A Look inside a Hammond Tone Generator . . .

[Legatoboy]

For many of us this is known information but many people don't really know how a Hammond organ functions inside. I learned some more from these vids myself, especially the 1st vid. below on the Tone Generator . . . (BTW, the 1st stops and start with pauses in between the segments)

 

So 96 Tonewheels equals 4 octaves times 2 manuals 48 X 2 = 96,

I would guess than that the Pedal Tones share tonewheels.

Is my math on this correct? lb

 

 

 

[video:youtube]

 

http://media.soundonsound.com/sos/nov03/images/fig01tonewheel.l.jpg

 

[video:youtube]https://www.youtube.com/watch?v=hopUp1qBbJ4

[MorayM]

I believe it's a bit cleverer than that. Each tonewheel generates a sine(ish) tone, but each key can trigger not only the fundamental for that key but also for 8 other harmonic overtones. 549 (61x9) is rather a lot of tonewheels, but remember that each overtone of one key corresponds to a different overtone of another key.

 

For example: 440Hz is the fundamental (8') harmonic for the A4 key, but the A3 key with only the 4' drawbar pulled (generating a harmonic one 8ve above) ALSO corresponds to 440Hz, as will playing D3 with the 5 1/3' drawbar pulled, and so on across all the keys. So in reality the number of tonewheels you need to cover all 9 harmonics for all 61 keys and extra pedals is far less.

 

This is about the point where the real Hammond experts will jump in with the engineering reasons why the reality isn't so straightforward, but that's the theory in any case.

[JMcS]

Hammond console manuals are 5 octaves. Each tonewheel creates one frequency and any note that uses that frequency takes it from the one tonewheel. Each key can use 9 tonewheels. Depending on the model the pedal tonewheels may not produce a constant single frequency. Also, in a B3 there are 96 'wheels but only 91 generate a tone, the last 5 are blank and are there only for balance (The H-100 and X-77 used all 96)*.

 

* from "The Hammond Organ - Beauty and the B"

[Legatoboy]

It's a bit more complex than I thought. Didn't know the sharing went on that MorayM explains! I thought it may have modulated through each 12 notes of the 5 octaves (not 4 as I misstated) through some other process that electronically transposed the same tone wheel for a note up through the 5 octaves, that was a wrong assumption on my part...there is much more complex sharing of the overtones going on . . amazing!

 

Thank you both for the clarification! That clears up a lot in terms of the math! lb

[mate stubb]

Random thoughts:

 

Think of a wheel/pickup like a guitar string/pickup, with the notched wheel standing in for the vibrating string. Put a periodic vibrating metallic object near an electromagnet and you get an oscillation. Filter it with a LC filter and you get approximately a sine wave.

 

Each wheel/pickup provides a tone in multiple places on the keyboard - for instance the 4' drawbar on middle C uses the same wheel as the 8' drawbar an octave up and the 16' drawbar 2 octaves up. However they are not at the same signal strength, because that is not pleasing to the ears. The higher on the keyboard you use a pitch, the lower in volume it is tapered. This is done with a harness of resistance wire inside each keyboard.

 

Crosstalk or ghost tones are caused by leakage between the 4 wheels sharing a single bin in the generator chassis.

 

The highest notes of the high drawbars are folded back and reused from lower octaves. This is to save hardware, and because we don't have critical hearing at high frequencies - a technique borrowed from pipe organs.

 

The lowest notes of the bottom drawbar are folded back upwards to make the pedals seem more powerful since they share the same pitches. This is not always desired by players who do left hand bass.

[Legatoboy]

I got the pick up, tonewheel/notchs - magnetic field concept fine!

 

It's a actually electronically much more complex that I had imagined in terms of the sharing.

 

I'm a systems guy (business programmer) by trade and write computer programs every day. To work out that sharing matrix and route it electronically was no small feat!

[zukskywalker]

I gigged for a while with an M3 but never opened it up. Later in life I was given a badly busted up full Hammond that became my first Hammond project. You want clever and complex? This baby has TWO tone generators in it, one tuned a few cents off!

 

[Mitch Towne]

Wow. I had no idea there was so much stuff packed into a Hammond SK. I mean...there must be, because "it's not a clone, it's a Hammond," right?

[The Real MC]

Hammond called it a "flute" tone. The raw signal from the tonewheel actually has imperfect harmonics (due to crosstalk from neighboring wheels) that is filtered out with RLC or RC circuits, so the signal isn't a perfect sine waveshape.

 

Then there was the intentional "robbing" designed in - as you added notes and harmonics, it wasn't a pure additive process there was some passive attenuation to cause levels to drop but the sound as a whole was balanced.

 

Those tone generators were one serious assembly and never meant to be serviced. They built them to LAST. Remember that Hammonds dating back as far as 1934 are STILL running.

[Legatoboy]

I have a 1966 vintage B3 with a 122 RV. I installed a Trek II reverb in it! Still a wonderful organ. Never leaves the house though! I record with it basically! Other people had to have a 70's Trans Am for their mid-life crisis. I finally bought my B3 about 18 years ago! Could never afford one as a kid though I gigged M3's, L's and an old CV in the 70's . . .

[Legatoboy]

Mitch

[mate stubb]

Resistance wires, which balance all the tones passively, without additional electronics:

 

http://1.bp.blogspot.com/-0PZ6Mh5OH70/UFJUuuGfbPI/AAAAAAAAABU/6vEcsWS__O4/s1600/20111231055.jpg

[Legatoboy]

I see Moe!

[mate stubb]

Signal flow:

 

generator->manual->individual resistance wires to individual key contacts->9 bus bars (one for each drawbar)->drawbar/preset panel bus bars->matching transformer->vibrato switches->preamp.

[Legatoboy]

Got it! Makes sense. The resistance wiring I had absolutely no clue about till now!

 

 

Your Chop cabinet design is nice from your photos . . .not the same old same old look. Doesn't look like any other chop I have seen to date!

Thanks Moe!

 

[marczellm]

Someone showed me a later Hammond model that had like a single octave of tonewheels and then transposed them down with transistor circuitry. Didn't have The Sound of course.

[WesG]

Marc, the only Hammond matching that description is the X66.

 

http://www.organforum.com/forums/attachment.php?attachmentid=1214&d=1303434432&blah=.jpg

[WesG]

MorayM, you are missing one more piece of information, some of the tones are repeated an octave down at the higher drawbars of the higher notes. This is called "foldback". if you pull, say, only the 1' drawbar and play a chromatic scale from one end of the manual to the other, the resultant output will drop by octave near the top....i think around the F# two and a half octaves from the right.

 

That foldback, not present in spinet models, is what really allows the console hammonds to scream with fatness in the high register.

 

Wes

[miden]

Thank you legatoboy

 

Very informative and interesting videos, especially for "non-hammond" folks like myself.

[KRK]

great!

 

some time ago i made this documentary, with one of most wellknown italian hammond tecnician.

 

ok, it's in italian

 

but you can go and see the video, for some addictional details, not mentioned in the other videos on youtube.

 

 

inside hammond - part 1

(yes, Mr. Larry Goldings was there that day ):

 

in particular at:

- this point you can see what happens during the START/RUN procedure

 

- this point you can see keyboards contacts and busbars

 

 

 

inside hammond - part 2

 

in particular at:

- this point you can see the vibrato scanner

 

- this point the Leslie 122

 

have fun!

[B3Nut]

Marc, the only Hammond matching that description is the X66.

 

http://www.organforum.com/forums/attachment.php?attachmentid=1214&d=1303434432&blah=.jpg

 

The X-66 is a strange beast. That machine takes pretty much all knowledge of how a Hammond is supposed to work and throws it out the window. It's the Un-B3 if there ever was one...very theatrical in voicing and can get some great liturgical tones happening too. Mine needs some TLC but it's a hoot to play.

 

TP

[J. Dan]

great!

 

some time ago i made this documentary, with one of most wellknown italian hammond tecnician.

 

ok, it's in italian

 

but you can go and see the video, for some addictional details, not mentioned in the other videos on youtube.

 

 

inside hammond - part 1

(yes, Mr. Larry Goldings was there that day ):

 

in particular at:

- this point you can see what happens during the START/RUN procedure

 

- this point you can see keyboards contacts and busbars

 

 

 

inside hammond - part 2

 

in particular at:

- this point you can see the vibrato scanner

 

- this point the Leslie 122

 

have fun!

 

Explanation please:

 

 

 

In that room....... 2 hammonds, 2 Leslie's, and.........

 

 

 

 

a Roland KC amp!

 

 

 

[MorayM]

MorayM, you are missing one more piece of information, some of the tones are repeated an octave down at the higher drawbars of the higher notes. This is called "foldback". if you pull, say, only the 1' drawbar and play a chromatic scale from one end of the manual to the other, the resultant output will drop by octave near the top....i think around the F# two and a half octaves from the right.

 

That foldback, not present in spinet models, is what really allows the console hammonds to scream with fatness in the high register.

 

Wes

 

I knew there was something! Thanks Wes. The 1' drawbar is connected to the percussion generator too I think?

[Legatoboy]

Miden your welcome, I put it up just for that reason. I thought other people would get something from it also. Though I've been around Hammonds my whole life there were still a few mysteries that I wanted to understand. The Tonewheels design was one of them. I never fully understood it completely until this thread!

[B3Nut]

The 1' drawbar in the upper manual "B" preset group on a -3 series console (B-3/C-3/RT-3/A-100/D-100) is disabled when the percussion is engaged, as the percussion circuit uses the 1' busbar in the manual for keying, grounding through the tone generator when a key is depressed. The percussion tone is taken from either the 4' or 2 2/3' (second or third harmonic) busbar.

 

Trek II percussion kits for earlier consoles intercept a different busbar than the 1' for keying, though you can wire them that way if you want.

 

TP

 

 

[Legatoboy]

[KRK]

Explanation please:

 

In that room....... 2 hammonds, 2 Leslie's, and.........

 

that's OT, but, for answering you....

that's just an isolated room in a bigger "warehouse" with dozens of hammonds, leslies, synths....

 

for your info, the healthy B3 in my previous videos (not the one disassembled for tutorial/didactic purpose) was previously owned by Joey DeFrancesco!

 

 

here you can see some other stuff in that same place, near to Milano (northern Italy):