AM1031 Mockup Introduction In 1970 Tonus (soon to become ARP Instruments) issued their first catalog which included details of the 2500 Synthesizer, with a detailed explaination of each production module. They also included a list of sixteen modules they planned to make, but unfortunately only the 1036 and 1045 modules made it into production. When designing the Behriner 2500 modules in 2019 we did consider making some of these “lost modules”, but we didnt think there would be sufficient customer demand and there were very few examples to base the designs on. Only the 1035 has been seen ..read more

Overview Behringer launched their clone of the RSF Kobol Expander I in late 2023 and I received one of the first to arrive in the UK on 23 October. The original design has some unique features including variable wave shape VCO’s and a filter based on the legendary SSM2040 chip. This post describes the technical design of the Behringer version, how it works and performs and the unique signal levels. It is importent to realise that the Kobol works to its own standard of control voltages which are not the same as standard 5V or 10V Eurorack levels and that control voltages are a mix of bipolar an ..read more

160 Module #2 Overview Roland expanded their 100M range of modules in late 1980 to a computer interface, the 160 module, which was only available as a prototype. This post documents the features and the possible technical architecture of the 160 module. The information has been gathered from rare picture of two 160 modules being used by Godo Irukayama and the schematics of the Roland CMU800, which was a follow on computer product from 1983. Alex Ball has contacted Godo Irukayama in Japan for more details, as Godo was the first person to use the 160 as a colloboration with Roland in 1979. Man ..read more

Minisonik Panel Overview In December 2021 I started to work on a replica of the 1974 Minisonic 2, designed by G.D.Shaw. The two PCB’s arrived in mid 2022 and by the Spring of 2023 I had completed the initial testing of the prototype. The original design has some unconvential design aspects, which make it tricky to drag into the 21st century! VCO’s The original design is a classic sawtooth exponential VCO that used a dual NPN transistor in the expo converter and a LM318 fast Op Amp in the comparator. I replaced the impossible to source dual NPN with a modern SSM2212 chip, and added an HF trim ..read more

M401 Flip Chip Overview In March 2023 I acquired a computer card from an old DEC PDP computer, the flip chip M401. It was originally launched in 1967 as part of the updated PDP-8/I mini computer. It’s a small single -sided PCB that holds a vintage oscillator that can be externally controlled; frequency and on/off. The original cards had gold plated  traces and carbon composite resistors but mine is from 1975 and has copper plated traces and carbon resistors. It was probably used in a PDP-15 computer with just 24K bytes of memory. This project converts this 50 year old flip chip into a E ..read more

The EP-11 Piano Overview In March 2023 I bought a broken Roland EP-11 electric piano from 1982 for £65. Rather than restore it, I plan to reuse the keybed to make my own 4 voice polyphonic 184 keyboard from Roland System 100M. Here is the plan! Roland 184 Keyboard In 1982 Roland added a 4 octave four-channel polyphonic keyboard to the System 100M. The keyboard electronics are straight out of the Jupiter-4, where the Assigned PCB has been reused, but the keybed is the new synth type rather than the clunky oatmeal design of the 1970’s. The four channels of CV and gate are available on both 3.5 ..read more

Roland 141 Module Overview Back in 1978 Roland introduced the System 100M which included a dual envelope generator (and LFO) module – the 140. Its famous for its snappy fast envelopes but it can also do longer timings as well. Its been cloned a few times but for 2023 and the AM8141 I wanted to get an accurate replica. The original timing is: 1.5ms to 7.5 s 4ms to 15 s Release 4ms to 15 s Achieving these timings with the correct stage curves and “feel” turns out to be a lot harder than it looks, especially in Eurorack with its lower voltage power rails! Let’s look at the issues and how to s ..read more

AMSynths 100M Introduction I built a clone of the Roland 100M modular system way back in 2009, before Eurorack took off, it was in FracRac format! Probably the first repliace ever made. The system was at the core of the development of AMSynths as a business from 2012. A few of the modules were reworked into Eurorack and were available as kits and completed modules. In 2018 I started to rework the modules with slider pots ready for a relaunch. But in April 2018 Behringer launched its own set of 100M replicas, which are very good with only a few issues that were corrected over time. Panel qual ..read more

Overview The RS-09 Organ and Strings keyboard was the most popular keyboard product from Roland from 1978 – 83. It sold over 15,000 units and had a hefty profit margin, and retail price of £500 back in the day. In May 1980 Roland refreshed the design, from serial number 94750 onwards, the same chassis but a sleek JP-8 front panel and synth like keybed. It went on to sell another  xxx units into 1984 before analog poly synths were increasingly cheap secondhand and could replace the RS-09 and do more. New Keybed 1982 Model Updates The Roland Service Notes for the version 2 are difficult t ..read more

Prototype PCB’s Overview Back in 2018 I bought an original Jupiter 4 Voice Card with the plan to turn it into a complete single voice synthesizer in a Moog 60 HP case.  In 2020 I got as far as a prototype (see photo of the Motherboard and Panel PCB’s) but with some problems, which resulted in the project being shelved. In 2022 I realised I could use the voice card to make a ProMars (without patches) by adding a second VCO. In May I redesigned the front panel and controller PCB’s to overcome the issues and to use the new AS662 chip. There are four PCB’s in the project: Original JP-4 Voi ..read more