[sdiy] Novachord resonator

Lanterman, Aaron lanterma at ece.gatech.edu
Thu Jul 23 09:02:29 CEST 2015


I’ve developed something of an unhealthy obsession with Clavichords and Novachords. Of course the latter is the only one really relevant to this list.

Anyway, I’ve been obsessively looking at pictures on websites of folks who have done Novachord restorations. There doesn’t seem to be a lot of actual technical info on the web. The most detailed info I found was a set of schematics here:

https://sites.google.com/site/hammondnovachord/schematics-and-information

fig13.jpg is an overall schematic showing how the main oscillators, divide down units, resonator section, and keys all hook together. It’s a bit hard to read, but you can get the main idea from it.

fig20.jpg shows the resonator section. I’m confused by “input from 4 tubes” marking. That suggested to me that there might actually be six instances of the Figure 20 schematic, one for each octave, with maybe different values for the inductors for different octaves, and the rotary switches being giant ganged rotary switches. 

But… looking at the pictures of restorations, for instance this one from the CMS website, it seems like those rotary switches aren’t ganged:

http://www.discretesynthesizers.com/nova/photos/filters.jpg

So it looks from that like every sound from every key is going through one instance of fig20.jpg.

Anyway, I thought it might be fun to build the resonance section on fig20.jpg as a stand-alone module. But some of the values are mysterious… the capacitance CN20, for instance, and inductances LN2, 3, 4, and 5, and the resistance values of switched by the rotary switches (shown on fig13.jpg, but that doesn’t show actual values).

- Aaron


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