Eurorack 303 filters

 This is a personal list of some filters which aren't too bad doing a acid version of the roland TB 303.

I actually think that the sequencer of the TB 303 is really the key to the sound but you can't really separate the parts.Trying to replicate the sound in Euro or any other format is like a dog chasing his tail

 

However, for what it's worth the filter is certainly important.

And you might get something new and interesting by experimenting.

There is magic behind how the resonance alters the cutoff. 

Plus how the envelope, slew and accent modulate
the filter is certainly beautiful to the ear. 

 

The 303 used a 24dB low pass filter - diode ladder. 

There is much dispute as to whether the filter is 18dB or 24dB.

It's definitely a 4 pole 24dB , but the last pole operates weirdly.

The filter has often been described as a "broken 24dB filter"

Re the ladder design.

The 303 used a diode ladder.

Interestingly, the diode filter was originally developed by EMS in order to work around a Moog patent. This diode filter is best known as the sound of the Roland TB-303.

 

Filters basically work by controlling current flow to a filter capacitor.

The diode or transistor, under the influence of a CV, controls the current flow to the capacitor.

 

The main difference between the two filters is that the Moog style, transistor filter 

design electrically isolates or buffers each pole of the filter.

The diode ladder filter however, doesn't behave this way. The poles interact electrically with each other.  This non-linear design contributes to the dirty, squelchy sound of the 303.

 

So when picking your filter, something like a 18 dB diode ladder should work, but don't let this narrow your choice too much. Experiment ... you may stumble on something new and interesting.

 

So here are some possibilities:

 

 

1. vcf303 - DinSync

    12HP,   It also includes the envelope generator & accent circuit.

    also features CV control over the cutoff frequency and an overdrive knob 

    for driving the input section.

2. Doepfer  a103 VCF 6

    18dB low pass , transistor ladder

3. RS500e.

    EMS synthi filter. 12hp, diode ladder, low pass.

    Switchable between 18db & 24dB

    Before 1974 all VCS3s had a 3 pole filter. After 1974 they had a 4 pole.

4. Post-Lawsuit

    STG soundlabs -  low pass, 1 pole & 4 pole outputs.

5. Snowfall.

    AM8071 - AM synths

     diode ladder low pass filter similar to that in the EMS VCS3, Roland SH-3, 

     System 100 and the PE Minisonic 2. The filter has a 4-pole ladder with an 18dB like response

 6. Doepfer A-122

    24dB Low Pass II (Curtis, Oberheim/CEM type)

7. Doepfer A-105.

     low-pass filter with 24dB/octave slope

     CEM chip (SSM2044 type) 

8. Doepfer A-106-5 

     12dB multimode filter that is based on the filter circuit of the Oberheim SEM module.

9. Blue Lantern Polivoks

10. Doepfer A-124 wasp

11. Doepfer A 102

      Diode filter design, 8HP, 18bD

12. Boogie's 18db

13. EQUINOX VCF

14. Endorphin.es - Grand Terminal 

      Digital emulation of the filter.

15. Sea Devils filter

      STG sound labs - 3pole 18dB low pass diode filter.

16. Sonic XV from AJH

      diode ladder filter with a slope of -24dB/oct.

      based on the classic Musonics Sonic V filter from 1970.

       includes a voltage controllable resonance and an extra bandpass and -6dB/oct lowpass outputs.

      Also added into this filter is a waveshaper/wavefolder.

 17 Studio electronics 3003 filter

      discrete analog 18 db/oct ladder low-pass filter, employing hand-matched transistors