Bill and Will's Synth
MOTM 390 Construction
"Micro Low Frequency Oscillator"

April 2007 -

The MOTM 390 has a "difficulty factor" of 2 so we figured we'd tackle it next.   The design of our synth calls for two 390s and we decided to build them simultaneously.

For those who are constructing a 390, Larry Hendry's site includes MOTM-390 construction photos.  Whereas we're going to try to provide good photos here our most complete set of pictures so far is the 120 photos - we won't get that detailed here - many of the steps are similar and you might take a look at those if you feel the need.

Table of Contents

This page has become really long, so here's a table of contents that we hope will make it easier to traverse:

Background - presents an explanation and Paul Schrieber's initial description of the Module with a couple photos from Larry Hendrey

Modifications - presents details of Larry Hendry's Fine Tune Modification and Paul Haneburg's Tracking Adustment

Construction Phase 1 - Resistors, Capacitors, IC Sockets, Power Plugs, MTA headers

Construction Phase 2 - Trimmers, Panel connections

Set up / Testing

Background

Paul Writes:

The MOTM-390 is the smaller version of the MOTM-320 VC LFO, but adds a second LFO. The first LFO uses a panel control, while the second is 1V/Oct voltage-controlled with FM. Individual LEDs follow the triangle waves for both rate & amplitude, adding visual feedback in complex patches. All outputs are available simultaneously.

• Two LFOs
• LFO #1: Triangle/Square Outputs
• LFO #2: Sine/Triangle/Square Outputs
• Voltage Controlled Rate on LFO #2
• LEDs indicate Rate and Amplitude
• MicroModule Series, 5U high x 1U wide

photo from Larry Hendry

Construction Phase 1

All the stuff in Phase 1 gets soldered using "Organic" Solder.  At every break in the action, we wash the board off to get rid of the flux.

here are the two resistors bags


sorting the resistors


after we've sorted and counted the resistors (part of the first step in building a kit is to account for the parts), we bag them separately to make them easy to find.

Now - in the process, we found a mistake in Paul's 390 User Guide - in the Parts List under the Resistors Heading he lists:

"1ea 6K8 (Blue, Gray, Orange)"

We checked it - and verified with Paul - it should read:

"1ea 6K8 (Blue, Gray, Red)"

Click here to see the handy-dandy Resistor Color Coding Chart I found at "Electrical & Electronic Knowledge Share" on line.

ready to start


the PCBs


resistors phase 1


resistors phase 2

As usual with us, whereas we are vigilant about orienting all the resistors, caps, etc. consistently so their values can be read easily (in case we need to trouble-shoot them later), we oriented the resistors with the "Tolerance" stripe on the left (relative to the text on the pcb).  Why did we do it this way?  'Cause the gold stripe is so pretty and easy to see (of course)... and so we put it on the left - well - just because.  You might want to do it the opposite way.  (For the table of resistor value markings click here.)

ready for Caps


axial Caps are in - we solder them in so that their value is "up" - so it shows


and the rest of the Caps


ready for ICs


pushing the IC leads into the PCB

solder the diagonals first - and check to see that the IC is flat against the board... if it's not, it can be easily corrected

it's  out of focus, but here's how the IC looks


ready for the power regulator / transistors


power regs and first transistors are in


transistors are in

Construction Phase 2

All the stuff in Phase 2 gets soldered using "No-Clean" Solder and the PCB doesn't get washed off from here on.

soldering in the POTs - for details click here.


soldering in the coax - for details click here.


ready for the jacks


the jacks are in


The PCB is mounted
for more detail, click here

the LEDs from behind


trimming the LED leads


the leads bent



LED wires prepared


soldering up the LEDs




the LEDs




wired up - done

Set up / Testing

Use Notes