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For a variety of reasons and purposes I previously found myself spending a proportion of my synth/electronics time modifying others' modules, firstly some earlier Doepfer ones, and then moving over to Plan B. This page gathers these in one place: most of the instructions for doing the Doepfer mods initially appeared at the now closed Doepfer Yahoo group, but thankfully I copied them here many years ago, so at least they are still around (consequently there are quite a few dead links on these pages, which I will try and edit out as time allows). Some of the Plan B mods arose out of discussions at the Modwiggler forum, and generally the pages linked below will refer to any relevant discussion; others simply arose from deficiencies observed on acquiring an example module.

     A-110 VCO: improving the sine waveshape
A-117 Digital Noise: to allow clocking from a 'sloppy' input
A-127 Triple VC Resonant Filter: switchable LP/BP selection for each filter
A-135 Voltage Controlled Mixer: obtaining the individual outputs from each VCA
A-140 ADSR: automatic re-trigger so it self-cycles
A-150 VC Switch (old type): to allow switching of signals greater than +8V
A-151 Sequential Switch (old type): reset on 2, 3 or 4 steps
A-155 Analog Sequencer: addition of a permanent 16-step facility
A-161 Clock Sequencer: adding a clock input and reset to the 161 to make it independent of the A-160
A-163 VC Frequency Divider: switchable DC-coupling for the output to allow division of slow clock-type signals
G3/G6 case: identifying/replacing a leaky IEC power inlet
Plan B:
     Plan B Summary: a summary of those modules I've looked at, some of the issues found, documented fixes, and currently undocumented (possible future) fixes
Model 9 Mixer: reducing the amount of bleed-through when a signal is supposed to be 'muted', and killing the spurious high-frequency oscillation
Model 10 Polyphonic Envelope: various modifications and corrections to the circuit
Model 11 Evil Twin Bandpass filter: no modification, just an observation on the 'twin feedback path' nomenclature
Model 14 Dual Voltage Processor: improving the crossfade transition
Model 15 VCO: improving the sine wave adjustment method and waveshape
Model 15 VCO: other various simple changes affecting the morph and PWM circuits, particularly for rev 1 versions of the module
Model 17 Triple Event Timer: two simple mods to rid unwanted pulses from the sum output, and reduce the maximum threshold level
Model 23 Analog Shift Register: a simple mod to correct the clocking when two or more modules are chained
Model 28 Tap Clock: synchronization upgrade to improve the 'phase lock' feature; 8th note accent mod; select levels mod for serial out; resistor R5 missing
Model 32 Vector Plotter: mods to improve kinetic gate performance and drastically reduce current consumption (by removing a design flaw)
Model 38 ADSR: modification to improve the controllability of the envelope
Model 38A ADSR Expander: modification to actually make it do something useful

Links for other modifications

Doepfer have a dedicated A-100 DIY page, containing not only various modifications to specific Doepfer modules, but also ideas on how to modify modules more generally, and basic explanations of some simple circuits.

Nick Keller has a page of interesting mods at the analoguehaven site, the distributor for Doepfer gear in the US.

[Page last updated: 08 Aug 2022]