I've had a Circuit Board made....

gstopp at fibermux.com gstopp at fibermux.com
Wed Apr 17 19:27:19 CEST 1996

     Hi DIY List,
     I've had a circuit board made. I just got the prototype back and 
     started to stuff the parts, and so far it looks like it's a cool 
     It has two saw/pulse VCO's, a multi-mode VCF, two ADSR's, two VCA's, 
     an LFO, and a White/Pink/Random Noise Source. It's basically similar 
     to an Oberheim SEM, except for the noise source and extra VCA. All 
     circuit sections are discrete - in other words, no hard-to-find custom 
     synthesizer chips! The circuits are based on the Electronotes modules 
     that I've experimented with lately.
     Here's a brief description of each module:
     VCO - based on the Electronotes sawtooth design, with a CA3140 
     integrator with FET reset, controlled by an LM311 comparator. The NPN 
     exponential converter can be an Analog Devices MAT-02 matched pair, or 
     a pair of hand-matched 2N3904's. A 1K tempco resistor can be used for 
     best stability but is optional. There are 6 exponential CV inputs, 2 
     linear FM inputs, 2 pulse width inputs, a sync input, a sawtooth 
     output (-5v to +5v), and a pulse output (-5v to +5v).
     VCF - based on the Electronotes state-variable design. The exponential 
     converter is based on one 2N3904 and two 2N3906's. The integrators are 
     CA3080's buffered by CA3140's. There are 4 exponential CV inputs, one 
     inverted exponential CV input, 4 audio inputs, and one buffered output 
     each for Lowpass, Bandpass, Highpass, and Notch.
     VCA - based on the Electronotes 3080 linear design. There are 3 CV 
     inputs, one (+) signal input, one (-) signal input, and one output.
     ADSR - my own design from a couple months ago, using an LM358 for the 
     input comparators, a CD4002 for the attack flip-flop, a CD4053 analog 
     switch, and a TL082.
     Noise Source - based on an Electronotes design. It uses a 
     reversed-biased NPN transistor junction followed by a series of op-amp 
     LFO - typical tri-square manually-controlled design.
     PCB dimensions are 4.8" by 11". Power required is +/- 15 volts.
     I wanted to try out my CAD package and local circuit board vendors, so 
     for the first project I decided to make something useful instead of 
     just a single module. I would like to offer this circuit board to 
     other people on the mail lists. I want to make a run of circuit boards 
     and sell them, and I need feedback to get some commitments on just how 
     big an order I should place. The more I order the cheaper they'll be.
     Note: I do not have any unrealistic ideas on making a huge profit 
     here. This is my hobby and my only monetary goal would be to recoup 
     the film and PCB setup costs (a few hundred dollars) plus some time 
     and energy spare change. I expect that I'll be able to sell the bare 
     boards for around $60 each.
     Any interest?
     - Gene
     gstopp at fibermux.com

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