Sandy....The gizmo is simply a plug fitting the tuner and a wire with a small gator clip on the end. Probably about two bucks at Radioshack. Leej would know. The Zen-On 331 and some others generally don't require it in most situations, but they are useful in an excessively noisy environment.
And Fortunato...I've built three and they've been OK, but nothing to write home about. Sounded fine, but just another autoharp. It is one of the easiest soundboxes to figure, but to me, the problem in autoharps is not one of sound, but ergonomics. When I finish the redesign of my hammered dulcimer and I'm building at a reasonable level, I want to talk in depth to Harpgirl about some specific ideas and questions about autoharps. If you don't know, she has a fine reputation and I would trust her judgement on things related to this instrument. I'll throw it to Bill too and to Rick, and open to the forum later. I already have made a few asymmetrical Appalachian dulcimers, but I'm going to focus on ONE model only of HD first, then add either the App or the autoharp next...again, ONE model only. One of the problems I experienced before getting sick was building too many of this and that, mainly because I was learning and it was fun and a challenge. But as a small time builder, I need to focus on building only one model that fits many circumstances at a cost that's livable.