From: strangewarrior@earthlink.net (Michael Fulk) Newsgroups: alt.music.hammond-organ Subject: Re: [HAM] E-112 percussion....long post...corrections welcomed Message-ID: <009101c06582$a23f86c0$5ad7fc9e@compaq> Date: 14 Dec 00 04:02:06 GMT -----Original Message----- From: Robert Hayton To: The Hammond Forum Date: Wednesday, December 13, 2000 6:15 PM Subject: Re: [HAM] E-112 percussion >There's something in the archives about modifying the E-xxx percussion. As I >recall (and I very well could be very wrong here), the mod requires that >certain resistors on a matrix circuit board be clipped. The post detailing > the procedure is archived on my computer at home... and I'm at work. > >good luck! >Robert Hayton >San Jose, CA > The answer to this problem, IMHO, is basically simple. Skip to last paragraph for mods, if the descriptions bore you. Descriptions below are accuate, but for the sake pf brevity, and the desire of my being as little complicated as possible....much detail is omitted On the B-3 et. al. the drawbar signal is diverted from a drawbar, (2nd or 3rd hamonic), to a "percusiion input transformer", and then on to the percussion circuitry........that is, the primary of this transformer has a small extra winding which returns the drawbar harmonic to the the drawbar. The secondary, which contains the percussion signal, goes to an amplifying tube and then to another transformer primary, the secondary of which, along with a 12AU7 tube constitutes the the percussion "gate" and then goes through still a *third* transformer, the secondary of which contains the signal which goes to the preamp, is amplified along with the vibrato scanner signal, and non-vibnrato signal which all meet at one point, and so on through the preamp to output. Without going into the intricacies of Hammond's "gate" on these models, suffice to say that +24 volts needs to be grounded to make the the "gate" start closing and then finally close, smoothly to give the characteristic percussion decay, either slowly or fast. Hammond could have added an extra contact to accomplish this grounding, but instead chose to sacrfice one harmonic to do it....even this drawbar could be left hooked up, and the percussion would work but then the DC would engender a *very* large click every time one played a percussion note(s). On the E-100, things are done *very* differently. The percussion input [or "matching"] transformer has several input primaries, one for every two harmonics which are used, and but one secondary. When any percussive effect is turned on the harmonic connected to the primary[also always remains connected to drawbar], plus one other which maybe connected also to any one primary, i.e. each primary may conduct as ,many as two harmonics. The secondary is connected push-pull style to the grids of of a dual triode whose cathodes are set by means of a pot so that the tube does not ordinarily conduct, (pot is "percussion cut-off" control"). Now when the percussion is turned "on" then a voltage, (source voltage 25 VDC run across 15k ohms and 6800 ohms to ground from end of 15k ohm resistor opposite to supply voltage), is run to 61contacts devoted solely to this purpose. Whenever a key is depressed with this voltage "on" then it is applied to an internal busbar[similiar to all other internal busbars, except that it carries DC instead of a signal]. This DC busbar voltage is applied to a pulse generator and shaper and capacitor whose pulse is fed to the grids of a double triode, (the "gate"), making it conduct as long as the pulse lasts and decays; that triode's signal is the amplified by another double triode , one of whose plates either goes to the non-vibrato preampmifier or the vibrato preamplifier, (Add-Vibrato Tab). The length of the pulse, and thus the decay time is controlled by the pulse's duration, which is in turn controlled by the discharge of a 1mfd capacitor's charge being dissipated to ground through either an 18k ohm resistor in parallel with a 330k ohm resistor....short decay, or an 18k ohm resistor.[not relevant here but the 18k ohm resistor will be found to be in series to ground with a 100k ohm po in circuit only when reiterarion is used.] As is the B-3, et. al. , all keys must be lifted for percussion to sound again. SOOOOoooooo..........find the percussion transformer and feed to its windings the 2nd harmonics and into another winding the third harmonic and Voila!...B-3 percussion.... or any old combination you may choose, e.g. 3rd and second together, or 2nd and 5th together...this latter, I have found to be a favorite of people. Experiment with the below values and have some fun......for cheap, cheap, cheap......all components or variations thereof can be purchased at radio shack. All above components are located in, on or near the percussion chassis. 1 mfd capaciror is C204, 50 volts 15k ohm resistor isR207 1/2 watt 330k ohm resistor is R411.1/2watt URGENT WARNING........THE ABOVE MODS INVOLVE, WHETHER THE INSTRUMENT IS TURNED ON OR OFF, OR UNPLUGGED, THE POSSIBLE EVEN LIKELY EXPOSURE TO EXTREMELY DANGEROUS AND LETHAL VOLTAGES !!! DO NOT ATTEMPT IF YOU DO NOT UNDERSTAND! INSTEAD ACQUIRE A COMPETENT SERVICE TECHNICIAN!!!