In 2011 I built an Italian harpsichord for a client in the Hague. His wish was a double with 2 x 8′ and a compass FF – f”’, with transposition 415-440. I decided that in this case I could adapt my usual Giusti model which has a compass of GG.AA – d”’. I could also fulfill a wish I had for a long time, making a harpsichord with a dogleg coupler, often called a “German coupler”, because of its use by German builders in the baroque. I was courious how this technique would work.
This coupling mechanism works quite different from what we call the “French coupler”, which is more generally used. In this last case the keys of the upper manual are moved at the back from the lower manual by coupler pegs. In the German coupling system a section is cut out of each front row jack so the upper part rests on the keys of the upper manual and the lower part rests on a little block glued on the lower manual keys. The lower keyboard can be shifted forward or backward so one can chose the jack being moved by the block so it will be played by both manuals or the long part will be behind the block in which case the jack is only played by the upper manual. So if you are playing the two 8′, you don’t see the upper manual keys moving. It is a weird sight.
The result of this set up is that there is less mass in the touch when playing coupled compared with the French coupler because the mass of the upper manual does not take part. The touch on this instrument is no different indeed from an Italian single, maybe even a bit lighter because of the longer lower manual keys.
The form of this jack reminds of the back leg of a dog, hence the name. Dogleg jacks were also used in English and late Flemish harpsichords but without the sliding keyboard so they always were played from both manuals.