Are Oscilloscopes Silly Scopes?
Mark Jenkins scopes out these mad scientist favorites, now synth studio must-haves
You’ve seen them in countless sci-fi movies, you’ve puzzled over them in your local synth service department, you’ve lusted after them as part of Keith Emerson’s giant Moog Modular. But now the oscilloscope is making an appearance as part of many Eurorack setups, with both classic and modern designs offering something uniquely eye-catching…
An oscilloscope simply scopes out your oscillations – in other words, displays how an electrical signal is changing over time. Properly marked up, the screen display of an oscilloscope can help radio, TV, and other engineers find out exactly what’s going on in any electronic system. Mostly these devices sit in a test lab, one small spike on the screen display giving away all sorts of vital service information.
But that’s not much fun is it? Feed an oscilloscope more interesting signals and you start to produce what can only be described as extremely cool static or moving light displays. Hollywood’s 1950s props guys knew all about this, equipping both sci-fi movies and plots about nuclear war with all the oscilloscopes they could find.
Meanwhile some musicians like Karlheinz Stockhausen were actually using oscilloscopes to help make music, since their studio instruments often consisted of nothing more than physics lab test oscillators. Stockhausen’s giant EMS Synthi 100 instrument had an oscilloscope built-in.
Users of other early synths also became used to having oscilloscopes around to check out their gear, not least because they could help in accurate tuning. Kraftwerk had one very early on in their KlingKlang studio.
But the first attention-grabbing live appearance of an oscilloscope was in Keith Emerson’s giant Moog Modular system – though ironically he usually took along a fake one, a real oscilloscope being way too risky to perch right at the top of that giant instrument.
That’s because early oscilloscopes were basically simplified TV sets, based on a CRT (cathode ray tube) made of glass, vacuum, and high voltage electro-magnetic circuitry. So yes, they can be heavy, bulky, and fragile – a dangerous combination. Most oscilloscopes sat on a test bench, but some were securely 19-inch rack mounted, making them a little safer. [4abcd] scopes
Next prominent live user of an oscilloscope was Chris Franke with Tangerine Dream in the early 1970s. He racked a Philips 3207 Dual Trace model in his giant custom equipment cabinets, many studios and university media labs doing the same.  Franke
Jerzy Skolimowski’s 1978 movie “The Shout” had great authentic scenes (now on YouTube) of John Hurt as a musique concrete composer in an EMS Synthi and oscilloscope-crammed studio. So generally the devices had a serious use – but often they were just left running in the background doing something cool.
So how exactly would you use an oscilloscope to create the type of psychedelic displays you want?
Sooner than oscillator. On YouTube there are some truly dreadful, long-winded demos about how to make the oscilloscope displays you want. But here’s all you need to know (see the video too).
Any Eurorack or other modular system, or semi-modular instruments like the ARP, Korg, and Behringer 2600 will provide the right range of input signals of a few volts, and you can also try inputting voice and other instruments from a suitably amplified microphone.
Send the voltage from an oscillator into your oscilloscope channel 1 (if it has two channels). If the oscilloscope had BNC or banana sockets you may need adapters, or you can make a cable from one of your existing minijack cables.
Adjust the display height, focus, and scan speed until you see a clear waveshape, like a sine or sawtooth.
Modulate the oscillator with a vibrato or tremolo and you’ll see the waveform display change entertainingly in height or width.
If your oscilloscope has two channels, connect another oscillator to the second, switch the channel on, and see two different waveforms, one above another (or one alternating after the other with each horizontal scan, if you have an “alternate” mode switch).
Feed both oscillators to a single oscilloscope channel to get broken and complex waveform patterns. Run one slowly and one quickly at audio speeds, or use the output of a ring modulator module to see spiky, misshapen waveforms. The oscilloscope can show a repeating ADSR envelope voltage too, and other types of output.
That’s about as much as you can do with the basic oscilloscope inputs. To get the funkier types of display – named Lissajous Figures after the French physicist Jules Antoine Lissajous, who first created them mechanically using reflected light beams – you must have an additional function on your oscilloscope.
This switches off the internal left-to-right speed control of the display – always driven by a sawtooth generator, so the display repeatedly moves gradually across the screen then flings itself back to the left hand side – and instead inserts a control signal of your own choice for left-to-right movement.  MUSEUM
You’ll find this function either as a switch called “X-Y,” or in the form of an alternative input socket (sometimes marked Z and on the back panel) coupled with an “Ext” switch to disconnect the internal “timebase,” or motion control.
And now it’s a whole new ball game, since you can make the left-right “X” position circle around while the up-down “Y” signal does the same. Input two oscillators at the same speed, one running slightly behind the other and, pleasingly, the first thing you see is a perfect circle.
When you start to adjust speeds, and the “phase” between the two oscillators changes, that’s when things start to go crazy. First your circle will double, then quadruple, then split into a whole mesh of interlocking curves.
Modulation can make brighter lines sweep up and down the mesh, spots and blobs like little UFOs will appear, and it all becomes VERY psychedelic indeed – straight out of those 1950s sci-fi movies.
Slowly varying synth sounds will make correspondingly ever-changing displays.
Beyond the CRT. Modern oscilloscopes are very much lighter and more compact, instead of a CRT tube using LED displays that can also be in full color, creating very eye-catching patterns.
A small one in kit form is typically £40/$50, and there’s an easy Eurorack conversion kit with faceplate called DSO150 Euroscope Mk.2, as well as complete Eurorack models like the Waveform Gateway. And the Dave Jones O’Tool Plus is a Eurorack format LCD oscilloscope and also a video synthesizer for complex shapes.  DSO EURORACK
But while such devices fit much more easily into either Eurorack or 5U high Moog-style format, these and modern desktop oscilloscopes (from companies such as Hantek) are never as gleamingly bright as their CRT predecessors.
For the real thing you still need to put up with the size and weight of an old classic model, and to find some kind of shelf or mounting that will bear its (often very substantial) mass and dimensions.  HANTEK
Check local electronics stores and pawn shops, and failing that eBay and other second-user sources, expecting prices to start at around $100/£100 for a working old CRT oscilloscope – though be aware that many sellers won’t ship to you, since these remain both very heavy and very fragile.
But if you can get one delivered safely, a classic old oscilloscope will forever help to give your music studio that priceless mad scientist look…