Behind the Panel

Starting the wiring

Starting the wiring

Slow but steady progress…  All the front panel components arrived, and the control wiring is started. Here are a couple of pictures showing most of the power and ground wires going to the pots (red=postive, blue=negative, black=ground).

Detail of panel wiring

Detail of panel wiring

More details after the fold…
Continue reading ‘Behind the Panel’


Starting the build…

The panel arrived from Schaeffer. It fits snugly into the Explorer case. The plastic in the case sides is slightly bent inwards in the middle meaning it’s held in place pretty securely. I’m starting to add all the panel controls. So far it’s looking good.

Panel in case

Panel in case

Aluminium angle will be fitted behind the panel to allow all the internal PCBs and components to be mounted. These are fixed to the front panel using countersunk machine screws – the holes around the edge of the panel. I manually countersunk the mounting holes round the edge, and the fixing holes for the matrix. I found the mounting holes for the P260P pots I am using were slightly too snug, so if I make another panel, I will enlarge these by 0.1mm. All other hole fixings were fine.

Due next is a lasercut acrylic front panel for the matrix…


Anyone for a Joystick group buy?

Joysticks with similar specifications to the one used in the original Synthi appear to be like hen’s teeth. The stick has 5K potentiometers, but only using the centre part of the track, giving a resistance somewhere in the middle of the range.

Apem Joystick

Apem Joystick as used in my VCS3 clone

Fortunately Apem based in the UK(EU) can supply high quality potentiometer joysticks made in the US by CH components. Unfortunately they’re very expensive if bought singly.

Apem UK’s product page is here, and this is a direct link to the brochure pages (pdf). It looks like a good one for a Synthi clone would be this model number: M11C661P
( 2 axes; circular split bezel; friction held lever; short straight tip handle; 5KΩ 220° resistance track ).

Group Buy?

Unfortunately they are expensive – but the price per joystick can be reduced quite a lot if bought in bulk. I got a quote from Apem for multiple quantities – the prices seem comparable to similar models available from RS/Farnell.

Continue reading ‘Anyone for a Joystick group buy?’

The AKS Panel Design

The design for the panel proved a tricky job – taking much longer than anticipated. Finally here is the design – details after the fold.

Sussex AKS Panel Design October 2013

Sussex AKS Panel Design October 2013 Click for larger version

Continue reading ‘The AKS Panel Design’

The new PCBs

New main boards

Boards A, B, C populated and ready for wiring

Following my success with the PCBs of the matrix buffer PCB and PSU I decided to consolidate the amendments and experiments from my home-etched VCS boards into a single project in Kicad and to get them professionally fabricated – I also didn’t fancy manually drilling all those holes.

A lot of time was spent in Kicad tweaking the layout and silkscreen – as getting such large boards made is a fair investment. The board connectors follow the original pinout, though I am using 2.54mm pin-headers instead of edge-connectors. The three boards plug into an ‘interface’ PCB which has the passive components that were panel mounted, and connectors for the matrix and pots. My plan is to use Molex KK style connectors, though I suspect I may have to solder wires to this board directly due to lack of space in the suitcase. Like my other PCBs they were fabricated by Smart Prototyping. Smart indeed. It was a bit of an experiment, as the main boards were all one project separated by V-groove.

Kikad screenshot showing new boards

From Kicad….

Bare Blue Boards

…to physical PCBs. A,B,C + interface board + add-on board D

Knowing that space is at a premium in the Explorer case I made the boards a little smaller than the originals, while keeping essentially the same layout. The main A,B and C boards are 9cm wide by 19cm long. The layouts follow the EMS originals pretty closely – but there are differences as I am using transistors with different pinouts and other less hard-to-get parts. Additionally there are various optional modifications included in the circuits. A fourth board has active circuitry for the various modifications. CV mixers for the filter response and oscillator shapes; inverter; trapezoid polarity; LED driver. This is designed to be mounted alongside the main boards.

More technical info after the fold…
Continue reading ‘The new PCBs’

Current Progress

Since the last post further progress has been made – details and more photos to follow in future posts:

  • Planning the portable AKS ‘suitcase’ build – to be made into an Explorer 4412 case.
  • Consolidated my additions and amendments into a single Kicad project. I have a set of new professionally made PCBs – these will be delivered soon. If no silly mistakes were made, these will be the basis of a refit of the VCS, and the AKS portable copy. An add-on ‘Board D’ has extras like 1V/octave, LED driver, Filter Response and Oscillator Shape voltage mixers, inverter/voltage processor module. Apart from the germanium transistors in the output amplifiers they use no hard-to-find parts.
  • A working touch sensitive keyboard controller prototype to fit the lid of the ‘AKS’ – based on a Teensy 3 microcontroller. Software needs to be written to turn it into a proper sequencer, but it’s currently working as a 1V/octave output 2 octave monophonic keyboard. Details soon. 🙂
  • +12V/-12V compact PSU PCB for the suitcase. This includes LM337/LM317 regulators and an encapsulated 30VA transformer. A -9V regulator is included on board A.

Some ‘teaser’ pictures:

Silkscreen of new PCBs

Silkscreen of new PCBs

Lasercut replacement Matrix top

Lasercut replacement Matrix top

Planning the AKS Panel layout

Planning the AKS Panel layout

Sussex KS prototype detail

Sussex KS prototype detail

Sussex KS prototype

Sussex KS prototype

A neater matrix buffer

A long time without a post – but things haven’t stayed still. I’m planning a portable version along the lines of the Synthi AKS – a luggable synth built into a suitcase. More of which in a future posting. So I’ve been pulling together the components needed for the new machine, including a Ghielmetti 20×20 matrix.

To fit everything into the confined space of a luggable case requires some planning and forethought. The original AKS was pretty well crammed, and my current project includes a larger matrix with more modules in addition to the Synthi copy main boards.

The Sussex VCS has a buffered matrix panel as per Graham Hinton’s recommendation – and I wanted one that was more compact than the one I created. The suitcase has limited depth and a double-stacked double-sided module I think wouldn’t be appropriate – so I set about working on a neater alternative.

Front of the matrix buffer PCB

Front of the matrix buffer PCB

Continue reading ‘A neater matrix buffer’