RE: Organ sound construction (non-Hammond)

[John Bittner <jbitt@primenet.com>]

Typically, the master oscillator for each note provides a pulse or
square wave to a divider chain.  The frequency divider is usually a
flip-flop which divides the input frequency by two to produce a tone
an octave lower than the input.  This is probably the most common way
of doing things in sold-state organs.  However, there are variations
where the pulse from the master or preceeding stage is used to excite
a circuit tuned an octave lower, or synchronize a free running
oscillator tuned roughly an octave lower.

Any case, all the octaves below the defective divider should be out of
tune with master but in tune with themselves.  If none of the octaves
are in tune with the master, then problem is with the first divider,
or the output pulse of the master feeding the chain.

Hope this helps.

jb

----------
From:   Hakan Eriksson[SMTP:e5he@etek.chalmers.se]
Sent:   Tuesday, December 05, 1995 1:01 PM
To:     hammond@zk3.dec.com
Subject:        Organ sound construction (non-Hammond)

Hello!

Another of those non-Hammond questions, I'm afraid, but it does regard
an organ of some kind, at least!

I've got this old Swedish organ prototype (made by a company called
Mustad or possibly Bergman (if that helps:-)). I do know it uses some
kind of frequency dividing of twelve 'sine' waves to create its
sound. Since there's something very wrong with it, I wonder - does
anybody in the group know extactly how this frequency dividing usually
is done? In general terms, of course...

The problem is that a couple of notes sound very disharmonic over the
entire keyboard, except for the highest note of each, which is the
original note, of course. If I turn the core of the inductor I can get
a decent sound on the corresponding note, but out of tune. It seems to
me as if some capacitor value or something has drifted.

I would be grateful if anyone can help me on this...


Bye,
-- 
              (           Hakan Eriksson             )
              (        e5he@etek.chalmers.se         )
              (  Chalmers University of Technology   )
              (         Gothenburg, SWEDEN           )



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