How A Tonewheel Generator Works (by synthpro)

[@armstronglance]

I’ve removed, repaired or adjusted many Hammond tone generators, and their construction never ceases to amaze me! We could never manufacture those affordably in the US today.

[@jeremybender401]

Before organs, Laurens Hammond was a clock designer, engineer, and inventor. What a brilliant man. You may want to look into a "foldback" kit for your M3. You would easily be capable of installing it, and it makes a spinet sound like a full Hammond (think B3) only with less keys. Boston (Tom Schulze) used an M2 (with foldback) on the first album (not to shabby).

[@ibanezleftyclub]

You should do a colab with Look Mum no Computer, this project is so up his alley and would amazing for his Museum of Everything Else.

[@FunnyBecauseItsTrue]

...this is awesome! I always knew the term “tonewheel organ”, but never understood how they mastered electric keyboard polyphony back it the 40s...

[@pvillez]

Thank you for sharing. Great idea. Gamechanger Audio later used this idea for their Motorsynth product.

[@wave8362]

Some pickups and big-ass wheels is all I need. Sure need me some hammond organ in my blues/ country band now.

[@leonarddobrzyn725]

Thank you for sharing --- very educational ... When I think of the fact these guys that made these organs had to go by trial and error and a lot of math, they really were genius!!!

[@TheNAPSince2005]

This is a very valuable technical and material value video. Thank you for publishing it.

[@synthpro]

Your very much welcome, glad you enjoyed it. Thanks for watching!

[@James_Bowie]

At 4:48 those coils on each note are not signal boosters. Together with their adjacent capacitor they form passive bandpass filters to suppress unwanted harmonics.

[@synthpro]

Thanks for the clarification.

[@rostintammen5867]

Late to the watching party, but I couldn't help but notice that at 7:10 it turns into those hearing test we used to have at school. Cool video though. I always wondered how a Hammond worked.

[@bcunderwater]

Very cool video. Thanks! Back in my "band days" I played (among a lot of other things) one of the L series Hammond, don't recal exactly which one, but that only applies to which cabinet. No Hammonds were made to be hauled around, but the L was much more portable than the others. It had some differneces from the larger ones, but sounded great to me. The tone gernator setup looks the same but it has been a long time. It did indeed have percussion and more options there than others as I recall. I think it had two percussion tabs that could be used individually, or together. You mention Keith Emmerson and at one point, he was carrying two of these babies around playing one with each hand! We used to cover "Knife's Edge" (ELP) where he did the power cycle and I was able to conver that too. Funny, it did not have the "overshoot" when powered back up that you show on the video, again as I recall. It just went down and then back up to pitch. Wonder why that might be? Thanks again!

[@paulromsky9527]

You can see each compartment has two tone wheels. They are grouped in 4 compartments (2 on the forward side and 2 on the rear side). There are 48 compartments in all, 24 compartments across so since they are in pairs per side, that is 12 notes of an octave across the whole wheel set. Starting from the left 4 compartments, I assume this is C (and since it has 4 compartments of two wheels each) that is 8 different pitches which correllate to the 9 "pipe lengths" of the slide bars (1 length uses a wheel in another compartment as a harmonic). The next four compartments are for C# and have the same 8 wheel sizes but are geared one semi-tone faster. All the way to the B compartments which too have the same wheel sizes but are geared 11 semi-tones faster than the C wheels. In each compartment you can see a wheel with just a few big lobes and one with a lot on tiny lobes next to it. Because these pickups are near each other, Hammond put a longer pipe (lower pitch) length (few lobe wheel) next to a shorter pipe (higher pitch) length (many lobe wheel) in the same compartment to reduce some of the crosstalk between the pickups. Because the lower pitch and higher pitch wheels are a few octaves apart, it's harder to hear the crosstalk. On this organ, 8 wheels are for (I assume) pipe lengths: 16' 5-1/3' 8' 4' 2-2/3' 2' 1-3/5' 1'. The 1-1/3' tone may come from a wheel in an compartment set used as a harmonic. The keys start each 12 note octave on: C2, C3, C4, and C5 on two Manuals (keyboards). So if you select the 16' pipes (the lowest frequency set) and play C2, this is the lowest pitch possible and thus the lowest lobe is selected in the C compartments. If C3 is played (one octave higher) then the wheel is selected with twice as many lobes in the C compartments than that was used for the C2 tone at the 16' length.

[@julesl6910]

Fun fact - at the end of Pink Floyd's Welcome to the Machine, this is the sound you're hearing (played through a filter and with tape effects). @6:45

[@synthpro]

@@julesl6910 I don't believe that is correct but does have a similar sound. Pink Floyd used a EMS synthi for that sound, it has wide range oscillator control so frequency could be swept from low to high and then they had the noise source in the backgroundto give that motor sound a realistic rotation effect.

[@julesl6910]

@@synthpro They used the recording in combination with the EMS synth

[@ROBOHO]

I'm in the process building a poly-synth with a C2 right now! So many design decisions related to the shear number of voices and mixing of harmonics

[@garycitro1674]

This project sounds absolutely ridiculous, and I'm totally excited to hear how it comes out! 😀😀

[@Transgrooving]

Really great video. I'm trying to troubleshoot my a100 and this may come in really handy. Thanks a lot. And I think your project idea is fantastic. If you get to the point where you have a working synthesizer. Make sure you publish it here so we can see it.

[@Rhythmicons]

That synth idea sounds awesome.

[@scrunchymacscruff1244]

Add the Leslie and you've got one of the greatest things that happened to the 20th century.

[@PracticalCat]

I too am working on a 3 osc divide down poly synth monster. I have finished all the 36 osc pcbs and dividers. I am currently working on the waveshaping and gating boards. Can't wait to see what you come up with! I think those outputs you showed may go to the various key contacts for each footage. The key contact busses then go to your drawbars and fixed filters. Thats how my farfisas are set up anyway.

[@ChinqMiau1]

So cool to see! Thank you for sharing mate, great stuff!

[@jeffperonto3234]

Very interesting. Thanks for sharing!

[@IvanRx76]

Very informarive, Is there any book where I can learn how the Hammond organ works? What I'm very curious about, is how the sound created from the tonewheel is amplified eliminaring noise...

[@misruler9370]

Jareth just wants to build a Polywheel!

[@synthpro]

Lol, that's a good name for it!

[@brian50g]

The warp drive unit on most alien motherships look exactly the same

[@ShelbyBryant]

You're one of the coolest people on the planet.

[@Ccyawn123]

Possibly even the universe

[@macronencer]

This is really interesting, thank you! I've never had a tonewheel organ but I've played a Hammond X5 on stage (transistor version with divider chips) into a Sharma Leslie amp - love the sound! I started looking into xentonality recently and that led me here after a comment from Sevish about Hammonds and equal-tempered partials. Looking at the notes you've written on the top of the housing, it seems like there are 8 octaves for most notes, arranged in four compartments. However, the pattern between the two main sets of tonewheels is staggered, so that, for example, there's a B directly opposite an F#. I initially thought that this must be a good design because of the 3:2 ratio of a fifth, allowing for a simpler central shaft gear... but that's not quite right, because the whole point of equal temperament is that it's NOT 3:2 :) I'd really like to know every detail of the design of these things and why the choices were made... what an incredible piece of engineering!

[@bluest1524]

That was fantastic! Thank you.

[@rationalemusic7747]

Just a couple thoughts on the synthesizer idea: Unless you need fully polyphonic filter articulation via an envelope generator, you probably don't need a filter for each voice since the harmonic content of each note can be shaped by mixing the harmonics from the tonewheels (which is what the drawbars do to make different timbres). Similarly, you can probably do away with waveshaping circuitry as well if you wire it up in such a way that allows you to mix in a greater range of harmonics rather than the standard organ drawbar frequencies of 16', 5 1/3', 8', 4', etc.)

[@synthpro]

That's a fantastic idea. What I had in mind was something similar to this but the waveshape circuits actually being VCA where the mix could be shaped/modulated in a way to morph the tones and would be a buffered/summed control across the voices. I was wanting independent articulation of the VCF/VCA of each voice but also thought about a single VCF similar to how the polymoog works. Still playing with ideas there.

[@rationalemusic7747]

@@synthpro Ah, that makes sense. You'd still need a lot of VCA circuits depending on the amount of harmonics you wanted to be able to control per note, but I wonder if it would make more sense to put a single DCA on each voice and then have a computer or microcontroller generate the envelope signals depending on which keys are being pressed and which harmonics you want present. Another idea would be to wire it up like a normal organ with the 9 contacts per key going into the drawbars but using 9 VCAs/EGs instead of drawbars to shape the sound. If you wanted to go really radical, you could have a VCA/EG on each tonewheel, use those purely to shape the timbre, and then change the motor speed to vary the pitch (though that would require installing a variable-speed motor). Certainly lots of options to be considered. Check out this link if you want some more info on the workings of a Hammond: electricdruid.net/technical-aspects-of-the-hammond-organ/

[@scrunchymacscruff1244]

Hey, can you geniuses suggest why all the C keys and C pedals on a 1957 RT-3 are weak or comparatively non-existent? Someone said it might be some stuck tone wheels, so I wedged a couple of pill bottles under the TG to lift it as far as it would go and delicately - I believe - manually rotated all the groups I could reach. I didn't find any that weren't moving; but..when I put everything back and started it, I got a shrill high pitch within 2 seconds of getting notes from the keys, which pitch drowns out the notes. The pitch, if I recall right is B. Also, the C notes are still off. I'm playing it through a JR-20 and I think it's the organ that's the problem. When I hook it up to the PR-40 I get real weird stuff, like pedal notes out of sequence and missing ones, but the distortion is much softer and more like a low growl and no difference when changing presets and drawbars and I think that's mostly problems with the PR-40 as it seems to have not been turned for a very long time. The A028 obviously needs new stuff but since the unpleasant pitch thing happened in connection with raising the TWG, I'm wondering if it is merely coincidence that the preamp might be the problem or if something happened by raising the TWG, taht would be the primary issue. Any thoughts? It's my first console I've had in 20 years and I'm excited about it, but I'm not an electronics wizard to go wading in deep waters.

[@Drenov]

Excellent video, thanks.

[@synthpro]

Thanks Drenov!

[@Drenov]

@@synthpro no thank you for making that video. I found it really interesting as it wasn't using electronics.

[@cyberpholk]

Great vid! Any progress on this project?

[@synthpro]

@@cyberpholk thank you! Yes, I have made some great progress but not quite to the point I'm ready to demo it. It's going to be 49 voices and I have about 9 built so far.

[@paulromsky9527]

The Transformers for each Wheel perfom 3 functions: Impedance match the Pick Up Coils to the Outputs, step the Low Voltage/High Current of the Pick Up Coils to a Higher Voltage/Lower Current to the Draw Bars for better mixing of the signals, and they filter out high frequency noise. The Capacitor and Resistor on the Transformers I beleive are Low Cutoff High Pass Filters to reduce the 'click' sounds from the key contacts. I need to see a schematic to be sure.

[@synthpro]

@@paulromsky9527 all fantastic stuff, thanks for sharing!

[@FerniFF]

Very cool. Thanks for making this

[@richardstevens7415]

Always wanted a polyphonic synth

[@Rhythmicons]

On the Rhodes, being farther away from the pickup would affect the volume (if memory serves). But depending on the angle of the tine to the pickup is where the tone shaping come into play. Check the Rhodes service manual for that. But wouldn't it be neat to have a drawbar to control the overtones?

[@RickDeNatale]

I don’t think those are transformers, my guess is that they are part af an LC bandpass, or lowpass filter to filter out harmonics so that the output of each tonewheel is basically a sine wave.

[@ericporterfield5531]

how is the coupling sping connected to each end? Is there a screw for either side?

[@tinkerwithstuff]

I think the spring coupling (in my funny mind anyway) also acts as a sort of mechanical low pass filter, to reduce remaining noise of this rather "jumpy" motor type that might perhaps not be fully eliminated by the flywheel. I think it was the B3 which allows you to sacrifice one of the harmonics, connect it to some simple kind of envelope generator, to create percussive attack sounds. Some blues players liked that especially, so my limited impression. Maybe this can be retrofitted to your new one if it's interesting. (I don't recall you mention this kind of stuff in the last vid, but maybe you're already aware of that IMO cool feature)

[@criqdekuyper9259]

Percussion uses the 2’ drawbar.

[@synthpro]

That is a interesting thought. I will say that this motor actually runs fairly smooth and delivers more torque than what the M3 has. The cap on this motor is critical for accurate RPM and stability. When I first got this tonewheel, the frequency was very unstable and the motor actually ran a little hot. I replaced the cap and it's dead on A 440Hz. You will also notice that there is no flywheel required for the H series. The B3 and M3 both do indeed have the percussion settings, definitely a cool effect.

[@tinkerwithstuff]

@@synthpro Ah, I wsa familiar only with descriptions of the B3, and this being a funny 1-phase motor which has quite pronounced torque fluctuations as the poles move around.

[@scrunchymacscruff1244]

Mm! interesting. @@criqdekuyper9259

[@scrunchymacscruff1244]

As does my RT-3@@synthpro

[@vhm14u2c]

More bumps on tonewheel, higher the frequency. Those ones with a few bumps/lobes produce lower frequencies. Be careful touching some tonewheel areas while it’s running. I have been sliced up pretty good one time putting my finger where it didn’t belong.

[@joshuaswannmusic6462]

My Hammond H-111 preamp blew up. Is it possible to bypass the preamp to just get sound from the generator?

[@phlattgetit]

Jareth, I worry for you. ha,ha You are slipping into the organ tinkerer's madness that can consume you if you aren't careful. Take care and congratulations on the new M3!

[@synthpro]

I have worried about myself since I got into synthesis in general, lol. Thank you very much!!

[@vrjb100]

Replace tonewheels with optical things for your synthesizer?

[@pablopicaro7649]

2022 jan ever make any progress on project? need a high pass filter to get that low buzz out of signal

[@synthpro]

I have made a little headway on this project but not much, synth Restorations take up the majority of my time.

[@TheMissing62]

The theeted wheel generates de tone; the second "flat" wheel thats has some kind of lobes are for generating the vibrato effect. Easypeasy...

[@jorgeandrade20]

No, that's not how it works. The two wheels serve the same exact purpose, to generate tone (basically a sine wave), one is a low-pitch tone and the other is a high-pitch tone. There's another device called vibrato scanner that along with more circuitry generates the vibrato and chorus features of this organ.

[@Alwaysdoinit112]

6:53 Whelen Vortex tornado siren

[@B3burner]

I would think the tone-wheels are made of metal. Aren’t those electro magnets that are pushed right near them to pull in the change in pulsing off the undulating teeth of each tone wheel? I don’t think a magnet would be attracted to Bakelite.

[@synthpro]

They are, I meant to say they have a coating. The drive gears are bakelite though.

[@vlzmusik]

maybe you could later replace the tonewheels with a divide down scheme?

[@synthpro]

That's exactly what you see later on. Electronic organs would use inductive oscillators, (sometimes you do see VCOs) running either discrete divider circuits or Integrated circuit based dividers. Eventually we would see the development of a top octave synth chip which would take a external frequency and create 1 full octave of frequencies that would then drive divider sets, (benefit of this design was you only had to have a single clock source to tune in the desired note reference were as before you still had multiple oscillators to tune). This is what you find in a lot of string machines and organs from the 70s. The polymoog uses these circuits as well but it's a bit unique as the divider frequency is really just used to set the frequency and then the Polycom chip per key handles waveshape including pulse width, filtering, VCA for independent contours of each key. VCOs are complex as well. It's very interesting because polyphony as we really know it derived from the tone wheel concept, engineers just found ways to go from mechanical to fully electronic.

[@vlzmusik]

@@synthpro yes, it's funny to think that the polymoog was a dead end in synth development once voice allocation logic was introduced. You might like this page here, apropos divide-down circuits electricdruid.net/adventures-in-top-octave-generation/ it's a great read. Anyway, I'll follow your development with interest!

[@Thegregcoulson]

Crazy how someone actually invented this for mass distribution…

[@celebutante]

I'm not too knowledgable about these, but I would think the tonewheels would have to be some kind of metal for the pickups to sense them in their magnetic field, right?

[@synthpro]

You are correct, tone wheels are metal but they have some kind of coating over them with only the teeth exposed metal.

[@celebutante]

@@synthpro Gotcha. :)

[@fraciscojgarciaguerrero6271]

Hola saludos me encantaría que sus videos la traduzca al español por favor

[@scrunchymacscruff1244]

A caballo regalado no se le mire en las dientes!

[@TractorMonkeywithJL]

Ok, I thought I understood how the tone wheel worked, but when you said the wheels are made out of a Bakelite type of material, I'm confused again. How are the wheels inducing a voltage into the coil pickups if they aren't made of a ferrous metal?

[@synthpro]

The clutch gears are bakelite but the tone wheels are indeed metal with a protective coating.

[@TractorMonkeywithJL]

@@synthpro Ok, thanks for the reply.

[@8546Ken]

Do you know about the granddaddy of the Hammond organ - the Telharmonium, invented in 1896. It used full size alternators for each tone wheel because they had no amplifiers then. The second version weighed 210 tons, so 46 pounds isn't so bad. Unfortunately there are no recordings of it. It was scrapped in 1962. en.wikipedia.org/wiki/Telharmonium

[@synthpro]

I sure do, it was pretty amazing. Shame it got scrapped.

[@wigwagstudios2474]

It sounds a bit like an old PC speaker at times

[@frankjamesbonarrigo7162]

Your email is broken. I emailed you a bunch of times. I WAS going to sell the polymoog, but decided NOT to. I am still interested in your packing philosophy. Also, Can running VCF into VCF to create feedback on the back of the polymoog cause damage?? Thanks!

[@synthpro]

Hey Frank, my yahoo account has gone stupid, don't update and then like three weeks later it dumps massive amounts of backlogged e-mails. Glad you decided to keep, won't find another in that great of shape restored. Packing is special in the sense that you want all sliders down and use 100 yards of bubble wrap and keep it loose enough to not press keys but tight enough it doesn't slide around. Wrap it front to back twice and side to side twice. Top that off with movers wrap to keep everything in place. Those are the keys to a proper safe travel along with a good solid box and plenty of filler to prevent polymoog from slamming around inside causing bubbles to pop. Doesn't hurt at all to run sections back into each other.

[@snoolee7950]

extremely impractical

[@boilinabag]

m3 is missing the lowest register that the b/c had. the m was a nice organ for our studio lounge.

[@scrunchymacscruff1244]

You can screw around with the ground-wires and an ohm-meter and soldering iron and bring that out.