From j3mes.eat0n@gmail.com Sat Sep 20 06:09:58 2014
Subject:Re: Mojo matching transformer settings

Have a look at p18 of http://www.hammondb3andleslietips.com/schematic/Hammond%20Organ%20B3-C3%20Service%20Manual.pdf http://www.hammondb3andleslietips.com/schematic/Hammond%20Organ%20B3-C3%20Service%20Manual.pdf



The relative strength of the tones is set by the matching transformer.


On the primary side it has 9 terminals or taps. The first one is grounded. A drawbar at 0 connects here. The remainder are 1-8. For example A drawbar at level 6 connects to the 7th terminal.


The circuit chain is as follows:


Tone generator coil-> filter (tones 44+)-> resistance wire (for manual tapering and mixing)-> key contact -> busbar -> preset panel/drawbars (depending on preset keys) -> 0-8 inputs on matching transformer -> vibrato switches -> AO28 preamp


Note that the busbars are connected to both the presets, and the drawbars separately, and then depending on which preset key is pressed the tones are then routed to the primary (input) of the respective matching transformer for swell and great.


On a Hammond tonewheel organ, none of the the wiring is (easily) adjustable. Actually even the presets on a B3 aren't that easy to adjust and they're intended to be adjustable. The resistance wire lengths (which determines their resistance) were decided at the factory when it was installed, are soldered to the terminals on the back of the manual, and then and spot welded to the back of the key contact. On a -3 series they are different lengths to achieve the nice balanced sound across the manual but on an M100 for example they are all the same length to save money in manufacturing, with a different taper used on the TG.


The taps on the matching transformer are based on the number of windings on the coil, which was done at the factory, the same for every B3. The 9 taps are fundamental the sound of the organ.


I doubt anyone has ever adjusted or rewound their matching transformer to get a better sound, but you never know. The Mojo settings are an innovation.


---In CloneWheel@yahoogroups.com, wrote :

James,


I looked at the wiring diagram.. It's not clear to me where the strength of the relative tones of the drawbars is determined, other than using that resister that seems to be on each drawbar..?


It's been years since I actually had to read and understand wiring diagrams.. and these ones are very difficult to read (copies of copies of copies scanned into a file).. I used to fix electro-mechanical stuff for IBM but that was 35 years ago.. ;-)


Let's see if I can get a definitive answer from some of the hammond techs on the hammond zone. Or maybe someone else here can speak to this with a definitive answer..?


Craig

Sent from my iPad

On Sep 19, 2014, at 10:47 AM, James Fry groups@... mailto:groups@... [CloneWheel] wrote:


Hi Craig,
I am pretty sure the presets and the drawbars both go to the matching transformers (as stated in section 1-20) - they'd have to in order to match the impedance from the coils to the preamp input. The resistance wires are used to taper the level of each used tone wheel signal per key. You can trace most of this through on the circuit diagrams.
Happy for you to ask on HammondZone or elsewhere (is there such a place?) though - would like to get a definitive answer!
Cheers,
James
On 19 Sep 2014 15:23, "ccmacdon@... mailto:ccmacdon@... [CloneWheel]" wrote:


James,

This doesn't make any sense to me... (although I could be wrong)..

"In the B3 service manual, section 1-20 states that the taps on the transformers are used for mixing. The logical way for this to work is the different primary taps provide progressively more signal to be induced in the secondary coil, thus it provides the volume adjustment for each position of the drawbars rather than a per-drawbar level."

I believe that the mixing/taps you refer to pertain to the preset keys and preset panel.. the preset panel slats are hardwired to different taps on the Matching/mixing transformer, but this is just for the presets.. On the other hand, I believe that the strength of the relative drawbar tones are accomplished with the resistance wires before the signal gets to the Matching transformer.

Honestly, this system of tonewheel generator, bussbars, drawbars, presets and tone/note/drawbar matrix, is all rather complicated, and not for the faint of heart!! ;-)

I will post this question on one of the other Yahoo forums and see if I can get a definitive answer.

Regards,
Craig MacDonald





From: "James Fry groups@... mailto:groups@... [CloneWheel]"
To: CloneWheel@yahoogroups.com mailto:CloneWheel@yahoogroups.com
Sent: Friday, September 19, 2014 9:19 AM
Subject: Re: [CWSG] Mojo matching transformer settings

On 18 September 2014 18:00, jlcason@... mailto:jlcason@... [CloneWheel] wrote:
and pedals. Each transformer has nine primary connection taps, and two secondary (output) connections. Each drawbar connected to different taps on the appropriate transfomer's primary, although they are in a definite arrangement with no mention of changing taps for a particular drawbar. The transformers served the function of changing the relatively low impedance of the tonewheel/filter sets in the generator,



Hi Jim,


I've been doing a lot of research and reading too as I've been starting to write my own modelling Hammond engine. My understanding is a bit different from yours, although I agree with the overall function of matching impedance.


In the B3 service manual, section 1-20 states that the taps on the transformers are used for mixing. The logical way for this to work is the different primary taps provide progressively more signal to be induced in the secondary coil, thus it provides the volume adjustment for each position of the drawbars rather than a per-drawbar level.


The wiring diagrams for many of the older organs (CV, B2 etc) labels the primary taps 0 to 8 (with 0 also being connected to ground) which would correspond far better to levels 0 to 8 rather than being per drawbar. While harder to see because of drawing, the RT3 and B3 are the same (trace the colours from the drawbars through to the matching transformers).


The L100 service manual shows the L100 works differently, using a resistor ladder and a simple transformer - presumably to keep costs down.


Variations between organs at the factory might possibly have been accomplished by changing taps on the transformers, but the way that the circuit diagram and wire diagram are drawn, I don't think so. There are resistors on each drawbar contact buss for which no factory value is given. I think it more likely that individual factory leveling of the drawbars was done by resistor substitution. Another place where factory changes are definitely shown is in the case of R10 at the output of tube V1, which shows 3.9 meg ohms nominal, but with a note that substation at test will be performed to balance channels.

My understanding is that there are resistance wires per harmonic per key, and therefore these resistors are the famous resistance wires and tapered accordingly. Kon's spreadsheet has measurements from a number of organs, as well as alsorts of other goodies (I'm surprised nobody has used the TG measurement tables to get another different 100 organs into their Mojos!)


The Mojo people use the name "transformer" and apparently have "sliders" to adjust. This is likely not to be literally a reproduction of a factory adjustment. However, regardless of how it is named, it does provide additional parameters for adjusting the sound and tonal balance. (I don't own a Mojo, so cannot really speculate further on this, just trying to give a not-too-technical explanation of some of the input circuits in the B3.



While the mojo has a "matching transformer" section I think it really adjusts the tapering (resistance wires?) for each drawbars tones but I'm not entirely clear on that, and I don't have a Mojo either. It's definitely a cool feature, and Guido has an impressive bit of software!


Cheers,


James