Synth Resources

ASM-1 Faceplate Builder's Tips

Introduction

This document provides tips and guidelines for building Gene Stopp's ASM-1 synth with the faceplate that I have designed. It is broken up into two sections; the module section that covers tips specific to the individual modes, and a general section that covers tips appropriate to the whole project. I have skipped modules like the Glide and LFO that I thought were pretty self-explanatory, and where the panel markings exactly match the inputs on the PCB. I suggest you read the whole document before you begin building.

General Tips

For starters, the worst part of this whole project is the wiring of the faceplate. To make this chore a little easier I would suggest the following;

1. Run all of the ground, +V and -V wires, working from one side of the board to the other, use solid core wire (it holds it's shape) and keep the wires pressed against the PCB and out of the way.
2. Connect all of the jacks to their pots where appropriate (VFC volume, VCO FM input, etc.).
3. Connect the "flying wires" module by module - starting with the more complicated modules and working to the less compliacated ones, and testing each as you go (VCO, VCO, VCF, ADSRs, etc.) The less wires, the easier it is to make fixes.

For mounting the PCB to the faceplate, you can do whatever you like. My personal favorite method is to use spacers and mount the PCB parallel to the plane of the faceplate - it makes the whole ASM-1 very small and compact- it'll fit in a briefcase. I use (4) 2", #6-32 screws (about 4mm) and drill holes in the faceplate for them in line with the four holes in the ASM-1. I put one hole right about where the boarder lines for the two VCO's meet at the top. Another above and between the sustain and release knobs of the top ADSR. Another where an imaginary line between VCO #1's saw output and VCO#2's PWM knob would cross the board line between the VCO's, etc. - see picture below. I lay the PCB component side up and the faceplate face down, so that the top edge of each is touching. I run all the wires (the VCF filter CVs wire will be really short if you're doing this right). Then fold the PCB over onto the screws with their spacers and nut 'em down. Note that the wires get messy and you don't have a lot of room to work when it's all done, so debugging is a drag.

MODULE NOTES

VCO

1. I prefer a 3M rather than a 1.5M resistor on the fine tune. This way the full range of the fine tune knob is exactly one octave..

2. I realized only after making the faceplate that I usually run both VCOs off of the same CV input and that it would be nice (and save a patch) to have an extra CV input that connects (via 100K resistors) to the CV summing nodes of BOTH VCOs. I put this extra jack on an unmarked section of the panel right next to the glide output, since I usually connect the glide to the VCOs.

3. Another way to save on patch inputs that are often used the same way is to make the Sync input on VCO #2 a SPST switch that is hardwired to the output of VCO #1.

4. The "Initial PW" is a pot that is connected to + and - V. Note that with this set up, the PW will hit 0% and 100% VERY quickly - I'd suggest replacing the 560K resistor for this PW input to 1.2 or 1.5M

5. The "PWM CV" pot is set up as an attenuator for the CV input (see Gene's notes for how to set up attenutators).

VCF

1. The "inverting scale" CV input is created by connecting the jack to the WIPER of the pot, then connecting the "+" side of the pot to the 47K "+" input resistor, and the "-" side to the 47K "-" input resistor. Note that this is an exponential input - not linear. Also note that with 47K resistors, if you turn it all the way to the "+" side you will actually be amplifying your input voltage - a +5v input will wind up acting like a +7.5v input. If you want it to act like +5v, you should use 61K resistors in place of 47K. I personally like a slight amplification, so I've used 56K resistors on the input.

2. The cross-fade output between high pass and low pass is made as follows;
· Connect the low pass output from the PCB to one side of the pot and the highpass output from the PCB to the other side of the pot.
· There are three TL082 opamps in the VCF, call the middle one on the PCB "Joe".
· Remove the three 100K resistors on the right of Joe (when holding the PCB with the filter at the top).
· Remove the 33K resistor on the left of Joe
· Connect a jumper wire between pins 6 and 7 on Joe (those are the two middle pins on the right side) using the holes that were supposed to be used by 2 of the 3 100K resistors.
· Run a wire from the wiper of the HP/LP pot to the lower of the two holes that were supposed to be used by the 33K resistor (this is the hole closest to Joe).
· Connect the band pass and notch outputs from the PCB to a faceplate mounted SPDT switch - the notch output is your HP/LP x-faded output.
· Connect the middle of the switch to the output jack on the faceplate.

ADSR

1. You can add an LED to the ADSR gate input so that you can see when the gate is active. Simply connect a 1K resistor to the upper (closer to the VCF) pin of the .001uF cap in the ADSR circuit, connect an LED between this resistor and ground. The flat edge on the side of the LED is the ground side.
2. Maybe I did something wrong, but my ADSR had troubles when driven from a bi-polar input signal (like the output of the LFO). To fix this, I simply soldered a diode between the gate input jack and the wire to the PCB (stripe on the diode goes on the PCB side).

VCA

1. All of my jacks are banana jacks, so I added a second jack to the output of VCA #2. It's a 1/4" jack that I placed just above and to the right of the regular output jack.
2. The output level pot is set up as an attenuator. One end goes to ground, one to the VCA output and the wiper goes to the output jack(s).
3. The initial level pot is connected to ground and +V. The wiper acts as a CV input. The input resistor for this CV should be 300K and not 100K. That way you will have Vout = Vin when the pot is turned all the way up. Some people have also suggested that instead of attaching the "low" end of this pot to ground, you may want to connect it to a 90K resistor that connects to -V. The idea here is to give you a slight negative input voltage, and that will guarantee that the VCA is completely shut off when the knob is down and no voltage is coming in the CV inputs.

Home