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Filters IV : A-103 18 dB Low Pass TB-303 Filter VCF6

The A-103 18 dB Low Pass filter (VCF6) is Doepfer's own 'TB-303 filter clone' ;
It uses a so-called transistor ladder with a slope of 18 dB/Octave as frequency controlling element.
It is very similar to the transistor ladder of the A-120 24dB Moog type Low Pass filter, but the ladder of the A-103 is a modification of the original Moog ladder and identical to the ladder used in the Roland TB-303.

The in -and outputs are very basic; Three CV inputs are available, and the sum of the voltages from these affects the filter cut-off.
And an audio in- and output are also available, with one level knob.
That is the same layout as the A-102 and the A120 so sadly there is no CV control over the resonance. 
Luckily the resonance cán be adjusted with a knob, all the way up to self-oscillation.

And how does it sound?
I've always loved the sound of a real Roland TB-303 and the sound of it's filter.
This one sounds very nice too, it has that nice warmth in the lows, and the typical sharp edge when resonating, but don't expect that you can re-create a whole TB-303 with just this single module.
Some of the TB-303's other features, like the glide, accent and envelope modulation are missing here, and they (partly) give the legendary acid machine it's very original character.With some creative patching you should get very close to re-creating that original Acid sound...

I got pretty close by using my MAQ 16/3 for the sequence, and the A-160/A-161 Clock Divider/Sequencer combo for additional 'accents'. (You can add an LFO, or Noise for more random accents to experiment with / ,an  A-142 VC Decay/Gate envelope is also a useful addition with CV modulation to CV2 of the A-103 to create basslines like that* )
Overall this filter module can be a nice addition to your Eurorack. (7/10)

Video: Doepfer A-100 does TB303


* thanks to Jakob Paulussen  (@Jakobsweb) for that last tip and the kind permission to embed his video here. More info on the video after the break:


" Legendary Bass Synth Roland TB303 has many clones trying to create that unique gnarly modulated bass sound made popular by techno, house and similar dance music styles.
Doepfer also created modules for his great modular synth system A-100 to achieve such sounds.
Here I used 1 A-110 VCO (TB303 also has but one VCO ... I tried the A-111 but it's too softish); A-103 3-pole lowpass filter (although according to Wikipedia the TB303 had a 4-pole filter contrary to public belief); A-142 Decay/Gate Envelope (TB303's envelope only had a Decay parameter) - Doepfer's A-142 allows VC modulation which I used to create some kind of note slide effect which seems essential).
At the beginning I use a square wave and after a few bars I switch to sawtooth.
I created a house music kind of track to show how it sounds in a musical setup.
Other equipment I use: Studio Electronics SE1x for subbass, Cwejman SE1 MK2 for the sweeping sound; Virus TI2 for housy keys; NI Maschine for all drums and vocal hits.
Enjoy! Leave a comment ( on YouTube, not here ) and rate if you like. "

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