There were several actual Panharmonicons, the first invented in 1805, from which Balzac draws on. These were mechanical orchestras that were programmed to play back musical pieces. But Gambara's doesn't merely play back, it's actually playable live by a performer, a feature which no real parharmonicon was capable of.
Gambara triumphantly showed him the little drums on which were grains of powder, with the aid of which he made his observations on the different natures of the sounds emitted by the instruments.
"Do you see," said he, "by what simple means can I prove a great proposition! The acoustics reveal to me similar actions of sound on all the objects that it affects. All the harmonies start from a common center and keep intimate relations between them; or rather, harmony, one like light, is decomposed by our arts as the ray by the prism. Then he presented instruments constructed according to his laws, explaining the changes he introduced in their contexture. At last he announced, not without emphasis, that he would crown this preliminary session, at best at the satisfaction of the curiosity of the eye, by making an instrument which could replace an entire orchestra, and which he called panharmonicon.
Marianna released, not without difficulty, from her covers an instrument as large as a grand piano, but having an extra upper buffet. This strange instrument offered, besides this sideboard and its table, the pavilions of some wind instruments and the sharp beaks of a few pipes.