Duck/Tame Release and Build Notes: Rev 0 PCB

Tame and Duck are now available.They both use the same PCB: it is a blue ROHS board marked as “Rev 0”. The panel is reversable: one side is for Tame, the other for Duck.

There are no known errors on the Rev 0 board.

Modification There is a circuit improvement related to predictability, detailed in the notes: this is not in the schematic. Please read the notes for Tame or Duck below before starting to solder.

These are passive modules, which means they takes current (at voltages outside +/-3V approximately) to faintly supply LEDs. TIP: Consequently, you may find it better to avoid putting this in series with some other passive LED-supplying module, e.g a passive LPG.

Table of typical Diode/LED Voltage Drops

Diode/LED	Threshold	Threshold (in series with 1N4148 diode)
1N4148	0.7V	1.4V
Red LED	1.8V – 2.2V	2.5V – 2.9V
Orange	2.0V – 2.3V	2.7V – 3.0V
Yellow	2.2V – 2.8V	2.9V – 3.5V
Green	3.0V – 3.4V	3.7V -4.1V
Blue	3.2V – 3.4V	3.9V – 4.1V
White	3.0V – 4.0V	3.7V – 4.1V

Step 1: Decide the Response you want

The first step you need to do is to decide what response you want for each of the limiters. There are four parameters that can be varied:

• The diode drop of the LEDs and diodes. This corresponds to the threshold. Diodes have different “drops” (forward voltages): the amount of volts they block before they start conducting (and lighting up). See the table above.
• The resistor connected to the LDR. This gives the maximum amount of limiting done. 2.2k for strong limiting default; try 2.7k or more for weaker limiting.
• The current limiting resistor connected to the LEDs, e.g. R4. This affects the strength of limiting. Again, 2.2k for strong limiting (for Tame); try 2.7k for weaker limiting. Examples are below.
• The brightness and colour of the LED. There are three generations of LEDs: the dull ones of the last century, the bright ones normal now, and the newer super-bright ones.
  • (The dull ones often just used coloured glass or plastic, which makes them very inefficient. However, they are often available super cheap, for example, most bags of 100 LEDs will be of this kind.)
  • I recommend the bright not super bright LEDs: between 200 and 6000 mcd.
  • I find the best deal is often in packs of 10, to avoid getting too many extras.
• The particular LDR selected.
  • I recommend always selecting the LDR with the lowest on-resistance from those available. A high on-resistance usually means a high off-resistance, which may or may not be desirable.
  • For consistency, go through the LDRs with an ohmmeter, shining a bright light on the LDR. Quick and dirty.

Pimp my Vactrol: You may decide to give each of the four sections a different response.

• To increase the threshhold, choose LEDs and diodes with a higher Forward Voltage: “dropout”.
  • LDR may not respond well to blue light, so avoid these in the light-dependent resistors. See the table above.
  • The PCB has holes for two diodes to allow the threshold to go beyond 5V if desired. A 1N4148 diode will give extra .6V drop per diode. So typically you would use LEDs instead of the small signal diode, including blue LEDs. See below for examples of this.
• To decrease the strength of limiting, increase the value of the current limiting resistors (e.g R4) e.g. from 2.2k (default) to 2.7k or further.
• To low the maximum limiting done, increase the value of the LDR companion resistor (eg R5). e.g. from 2.2k (default) to 2.7k or further.
• There is no good way to change the response time, unless you pick LED technology to get the one you want, if it is available in the right color spectrum for the LDR. LEDs may have between 10ms and 250ms “afterglow”, which is good for this application.

---

Building Tame Quad Limiters

• Use clipped-off resistor leads to bridge pins 1 (square pad) and 2 of all headers: JP2, JP4. This gives four isolated sections.
• Requires 4 of the special home-made vactrols.
• For R1 and R2 there is a modification: we split this resistor into two 2.2k resistors (R1, R1a, R2, R2a) and tap the LDR from the centre point of these. This is to give a more predictable and higher resistance for the incoming leg of the voltage divider formed by Rna and the LDR. (Also, see Note 1 below.) (There is no convenient place to do this modification for the second and fourth limiters, which remain as they are.)
  • Insert a 2.2k resistor vertically (“Japanese” or “dead-bug” style) into either hole of R1. Solder. (This is the resistor R1a.)
  • Do the same for R2a.
  • Insert a 2.2k resistor into the other hole for R1 also vertically. Solder, making sure the leads do not touch any nearby holes or components on the PCB.
  • Do the same for R2.
  • Trim a 5 cm length of hookup wire and solder one end into the middle hole of JP1, and the other end to the join of R1 and R1a.
  • Do the same for R2, R2A and JP2.

Example: This is picture is an early version my own Tame module in the Wind Rig demo system, where you can see the LEDs used instead of the 1N4148 doide in most positions. The diodes, LEDs and resistors I chose are given after the picture:

• The top-two sections have yellow LEDs in place of the diodes, and white LEDs in the home-made Vactrol, with 2.2k for both resistors. This starts limiting signals when +ve or -ve goes over 6V, and tames a wave with a +10V excursion to +7V.
  • This performance may be useful for after the Shell waveshaper, which can generate hot output.
• The third sections has green LEDs in place of the diodes, and white LEDs in the home-made Vactrol, with 2.2k for both resistors. This starts limiting signals when +ve or -ve goes over 5V, and tames a wave with a +10V excursion to +6V.
  • This might be useful as a final limiter in a chain.
• The fourth section has 1N4148 diodes and red LEDs in the home-made vactrol, with 2.7k for both resistors. This starts limiting the signal after about 2V and tames a wave with a 10V excursion to 5V.
  • This might be useful for waves which are generally quite soft but with a big dynamic range.

Test: What you should observe when using Tame (depending on the configuration you chose) is:

1. The general signal level for a 10V PP signal is a little lower than normal
2. Some limiting may kick in after e.g. 12VPP
3. If you have a loud signal, it will be limited never be more than say 12V PP.

Problems: If the Tame module over-reacts, so that the output actually reduces as the input rises, that is too much. You may have used a new super-bright LED. The easiest way is to increase the value of the current limiting resistor (e.g. R4).

If the Tame barely reacts, then it may be you are using too-blue LEDs: decrease the value of the LDR companion resistor (e.g. R5) or change LEDs. (TIP: I dont recommend reducing the value of the current limiting resistor, unless other avenues have been used up: be careful below 1k or 600 Ohm, as it is difficult to see if you have blown an LED and cumbersome to make a replacement Vactrol.)

---

Building Duck Dual Side-Chain Limiters

• Use clipped-off resistor leads to bridge pins 2 and 3 of headers JP2, and JP4. These have the round pads: the middle pad and the pad furthest away from the sockets.
• Use clipped-off resistor leads to bridge D1, D2, D5, D6 if a low threshold is required.
• Requires 2 of the homemade vactrols. Choose as low on-resistance LDRs as you available.
• The components on the lower half of the circuit digram should not be installed.
• Install components on top half of schematic only: on the PCB this is the top of the four sections, and the second from the bottom only.
• The other two sections, R9 and R11, is the only component to be installed, however there is a modification: we split this resistor into two 2.2k resistors (R9, R9a, R11, R11a) and tap the LDR from the centre point of these. This is to give a more predictable and higher resistance for the incoming leg of the voltage divider formed by Rna and the LDR. (Also, see Note 1 below.)
  • Insert a 2.2k resistor vertically (“Japanese” or “dead-bug” style) into the R9 hole next to the label “JP1”. bend te othe side and insert into the middle hole of the JP1 trio. Solder. (This is the resistor R9a.)
  • Do the same for R11 and JP2.
  • Insert a 2.2k resistor into the other hole for R9. Lay it flattish and solder its lead up onto the top lead coming out of the vertically-mounted R9a. Solder, making sure the leads do not touch any nearby holes or components on the PCB.
  • Do the same for R11 and JP2.

Configuration for overload limiting: Sometimes when output is overloading, it is better to dynamically attenuate the signal upstream rather than downstream. In this configuration, the Sidechain In comes from e.g. the input or output of the final VCA, but the Input is earlier in the pipeline.

---

Note 1: Also, there is a concern that if the driving module is improperly design to have extremely low or no output resistor, you could get its output connected (through the maximum on LDR) to something close to 0V, causing stress or failure on the input module; this should never happen because Eurorack modules should not do that and because the LDR never goes down to near 0 ohms. However, better safer than sorry.