Clean Release Notes: Rev 2 PCB

The PCB has one major error to fix and several highly recommended improvements.

The panel has no known errors.

Mandatory Fix

The collector pin of Q5 is not connected. It needs to be connected to +12V. Use the clipped leg of a resistor, solder in a connection between the collector pins (pin 1) of Q5 and Q4.

Strongly Recommended Fixes

The schematic and components have several tweaks that are strongly recommended.

There is no need for diode D4 when only normal Eurorack Gate signals are connected to the Gate In input. Install a wire short (e.g. the clipped leg of a resistor) instead of D4. It is useful for very dirty signals only, from a particular signal-to-gate extractor with high levels, to prevent misfiring. This explains the strange bypass in the schematic, which is not in the Rev 2 PCB. (If you wish to use Clean to trigger on low-level blips on the input, you could remove and short D5 as well.)
Some bias signals are applied in a non-optimal position, causing a delay effect. Leave the positions on the board marked for resistors R32 and R33 vacant (and not shorted). Instead solder a 1M resistor between R21 outside and R6 inside. This is resistor R34 in the schematic. Also solder a 2.2M resistor from R6 inside to R15 outside. This is resistor R35 in the schematic.
Better discharge of the phrase capacitor is available. Solder a 1M resistor in parallel with either D1 or D2, e.g. on the underside of the PCB. This is resistor R33 in the schematic.
Better control of the Velocity knob is available. On the underside of the board, run a 100k resistor from the negative pin of C7 (i.e. GND) to the inside end of R11. This is resistor R32 in the schematic.

Component Selection

Diode D5 is shown as 1N4148, however it can be a BAT43 like the other diodes.
The bus Gate and the +5V line on the power cable are used by this module, so you cannot install a 10-pin power socket instead of the shown 16-pin socket.
The 4HP module is tightly packed. There are small “micro knob” for the T18 shafts that work better than, say, Davies style knobs, carried by Thonk in 2019. (However, you may also consider locating the module so that its neighbour provide some clear space, especially if you have generous sized fingers.)

Test Points:

TP1: Gated Velocity CV = Gate limited by Velocity.
TP2: Output of first lag generator for “Phrase AR”; same signal as drives LED
TP3: Envelope CV before final amplification/rectification
TP4: Envelope output CV
TP5: GND

Customizing: Pimp my Clean

Clean will act as an gate detector on analog signals. Diode D5 will prevent spurious triggering on low-level noise, however if you want greater sensistivity, then short out D5.
For sharper attacks, reduce R4 to a few ohm.
For longer fade-ins (and phrases) increase the value of C3. Note that there may be some delay effect as well as the fade in.
To remove the initial low-level CV, remove R35 and R21. Note that the position of the accent knob will usually have an effect here as well.
In theory, reducing capacitor C3 (e.g. to 10 to 100 nF?) will allow the same circuit to function as a kind of envelope follower that discriminates against small bursts of spurious signal. This has not been tested.
In theory, reducing both C3 and C4 to operate at audio rates will convert the unit into a kind of squaring waveshaper with angled peaks; for this use a 1uF bipolar DC blocking capacitor instead of D3 would be appropriate. This has not been tested.

Knob Oddness: Accent

The Accent knob needs to be explained. If no signal is connected to the Velocity input socket, then the knob controls a fake velocity signal: 0% will be 0 velocity and no note will sound, 100% will be equivalent to loud velocity: so probably 80% to 100% is a good setting. If there is a velocity signal attached, then 0% will be that velocity sign and 100% is equivalent to a full velocity: this may be backwards to what is expected as the accent signal sets how soft a low velocity signal is, more than how loud a high velocity signal is.

LED

The LED follows the phrase envelope: if it is on, then a fast next note will use the attack of the “Note AR” (i.e. portato). You know the portato effect in available when the LED is on; when it is off, your attack will be determined by the phrase AR knob.

Gate

If nothing is connected to the Gate In input socket, it will switch to use the Gate signal provided by the Eurorack bus, if any.

Signal Levels and Use as a Slew Rate Limiter/Lag Generator

The module is designed for typical Eurorack signal levels. However, it does not treat the Gate In as a gate signal but have different envelope responses to different levels. So Clean can be used as a dual slew limiters or lag generators, with eccentric linearity and a kind of VC control from the Velocity input.