AndreasKrebsBlog

The Max / Min is a much underrated audio tool. Did you even know it? You possibly regarded it as some kind of freaky elektronic calculator (maybe useful for some kind of weird modulation stuff). In fact, it is a very interesting waveshaper. Much like a clipper, you can feed an audio source (e.g. a sawtooth from a VCO) and a constant voltage in two of its four inputs - and you will have clipping signals at both “max” and “min” outputs.

You may, however, use two or more audio sources as input signals - this little unit will create two different output signals with combined waveforms: one output will only use the higher, the other one only the lower parts of both waves. And these parts will change dynamically, if your audio sources are slightly detuned.

Technical details can be found on Doepfer’s homepage:

http://www.doepfer.de/A172.htm

For my little audio example, I’m using two A-110 VCOs: one with its sawtooth, the other with its pulse output, both VCOs are sent directly into the Max / Min. The two “Max” and “Min” outputs of the A-172 are spread left and right in stereo. No filters, no VCA. I’m starting with 100% pulse, and decrease pulsewidth slowly by hand. Then I start detuning the two VCOs a little. Here we go:

http://www.andreaskrebs.de/assets/media/A-172.mp3

Have fun,

Andreas

The A-102 is a 24 dB lowpass which uses diodes (and not transistors), which leads to quite unusual resonance behaviour (resonance is dependant on filter frequency). The filter can easily be overdriven, which adds some interesting harmonics. In this sound example, I use three A-110 VCOs (sawtooth, one VCO tuned down 1 octave), mixed and put through the A-102 and then into an A-132-3 VCA. Both VCA and filter are controlled by an A-140 ADSR, the sequence is made with an A-155/A-154 Sequencer.

Technical details on the A-102 can be found on Doepfer’s Homepage:

http://www.doepfer.de/a102.htm

• We start with comparably low input level, no resonance and cutoff frequency at minimum. Then I manually increase cutoff frequecy up to maximum and back to zero.
• Starting around 0:35 same procedure, but with medium resonance (value ca. 3)
• From 1:10 on: full resonance.
• Then back to zero resonance, but from 1:50 on maximum input level.
• Starting at 2:25 we hear medium resonance again (full input level).
• Finally, around 3:05 we have max resonance and max input level.

Here we go:

http://www.andreaskrebs.de/assets/media/A-102.mp3

Have Fun, 

Andreas

The A-111-5 is a “Dark Energy” in Eurorack format (without Midi and wooden side panels). This is a nice and versatile module: quick sound changes are possible without patch cords, overall sound is very good and the filter will follow 1 V / octave extremely well, thus being something like a “second VCO” when self oscillating. Technical details can be found on Doepfer’s homepage:

http://www.doepfer.de/A1115.htm

I’m using an A-155 Sequencer together with an A-156 Quanzizer to tonally control both VCO as well as VCF of the A-111-5. So we have some kind of “twovoice synthesizer” in that little box. I start with the pure filter sound (self-oscillating), then I add the VCO (pulse wave) and later some LFO modulations of VCO / VCF). Finally, filter resonance is reduced until we only hear the VCO. No additional processing was necessary. Here we go:

http://www.andreaskrebs.de/assets/media/A-111-5-twovoice.mp3

Have fun, 

Andreas

This is one of Doepfer’s older filter designs, nonetheless it is quite an interesting one. It offers four filter modes: Notch - Highpass - Bandpass - Lowpass, each with a separate output (so you may use it together with a switch or a voltage controlled mixer). Soundwise, it is a bit rough and would be a good companion for e.g. an A-108 or an A-106-6. It can self-resonante in all four modes and its 1V/Oct-scaling is among the most exact ones I know (so this may be used as an oscillator as well). Unfortunately, the special circuit CEM3320 (Curtis) is no longer available, so this filter will run out of stock. Technical details can be found on Doepfer’s Homepage:

http://www.doepfer.de/a121.htm 

I have used three A-110 VCOs (sawtooh, one A-110 is 1 octave below), driven by an A-155 sequencer and put into the filter with high audio level. Filter out is then sent into an A-132-3 VCA (controlled by an A-140 ADSR).

We start with Notch mode (0:00-1:22), then Highpass mode (1:22-2:53), Bandpass mode (2:53-4:30) and Lowpass mode (4:30-6:17). Within each mode, I start with no resonance and filter frequency only being modulated by a very slow LFO. Then I slowly increase resonance up to maximum, add ADSR modulation of filter frequency, decrease resonance back to zero and finally fade out.

Here we go:

 http://www.andreaskrebs.de/assets/media/A-121.mp3

Have fun,

Andreas