Project · Filters (Envelope)
DOD™ 440 Enevolpe Filter
This is a DOD™ Envelope Filter 440 replica called EF440. It is a very nice little filter circuit. Probably the simplest to build filter we have on the site. We made the layout of the PCB very small so that it will fit in a box the size of the original unit.
What you will need
Bill of Materials
Version 2009 · Copyright 2006 JD Sleep · Permission refused for posting/serving this file from any site other than www.generalguitargadgets.com · Trademarks are property of their owners
Resistors
| Resistor ID | Value | 3-band Marking | 4-band Marking |
|---|---|---|---|
| R1 | 10k | brown-black-orange | brown-black-black-red |
| R2 | 100k | brown-black-yellow | brown-black-black-orange |
| R3 | 100k | brown-black-yellow | brown-black-black-orange |
| R4 | 10k | brown-black-orange | brown-black-black-red |
| R5 | 2M2 (2.2 M) | red-red-green | red-red-black-yellow |
| R6 | 2k2 (2.2k) | red-red-red | red-red-black-brown |
| R7 | 22k | red-red-orange | red-red-black-red |
| R8 | 22k | red-red-orange | red-red-black-red |
| R9 | 220k | red-red-yellow | red-red-black-orange |
| R10 | 220k | red-red-yellow | red-red-black-orange |
| R11 | 220k | red-red-yellow | red-red-black-orange |
| R12 | 430k | yellow-orange-yellow | yellow-orange-black-orange |
| R13 | 100k | brown-black-yellow | brown-black-black-orange |
| R14 | 22k | red-red-orange | red-red-black-red |
| R17 | 1k | brown-black-red | brown-black-black-brown |
| R18 | 1M5 (1.5M) | brown-green-green | brown-green-black-yellow |
Capacitors
| Capacitor ID | Value | Type | Possible Marking |
|---|---|---|---|
| C1 | 0.01uF | Film | 103 |
| C2 | 0.1uF | Film | 104 |
| C3 | 4.7uF | Aluminum Electrolytic | 4.7uF |
| C4 | 1uF | Film or Aluminum Electrolytic | 1uF |
| C5 | 10uF | Aluminum Electrolytic | 10uF |
| C6 | 0.022uF | Film | 223 |
| C7 | 0.022uF | Film | 223 |
| C8 | 0.047uF | Film | 473 |
Potentiometers
| Part ID | Value | Type |
|---|---|---|
| R7 - Level Control | 100k | Log Taper |
| R8 - Fuzz Control | 100k | Log Taper |
Other
| Part ID | Part Name |
|---|---|
| IC1 | TL022 or other dual opamp |
| D1 | 1N914 or 1N4148 |
| D2 | 1N914 or 1N4148 |
| OC1 | VTL5C4/2 Vactrols LED/LDR unit |
| J1 | Stereo quarter-inch jack |
| J2 | Mono quarter-inch jack |
| J3 | DC Jack |
| B1 | 9 volt battery (not included in the Kit) |
| Sw1 | Heavy Duty 3PDT foot switch |
9v battery snap, Printed Circuit Board, 24 gauge stranded wire, Enclosure, Knobs, LED, LED clip or bezel
How to build it
Instructions
Version 2012January20 · Copyright 2006 JD Sleep · Permission refused for posting/serving this file from any site other than www.generalguitargadgets.com · Trademarks are property of their owners
This is a replica of the DOD™ Envelope Filter 440 referred to as EF440 in these documents. It's got a nice fat auto-wah sound, a lot of fun to build and play. Use the project documents provided, starting with the General Build Instructions. The EF440 project has a minor upgrade from the original. R5 is listed as 470k on some schematics, this project uses R5 of 2M2 value which gives a much improved Range control. We decided to make R5 of value 2M2 as the default in this project since it provides vast improvement on the overall sound of the unit. You must use the VTL5C4/2 LED/LDR unit listed, or equivalent for OC1. The "/2" at the end of the part number is essential. It is a unit with one LED controlling 2 LDRs with a common leg so it has a total of 5 legs. The schematic shows the internal workings of this unit, highlighted by a dashed, purple outline. Other LED/LDR units can be used, including DIY units, but we have found this to be the best sounding unit. The C4 capacitor can be film (non-polar) or aluminum electrolytic. If you use the film, there is no concern about polarity when installing the capacitor. The controls on this stompbox are strange. As far as I can tell, it has to be tuned in to one sweet spot and that's about the best it can do. Most of the controls rotations don't produce the filter “wah type” sound at every (or any) input sound frequency. Anyway, the sweet spot is very sweet. Here's an inside view of the unit I built to give you some general ideas if needed. We built ours in a 125B enclosure.
Have fun, comments and questions are welcome and can be sent to [email protected] Here is a chart of voltages taken at the IC pins. This information can be used as reference to help find and fix problems if needed.
Component
Location
9 volt power supply
Voltage
8.7v
IC1
Pin 1
4.34v
Pin 2
4.30v
Pin 3
4.37v
Pin 4
0v
Pin 5
4.30v
Pin 6
4.37v
Pin 7
4.36v
Pin 8
8.7v
More about this project
Notes, sounds and related links
- EF440 Sound Sample Will Thorpe plays an EF440.
Modification Information from Mark Hammer:
1) Sensitivity is determined by the gain of non-inverting stage IC1a. When gain is altered by changing the pin 2 to ground resistance, bass rolloff changes as gain is increased, such that at max sensitivity there is less response to lower notes. As with the MXR™ Dist+, loss of low end in this stage can be fixed by increasing the value of the cap. Let me emphasize, though, this does not change the bass output of the pedal/circuit, just how much the envelope follower responds to lower notes.
2) If you want the sweep to linger, make C4 bigger (e.g., 4.7 or even 10 uf)
3) If you want to slow the attack, stick a small-value resistor (<1k) between D2 and C4
4) If you want to use if with bass, stick a small-to-medium value (say, 10k) resistor in series after C8, and run another similar-value resistor from the R1/R2 junction to the free end of the resistor after C8. Now run a 100k terminating resistor to ground. That will mix in some straight signal with the swept filter so you don't lose bottom during the sweep. Note that since the dry signal is tapped before processing, and since the filter build around IC1B is inverting, the filter will be subtracted from the dry signal at the output, yielding a swept notch. Very funky in its own right. You may have to tinker with mixing resistor values to get a decent balance or simply stick in a trimpot and tweak.
5) R15 injects some DC from the supply into the LED to adjust the default brightness and the starting point of the sweep. Not having used one I can't say how much useful variation this provides. However....the min and max DC offset available at the R6/LED junction is set by resistors R13/R14. To move the range downward so that initial starting point is lower, make R14 smaller by the same amount you make R13 bigger. To move the starting point upwards, do the opposite. To allow finer start-point adjustments, make R15 a 47k pot and divide the "missing" 50k between R13 and R14.
The ways of Wien Bridge filters are a mystery to me. I have no sense of what needs doing to adjust Q. It may be worth making any switching of filter caps independent, though, to see what that does to the passband. So, use two toggles, one for C6 and another for C7, for rangeswitching purposes. Certainly tinkering with the passband would have implications not only for filter-inly sounds but for dry+wet mixtures.