[sdiy] Hammonds (was: Programmable Logic?)

[Gene Stopp]

The Hammond organ is really my first love, even before the Moog. So me being
me, I've had my hands in the guts of many, many Hammonds, minor repairs,
complete restorations of gutted chop-jobs, etc. I've been *so* down this
philosophical road before! Here's my list of challenges in Hammond sound
synthesis:

The Electronic Challenge:

* Duplication of the frequencies of the tone generator, including the
various beat frequencies and jitters

* Duplication of the waveforms from all the tonewheels - they're not going
to be perfect sinewaves, in fact some tomewheels have intentional
harmonic-adding teeth

* Duplication of 9 contacts closing at different times when a key is
depressed (which adds a bit of velocity-determined variation)

* Duplication of the crosstalk from millivolt-level tones traveling in
bundled cable harnesses

* Duplication of the frequency response and distortions of the signal chain

* Duplication of the amplitude decay curve in the percussion circuit

* Duplication of the tremolo, vibrato and chorus characteristics - lots of
variations here, the first Hammonds had mechanical tremolo, then the "V"'s
had scanner vibrato, which carried over into the B2/C2/B3/C3 and their
variants (RT's, A-100's, etc.), then the "L"'s had electronic vibrato, etc.

The Subjective Challenge:

* Duplication of the physical characteristics of the waterfall keys on the
manuals, which influences playing style

* Duplication of the weight of the machine, whose rock-steady presence leads
to getting carried away with your body movement when you're really "rocking
out"

* Duplication of the smell of grandma's living room dust burning on the
tubes, old wood and oil, and cloth wire insulation

All of this is before you even get to the spring reverb stuff, and the
Leslie stuff is a complete subject of its own. I think there are two
approaches to getting the Hammond sound - the "thrill of the hunt", so to
speak, which is the synthesis of the above (or most of them, anyway), or the
"Real thing" which is finding a real Hammond (and the room for it!).

Latest Hammond project was the stacking of a Leslie 125 on top of a 147,
slaving their motors together with solid state relays, and plopping a tube
amp head on top (Fender 140) which drives all the drivers. So I have this
seven-foot-tall stack with reverb and EQ, 140 watts of 6L6 power, extremely
grungy and rude when running with an old CV with a home-brew percussion
circuit. I usually only mess with it for a few minutes at a time, long
enough for the neighbors to rush out of their houses wondering what the heck
was going on. Afterwards I have to make nice with my wife.


- Gene


-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of James Patchell
Sent: Tuesday, July 20, 2004 10:19 AM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Programmable Logic?


Very interesting....I can see that it is maybe even more complicated than I 
imagined...


At 08:03 AM 7/20/2004 -0700, Tim Ressel wrote:
>Yo,
>
>
>Ah, gearboxes. As it happens I have a bit of
>experience with this kind of thing. I worked at a
>place that was doing spectrums of gearbox vibrations
>to determine driveline health. Basically what you'll
>see in a gear train like the Hammond tomewheel setup
>is frequency (or phase) modulations from various
>sources. Any gear has a 'pitch circle' which
>more-or-less the middle of the gear teeth. Nothing to
>do with musical pitch; but an amusing coincidence.
>
>See:
>http://shopswarf.orcon.net.nz/spur.html