Saturday, 29 June 2013

Additive Programmers 3

The DM7406 chips all tested fine, so decided to simply rebuild the boards. The vero-board has two additive programmers and a hi-gain pre-amp. Nearly finished wiring it up (only about 80 wires involved).

MC1494 Ring Modulator

This PCB pretty much follows the test circuit given in the datasheet, although I'd like to know where it came from. Please add a comment if you know - thanks.
It has not been tested yet. If the chip is okay, the components will get a makeover. If the chip is dead, the board will be replaced by an early Serge RM, as 1494s are a bit rare now.
see below for updates

Dave Jones of kindly gave me a bit of info on these - "The chips are dated late 1971 and early 1972. Allowing for time in the supply chain the board is still probably from the early 70s (1972/73).

The op amp might be an industrial part numbered UA741. (metal can pin numbers are the same as MC1456, but the marking contains 741 in it)

The board is virtually identical to the "typical" diagram from the data sheet. Right down to the trimpot I crossed out (board was laid out for it, but it was jumpered out).

The board has a spot for a pair of zeners that are independent of the rest of the circuit, except for one leg going to ground. But those parts aren't installed."

Serge TKB

This took a bit of poking and prodding to get running again, the main problem turned out to be a semi-dead inverter chip.
Found some interesting mods on the PCB, not sure if this was due to an error with the PCB layout or the connector:

Quad Pan 104A & Quad VCA 101A

Monday, 17 June 2013

Additive Programmers 2

Stripped and ready for rewiring
Despite instructions not to clean the front of the panel, I just had to get the knobs off and clean away the genuine 70s fluff and dust........sorry Jono

Tuesday, 4 June 2013

Additive Programmers

These are very interesting circuits, they mix CVs and produce arrays of triggers in reponse to changes in the CVs.
Each programmer contains two circuits: a non-inverting summer and a trigger generator which produces triggers as the CVs on the inputs cross the threshold of the inverters. The main chips are the long obsolete DM7406 which have open collector outputs that are quite suited to the circuit. This circuit is likely easy enough to build with a CMOS 4069 with a few resistor value changes.
There are a number of broken wires and the circuits are looking a bit grotty, most likely the easiest solution will be to rebuild these from scratch.

edit - updated schematic (was missing a resistor)

Saturday, 1 June 2013


This blog intends to document & record the repair and restoration of a set of vintage Serge and Driscoll panels.
These panels were mostly built by Warren Burt with others built by Julian Driscoll back in the 70s and early 80s.
The panels contain a typical array of the 1st generation Serge modules and standard Driscoll modules, plus a few unique modules either designed & built by Warren Burt or designed by Warren Burt and built by Julian Driscoll.

Aside from the rarity of early Serge and Driscoll synths, these particular panels represent an important chapter in Australia's electronic/experimental music history......and they sound great!!
The new owner wants these brought back to working order without altering the appearance or sound, so no cleaning the grime off the panels and no subbing in high spec op amps. several modules no longer work and need some TLC. One thing I will be doing is replacing all the tantalum caps with regular electros, I hate tanties.

Mostly this blog will contain photos of dusty old circuit boards, some descriptions of circuits and their functions and possibly some schematics.