Irwin Dual VCA: 20+ Years Later

Readers: If you'd like to build the project featured in today's post, please go to PCBWAY's Community pages--gerber file (main board); KiCAD project/PCB/schematic/library files, and a B.O.M. are here for a socketed SSM2164 version or clone and here for an SOIC IC build.

You can also help out this site immensely by checking out PCBWAY using the link here. Thanks!

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One of my first DiWHY projects from 2002 was Mike Irwin's dual VCA I found in an EDN article (copy of Mr. Irwin's original is posted here).  

Around 2004 I fabricated a bespoke PCB around Mr. Irwin's design and sold several dual-VCA's PCB's.

Unfortunately those PCB's are long gone....Easy! Using Kicad and help from my friends at PCBWAY I made more.

 

SSM2164 Quad VCA. I have a few tubes of New Old Stock (NOS) SSM 2164 IC's but you probably don't....fortunately, 20 plus years later you can get 2164 clones, e.g. here.

FABRICATION 

My 2002 design was through-hole, but nowadays, for quick prototyping, I think using SMD, a stencil, solder paste, and a hotplate are the way to go (fabrication in this manner is described in the high pass filter post here). 

 

getting ready to stencil....

I am always a bit surprised that solder paste, in spite of its name, is not very pasty. I carefully lifted the populated board onto the hot plate after hand-placing the SMD components so they wouldn't slide off.

Bake-o-rama....baked to 215 degrees C for a few minutes then let it cool to 150C, worked!

Quick power test...Power tests OK, no shorts.

Testing the THT version....

Did it work first time (WFT?)  Nope. Power draw from the board was about 20mA with all IC's installed...about right....but no sound, anywhere, no matter what.  

Instead of spending hours troubleshooting I did something both difficult and usual for me: I walked away. 

That night I sprang up from a deep sleep--eureka! I knew why it didn't work. 

The board has 2 power terminals, one for large format (right), one for Euro (left top).  On the bench I used the Frac header, but the latter Euro power connector SV1 has accommodations for ferrite beads, FB2 and FB1.  

On the bench I left the beads out, thinking: if I am not using the Euro header, why use ferrite beads?  

Doh! The power traces went from frac power header through the Euro power header to some of the rest of the circuit so yes, the beads were needed. I soldered in jumpers instead of ferrite beads and the board worked.

PCBWAY--This Blog's Sponsor

If you want to build your own dual VCA--I posted the THT and SOIC versions on PCBWAY's community site; many thanks to PCBWAY for sponsoring this blog and for all the help they've provided over the years.  

You can help out this blog immensely by checking out PCBWAY, here.  

A build option: setting the bias offset of the VCA's op amp buffers to something other than ground is possible.  

If you want to do that, leave the 0 ohm resistors off and put present a DC voltage to the OFFSET JST pins. 

This VCA will show up in some future designs. 

The boards I posted on the PCBWAY community site have a few minor improvements to things like silk screened legends, other than that, it's all Irwin, baby.