[sdiy] hammond again

[Tim Ressel]

Yo,

I believe this effect would be akin to phase
modulation. The way you detect this is to get a
high-stability oscillator and use a frequency mixer to
get the sum and difference, then use an audio spectrum
analyser (sound card with FFT software) to look at the
results. If the motor is being back-modulated it will
show up as a frequency difference.

I do not think its likely, though. That gear sstem has
lots of mass and takes a bit to get spun up to speed.
Any drag from the pickups would be minimal.

--tr

--- Gene Stopp <gene at ixiacom.com> wrote:
> I'm not sure how to quantify this either! Perhaps a
> scope connected to some
> generator outputs, visible from the front of the
> Hammond, and then play some
> heavy chords using those tones? I've not detected
> any effect before, but
> perhaps it's too subtle and gets masked by the
> Leslie? This is a fascinating
> new twist on the analysis on why Hammonds sound the
> way they do. Juergen,
> you are always so good at this. Maybe some day I'll
> get the chance to
> experiment with this. I can see my wife now - "what
> the heck are you doing?"
> :)
> 
> Message to Harry - I heartily recommend finding an
> old Hammond. Ebay can be
> useful for this, but you must "search without
> trying" and one may fall into
> your lap (ouch!). Geographics plays into this, since
> the sellers rarely say
> anything other than "come and get it, you sucker".
> However without a garage
> it's a bit of a space-stealer, and if you have
> stairs, well that's another
> issue :)
> 
> For some younger people the lure of the Hammond may
> be a mystery. For old
> farts like me who grew up listening to Steppenwolf
> et al, there is a certain
> charm to the beasts. Something about the smell of
> dust baking on the tubes,
> the smell of the old wood and generator oil, the
> fabric-insulated wires, and
> of course the sheer weight of the machine (so that
> it doesn't even wiggle if
> you get a little too "inspired" whilst playing).
> 
> In the past I have considered what it would take to
> build a clone - start
> with a top octave generator, divide it down to get
> the whole range of
> frequencies, use passive R/C filters and some
> buffers to get it all down to
> sinewaves, then wire it up to a 9-bus keyboard. The
> busses get sent to
> drawbars for mixing. If a 9-bus keyboard isn't
> available, you could use
> analog switches in banks to do the contact
> simulation. But wait - add up all
> the time and energy! Much easier to find an old
> machine that already has it
> all. Not only that, the contacts don't close at the
> same time! And also,
> real metal contacts running at millivolt levels make
> a popping noise! And
> the frequencies from a top-octave generator aren't
> the same! The Hammond is
> a great example of the "it's just not the same"
> syndrome.
> 
> This brings up something more - why do these
> machines cut through the mix so
> well in a live situation? Oops, this is another
> topic, but one that I'd like
> to discuss.
> 
> - Gene
> 
> 
> -----Original Message-----
> From: jhaible at debitel.net
> [mailto:jhaible at debitel.net]
> Sent: Tuesday, November 05, 2002 7:05 AM
> To: synth-diy at dropmix.xs4all.nl
> Cc: jhaible at debitel.net
> Subject: [sdiy] hammond again
> 
> 
> Thanks to all who replied, on-list and off-list.
> 
> I think I wasn't clear enough about this. 
> I was neither talking about slow lesley effect /
> chorus vibrato, nor
> did I expect any effect back to the motor.
> 
> I was talking about the tonwheel / pickup system,
> back to a
> mechanical junction where there is no stiff coupling
> to the motor.
> I think there is a resilent part in there somewhere,
> which would
> certainly form a system which can "oscillate"
> against its nominal
> rotation. Also, a sudden loading of the system will
> certainly cause
> such oscillation, if ever so tiny.
> 
> My question is: would this be a *perceivable*
> effect??
> I have no idea how to quantify this.
> 
> Again, what I was talking about was not a "chorus"
> type of sound.
> It's more like "liquid" versus "dry".
> The funny thing is that samples of a tonewheel organ
> often *have* this
> liquid character, but an electronic drawbar organ
> doesn't have it.
> 
> JH.


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