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Showing posts from February, 2011

A-101-2 Vactrol Low Pass Gate

I must say i am very happy with my latest module, the A-101-2 Vactrol Low Pass Gate.
This module is a combination of a 12dB Low-Pass Filter and a Voltage Controlled Amplifier (VCA), with 2 vactrols as controlling elements with very unique characteristics and is very popular amongst the members of the Doepfer A-100 Yahoo Users Group.

The module is based on the Buchla Model 292 Quad Voltage-Controlled Lopass Gate module. '
The term "Low Pass Gate" was first used by Don Buchla for a module that can be switched between Low-Pass and VCA.
Buchla's current (2004) update is the Model 292e Quad Dynamics Manager ,that is functionally identical to the older model, but includes some extra functions like velocity inputs, allowing controllers to control note volumes with performance gestures and preset storage.

Doepfer's LPG module can handle 2 different incoming control voltages that can be used to control the Low-Pass filter, or to open or close the VCA.
Additionally a comb…

Analogue-Systems-to-Doepfer Adaptors

Ever thought of installing Analogue Systems modules in your Doepfer Eurorack (or the other way around) without much trouble?

Tony from Synovatron came up with a few nifty solutions for that;
His latest 'inventions' are small adapters that allow you to simply plug directly into your  AS or Doepfer module, or that fit the connector on the module's PCB.

Installing is as easy as it looks;
 Note the red stripe - just line up the Doepfer cable's red stripe with it.
 The adaptors are also marked with pin 1 and have an orientation mark so pin 1 goes to the top (in fact to pin 1) and the red stripe goes at the bottom.

The order code for the socket-to-socket version (left) will be ASM2DB Adaptor (or Analogue Systems Module to Doepfer Bus Adaptor). The code for the plug-to-plug version (at the right) will be DM2ASB Adaptor (or Doepfer Module to Analogue Systems Bus Adaptor).

More info at

Vactrol Basics

A Vactol is an opto-isolator device that is often used for channel-switching in many modern amplifiers, but these electronic parts can be used in various other ways too, for example in synth-modules like Doepfer's A-101 Series and the A-102 Low Pass Gate module.
There are many kinds of optical isolators, but the most common is the LED/photo-transistor type.

A vactrol is a combination of a light depending resistor (LDR) and light source (LED) both put into a small 100% light-proof case.
The principle of a Vactrol is very simple.
When an input current is applied to the LED, the output phototransistor turns on.
The only connection between the LED and phototransistor is through light -not electricity, thus the term optical isolator.  These optical isolators are primarily digital in nature with fast response times suitable for interfacing with logic gates. Rise and fall times of a few microseconds, faster for some isolators, are typical.
So together, the coupled pair act as an electric…

Arranging Modules

Like most of you all know i recently installed my 4th metal G6 frame.
It was about time that i did that, because i already had a few modules that didn't fit the old rack and that were lying loose in a drawer.
After installing the new frame i came up with the idea of this blogpost.

Of course i had to re-arrange my modules again... The old layout just didn't make any sense anymore. Some modules were so weirdly placed that patching them always resulted in a whole spaghetti of cables.
I couldn't find many guidelines for arranging modules on the web, so I just started and made a few notes during the process.

A few of my personal guidelines that work the best for me are:
-    Before you start, disconnect all racks from the power supply! Safety first!
-    Work from top to bottom. I'd almost say work from top left to bottom right. That will keep the system and the flow of signals much more 'readable'
( I'm not sure if this works for Arabic countries, where they rea…

Quick Tip V : Solving Jack Socket Contact Problems

Some ( minor ) contact-problems have been reported with the older mini-jack sockets ( S6PC, manufacturer: Cliff / England ) that were used by a variety of manufacturers of electronic equipment.
Unfortunately Doeper also used these sockets in their earlier modules, so these problems can happen with your module too, if yours was made before the end of 2002. 
The 3.5 mm miniature jack sockets used in the A-100 system before about 2002 have been very sensitive to the diameter and shape of the jack plugs of the cables used to interconnect the modules.
If you have contact problems with older modules Doepfer advices the following procedure:
Disconnect the A-100 system from mains due to safety reasonsRemove the module from the rack and disconnect the bus cable if necessaryInsert the jack plug into the socket causing contact problemsPress down the hollow of the "hot" contact very carefully using a slotted screwdriver (see picture at the right)This should lead to a good contact between j…

Quotes V : Alan Pearlman

"The electronic instrument's value is chiefly as a novelty. With greater attention on the part of the engineer to the needs of the musician, the day may not be too remote when the electronic instrument may take its place ... as a versatile, powerful, and expressive instrument."

Alan Pearlman wrote this in 1948... 21 years later he founded ARP Instruments Inc.

Most Wanted IV - A-157 8x16 Step Trigger Sequencer

At NAMM 2010 in Anaheim USA, Doepfer showed a very early prototype of the A-157 8 x 16 Step Trigger Sequencer. There's not much information available about this module, besides the info in the NAMM 2010 News PDF on the Doepfer site. Even Doepfer's own Future/New Modules section doesn't have any info on it.

What we do know ( about the prototype(s) ) is that it will be a 'simple' and affordable trigger sequencer (only 8x8 steps, no preset management).
The final module will be equipped with assigned LEDs (arranged in 8 rows with 16 steps each), 8 trigger outputs and clock/start/stop/reset inputs.
It generates 8 trigger signals that are set by the buttons. The LEDs are used to show the active steps and the external control signals clock, start/stop and reset are used to sync the unit to other A-100 modules (or via suitable interfaces to Midi/USB).

An additional preset management will be added to the final version of the module. At the time Doepfer was also thinking abou…

Booktip VI - The Museum of Synthesizer Technology by Martin J. Newcomb

Okay... the cover-design of this book isn't outstanding, but the content is in fact very interesting. This book, simply called The Museum of Synthesizer Technology, written by Martin J. Newcomb in July 1994 shows the huge collection of what used to be the Museum of Synthesizer Technology that was situated in a  part of Berkshire, UK.
The museum, opened by Bob Moog, only existed for a few years ( 1994 - 1997 ) and was at the time the largest collection of analogue synthesizers in the world.
The idea was nice; the aim was to preserve all these analog synthesizers for future generations, and today's generation would be helped by exhibiting them and by keeping the (service- and normal) manuals available for the public.

Basically the book ( A4-sized, 118 pages ) is an overview of the museum's collection, with a lot of large (color-) pictures and accompanied by well-written background-information on the different synth-companies and types.
...most of all i like it for it's …

Racks, Cases and Monsterbases

In the beginning it was easy; you only had a few choices:
You could either buy a 3-unit high rack (A-100G3), a 6-unit high rack (A-100G6) or the 6-unit high suitcase version (A-100P6) from Doepfer to mount and organize all your A-100 modules.
Nowadays you can choose from a huge variety of other housings from Doepfer, from 32HP width miniature-cases up to 168HP monster-cases.
You can even make your own cases/cabinets with the low-cost DIY-kits containing rails, a power supply and bus-boards.

The most economic versions nowadays are the low-cost plain wood cases (A-100LC6/LC9) ,which cost about 35% less than the metal and standard suitcase versions.
If that is not your thing you can always go for the monster-cases;
Twice the usable width of a 'normal' rack, but finished with a black or grey finish in a flightcase-look are available in many different shapes and sizes.
There's even a monster-base that fits under these cases, with 2 rows of 168HP width, one with horizontal alignm…

A-136 Distortion / Waveshaper

The A-136 Distortion/Waveshaper module is a nice distortion/wave-shaping module with external CV control possibilities. It can be used for audio-distortion, but also to modify control voltages ( create new control waveforms made from LFO, ADSR, or Random voltages ) with it.

The module divides the incoming signal into 3 different components; the positive, the negative and the original signal. The 5 knobs and the 2 CV inputs let you adjust the positive and negative amplification and the clipping levels.

With all the different different settings you can create complex wave-shapes and impressive sounds, but to be fair, i have heard better (extended?) distortions. This might perhaps be the reason why Doepfer advices you to use it in combination with filters... not sure though...

For mild and subtle distortions this module sounds alright, but the wilder, clipping distortions are a bit too extreme for me.
Personally i prefer the A-137 Wave Multiplier or the A-116 WP Waveform Processor contro…