Bill and Will's Synth
MOTM 310 Construction
"Micro Voltage Controlled Oscillator"

January 2009 -

Still on our way toward our work on the "One Mad Track" record,  Will and I just finished construction (although not testing, etc.) of the MOTM300 Ultra VCO.  So now we're moving on to the MOTM 310 - building two of them and including modifications equivalent to those we did on the 300.

We built our 310s from an old-style Synthesis Technology kit. For those of you who are building this as of "MOTM 2.0," you can download a Bill of Materials (BOM) we made for 2.0 users by clicking here.

There are some great photos and modification info on the Larry Hendry site. 

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-310 is perfect for adding additional VCOs to your system. Using the same "core" circuitry as the MOTM-300 UltraVCO, the MOTM-310 retains its superior stability and sonic characteristics in half of the space. Great for driving the SYNC of MOTM-300's, and for building portable systems.

• Superior Tracking, <0.05%
• Ultra-Low Drift, <0.5Hz/24 hours
• Variable Waveshape Output
• PWM Input
• Variable FM Input
• Wide Range, <0.05Hz to 32kHz
• MicroModule Series, 5U high x 1U wide

photo from Larry Hendry

Modifications

1.  Fine Tune Mod.

Larry Hendry wrote:

"Just as with my MOTM-300, I found the fine tune range on my MOTM-310 too wide for my personal preference. On the unmodified MOTM-300, it is about 11 semitones. I changed mine to 4 semitones. See my MOTM-300 modification document for details.

I found the unmodified MOTM-310 fine tune to have a range of 8 semitones. I wanted to change that to approximately match my modified MOTM-300 range of 4 semitones.

The change is again simple (although applied differently than the MOTM-300). You have two easy choices:

1. Change R17 from a 4.7 Meg-ohm to 10 Meg-ohm resistor. However, a 1% tolerance resistor of 10 Meg-ohm can be difficult to find.
2. Add a 4.7 Meg-ohm resistor in series with R17. This involves cutting one trace that connects two via holes and adding the 4.7 Meg ohm resistor connecting to these two via holes.

The resistor addition is very near the tempco resistor...

  
PCB top and bottom
photos from Larry Hendry

...This modification is easily reversible. You can restore the cut trace by soldering a resistor lead between the two via holes where we are installing the 4.7 Meg-ohm resistor."

2.  VCO Tracking Mod.

Larry Hendry presented a procedure for tweaking the VCO tracking developed in 2002 by Paul Haneburg. The procedure involves determining a value for R36 that provides the best tracking for the specific VCO and you can download Paul's detailed procedure instructions here.

So for now, we're going to leave R36 out.  We'll put clips in there like we did for the 300.

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.

PCB front


PCB back


Here's where the modifications will be

The whole first phase - -

resistors sorted, ready to begin


if you'd like step by step detail, check out the MOTM300 page.  That module is similar.

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.

Pots

R36 wires with sleeves

OK - now we're going to solder in these cool little sleeves Gino Wong gave us so we can change the value of R36 if we need to per the Paul Haneburg procedure.

Tempco Resistor

Wires

Fine Tune Modification

We didn't find a 1/4 Watt 4.7M Resistor for the modification, so we used a 1/2 Watt one.

Jacks

Bracket

for more detail, click here

Panel Connections

Here's the order in which we connected the jacks - it's different than Paul's instructions and worked better for us.

first the jumpers connect to the middle contact of the 1V/OCT and FM jacks


1V/OCT signal connection


1V/OCT ground connection



FM signal connection


FM ground connection


PWM signal connection


PWM ground conncetion


OUT signal connection


OUT ground connection


tied up

R36 resistors with pins

OK - now to solder the cool little pins Gino Wong gave us to the R36 resistors.  We're using 1% 1.8M resistors.

Knobs

ready for knobs.

Construction done!

Set up / Testing

Use Notes