plan B M15 VCO FM'd by Doepfer's A-143-9 QLFO. The gated sound was fed to an A-199 spring reverb with the feedback routed through Cwejman's FSH-1 frequency shifter. I added a touch of Logic's Ensemble, but 90% of the effect is the shifting reverb. Lovely.

Look forward to seeing you tonight at BE#6!

The Shape of Things That Were

I've just binned over two decades worth of magazines. It broke my heart, but I don't have the space for the paper mountain it had become. Among the disposed were Electronics & Music Maker, Music Technology, The Mix, Future Music and Sound on Sound.



I went through as many issues as I could, looking for interesting articles, keepers. The above question from a bewildered Mathew in Camberley warmed my heart. Peter Forrest's scoop on the Doepfer A-100 in December 1995's The Mix is presented below as a historical document. Dieter's system, which then sought to provide a modern alternative to vintage Moogs and Rolands, is now itself almost 20 years old and still growing.

A few observations from my purge: the death of small ads due to the internet, musicians should leave video and graphic art to the experts, computers today might be faster and software better but the rate of genuine change seems to have slowed in the last ten years, DJs have a lot to answer for, Paul Farrer's 'Notes from the Deadline' is the first thing I jump to when I get my copy of SOS, Future Music is throw-away and the writing is shit.

Peter Forrest's review of the A-100 in The Mix 12/95
The Mix, Feb. 1997, Doepfer A-100 Review 2
Future Music, Feb. 2002, Peter Forrest Interview

For future scan updates, click on the media tag.

On the subject of clear-outs, I notice Schneidersbuero are having an end of summer sale. Might be something there to fill my now empty shelves. And, of course, there is one last question: did Mathew from Camberley ever figure out how to use his modular?

PotD - Mutant Horse 2

A gentle gallop into Basic Electricity #5 on Friday. This is a take on the patch Tom & I played at BE#4, likened by Ian Boddy to "riding a mutant horse".



A Sport Modulator provides both timing information and CVs, driving Maths, a VCO-2RM, Triple Wave Folder, A-112 Sampler/ Delay and VCA-2P panner. The oscillators are FM'd before being gated, folded and sampled. A stepped and manual CV controls the rhythm, delay time and panning. Flipping between track- and sample-and-hold on the SM delivers the final crack of the whip.

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.

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.

Simple-Mod Tuesday

Two easy Doepfer modifications: a port-hole for the A-199 Spring Reverb and another cap change for the A-162 Dual Trigger Delay.



Like many A-199 users, I keep my tank outside my case. It's less noisy and means I can play the springs. Until today, this meant an ugly, useless 1HP gap next to the module to allow the cinch cable out of the box.

Once drilled and threaded, the hardest part was feeding the cinch back under the second cable tie before soldering. I gave up, snipped the plastic tie and used one of those twisty things everyone has lying around the kitchen.

It's such a simple, useful mod - maybe Doepfer could be persuaded to offer it as an option?



While the soldering iron was out, I took the opportunity to change the timing cap of the delay section of my A-162. I'd already fixed the length parameter to make the module suitable for pinging filters and was unhappy with the delay too. The stock 10uF cap provides delay times of up to 10 seconds - far too long for my uses. I still had a previously-soldered 1uF from my length experiments, so in it went. Here's how it sounds:


(original left, delay right)

The 1uF gives a maximum of around one second delay time. This is more appropriate for echo-type delays. Depending on the frequency of the incoming trigger, higher settings can still be used to generate clock divisions, audible as 'missed/ skipped' notes in the above recording.

It's another simple mod that enhances the use of this module. To be honest, I don't know why the A-162 comes fitted with such large caps as most musical uses lie within the first 10% of the pot's throw.

So, just to re-cap, I swapped out both 10uF capacitors in the top section: a 1uF for the delay and a 0.01uF/ 10nF for the length. I left the lower section un-modded for now, but it's just a matter of time …

Patch of the Day - Basic Variations

Two takes on a theme. One involving FM, the other AM techniques. My Basic Electricity #2 epilogue.



This first patch was inspired by Richard & Rastko's jam on Friday night. It features the FM and Low Pass Gate action of the former and the lo-fi Ciat-Lonbarde sound of the latter. I recorded two passes of a Wogglebug & Maths driving Plan B's models 15 & 13 and Doepfer's A-112 sampler delay.





This second patch has a similar core, but the sound is based on amplitude modulation. The dual peak sine of a Cwejman MMF-1 modulates a VCA-2P. The carrier was the sine of an A-143-9. I altered the C:M relationship throughout the patch. Delay was courtesy of the EHX SMMH.



These patches show the types of complex timbres that can be achieved with modulation. With the current trend for 'West Coast' synthesis, FM is a familiar technique. AM seems to be regarded as ring modulation's poor cousin, but it can be a rich source of sounds.

For me, part of its strength lies in the fact that the carrier, effectively the fundamental, is still present in the resulting signal. To get the most from AM, you'll need two VCAs and possibly some form of offset/ attenuation. As ever, Gordon Reid has the dope.

Thanks to everyone who came to the gig and to Rastko, Hayden & Richard for the wonderful performances.

PotD - Return of the PLL Arabesque

Using a min/max analogue logic module as a phase comparator. Inspired by dougcl's classic PLL patches (1, 2) and this post by Giftnudel.



PLLs seem to be a hot topic again. The jury is still out on whether they're used in the Buchla 259. Make Noise and WMD have announced PLL-equipped VCOs. They form part of the Wogglebug's chaotic heart and can be heard sputtering in the Hertz Donut's bad tracking modes.

I'd read about the inner workings of Doepfer's A-196 and PLLs in general in Horowitz/ Hill's Art of Electronics, but only just tried Giftnudel's patch. The A-196 employs a linear VCO, but as you can hear, the patch works just as well with standard, exponential VCOs:


minmax-pll (master left, slave right)

Two VCOs are compared in a min/max module like the Doepfer A-172. The minimum signal is subtracted from the maximum and the difference fed back to the 'slave' via a slew limiter, thus generating a CV. Depending on the initial frequency difference between the two VCOs and the lag time, you can imitate the wonderful glitches made famous by dougcl.

One nice thing about using this method over traditional sync is that it doesn't affect the sound of the slave as much. The other is that the slew limiter offers control over how well, or poorly, the oscillator tracks.