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.

Parts - presents a Bill of Materials and notes about it

Panel - presents the MOTM format panel

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

Construction Phase 2 - Trimmers, Panel connections

Set up / Testing

Use notes


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


In 2008 (or about that time), Synthesis Technology stopped producing full-blown kits, and moved toward what Paul calls "2.0" (two-dot-oh) DIY. This assumes the builder will buy certain parts from Synthesis Technology - PCB, Panel, and in some cases a Special Parts Kit of the particularly hard to find parts - and will get the rest of the parts from Mouser or Digikey or - well - wherever.

For those who are building this as a "two-dot-oh" project, Will and I, with feedback and review from others, have developed a parts-list / bill-of-materials in the form of an XL spreadsheet (as usual).

Please don't take it as gospel. We've been over and over it and are relatively confident in our specifications - and we hear that several people have used it successfully so you should be good.  The BOM assumes that you get the "extra parts kit" from Synthesis Tech.  Synthesis Technology offers some parts like pots and knobs at particularly good prices... these options are offered in the BOM.

Click here to download our XL spreadsheet Parts List


If you're building this as a "two-dot-oh" project, we also assume you get the panel from Synthesis Technology:

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.


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


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


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We are self-proclaimed idiots and any use of this site and any materials presented herein should be taken with a grain of Kosher salt. If the info is useful - more's the better.  Bill and Will

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