ER-ADSR-555-01

Eurorack ADSR Module

Features

3U tall, 6 HP wide Eurorack module
Attack-Decay-Sustain-Release ADSR Module
Takes in Gate signal, generates CV to VCA
Attack, decay, and release pots control speed
- Attack, decay, and release times can range from 200ms to 16s
Sustain pot sets the sustain voltage level
LED dims to level
555 Based design

Credits

Benjie Jiao MiniADSR
- Original was based on Barry Klein design
- As built by schmitzbits design - "The Fastest Envelope in the West"
Benji's build has a three card stack-up and is 4 HP wide
This card is wider but uses 2 cards

Schematic

Rev 1 Checkout

Ordered wrong (earlier) version of the board
- Missing 1M decay fix resistor
- Pots are backwards
Annotated schematic with Rev 1 reference designators

Drive IN jack with Erica Synths EDU Sequencer
- GATE Out output
My schematic symbols are Schottky but installed 1N4148 like schmitzbits schemati
- A, D, R need to be log (Type A) pots
All of the pots are backwards (rework below)
- A, D, S pots should be CCW for no delay
- S pot should be CW for full output
ADR series resistors are 220 Ohms but should be 100 Ohms per schmitzbits note
Attack overshoots
May need > 100 ohms
C3 s/b 1 uF for the pots to have a good range
Updated Pl for above
Log pot curves

Scope capture

Schematics

Benjie Jiao - DIY Modular Video

Card Test Procedure

Drive in GATE in for the following tests
Measure output with scope
- Trigger off Input
Set Attack to CCW (min)
Set Decay pot to CCW (min)
Set Sustain to CW (max)
Set Release to CCW (min)
Output should be a square wave that matches the input
- Output level about 0-10V

Test Attack

Set Attack to CCW (min)
Set Decay pot to CCW (min)
Set Sustain to CW (max)
Set Release to CCW (min)
Adjust Attack
- Front edge rounds over - scope cap

Test Sustain

Set Attack to CCW (min)
Set Decay pot to CCW (min)
Set Sustain to CW (max)
Set Release to CCW (min)
Output should be a square wave
Adjust Sustain pot
- Level goes from 0 (CCW) to max (CW)

Test Release

Set Attack to CCW (min)
Set Decay pot to CCW (min)
Set Sustain to CW (max)
Set Release to CCW (min)
Adjust Release pot
- Back edge rounds down- scope cap

Test Decay

Set Attack to just above CCW (8 0-clock) - just a bit of round over on output
Set Decay pot to CCW (min)
Set Sustain to just below mid (10-11 o'clock)
Set Release to CCW (min)
- Release pot set to min (CCW)

Issues

Rev 3

Adds 3.3K resistor (decay fix) to card
Change R4 silkscreen to 1M
Order new PCBs when stock drops from Tindie sales

Rev 2 Issues

Silkscreen shows 10K for R4, should be 1M
- PL updated to 1M
Attack works
Sustain works
Release works
Decay has noise issue
- Adjusting Decay pot near min (CCW) shows noise issue
- See fix below
- Decay starts drop but bounces back up

Schematic of front end

Layout

Debug Decay Noise

Goal - find Decay Noise mitigation strategy
Card is sensitive to Eurorack Switching Power Supply noise
- This issue is also present on Rev 1 cards with noise power supply
  - Issue did not present for prior testing since rack was lightly loaded at the time
Tracing noise path (1)-(3) in schematic
- (1) +12V Vcc noise
- (2) Q2 is "Off", noise through R5 couples through C5
- (3) to Q3 to TRIG
TRIG (bottom) measured at R7

Voltage from R2 into Q2 base looks OK

Voltage at C1/R6 node

Decay Fix

Add 3.3K to ground
- Creates a voltage divider that still lets through the pulse but not enough to turn on Q3
Also made C1 a 0.1uF (may not be necessary)

3.3K Resistor on rear of card
- Could be installed on top of card into the same holes and vertical

After fix

Rev 2 Changes from Rev 1

Fixed pot ends (swapped ends)
Added 1M decay resistor "fix" (dashed lines on Schmitz schematic)
Moved up S, R pots to space them up from jacks
- Updated controls card and front panel
Added LEVEL legend to front panel silkscreen
Re-sequenced reference designators
Change transistor footprints to offset pins/re-oriented
Better spacing between parts in upper left of controls card
Added power supply bypass caps (1 per power pin)
Added URL, Rev 2 marking to rear of card

Rev 1 Issues

Silkscreen has "DELAY" should be "DECAY"
A, D, S, R pots ends are all backwards
A, D, R pots should be Type A, 1M Ohms (log pots)

Cuts

Perform cuts before installing parts on card
Cut at RV1 (pins 2-3) top side

Cut at RV2 (pins 2-3) bottom side

Cuts at RV3 (pins 1, 3) top side

Cuts at RV4 (pins 2-3 and pin 1)

top side

Change Pot Series Resistor Values

220 Ohms on A, D, R pots s/b 100 Ohms (PL below is updated already for this)
- Change R7 to 100 Ohms (A pot)
- Change R8 to 100 Ohms (D pot)
- Change R10 to 100 Ohms (R pot)