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Synth Releated Schematics

This is just a central collection of all the synthesizer schematics that are scattered across my site. In time, I will add some useful circuit building blocks as well. Ordered most reccent first.

CMOS MS-20 Filter - A version of René Schmitz' late MS-20 Filter using 4069U inverters.
AR/AD Transient Generator - A variation of Ray Wilson's Retriggerable AR Envelope Generator. Several changes were made to the design.
VC-Echo - PT2395 based delay.
Linearized LM13700 VCA (untested) - This uses a dual OTA with one in an opamp's feedback path. It seems to simulate ok, but there may be stability problems.

Technical Notes and Circuit Analysis:

Here are some technical notes and works for analyzing certain syntheiszer circuits.  Most of this came from my own personal notes, but I thought they might be of some use to other people trying to learn about electronics and analog synthesizers. Eventually, I intend to add some notes or tutorials on digital synthesis with software and hardware (verilog). These are not, by any means, meant to be formal, technical writings, so don't expect anything like that. In the circut analysis, I usually show many steps so that a beginner might be able to make something of it. The math can sometimes be a little intense (depending on your math skills). If you are afraid of it, hopefully the explantations will still be of some use. For anyone who might spot an error or if you just have some questions/comments; please drop me an email.

Potentiometer Linearity - Just some description/plots of loading effects on potentiometers when used as an attenuator. It may be obvious, but it can be helpful to see a plot. note: I saw something like this a while back but could not find it so I made my own.
SSM2040 Analysis Part 1 - A basic analysis of a single filter stage and current sink for an SSM2040 filter clone. The design being analyzed is René Schmitz' version of Jürgen Haible's SSM2040 clone. Check those two sites for the complete schematics. note: I have done this while constructing my own slightly modified version of the filter, which will be published here soon. A Part 2 of this analysis will follow. 
Triangle to Sine Conversion with OTAs - A demonstration of tri->sine conversion by overdriving an OTA. Two designs, with and without feedback are considered.
Tempco Calculations, Part 1 - A design example of a temperature compensated expo converter using a  PT146 resistor. If part 2 ever comes, it will be an active compensation but that will only happen if/when I finish and test the design.

Links to Other Articles of Interest:

The following papers, articles, and circuit descriptions have helped me in my study of analog syntheiszer electronics. These are links to writings by other authors. Some of this knowlege is assumed in my own notes listed above.

Operational Transconductance Amplifiers - Achim Gratz' notes on OTAs. These notes describe the derivation of OTA equations for several different ICs. Methods to reduce distortion are also discussed. The analysis will certainly help in understaning voltage controlled amplifiers and many voltage controlled filters.
Whats that exp and tempco stuff? - René Schmitz' tutorial on exponential current sources. These circuits are common in synthesizers. The basic expo current source/sink is explained as well as a few methods of passive temperature compensation using "tempco" resistors.
Non-Linear Digital Implementation of the Moog Ladder FilterAntti Huovilainen. This is a wonderful paper on digital implementations of analog filters. Euler's Method is used to solve the non-linear differential equations in real time. This paper was published in the DAFx'04 Proceedings.
Derivation of the Transfer Function of the Moog Ladder Filter - Timothy E. Stinchcombe.

Ryan Williams : 2005