Bill and Will's Synth
MOTM 820 Construction
"Lag Processor"

February 2009 - 

Now for the MOTM 820 Lag Processor Module - rated a difficulty of "2" on Paul's difficulty scale of 1 to 5 - and now that we've built so many of these modules, we're thinking we'll knock this off in one evening.

For those who are constructing an 820 there are some great construction photos on Larry Hendry's site by way of cross-reference.

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.

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-820 is used to add slew to an input. The most common use would be to add portamento to a control voltage feeding a VCO (hopefully, a MOTM-300 VCO). In analog keyboards with portamento (Moog called this glide) the rise and fall times were the same. This is because a simple RC filter is controlled by a single pot. The shape is the same: an exponential rise and fall. Although we are used to hearing this shape, the fact that we have an exponential voltage feeding an exponential response (1V/Oct of the VCO) means that musically we are limited.

The MOTM-820 is your solution! It is the most advanced lag processor ever designed. How can we claim this? Well, just check out the features:

• Independent voltage control of both rise (UP) and fall (DOWN) times
• Times variable from 500us to 5 minutes
• Ganged UP/DOWN control to emulate standard portamento effects
• A new SHAPE control that varies the glide slopes from Linear to Log
• Remote or panel BYPASS to turn the effect off without any DC shift!

The MOTM-820 also offers a "hidden multiple": it can drive 3 VCOs (or other modules) from a single input! The output stage is a special "capacitive cable driver" for driving long cables (up to 20 feet) without any voltage drop!

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.

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.  To see our handy-dandy Resistor Color Coding Chart, Click here.

resistors are in

Capacitors - Misc - Semiconductors

Misc and ICs are in.  A note - we solder one contact of the ICs first. Then we make sure it's down on the pcb correctly and solder the diagonal contact and finish the other contacts up.

Via Holes

Construction 1 done.

Construction Phase 2

All the stuff in Phase 2 gets soldered using "No Clean" Solder. 

Pots, Temco, Wires

the PCB mounted pots and wires


time for the tempco resistor


but we're missing the long orange and white twisted pair - so we're going to make up our own... only with blue wire (we don't have orange)


all the wires are in

Prepare the panel

ready for the jacks




a jumper goes on the IN jack - we used a piece of the gold lead from one of the pots - we soldered only the center jack terminal

Bracket

the mounting bracket


fitting the pcb onto the bracket




for more detail, click here

Wiring the switch and LED

switch mounted in the panel and wired up




wiring the LED




heat shrink shrunk <G>

Wiring the jacks

 
J4 (UP/DN) signal and ground


J8 (OUT3) signal and ground


J3 (DOWN) signal and ground


J7 (OUT2) signal and ground


we did J2 (UP) then J6 (OUT1) then J1 (BYPASS)
now here's J5 (IN) signal

  
and now for J5 ground

Knobs, Ties

wires tied up[

Construction Done

Set up / Testing

Use Notes