Do you need an oscilloscope to use a synthesizer? No, but it can be useful.
Do you need an oscilloscope to build synth modules? No, but it can be very hard to troubleshoot without one.
Do you need two oscilloscopes, one for using your synth and one for building modules? Of course not, not if your synth is set up next to your building bench. Or if you’re fond of hauling your scope from one to the other.
My bench is two flights of stairs above my synth.
I have a little pocket scope but it’s always out of battery and there’s a defect in the display and connecting it to a synth output is hard. And I have a bench scope that’s great but it’s AC powered and a nuisance to unplug, gather up the power cord and probes, haul it downstairs, plug it in, and then reverse all that when done.
Someone on the LMNC Discourse group was selling a Jye Tech DSO138 kit a while back for $25, so I picked it up. It’s a small, inexpensive, very basic but not bad oscilloscope. It’s sold as a kit, with a bunch of through hole parts to solder; it goes for about $35. (It’s also obsolete: Jye Tech recommends the successor DSO138mini. And it’s widely counterfeited. So caveat whatever.)
The kit doesn’t include the needed 9 V DC power source. It’s a sandwich of two PCBs, no case. It has a BNC input jack. If you want to use it to look at a signal you’re also using in a patch, you have to somehow split the signal to two destinations, one of which ends with a BNC connector. You also have to find it in the first place, it’s probably buried under a bunch of cables or something.
Or, you can do some hardware bending.
Here’s my new scope module.
(The display is a little cockeyed on its PCB and there’s not enough play for the mounting screws to correct it — maybe I’ll drill out those mounting holes a little sometime.)
People have done this sort of thing before; at the most basic, they’ve mounted the scope to some rails which in turn screw into the synth case rails. Or they’ve done more elaborate things, but I don’t know of anyone who’s done a Kosmo DSO138 module, so I designed one.
Slide switches, tactile buttons, and trigger indicator LED are mounted to an auxiliary PCB mounted behind the panel. Also on this board are a Eurorack style 10-pin power header with 10 µF caps and power reversal diodes, and a 9 volt regulator and TL072 op amp with associated passive components.
A BNC jack and a 1/4″ phone input jack are mounted on the front panel. A toggle switch selects whether the scope input is connected to the BNC or to the 1/4″ jack signal after being buffered with the TL072. The latter signal, buffered, also goes to a second 1/4″ panel mounted jack, so the signal can be passed on to another module.
Also on the front panel is another toggle switch, controlling the 9 V power. (It’s good to power off the scope when not in use, for at least three reasons: the scope draws about 130 mA current on the +12 V rail, it probably puts out some digital noise you don’t want getting into your synth sound, and leaving it powered off when not in use will help extend the life of the display.)
The main DSO138 board is mounted perpendicular to the front panel. I used a 3D printed carrier and long spacers to attach it. The display board is parallel to the front panel and connected to the main PCB with a ribbon cable. More ribbon cables and a couple wires connect the auxiliary PCB to the appropriate points on the main PCB.
Design files, Gerbers, STL for the mounting fixture, and docs in the GitHub repo: https://gitlab.com/rsholmes/dso138
Analog Output 
One thought on “DSO138 Kosmified”