3.5mm Breakout Board--No More Sequencer Flipping!

Hello again! I don't work for these guys and here's a plug for what I think is a very good and affordable (not DIY) sequencer:

It's an Arturia Beatstep Pro. I have used all sorts of sequencers, from cheesy/crappy/cheap to homemade to buggy to the really high end ones, and I go back to the Beatstep, it's extremely affordable for what you get, surprisingly well made, and has best of all, has awesomely musical "swing"settings.  Does it do everything you can think of? Of course not. But for $250 or so USD new in the box, it's a damn amazing bit of kit.

So what is so DIY about this? (Hello?)  Nothing yet--Go ahead--build a better sequencer for $250--when you do let me know and I will most-definitely post it.

By George no sequencer has everything! Not a feature, a bug: all the Beatstep Pro's 3.5" jacks are all on the back. That makes plugging this sequencer into other modules, at least in my rack, a bit of a pain--lift it up, turn things over, plug in your patch cables, wiggle the cable to see if it's in all the way, etc.

DIY to the rescue!

To connect the front TS to back, solder jumpers in the box in the middle. The remaining pads are for whatever else I might think up for this PCB....

The PCBs used in my prototype are super simple--it's 10x Switchcraft 35RAP2CAV 3.5" PCB mounted jacks mounted end to end, 5 per side. Two PCBs make 10 front to back connections good to go, ready to plug into whatever 3.5 gizmo you have in your rack, for easy front panel access.

Note that I had to create the eagle device for 35RAP2CAV for this (how to do create new parts in Eagle is posted here), I couldn't find it on the net, and it worked. Anyone interested? I am happy to get you the Eagle part description. Comment below.

The 35RAP2CAV is a useful jack for all sorts of DIY, solidly built, not too expensive--I find myself using them more and more. The jack has a switch built in, which is wired up on my breakout board, but not used in this application.

For my Beatstep Breakout board: here is what I came up with so far:

The front panel, which now has p touch labels, will be, after a shakeout and some more noodling, replaced by a 2mm thick frac panel from Front Panel Express.

Cables used to connect from the back of this panel to the sequencer are 6' Euro color thin patch cables, I bought them from Modular Addict, here.

The only hitch, to get everything to fit I had to Dremel off about 1/4" from the front of the PCB.  Oh well.  Maybe next run I'll fix this, but it wasn't hard to just cut off a bit of the PCB. UPDATE: easy fix. Change the Eagle's DRC rules to match JLCPCB's requirements. Turns out Eagle default DRC is much more conservative about how close a trace can be to the edge of a PCB vs. what JLCPCB supports. I figure a lot of other PCB makers are the same. 

Beyond that, this is another "Simple as it can be" sort of project.

UPDATE 9-26-19 I created another version of the same board, with 3x jacks per side instead of 5x. Since I have 6 more cables to run for this project.  Why not?  

You can get Eagle files, PDFs etc. for the breakout board on my website, go here. If you modify it (use different jacks, more jacks, less jacks, whatever) please let me know in the comments below. I will probably cook up variations myself and post more down the road.

OK back to the studio! Now that this breakout panel is mounted to my frac case I can get clocks, CV's etc quickly, no more having to flip the sequencer around! Yeh!

Electronotes Sample-Hold Modded with SMT

Continuing from last time--it's time to keep holding my nose and fab using SMT (surface mount technology).  It's not 1980 any longer.../

This time I take a classic Electronotes preferred circuit "SH-2" (EN#61, posted online here) designed by legendary Cornell Professor Bernie Hutchins and add two of the SMT op amp boards-- information here--to make the module more compatible with my setup.

I initially laid out the PCB and built this S/H module in 2017. I believe the design to be 35+ years old--all analog. I am impressed how flexible this S/H is, you can sample pretty much anything in the audio or control voltage realm, run very fast clocks into it and get good sonic results. 

Another great Electronotes design. You can get the original schematic here or buy the book; I highly recommend Electronotes Preferred Circuits and the entire Electronotes package to any synth DIY'er, it can be a source of a lot of ideas.

My somewhat simplified version of the Bernie S/H PCB worked first time, but was a major issue interfacing it to my modular DIY rig: for external clock, as I initially laid the circuit: only clock signals going a few volts below ground would tell the circuit to sample. 

But: almost all my clock generators go 0V to 5V or more, not 0V to -5V or below.

Lots of ways to fix this; for me, it was easily corrected with a familiar op amp inverter:

Two stage op amp inverter turns positive going clocks to negative--INV GATE OUT feeds the circuit's clock input, while second stage OUT could be brought to the front panel.

I also wanted to add a bipolar LED to indicate if I was using external or internal clock and have it pulse for each sample held. I used a second SMT op amp proof of concept PCB from last time:

A second 2-stage op amp daughter board provides a bi-color LED indicator for the module.  It's in series with the inverter already discussed.

For both boards I tweaked the 2 100K trims until the LED colors looked the way I wanted.  For internal: bright green, for external flashing red.  Yeh!

So there it is: the main PCB (Green); the two SMT op amp daughter boards are the red ones on the back.

Only the op amps are SMT, I am still a bit chicken to go all in with SMT! 

And even for the IC, I could have used PDIP I guess, but this mod would have been harder; the boards need to be small to fit the footprint of a 1U frac.

OK that's it, it was a fun morning modding this board and it made a really useful and reliable S/H even better. Not sure where the SMT thing is going to go right now but I'll think about it.

See ya next time!

Getting Started with SMD

 As my eyesight gets worse, the parts I use for DIY get smaller.  

Surface mount devices ("SMD") have become ubiquitous in electronics, along with SMT components (SMT: "surface mount technology), and perhaps an impending desire to DIY in the Eurorack format, meant it was time to tool up and solder my first SMT parts.

First off, I needed to be able to see what I was doing, so I bought a microscope used for SMT/SMD work and rework:

There are many 'scopes to choose so picking one was hard. After some research, I decided to go with AmScope and ultimately the scope recommended by this youtube dude--find it on Amazon, here.

(Apparently the YouTube repair dude makes some sort of commission? Fine with me. He makes funny, acerbic videos, and has a great NY accent and I enjoy his New York/New Jersey screw-you attitude).

Also, you will need the microscope light (the scope does not come with one but it's a requirement), a Barlow Lens, and eyepiece eye shields.  And of course: appropriate fine gauge solder, a good soldering iron, tweezers, flux and most all the rest of the stuff you'd use with through-hole. 

Go to the web page here for links to a lot of what you'll need.

The microscope works great....there were no instructions included about setting up the stand; I followed the photos from Amazon; it was a puzzle but ultimately figured it out. 

OK I had a microscope--and bought extra flux and some fine point tips for my soldering iron. 

What to build?  

From Tayda I bought SOIC op amps, then got some Eagle boards fab'd for proof of concept: a single SMD op amp buffer--can't get much easier than this?

 tiny TL072s.....

Here's the Proof of concept board:

Use 100K resistors for R1-R4 for higher impedance at input.....

So how did it go? Turns out building this board, with the microscope, was easy.  I knew nothing about soldering SMT so I followed the tutorial here. I made a few solder mistakes but as per the tutorial it's easily cleaned out and fixed up with solder wick. 

In the end I whipped up 4 boards:

And then built one out enough to test that a bipolar LED works.  It does!  

Input -5V relative to ground: blue

And 5V relative to ground--red.  Works!

UPDATE 7-13-19: to further shake out this SMT op amp board I modded my trusty Electronotes sample and hold using two of these SMD PCB's, more in this post.

Onward!

As with many things in life, this was all much easier than I thought; plunking down the dough for the Microscope helped a lot, although it was a pretty big investment.  But, this would have been hard to do without it. Update: I have found I don't always need a microscope for SOIC IC's, and/or 1206 sized passive components, but for smaller footprints the tools I bought for SMD work have been a lifesaver. Recommended!