One of the problems I have been experiencing with my latest synthesizer projects is the amount of time it takes to do the front panel wiring. There are several reasons for this. The biggest one is I just can't see as well as I did about 20 years ago, and that really hampers things. So of course the big question in, what can be done to build a modular synthesizer module without having to do a lot of tedious wiring. Well, mounting the jacks and the pots on the printed wiring board is of course one answer. I discovered that this was a lot easier said than done. The jacks were fairly easy. I am using the Switchcraft SC112 phone jacks. Pots, on the other hand, are a big problem. A problem that is only partially solved, at this time. Currently, I am using the Vishay Model 248 pots. These are a bit pricey. But, the feel good. There is sort of a problem in mounting them to the board, in that the ceter of the pot does not line up anywhere close to the center line of the Jacks. I plan to solve this by making a jig to solder the pots in the board with. I would first mount the Jacks, the mount the board in the jig using the jacks to support the board, and then solder the pots.
Also, this will be the first Synth project that will use a panel made by Schaeffer. It will cost about $400 to get this panel made (I use a 14" x 19" panel), but they look great, and besides, it takes me somewhere between 10 to 20 hours to make a panel by hand. And these days, finding 20 hours of spare time is getting more difficult. The rest of the chassis will be a 14" x 17" x 3" aluminum Bud chassis box. I put pem nuts in the lip and then screw the front panel to the box. Looks pretty clean. The first module I did this with was the prototype of the Mikado. The only problem I have not solved is where to put the power supply...
Right now, this is going to be the complement of modules:
2 4in1out Mixers
2 Simple CV processors (Gain, Offset)
3 Complex CV proecssors (Gain, Offset, 2 break points)
1 Noise Generator
1 Midi-CV Interface
1 Balanced Modulator
The PC boards are 2.75 inches by however long they have to be to accomodate the number of jacks and pots the module needs. The Midi->CV converter actually got a couple of jacks added to it because I had to stretch the PC board out an extra two inches to accomodate the components.
This VCO uses the temperature compensating circuit that several others (especially Jurgen Haible) and myself were able to come up with. The core of the VCO is pretty much a standard sawtooth VCO, often refered to as an ASM-1 type VCO. Actually, this VCO was originally concocted by Terry Michaels and was published in Electronotes. The VCO also features a fairly sophisticated Triangle to Sine converter using a CA3280. Also, the VCO has an onboard driver for powering the main Frequency Adjustment control. It is intended that a multi turn pot be used here. The onboard driver has a gain control so that it is posible to set the VCO up so that 1 turn of the pot equals one octave exactly. There is also an auxiliary connector on the VCO so that it would be posible to have a master pitch adjustment knob as well as a master PW knob.
This is a fairly standard Voltage Controlled State Variable Filter (Multimode). It features a temperature compensation circuit similar to the VCO. Limiting is accomplished using a pair of LEDs. The LEDs can poke through the front panel so that you can get an idea of when the filter is going into limit. This filter also features voltage controlled Q control as well.
Simple CV Processor
This circuit is by far the simplest of them all. It has 1 input and 1 output. You plug the output of a module into the input, and you can vary the gain, from -1 to +1, as well as the offset, from -10 volts to + 10 volts. Very handy for modifing the output of an ADSR.
Complex CV Processor
Similar to the simple processor, except, you can set two break points where you want the gain of the module to change. In this way, you can shape an incoming signal if many ways. This module was primarily intended to be used with the filters to create phonemes.
The noise generator I chose for this projects is a 32 bit maximum lenth shift register type. It has an internal clock, but, this can be over ridden by using the clock input to supply it with another source. This is handy for generating random sequences of notes. Also, there is a reset input that will set the shift register back to its initial state so that the sequences can always be the same if you wish. It would have been cool if it were posible to set the "seed" that it reset back to, but, that would have been too complicated.
This modules uses an Atmel AT90S8515 micro controller (AVR). The board has an ISP connector on it so in therory, if you wanted to do some hacking, you can program this thing yourself. Other features of the board include 8 control voltages. Four come out on jacks, the other four are on an aux connector on the board. The standard firmware also support Midi Clock, RESET, and START/STOP.
Please Note, as of 11-23-02, I have not checked this schematic for acuracy. The Midi connectors could be backwards.
This is the quantizer out of the Mikado. I
am not sure if I am going to include this in the synthesizer of
Because of the way I designed the Noise generator, I probably don't