Vactrol Envelope Follower: Double Sided SMD Fabrication

 Readers: If you want to build the project featured in today's post, please go to PCBWAY's Community pages--a gerber ready to download and/or fabricate as well as KiCAD files, PDFs, a BOM, the front panel gerber etc. are here.  

Also please visit PCBWAY's site using the link here--it will help this blog immensely. Thanks.

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This time I revamped a circuit I laid out a long time ago--a envelope follower based on a 5C3 Vactrol.  

The reason: the original  module was large; could I shrink the size of the module by putting all hardware and SMD components on a single PCB?

Sure.

HISTORY

I began exploring envelope followers when I got a Mutron III decades ago, a stompbox I seriously wish I still had. 

It's a filter fed by control voltages derived from the amplitude of an incoming audio signal. 

The Mutron (schematic here) responsed to the incoming amplitude in a way I found musically pleasing. It uses a 0805 opto coupler; to get its slow, sloppy feel I breadboarded the amplitude to CV subcircuit based on a 5C3 vactrol. 

I found the Vactrol version useful for things other than auto-wah--used in front of a VCA for instance I got some interesting audio compression effects.

Soooo...20 years later I wanted to see if I could make a smaller version of this for Euro....to get it to 6HP I had to put SMD parts on both sides of the board.

Thanks to PCBWAY for sponsoring this blog....new boards are back from them....

Turns out the layout (in Kicad) was a bit tricky since I had to keep straight what parts were on what side of the board; where it made sense to put vias, etc., but after a bit I got the hang of it.

SMD parts on both sides....

I used a small vice to hold the board in place while I soldered SMD parts (I have settled for now on 1206 and SOIC, which are large enough to not always require a microscope for hand soldering).

The board and module worked first time. The only thing I'd like to redo is the front panel, which could be laid out to make the legends easier to read from a distance. 

Overall I thought hand soldering SMD parts on both sides of a PCB, including SMD electrolytic caps, would be challenging, but no--this was a piece of cake. 

Using the Vactrol EF

Plug in a preamp'd guitar or clav; the EG CV out goes to a bandpass filter; turn the EF's three knobs until the LED lights the way you like; riff on like Jerry Garcia and Stevie Wonder.  

My goodness, it was 1984, it's 2024 already. See ya next time.