The Doepfer A-106-5 SEM Filter Module is a 12dB multimode filter that is based on the filter circuit of the Oberheim SEM module.The filter is equipped with a band pass output and a combined low/notch/high pass output. For this output a control knob defines the relation between low and high pass signal. If both signals appear at the same level (i.e. middle position of the Mix knob) one obtains a notch filter. Otherwise the low or high pass signal predominates. The module does not feature self oscillation in contrast to most of the other filters of the A-100 system. The module generates a distorted audio signal if the level control is set to about 50% (i.e. center position) or more with A-100 standard signals like VCOs.
The main features of the Doepfer A-106-5 SEM Filter Module include:
I absolutely love this. I haven't been using it in a conventional modular set up with oscillators, envelopes etc, but rather to process external analogue synths and other signals. It sounds excellent, and is very flexible yet with only a few controls also simple to use. Being able to vary from LP through notch to HP on a single knob is a genius design. The settings between LP and notch, and notch and HP, give a very distinctive sound, like combining a filter and a static phaser. The level control is also very handy.
The 12dB slope and range of different filter types make this filter really versatile. To my ears it has quite a smooth, musical sound where the resonance is useable in tracks rather than just whistling and screaming all over the place - that might sound fun on a Youtube demo, but I find it's rarely what is needed in a track. This filter has a nice well controlled sound, precise but without being cold or clinical. The res will go full on if you crank it up, if that's your thing, but I prefer it with res around 30-50%, where it can pick out harmonics nicely without going into screaming psy-trance meltdown.
In particular I have been using this to process my Korg Minilogue and Prophet VS. Both are great synths, but I'm not a massive fan of their filter sounds, particularly once you crank the res to any extent, they suffer volume drop and get really whistly and thin. So I have been setting the synth filter to make a basic patch that sounds OK, and then feeding into the SEM filter and doing live tweaking with that. The results are great - you can get a lot of musical variation. Great for dub type modulations. I suspect it might also work a treat in the feedback path of a delay or tape echo - I've yet to try this.
This was my first Eurorack filter, and for my purposes it has been perfect. Much more versatile than a standard LFP. It's also inexpensive - and yet doesn't sound cheap in any way at all. Well done Doepfer.