Personal web pages of

Tim Stinchcombe

Analogue Synthesizers

Through the period in which I have been interested in, and been collecting, synth gear (approaching two decades now—here's the story of how that evolved), it has become clear to me that what I enjoy most are the technical and engineering aspects of synthesizers, rather than making sounds or music with them (I am not a musician)—I particularly enjoy reverse-engineering stuff to find out what makes it work (or sometimes to find out why it doesn't work). The majority of my modular gear is made by Doepfer, and I also have a near-complete set of modules that were manufactured by Plan B, plus a handful of modules in other formats. I also have a number of ordinary synths, including a few early Korgs and several EDPs.

This page is just a collection of links to other synth and/or electronics related topics.

DIY Modules

The DIY modules page lists the small number of modules that I have made for myself.

Modifications

This page of modifications lists the mods I have worked out for a number of Doepfer and Plan B modules.

Diode Ladder Filters

A page dedicated to diode ladder filters, including my views on the perennial TB-303 'dispute' between 'its an 18dB 3-pole filter' versus the 24dB 4-pole reality... (Note also that my updated paper, which is detailed below, now has a good deal about the diode ladders in it.)

A Study of the Korg MS10 & MS20 Filters

I have moved the link to my paper onto this new page, which also contains many other links to material relating to the Korg35, the MS-10 & MS-20 filters, and various copies/clones of these filters, and the like.

You can't move far in the world of synthesizers without coming across the fabled 'Moog transistor ladder filter', or one of the diode ladder filters derived from it. In Feb 2004 the first version of this paper came about because I couldn't find the derivation of the transfer function of the Moog filter anywhere on the web, so I had to work it out for myself. As of Oct 2008 I have re-titled the paper 'Analysis of the Moog Transistor Ladder and Derivative Filters' to reflect the fact that it has had a major re-write: not only have I now included derivations of the transfer functions of some of the diode ladder filter configurations, but there is lots of stuff on poles, frequency responses, and comparisons between the functions and the like. [The document is about 50 pages, 2.1Mbyte big, is paginated for double-sided printing, and for best effect should be printed in colour.]

Here is a page of links to research papers on digital implementations of the Moog and other ladder filters.

Being fooled by SPICE

Many years ago whilst designing a ladder filter I foolish placed a capacitor on the output of a transconductance amplifier, in a manner which didn't make much sense. Unfortunately for me, my SPICE simulations colluded with my stupidity to reinforce the impression that all was well, when it wasn't. After more years had passed, and when I finally spotted the mistake, I set out to learn how SPICE had so successfully fooled me.

Filter Pole Animations

I spend a lot of my time trying to understand how filters work, and analyzing various filter circuits. Recently, in order to try and better understand how the pole positions affect the frequency response of the filter, I produced some 3-D plots of the transfer functions as a surface over the s-plane, using Mathematica. Then I discovered I could put many together and actually animate the surface as the pole positions moved. Not only was this educational, but it was also a good deal of fun: I have put a load of them together on a separate page.

How the Serge VCS Works

Having become fascinated by this module, I found it a real challenge to fathom out exactly how it worked, and eventually I decided to write up a page detailing my findings. I am in complete awe of anyone with the level of intuition that it seems to me you need to design something like that from scratch - I can only dream of getting to that sort of level of understanding!

EDP Gnat Synthesizer

I have a few of these now, and when I acquired them they were in various states of repair. Finding absolutely no possibility of acquiring the schematics and/or a service manual off the web, I eventually decided to sit down and reverse-engineer the entire thing. The resulting (hand-drawn) schematics are linked on this page.

Old Synthesizer Brochures etc.

As a lad I was forever writing off to various companies to obtain their glossy brochures on whatever product. I had quite a collection of synthesizer-based ones at one time, and I kept some of the better ones for nostalgia's sake - I have recently scanned some of these and made a page of them here.

PE Minisonic & PE Sound Synthesizer

Complete sets of scans of the both the Practical Electronics magazine Minisonic synthesizer and the original PE Sound Synthesizer.

Electronotes is a newsletter-like publication produced by Bernie Hutchins, covering technical details of music synthesis and sound processing: back-issues up to the very first issue in 1972 are available, and the complete set is a rich repository of circuits, techniques and ideas. When I bought mine a few years ago, I came across an index of them on the web: subsequently I expanded the files and brought them up-to-date, and they may be of use to others (simple text files which makes searching for a particular topic easy):

[Apr 2012: more up-to-date files contributed by a kind reader!]

Electronotes Index

Indices of Mid-Month Letters, including 'Perspectives', 'Webnotes' and 'Bibliographies'

Application Notes index

Supplements index (now including 'Theory and Practice of Musical Sound Synthesis' and AES paper titles)

[Please don't message me with a request to scan some random Electronotes article or other, as 'refusal often offends', as they say. There have been numerous, easily-findable discussions online about making soft-copies of Electronotes available, and the reasons why they are not: I do not know if all the reasons on this fairly old page are still valid, but it is a good place to start, and should give the gist of the considerations involved.]

[Page last updated: 20 Nov 2020]