555 Envelope

This is a classic envelope generator with attack and decay controls which can be configured as an AD (Attack Decay) or ASR (Attack Sustain Release) envelope. As well as the standard envelope modes this module features a special retriggering mode, and can also be set up as an LFO in loop mode.

At a Glance

Classic AD / ASR envelope generator in 4HP
Retrigger mode allows the envelope to reset during the attack phase
Loop mode configures the module as an LFO

Why We Created This Module

There are lots of options for envelope generators in eurorack, but most of them are too big, too complicated or too expensive. We wanted to create a small and inexpensive envelope generator that could also double up as an LFO. We also wanted to add retriggering as this is not a common feature available on other similar modules.

What Is This Module?

This module has 2 main modes of operation, determined by the loop switch. With looping set to "off" the module acts as an envelope generator, and takes a trigger or gate input and produces an envelope which rises and then falls.

Envelope Mode

In envelope mode, the trigger mode switch determines how the incoming trigger is handled. If trigger mode is set to "trigger" then the rising edge of the incoming signal will cause the envelope to rise and then immediately fall. In this mode the envelope functions as an AD (attack decay) envelope.

If trigger mode is set to "gate" then the rising edge will cause the envelope to rise, and it will stay high for as long as the gate is held high. When the gate signal falls back down to 0v the envelope will then start to fall. In this mode the envelope functions as an ASR (attack sustain release) envelope.

The final envelope mode is retrigger mode. In this mode the module responds to the rising edge of the trigger input, just like in trigger mode, but with one key difference: if a second trigger is received while the module is still in the attack phase, the envelope will reset and start the attack phase again from 0v.

Loop Mode

If the loop switch is set to "on" then the module acts more like an LFO, with the envelope triggering repeatedly on its own. Whenever the output is 0 volts the envelope will automatically trigger, rising and falling based on the attack and decay parameters, and once it gets back to 0 it will trigger again.

In this mode, if the trigger mode is set to "gate" or "trigger" it is completely ignored. If the trigger mode is set to "retrigger" then the incoming trigger will interrupt the rising part of the cycle and reset the voltage back to 0. Note that the trigger is still ignored if the output is in the falling part of the cycle.

What Isn't This Module?

If you need a super precise envelope with CV control and control of the linearity of the attack and decay phases, then this is not the module you're looking for - there are many modules available with those features but they are going to be bigger or more expensive.

If you want a simple envelope and LFO generator with quick and easy controls and the classic envelope shape, then this is going to be well suited to you.

How It's Made

Final assembly of all of our modules is done by hand, by us in Cambridge, England.

Some of our modules have surface mount (SMD) components already populated when we get the PCBs. We then add the remaining SMD components and hand solder them, and finally hand solder all of the through hole (THT) components.

Once the module is assembled we will do any additional setup such as flashing the firmware and calibrating the module before testing that everything works as it should.

We are very careful to select good quality components, especially for the mechanical components. We always use high quality Alpha potentiometers, Thonkiconn jacks and high quality switches.