Doepfer A-121 Multimode Filter Re-Design

A-121-2 Re-design

We all knew a re-design of the Doepfer A-121 Multimode Filter has been in the pipeline for a while, due to the unavailability of certain chips inside.

Since the beginning this has always been one of my favourite filters, because of it's sophisticated sound and the VC infut for resonance control. Oh, and the multiple simultanuous outputs...

At Namm 2016 Doepfer will present the A-121-2, the successor of the obsolete module A-121.

The circuitry is totally different from the A-121 which used the obsolete CEM3320 filter circuit. 

Module A-121 is a voltage-controlled multi-mode filter with a cut-off slope of -12 dB / octave.

Four simultaneous outputs are available, each with different characteristics: low-pass, band-pass, high-pass and notch (or band reject). 

The cut-off frequency determines the point at which the respective filter effects appear. 

The frequency can be adjusted manually, or by voltage control (Filter modulation, for instance by an LFO or ADSR). 

Two CV inputs are available, whose control voltages are summed. Resonance (Emphasis or Q ) can be adjusted manually, or by voltage control, right up to self-oscillation, in which case it will behave like a sine wave oscillator.

The sound of the new module A-121-2 is identical to filter of the Dark Energy II but has been expanded by the voltage controlled resonance feature (like the original A-121).

Read all about the specs of the original A-121 at http://patchpierre.blogspot.nl/2011/03/filters-ii-121-vcf2-multimode-filter.html

The modules will cost Euro 120.00 and will be available around March 2016

Source: Doepfer.com

Doepfer A-121 Multimode Filter Tutorial Videos by Raul Pena

As promised, a new series of Raul Pena's excellent tutorial videos has started today.
This time Raul digs deep into, and explains all about one of my favorite filters, the Doepfer A-121 Multimode Filter.

Video 1: Doepfer A121 Multimode Filter Basics

" A brief look at the Doepfer A121 Multimode Filter. Basic Features and functions are discussed.
Audio demonstrations in the next video in the series.
Sound and Video by Raul Pena."

Video 2: Doepfer A121 Multimode Filter Low and High pass Filters Demonstration

" A brief look at the Doepfer A121 Multimode Filter.
Audio demonstrations of the Doepfer A121 Multimode filters.
A specific look at the Low and High Pass Filters. Next video in series looks at the Band Pass and Notch filters.
Sound and Video by Raul Pena."

Video 3: Doepfer A121 Multimode Filter- Band Pass and Notch filters Demonstration

" A brief look at the Doepfer A121 Multimode Filter. Audio demonstrations of the Doepfer A121 Multimode filters. A specific look at the Band pass and Notch Filters. Next video in series looks at Modulation of the filter.Sound and Video by Raul Pena."

Video 4: Doepfer A121 Multimode Filter- Modulation Demonstration

" Last segment in the Doepfer A121 Multimode filter series. Segment explores modulation of the A121 via the 1/V per octave inputs for frequency and resonance. Sound and Video by Raul Pena."

Check out Raul's latest survey at http://www.surveymonkey.com/s/K3Z9PVF

Other places to find Raul's World of Synths on the Web

raulsworldofsynths on YouTube

raulsworldofsynths on Vimeo

raulsworldofsynths on SoundCloud

raulsworldofsynths at iTunes

raulsworldofsynths at CDBABY

Discontinued A-100 Modules

Good things come and good things go...
There are many different reasons for manufacturers to stop producing certain modules.
Sadly for some people, some components of a few Doepfer modules aren't available anymore.
Some of the special circuits ( or IC's) in the modules have become scarce, or not available at all ( like the original knobs ) , and that has been a reason for Doepfer to discontinue the production of some of these modules.

Another reason to stop producing certain modules is because they just don't or didn't sell... maybe just because they are not very useful (anymore) or they disappeared when newer modules appeared with (almost) the same function(s).

Soon a collector's item?

An overview ( updated February 2012 ) :

A-111 High End VCO  As the special circuit CEM3340 used in this module is no longer available the module has to be discontinued.
/ Sale while stocks last.

A-121 Multimode Filter As the special circuit CEM3320 used in this module is no longer available the module has to be discontinued soon.
/ Sale while stocks last (only 20 left in Januari 2012)
Doepfer recommends the A-106-6 XP VCF, that is based on the filter circuit of the Oberheim Xpander, as a replacement module.

...the A-101-9 Universal Vactrol Controller is the latest addition to the running out/ sale while stock lasts list... more info on this later

The A-111-5 Mini Synth Voice (and the Dark Energy) will also be discontinued because of CEM3394 chip running out... Stock is still available.
More info on this HERE

The following Doepfer modules are not available anymore:

A-123 24dB High Pass was discontinued at the time by poor sales, and the special circuit CEM3320 used in this module is no longer available.

...and another one...

A-126 Frequency Shifter Because the special circuit CEM3382 used in the internal quadrature VCO of the A-126 is no longer available Doepfer had stop the production of this module too.
But they are about to plan a succeeding model ( A-126-2 ) without internal VCO. The advantage of this solution is that even frequencies below 50Hz are available for special beat effects based of frequency shifting at low frequencies.

A-138x Mix Expander - Because of the poor inquiries the production of this module had been stopped too.

A-139 Headphone Amplifier, a 2-channel headphone amplifier with 2 audio inputs (3.5 mm jack sockets) and level controls, common loudness/master level control, 2 headphone outputs (stereo 1/4" jack sockets) - no longer available

A-177 External Foot Controller is now replaced by the A-177-2, a more economical replacement with a little less control (without LEDs and without scale controls), but with almost the same functions.

A-179 Light Controlled Voltage Source is also no longer available as the special circuit CEM3320 used in this module is no longer available. That is why this module also had to be discontinued.

A-191 MIDI-to-CV Interface / Shepard Generator no longer available

A-197 Analog Meter no longer available ( i personally never really expected an analog meter to be very useful, and i guess i wasn't the only one )

A-197-2 Oscilloscope kit no longer available -
I am still looking for an affordable oscilloscope though. I was thinking about something like a MFB VD-01 Videoscope, but sadly there's no budget at the moment...

Latest update: A-188-1Y BBD Module (256 stages) is also on sale while stocks last


Curious what chip is inside your synthesizer?
Check http://synthtech.com/cems.html and
http://sequencer.de/synth/index.php/Chips_in_Synthesizers

Filters II : A-121 VCF2 Multimode Filter

The first Doepfer filter that i ever bought was the A-121 Multimode Filter. It is a 12 dB/Octave filter, and has multiple simultaneous outputs available; a Low-Pass, Band-Pass, High-Pass and Notch (or Band Reject).
It also has 4 CV inputs, 2 for adjusting the cutoff frequency and 2 for resonance.

This is still one of my favorite filter modules, the multiple outputs are very useful, and i  like all the CV inputs. It just gives you so much more control over the filter, and that's what i like most in a module; maximum control.

Although it is 'only' a 12 dB filter it sounds very nice, from very smooth and warm up to quite rough, especially with the resonance turned up ( ...up to self-oscillation ).
Most of the times i patch an A-174-2 Wheels CV into FCV1, and a simple envelope CV to the (adjustable) FCV2. Works fine in most situations.
With some analog or digital noise added to QCV2 to give it a touch of unpredictable resonance you will quickly get a convincing fat bassline.

Together with an A-138 B (exp) Mixer you can easily make some pretty impressive stacked bass-sounds, all with just a single filter-module.

Find A-121 sound examples at Andreas Krebs Blog : HERE

As the special circuit CEM3320 used in this module is no longer available the module is discontinued. I believe there are still a few available, but they don't make new ones anymore. Doepfer advices modules like the A-106-6 ( with eight simultaneous outputs! ) or A-107 Multi-Type Morphing Filter as a replacement.