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.

Cwejman MMF-2 Demo

Impressions of the Cwejman MMF-2 stereo multi-mode filter.



The MMF-2 came out this summer and quickly sold out. Having spent some time with one, it's easy to understand why. It offers a wealth of possibilities and sounds great. Have a listen:


Buy the album to access the full recordings (10 tracks, 55 mins).

The MMF-2 can be used to process mono or stereo signals. The filters can be run in parallel, or if patched, in series. It features two types of saturation and a dry/ wet mix. For a full description, see the MMF-2 product page linked above.

The MMF-2 shares much in common with the MMF-6. It's confident, bold and, to my taste, more musical than its single-sibling. It FMs beautifully and, when oscillating with some saturation, can be used for plucked/ percussive sounds or aggressive basslines. It can also be self-patched to make crazy, chaotic noise. It really comes alive when using the mix feature.

Here are some thoughts that cropped up in use: the initial frequencies of the left and right channels need to be manually balanced in stereo patches. You can't sweep the entire frequency range with the master as the L&R cutoff pots are offsets. Inter-channel CV normalization and attenu-verters would be useful e.g. in a LP/ HP configuration. The filter slopes might be too steep for some external audio processing tasks. Saturation is either on or off, but the amount is determined by the input level. I would have liked an input VCA but, as Wowa told me, the MMF-2 is already 'a beast', both in terms of size and stereo circuitry.

The MMF-2 can be clean or brutal, used to transform mono or stereo signals or even as a dual voice module. Look out for the next run.

Thanks to Wowa for answering my questions and to Schneidersbuero for the loan.

Patch Tips #25 - Filters do Maths

Wave-shaping with state variable multi-mode filters, or how to integrate a square into a saw.



A while ago Josh from Toppobrillo made an aside in a forum thread that his Multifilter could be used to bend squares into saws. Infuriatingly, he never said how. Well, I love a patch challenge …

Send a square to the input of your filter and monitor the lowpass output. Wind the frequency knob back until you get something resembling a triangle. Patch the bandpass output to the CV input and start to raise the resonance. Play with the input level, amount of feedback and resonance until you get something resembling a saw. It won't have a perfectly vertical flank, but it's pretty close.



This patch works because of phase offsets between the lowpass and bandpass outputs. Positive feedback will give you a saw, negative feedback a ramp. If you increase the amount of feedback, you'll be able to generate sub-harmonics of the input frequency. If you send your pitch CV to both the VCO and 1V/O input of your filter, the saws should maintain their shape as the frequency changes.

Fonitronik mh11 ADC Pattern Sequencer

Hands-on preview of Fonitronik's novel 8-step CV & Gate sequencer.



The mh11 offers a new take on the basic sequencer concept. An analogue to digital converter generates 256 patterns. The notes and direction stay the same, but the sequence of steps that actually get played is under manual or voltage control.

For more on the concept, see Matthias' own description and video. Here's a demo of the effect of CV-ing the pattern on notes played & (0:34) gate length and (0:57) the mh11 as graphic VCO.


(edit: Bandcamp's MP3 conversion has mangled the graphic VCO example. Download the WAV.)

To understand what's happening, feed the mh11 a clock and set all step switches to the up/ on position. All steps play. Then 'mute' certain steps by setting the switch to the off position. The ADC is used to automate this muting - it generates an 8-bit string of on & off values which is AND gated with the incoming clock. To test this, stop the sequencer, set all switches down to the ADC position and turn the manual PCV pot until all lights of the pattern LED-bar are lit. Restart the sequencer and turn the pattern knob. Any incoming CV is summed with the manual offset to generate a new string of on & off values.

Programming the mh11 is easiest with another sequencer or S&H (running at a clock division) or a S&H-synchronized manual CV from Pressure Points. This is because the ADC 're-computes' the pattern with every change. You can use an LFO, but depending on the speed, things can get glitchy. At audio-rates, as per the graphic VCO example, this is not a problem. The 4MS PEG makes a good partner for the mh11 as its swings can be synced.

In use, I found a few minor issues: if fed more than 8V, the ADC can lock up. Remove the external CV and twist the offset pot to reset it. I felt this offset should be inverted so that one can start with all steps on and then progressively mute them with a +ve CV. The output CV droops slightly when passively multed, so you may want to buffer it. Finally, the ADC controls both the CV and gate signals. Muting a trigger or tying a gate also mutes the CV. So, you can't send the CV to two VCOs and have one follow the pattern and the other the master clock. I asked Matthias whether this could be changed, but quickly realized it would require a second, parallel ADC.

The build quality is solid, the layout generous and the LEDs give good visual feedback of the ADC's current pattern. A microprocessor-based sequencer might offer more options, but I do get a kick out of imaginative designs like the mh11. Thanks to Matthias for the loan of the module and for keeping it analogue!

Basic Electricity #7 - Concert Tonight!

A reminder of BE#7: tonight's gig with Hainbach, Electronicpresskit & Trouby Modular. Doors open at 21:00, music at 22:00 sharp at the cinema on Kastanienallee 77, 10435 Berlin Prenzlauer Berg.



We've got tunes for the ladies, noise for the boys and modules for the musicians. Hainbach will present songs from his new album:
 
Brave the cold tonight and snuggle up in a cosy Kino with some great music, chilled IPA and special snacks!

Basic Electricity #7 - Friday Nov 16

The next Basic Electricity concert is on Friday week, 16th November. We've got another great line-up with Hainbach, Electronicpresskit and Trouby Modular. See the BE blog and Facebook event for more.

BE#7, 16.11.12 Doors: 21:00, Music 22:00 sharp
Kastanienallee 77 (Kino) 10435 Berlin P-Berg



Here are some pictures from BE#6 with Derek Holzer, Vanessa Ramos-Velasquez and JenaMu6.



Thanks to everyone who came and see you at BE#7!

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.