MM3203A Test Eagle
I had been using rough and-ready banana-to-minijack adaptors, with all the connectors hanging off the leads of a 100k load resistor, to connect multimeters to CV sources for calibration purposes for years. With the acquisition of a large quantity of old test oscillators and lab equipment, I started to think about something more sophisticated....
There are already some great options in the Euro market for interfacing banana jack modular to minijack, but I felt there was an untapped niche for something specialised in interfacing lab and test equipment as well as DIY prototyping setups to and from Eurorack, and this idea guided the design in the following ways.
Firstly, the standard retail version uses high quality Pomona recessed panel-mount banana jacks. These are more solid than the relatively inexpensive Johnson jacks used in both classic and modern "west coast" synths (machined solid insert rather than stamped sheet metal). As an option, it is possible to substitute Pomona double binding posts, which will interface just fine to standard banana jacks but also have screw terminals which can either connect jumper wires from breadboards or attach load resistors of your choosing, as well as connecting banana jacks!
Secondly, each signal connector (red) has a paired ground connector at the industry-standard 3/4 inch spacing which permits the use of dual banana plug test leads or BNC coax adapters which can be readily sourced through eBay.
Thirdly, each interface has a switchable shunt load.
Interfaces 3 and 4 can switch in either a precision 100k ohm resistor (to ensure that CV signals being sent to multimeters have a standard input load for accurate calibration, or a 600 ohm resistor for ensuring that older transistorised signal generators have a standard output load to work properly when they connect to Euro (and their output levels are attenuated to safe levels). The centre position of each switch is a no-load passthrough setting, for connecting bananafied modular synths to your Euro or where you have external termination (ie 50 ohm coax).
Interfaces 1 and 2 are a bit more specialised. These are designed for interfacing older valve equipment which can produce huge voltages and power outputs without breaking a sweat-enough to make life unpleasant for a Eurorack setup. Therefore these interfaces have two switch settings for 600 ohm load-the lower of which divides the input signal by 10 for a -20dB input pad. This will make input levels safer, indeed any signal generator which outputs 5W or less into a 600 Ohm load can safely connect to a Euro synth via this setting. The top switch setting is an unterminated, unattenuated passthrough setting.